The morning launch of Apollo 15 from Pad A at Launch Complex 39 avoids the high heat of a Florida summer but the weather is clear and bright, with few scattered clouds, which will allow the crowds watching the spectacle to track the flight for much of its ascent to orbit. Launch Complex 39 at the Kennedy Space Center was built with 2 fully operational launch pads; in the expectation of a much higher launch rate than was ever achieved. Only Apollo 10 departed from Pad B at a particularly busy time in the Apollo program, leading up to the launch of Apollo 11. Every other Apollo/Saturn V launch, including Apollo 15, began from Pad A.
The spacecraft/vehicle stack is designated AS-510, signifying that it is the tenth launch of the Apollo/Saturn V combination. As the Apollo spacecraft components came off the production line, they were also assigned serial numbers to help distinguish them. Each had modifications which built on the experience gained from previous missions or which came from requirements of their particular mission. Therefore, each had checklists pertaining to their individual configurations.
This mission was originally intended to be similar in scope to Apollo 14, both classed as 'H' missions, the extent of lunar exploration being limited by the walking range of the landing crew. However, the H mission for Apollo 15 was cancelled on 2 September 1970 as part of NASA's budgetary cutbacks and the advanced 'J' missions were brought forward to take advantage of the enhanced exploration promised by the Lunar Roving Vehicle, a 2-man buggy which would allow astronauts to explore up to 10 kilometres from the Lunar Module. Because of this, Apollo 15 is jumping the numerical sequence of modules, missing out CSM (Command/Service Module) 111 and LM (Lunar Module)-9. LM-9's destiny is to be located in the Apollo/Saturn V Center at KSC, where it now forms part of an impressive visitor attraction dedicated to the Apollo Program.
CSM 112, among its upgrades, includes an array of scientific instruments and cameras called the SIM (Scientific Instrument Module), installed in a previously largely vacant sector of the Service Module. The Command Module includes controls for operating the SIM bay. The Lunar Module for this mission, LM-10, also has extensive modifications to permit an extended stay on the Moon, including improved propulsion and guidance, as well as the Lunar Roving Vehicle, cleverly folded on its side. The launch vehicle, AS-510, also has modifications to allow it to lift this heavier Apollo spacecraft to Earth orbit and then on to the Moon.
The timing of an Apollo launch to the Moon falls within certain 'windows' or periods of time which are influenced by daily and monthly factors. The daily restriction to the window is due to the rotation of Earth bringing the launch site to the correct relationship with the Moon's position in its orbit, to allow enough of a parking orbit around Earth before the boost to the Moon. The monthly factors are the lighting requirements at the landing site. The landing should take place in the early lunar morning so that the Sun will be behind the astronauts as they approach from their east-to-west orbit. A low Sun-angle will also produce shadows on the lunar terrain that allow the Commander to recognise landmarks as well as aiding speed and distance perception. With a lunar day lasting 29.5 Earth days, the correct conditions for the landing only occur monthly.
The first launch window for Apollo 15 begins at 09:34, Eastern Standard Time, on 26th July, 1971, and lasts 2 hours, 37 minutes. If technical problems or poor weather delay the launch, they can try again on the 27th, otherwise, they must wait for two opportunities in late August, or three more in late September.
Before the voyage commences, there are two sections to the CSM Launch Checklist to be followed. The lift-off configuration is set and verified by the back-up CMP (Command Module Pilot), in this case Vance Brand, who checks that each switch, knob, adjustment and talkback indicator is correctly set for the arrival of the prime crew. The CSM launch Checklist systematically covers each of the 57 panels in the Apollo 15 CSM. There are 454 lines in the checklist. Some panels are covered by a single line, while panel 2 on the main display console requires 78 lines.
Command Module Main Display Console from Apollo Operations Handbook Block II Spacecraft (October 15, 1969). This console comprises panels 1, 2 and 3, and is very similar, though not identical, to the console in the Apollo 15 Command Module. This and other diagrams of the Apollo spacecraft are available from the Diagram page of the NASA History Website.
At first glance, the Main Display Console of the Command Module is utterly overwhelming. But for those to whom an aircraft cockpit is unfamiliar territory, the "front office" of a Boeing 747 is also a visual racket. Not unlike the tales of people who regain their hearing after a lifetime of deafness, and perceive sounds as a jumble and without structure, finding order in the Apollo spacecraft is a concentrated learning process. When viewed with the skilled eye of the Apollo 15 crew, the cockpit quickly turns into, perhaps not a thing of beauty, but an entity born of structure and function.
In February 2004, Dave Scott joined us for a review of the Journal.
Scott, from 2004 mission review: "People don't have any idea how much stuff was in there."
Three hours before launch, the prime crew enters the spacecraft and once settled, they continue the prelaunch checks. CDR (Commander), Dave Scott, takes the left couch facing the major flight controls and the abort handle. CMP, Alfred Worden occupies the centre couch, facing the caution and warning panel and ready to monitor the computer's display during the critical minutes of ascent. The electrical and environment systems are monitored during launch by the LMP (Lunar Module Pilot), Jim Irwin, who takes the right couch. The checklist for boost preparation will be performed starting at T minus 20 minutes.
This is Kennedy Launch Control. T minus 2 hours, 16 minutes and counting. All aspects of the countdown still Go, aiming toward our planned T-zero at 9:34 am Eastern Daylight Time. Scientist-Astronaut Karl Henize, who in actuality has been the fourth astronaut inside the cabin, giving the three prime crewmembers a hand as they go thought their initial preparations and initial checks, now has departed from the spacecraft after completing his job. The astronauts, fully suited, are of course now on the suit circuit. Henize has aided them in making some checks of the circuits to assure they are getting a good flow of pure oxygen into their space suits. We also have made medical readouts from the astronauts to assure that we are getting satisfactory medical data. And at this point, Houston Flight is sending some real-time commands to the spacecraft to assure that we have the proper links between the Control Center in Houston and the spacecraft here at the Kennedy Space Center. All is still going well. The crew here in Firing Room 1 monitoring the status of more than a million gallons of propellants that now are on board the Saturn V space vehicle and the mission is Go. 2 hours, 14 minutes, 40 seconds and counting; This is Kennedy Launch Control.
This is Kennedy Launch Control. T minus 2 hours and counting. T minus 2 hours and counting and all going very well with our countdown here on Apollo 15. The crew here in Firing Room 1 is monitoring the status of the various propellants on board the Saturn V rocket while the astronauts in the spacecraft at the 320-foot level at the pad now busy performing some final checks before the hatch will be closed on the cabin. The spacecraft commander Dave Scott coming up shortly on one of our major milestone checks. This is a check of the Emergency Detection System on board the vehicle. The Emergency Detection System senses initial development of conditions which could cause a launch vehicle failure and relays this information via cue lights or abort lights on the commander's panel; Dave Scott's panel on the left-hand side of the spacecraft. Our countdown has been going excellently since it picked up at 11:34 pm last evening. We've loaded more than three quarter of a million gallons of liquid oxygen and liquid hydrogen aboard the three stages of the Saturn V launch vehicle. We have had no problems during the count and all has gone well. The prime crew for the mission; astronauts Dave Scott, Al Worden and Jim Irwin; were awakened as planned in the countdown at 4:19 am Eastern Daylight Time. A short time later, Dr. Jack Teegan came by the crew quarters and gave them a brief physical examination, declared them physically fit and very well rested. The astronauts then sat down to breakfast. They had six guests for breakfast in the crew quarters this morning. The menu was the usual astronaut fare on launch morning of orange juice, eggs to order, tenderloin steak, toast and coffee. Joining the astronauts for breakfast were their boss, astronaut Donald Slayton, who also was the man who awakened them at 4:19 am. Also at the breakfast table was Vance Brand, the backup Command Module Pilot, and scientist-astronaut Jack Schmitt, the backup Lunar Module Pilot. These two men, of course, have worked very closely with the prime crew over the many months of launch preparations. Also one of the key members of the support team for this mission, scientist-astronaut Dr. Joe Allen also joined the crew for breakfast along with the administrative head of the Crew Quarters here at the Kennedy Space Center, Harold Collins, and Mr. Jim Smotherman who is the training director for the Apollo 15 crew operations. Following breakfast, about 45 minutes after they began their breakfast, the crew went down the hall at the Crew Quarters to the Suit Room to don their pressure suits. They departed from the Crew Quarters on time as far as the countdown is concerned at 6:28 am Eastern Daylight Time, and took the 18-minute ride to the launch pad, a trip of about nine miles from the Crew Quarters to the launch pad itself. They then boarded the first of two elevators that took them to the 320-foot level, the location of the spacecraft hatch. The astronauts went aboard in 15-minute sequence starting at 6:53 am this morning when the spacecraft commander Dave Scott went aboard and took his seat on the left-hand side. Next to go aboard, the Lunar Module Pilot Jim Irwin at 6:58 am. Jim Irwin sits on the right-hand side of the cockpit. And finally, the third member of the crew, Al Worden, the Command Module Pilot, took his seat in the middle of between Scott and Irwin. That's our status at the present time as our countdown proceeds. The astronauts visually checking out systems onboard the spacecraft. We note the hatch has now been closed, and the close-out crew will now begin the purge sequences to bring the cabin atmosphere to the planned 60/40 combination - 60 per cent oxygen and 40 per cent nitrogen - for lift-off. The astronauts, of course, are breathing pure oxygen through their spacesuits.
Weather conditions are very satisfactory for a launch attempt this morning. The forecast is for clear to scattered clouds in the Kennedy Space Center area. Surface winds here at KSC are from the south at about 5 to 10 miles per hour. We expect a temperature of about 83 degrees [Fahrenheit]. The weather around the worldwide track as far as our - the first few hours of the flight are concerned, also very satisfactory. In fact, one of the contingency recovery ships, the USS Austin, which is located 520 nautical miles off the coast here from the Kennedy Space Center, reports that in their area, the seas are calm, they have winds about 4 knots, a five-tenths cloud cover and 10 miles visibility. All is Go for the mission. Dave Scott now beginning this lengthy series of checks of the key Emergency Detection System, working with the members of the launch vehicle team here in the Firing Room, and the spacecraft team located in their control room back at the Kennedy Space Center Manned Spacecraft Operations Building. 1 hour, 55 minutes, 45 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control. 1 hour, 51 minutes and counting. All still Go with Apollo 15. Spacecraft commander Dave Scott now busy starting key Emergency Detection System test as our countdown continues. Here in the Control Center, we're making some computer checks of the flight computer onboard the Saturn V launch vehicle, located in the Instrument Unit which is atop the third stage. All aspects of the mission still going well. 1 hour, 50 minutes, 30 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control. T minus 1 hour, 41 minutes and counting. All aspects of our countdown still Go for Apollo 15. Spacecraft commander Dave Scott has wound up his rather extensive test of the Emergency Detection System working with members of the launch vehicle and spacecraft team. At this point, the close-out crewmembers at the 320-foot level who closed the hatch some 30 minutes ago now report that the cabin has been purged. The cabin is stable following some leak checks and we have the proper environment onboard for lift-off. The close-out crew now proceed to put on the Boost Protective Cover, the protective covering that goes over the hatch for flight. They'll be pulling out, oh, perhaps in about 40 minutes or so prior to the time the Apollo access comes back to position some 6 feet from the spacecraft. In the meantime here in the Launch Control Center, the launch team here working with Mission Control in Houston as some commands are being sent directly to the launch vehicle flight computer located in the Instrument Unit. These tests also going well, as all aspects of the count have gone since it was picked up shortly before midnight as far as the final countdown is concerned. T minus 1 hour, 39 minutes, 38 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control. T minus 1 hour, 31 minutes and counting. All still going well with Apollo 15. The astronaut crew onboard the spacecraft at the 320-foot level are still working on their final checks, working with Spacecraft Conduct - Test Conductor Skip Chauvin. Chauvin, just a short while ago, instructed the Pad Leader to start breaking up the White Room. This is one of the final processes before the crew is moved - the close-out crew departs from the spacecraft area. The close-out process, at this point, is to remove certain panels so that the swing arm will be able to come back without any problems at the 43-minute mark in the count. This is Swing Arm 9, the Apollo Access arm, which is first moved some 6 feet away from the spacecraft. Here in the Control Center, we're getting into some checks of the tracking beacons on the Saturn V launch vehicle, and the checks both here in the Firing Room as far as launch vehicle, and in the spacecraft control rooms still going very well. 1 hour, 29 minutes and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control. T minus 1 hour, 21 minutes and counting. All aspects of the countdown still Go for Apollo 15. Still aiming toward our planned T-zero and lift-off at 9:34 am Eastern Daylight Time. The Administrator of the National Aeronautics and Space Administration, Dr. James Fletcher, has just arrived here in Firing Room 1, the control room for this launch. He's being briefed by the Deputy Administrator Dr. George Low and is being told that the countdown is still going excellently, as it has since it picked up late last evening. The spacecraft commander Dave Scott aboard the spacecraft with his two comrades at the 320-foot level at the pad. Scott now working on some command and guidance checks. Working with Spacecraft Test Conductor Skip Chauvin and the spacecraft checkout team. Here in the Firing Room under the direction of Test Supervisor Jim Harrington and the Launch Vehicle Test Conductor Norm Carlson, the launch team making some final telemetry checks of the status of the tracking telemetry in the three stages and Instrument - Instrument Unit of the Saturn V launch vehicle. Still counting, still Go. Weather report excellent for a launch attempt. A beautiful morning for a flight to the Moon. 1 hour, 19 minutes, 45 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control. T minus 71 minutes and counting. 71 minutes and counting; all still proceeding very satisfactorily with the countdown for Apollo 15. Spacecraft commander Dave Scott, who sits on the left hand side of the spacecraft, still very busy on board working with Spacecraft Test Conductor Skip Chauvin as they make final checks of the guidance and stabilization control systems aboard the Apollo spacecraft. As a part of this test, Dave Scott actually will send commands to cause that big engine below them in the Service Module to swing or gimbal in response to commands from the guidance system. The Service Module Propulsion System, which is capable of some 20 thousand, 5 hundred thousand [means 20,500] pounds of thrust, is used for all the major maneuvers on the flight to and from the Moon once the big Saturn V launch vehicle has done its job and placed it on the proper trajectory toward the Moon. Here in Firing Room 1, our checks of the various telemetry systems and calibration of telemetry, the tracking information we'll receive from the vehicle, is still continuing. We'll also be coming up shortly on some more checks of the tracking beacons onboard. We have been alerted that the swing arm, the Apollo access arm at the 320-foot level, may come back about 10 minutes earlier in the count, because the count has been going so well and we've been a little bit ahead on many of the procedures. The closeout crew, who have been aiding the astronauts at the 320-foot level, have completed that - their job and have now departed. That's our status. All is Go. 79 minutes [means 69 minutes], 20 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control. T minus 61 minutes and counting; T minus 61; the countdown still proceeding very satisfactorily. Now just a little more than an hour away from our planned lift-off here on the Apollo 15 mission. Astronaut Dave Scott, who will be making his third space flight, is still working with the Spacecraft Test Conductor in the spacecraft cabin at the 320-foot level at the pad, working with Spacecraft Test Conductor Skip Chauvin back at the control room. We have completed our final guidance alignment checks of the spacecraft systems and we're now making some bi - some final checks of the Entry Monitoring System, the system that would help guide the spacecraft back in on a re-entry from a trip of - from a trip from the Moon, and also of course, if there was an emergency condition where the spacecraft had to come back in. Skip Chauvin has just advised the astronauts that the swing arm, which is now still attached to the spacecraft, probably will be coming back in about 7 minutes from this time. The swing arm is moved to a position about 6 feet away from the spacecraft so that if there was an emergency condition where the astronauts needed to egress the spacecraft in a hurry, that swing arm could be brought back in in a matter of seconds so that the astronauts could get out. At the 5-minute mark in the countdown, the swing arm is retracted to its fully retracted position at the pad. Here in the Launch Control Center, our telemetry calibration checks are still in progress. We'll be making some checks of the Range Safety Command destruct system aboard the vehicle. This system, that would be used to destroy the vehicle after an abort sequence had occurred and the astronauts had escaped from the vehicle in trouble. That's our status; all is Go. 59 minutes, 10 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control at T minus 56 minutes and counting. All still going well with the countdown at this time. Coming up in just about 3 minutes, that Apollo access arm, the arm that the astronauts used to go across to board their spacecraft, will be retracted to a standby position. It's retracted 12 degrees or some 6 feet from the spacecraft. Once this does occur, we arm that Launch Escape System, the Launch Escape Tower on top of the spacecraft and from that point down in the countdown, if there was any critical emergency situation, an abort could take place right on the launch pad with the solid-fueled motors in the Launch Escape Tower, which generates some 155,000 pounds of thrust, pulling the spacecraft away from a launch vehicle that would be in trouble and an explosion imminent. This is one of the number of emergency conditions that we do plan for, and do have systems to handle in the last hour or so of the countdown. All aspects of the count still going well. We're at 54 minutes, 45 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control. The swing arm is now moving back from the spacecraft, on command right at the 53-minute mark. It'll be moved some 6 feet away from the spacecraft and remain in that standby condition for contingency purposes through the remainder of the countdown until like 5 minutes, it is fully retracted. The astronauts, of course, were alerted that this event would occur because they do feel a slight jolt as the swing arm and the White Room attached to its tip is pulled away. The astronauts can still continue in their final checks aboard the spacecraft, and the crew here in Firing Room 1 at the Launch Control Center here at Complex 39 still monitoring the status of the propellants aboard the vehicle. We loaded more than three-quarters of the million gallons of liquid oxygen and liquid hydrogen aboard the Saturn V this morning from the time the countdown picked up late last evening. A power transfer test, one of our key tests over the last hour or so in the countdown, has been successfully accomplished here in the Firing Room. We have switched from external power to the internal batteries on board the three stages and Instrument Unit of the Saturn V to ensure that they are operating properly. To conserve those batteries on board, we now return to external power. We will finally switch internal with the rocket at the 50-second mark in the count. The countdown has been going very well. In fact, we're about 10 minutes ahead on events both concerned with the spacecraft and the launch vehicle. We're now 51 minutes, 25 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control. T minus 46 minutes and counting. T minus 46 minutes and counting; we are proceeding satisfactorily, aiming toward our planned lift-off here for Apollo 15. The Apollo 15 astronaut crew standing by in the spacecraft at this time. They'll have quite a bit more work before we reach our T-zero, but they're standing by at this point. They've completed their guidance and alignment checks and are waiting as certain key launch vehicle checks are taking place at this time. We have just completed a check of the digital Range Safety command destruct system. These are the destruct packages aboard the three stages of the Saturn V that would be activated if the vehicle was flying off course and was a danger to personnel below. Of course before the destruct system would be activated, the abort sequence would take place and the astronaut crew and their spacecraft would be separated from the launch vehicle. Our weather is Go and all aspects of the countdown, Go. 44 minutes, 57 seconds and counting; this is Kennedy Launch Control.
Each stage of the Saturn V launch vehicle has shaped explosive charges attached to its outer surface which, in the event of an abort, rupture the fuel and oxidiser tanks, dispersing their contents into the atmosphere rather than allow them to impact Earth with dangerous loads still on board. The charge for the S-IC (the designation of the first stage) cuts a longitudinal breach in the fuel tank on the opposite side of the vehicle from that for the oxidiser tank so as to minimise their mixing during dispersion. Charges for the S-II (second stage) cut a 9 metre longitudinal opening in the hydrogen fuel tank and a series of lateral 4 metre ruptures in the squat LOX (liquid oxygen) tank. Those for the S-IVB (third stage) make two parallel 6 metre openings in the fuel tank and a 1.2 metre diameter hole in the LOX tank. These charges are fired only after the Command Module has separated from the launch vehicle. During a normal ascent, the destruct system is safed soon after the Launch Escape Tower is jettisoned; after about 3½ minutes of flight.
Early in the Apollo program, the Air Force had insisted that the LM, a vehicle from which every ounce of unneeded weight had been trimmed and which would be a home to men on the lunar surface, also had to have destruct ordnance attached. This was based on the premise that, in the event of a launch abort, it was better for propellants to be consumed before reaching the ground. After all, the LM would be unmanned at this stage. NASA pointed out the weight and safety penalties of this arrangement and eventually won what was a substantial argument by pointing out that the LM was hardly likely to survive the destruction of the S-IVB stage anyway. A similar conflict occurred over demands by the Air Force that the Service Module also carry destruct charges.
This is Kennedy Launch Control at T minus 40 minutes, 54 seconds and counting. Still proceeding very well at this time, aiming toward our planned T-zero at 9:34 am. [Eastern Daylight Time, 4 hours behind Greenwich Mean Time]. The astronauts will be busy again shortly in the spacecraft, particularly Command Module Pilot Al Worden, as he proceeds to go through the sequence of pressurizing the Reaction Control System [RCS] of the spacecraft. This is primarily concerned with those four quadrants of hundred-pound [445 N] thrust rockets on the side of the Service Module. We pressurize that system before launch and Al Worden reads off the status of the overall system so that Spacecraft Test Conductor Skip Chauvin and the crew, back in the spacecraft control center, can determine that that system is Go for launch. Of course, the Reaction Control System [is] used extensively on the flight to and from the Moon for small refinements on trajectory. Here, in Firing Room 1, we're Go for the final portion of the count. We have a clearance from the range to launch and our countdown is continuing. The countdown has been going excellently since it picked up at 11:34 pm last evening following a 9 hour, 34 minute built-in hold. Since that time, a major portion of the count was devoted to the propellant loading of the Saturn V launch vehicle, bringing aboard liquid oxygen and liquid hydrogen or so called cryogenic propellants aboard the three stages of the vehicle. We loaded more than three quarters of a million gallons [2.8 million litres] of the oxygen and hydrogen on board and at lift-off we expect to have the vehicle weighing close to 6.5 million pounds [nearly 3,000 tonnes] on the launch pad. The Saturn V space vehicle stands some 363 feet [110.6 metres].
Journal contributor Henry Spencer "The actual countdown first appeared in Fritz Lang's movie 'Frau im Mond' (usual English translation 'The Girl in the Moon', although 'Woman' would be more accurate), and it appears to have been Lang's invention as a way to add suspense to a silent movie. The rocket experimenters at the VfR (Verein für Raumschiffahrt or Society for Space Travel) picked it up, and it spread from there, gradually elaborated into a lengthy pre-launch schedule."
Early countdowns did not have built-in holds. However, the countdown, even in the early years of rocketry, was not just a clock ticking down toward launch, it specified when various things happened pre-launch. During development, operational missiles suffered inevitable delays due to minor snags cropping up, despite their supposedly predictable schedules. While difficulties were ironed out, the count had to be paused, holding up other events. By building pauses into the count at carefully chosen times, engineers could use this time to appraise problems and deal with them appropriately when this would not cause trouble. A simple way to implement such a pause is to stop the clock.
The built-in hold became firmly established in the launch event schedule during the Gemini program, when it was important that launches of the spacecraft and their rendezvous target vehicles, the Agenas, were carefully choreographed and had to be on time.
As far as the Apollo 15 crew is concerned, the crew was awakened by their boss, Donald K. Slayton, as planned in the countdown at 4:19 am Eastern Daylight Time. They were given a brief physical exam by Dr. Jack Teegan a short time later and he declared them in excellent physical condition and very well rested. The crew then sat down to breakfast with a number of the astronaut members of the back-up team and support team who have worked so hard with them in preparation for the mission and then were ready to proceed to the suit laboratory to don their pressure suits and go through final checks prior to being ready to go to the launch pad. Once again as planned in the countdown they departed the crew quarters at 6:28 am Eastern Daylight Time, arrived at the pad about 18 minutes later and then went on board the spacecraft at about the 2½-hour mark in the count. Since that time, Scott, Worden and Irwin have been performing various checks, working with the spacecraft control team, and all these checks have gone well. Our status is excellent at this time. The weather forecast certainly a Go for launch with clear skies, clear to scattered skies, the surface winds about 10 miles per hour from the south and the weather situation on the worldwide track as far as contingency purposes, all Go. That's our status; T minus 37 minutes, 35 seconds and counting. This is Kennedy Launch Control.
This is Kennedy Launch Control at T minus 31 minutes and counting. T minus 31 on mission with Apollo 15; still Go. This is the fourth flight intended for a lunar landing and all is going well. [Strictly speaking, this is the fifth flight, as Apollo 13 was intended for a lunar landing until an explosion aborted the mission.] We're still aiming toward our planned T-zero at 9:34 am Eastern Daylight Time, when, if all goes well, those five big engines in the first stage of the Saturn V will ignite, generating more than 7.7 million pounds [34,250 kN] of thrust to start us on the way on a long trip to the Moon. 30 minutes, 25 seconds and counting; this is Kennedy Launch Control.
Of the 110.6-metre height of the entire Apollo 15/Saturn V stack, 42.1 metres comprise the S-IC first stage. Five F-1 engines are clustered at the bottom of the stage to provide 34,025 kN (7,700,000 pounds) of thrust in total. The propellants used are RP-1 (Rocket Propellant-1 or highly refined kerosene) as the fuel and LOX as the oxidiser. Twenty days prior to launch, the lower of two tanks was filled with 810,000 litres of RP-1 with a final topping up occurring at T minus 1 hour. At nine hours before launch, the larger upper tank has nitrogen gas pumped through it to purge it of air and water vapour contaminants. Six and a half hours before launch, it is precooled to prepare it for the loading of 1.3 million litres of LOX at a temperature of -183° C. Initially, the LOX is fed at a slow rate of 95 litres per second until the tank is sufficiently chilled to retain the liquid up to 6.5 per cent full, then the tank is filled to 98 per cent at a rate of 630 litres per second, a process lasting over 45 minutes. The slow fill rate is re-established until the tank is full at about 4 hours 55 minutes before launch. From then on, until three minutes before launch, the level is replenished as the volatile LOX boils off. Both of the first stage tanks are then pressurised prior to launch using helium; the fuel tank at T-96 seconds, the LOX tank at T-72 seconds.
This is Kennedy Launch Control at T minus 26 minutes and counting. We're still proceeding very satisfactorily here in the final minutes of the countdown. All still going well. The busy activity right now, [is] astronaut Al Worden giving final verification of the status of the propellant system on board the Apollo spacecraft. He's working with Spacecraft Test Conductor Skip Chauvin, giving the key readings on the various systems, temperatures and pressures, to assure that that Reaction Control System is Go for the launch. They [the RCS] will have a lot of work to do during the mission and we want to make sure that it is precisely right before we're ready to commit to launch. Skip Chauvin now informs the astronauts that we're still about 10 minutes ahead in the countdown, and Dave Scott replies back with a rather quick 'Roger'. The countdown is still going. Launch vehicle status is Go. 25 minutes, 2 seconds and counting; this is Kennedy Launch Control.
This is Kennedy Launch Control; T minus 20 minutes, 56 seconds and counting. All aspects of the count are still Go, still aiming toward our planned T-zero at the appointed time of 9:34 am. Astronaut Al Worden - Worden, the Command Module Pilot in the middle seat, has completed his checks of the pressurization system for the reaction controls of the Apollo spacecraft and all is still going well. Here in the Launch Control Center, the crew has started a sequence to chill down the upper two stages of the Saturn V because of the extremely low temperatures of the liquid oxygen and liquid hydrogen involved in the propellant system and it is necessary to condition the engine chambers in both the second and third stages so that they will be at a lower temperature when the propellants are introduced at ignition time during the powered stage of the flight. We'll have more than 11 minutes of powered flight in the first stage of the mission [not the first stage of the launch vehicle], before the spacecraft - the Apollo spacecraft is placed into a parking orbit some 90 nautical miles [166 km] high, still attached to the third stage [of the launch vehicle]. A second burn of that third stage of the Saturn V will place the spacecraft on its proper translunar trajectory. Our status; 19 minutes, 40 seconds and counting. All aspects still Go. This is Kennedy Launch Control.
The second, or S-II, stage of Apollo 15's Saturn V vehicle is 24.9 metres tall and is powered by the combustion of LH2 (liquid hydrogen) and LOX in a cluster of five J-2 rocket motors which generate a total thrust of 5,115kN (1.15 million pounds). A million litres of LH2, cooled to -253°C to get it into a liquid state, is loaded into the large, upper tank of the stage while 331,000 litres of LOX is loaded into the smaller, squat tank below. These tanks share a single insulated structure with only an insulated, common bulkhead between them. With both propellants being so cold - LH2 is only 20 degrees above absolute zero - the tanks must be prepared and chilled down before they can be filled.
Air and water vapour is purged from the tanks by repeated pressurisation and venting with helium. Helium is used because nitrogen would freeze in the presence of liquid hydrogen. Once clear of contaminants, the tanks are cooled to accept the propellants by first passing cold gas through the system then feeding propellant at a slow rate and allowing it to boil off, taking heat with it. Seven hours before launch, LOX is fed at 31.5 litres per second until it is 5 per cent full, then the fill rate goes to 315 litres per second to take the tank to 96 per cent full. This takes about 25 minutes and then the tank is topped up at 63 litres per second. Five hours before launch and after purging and cooling, LH2 enters its tank at 63 litres per second, further cooling the walls so that propellant begins to remain liquid and rise in level in a process similar to that for the LOX tanks. Once the level of liquid propellant reaches 5 percent, the fill rate is increased to 630 litres per second until the tank is 98 percent full, when the fill rate reduces again to 63 litres per second to top off the tank's load. To compensate for loss due to boil-off, both tanks are replenished until about three minutes before launch when the tanks are pressurised. Up to the launch, pressurising helium gas is supplied from the ground. After launch, the boil-off of the propellants is enough to maintain pressure until the engines are ignited 2 minutes and 40 seconds into the flight.
Atop the S-IVB stage, a ring 1 metre high and the same diameter as the stage, called the IU (Instrument Unit), carries the guidance and control electronics for the Saturn V. Particularly important among these are the LVDC (Launch Vehicle Digital Computer) and the inertial platform, the ST-124, which has to be aligned to the intended trajectory before launch. The angle between north and the groundtrack of the vehicle's flight path is called the flight azimuth. For this launch, it is to be 80.088° or slightly north of east. The gyroscopically stabilised platform at the heart of the ST-124 is aligned with the intended azimuth just prior to launch by rotating the X stable member with reference to a theodolite mounted some distance away from the launch pad. There is a small window in the skin of the Instrument Unit for this purpose.
At T minus 20 minutes, the Boost Preparation checklist deals with alignment of the X Stable Member Azimuth and checks that the various RCS (Reaction Control System) thrusters on the side of the Service Module (SM) are powered from the two main electrical busses in such a fashion to allow maximum RCS control, should one bus lose power.
This is Kennedy Launch Control. 16-minute mark has just been passed. We're at 15 minutes, 53 seconds and counting. The astronaut crew standing by for some important functions that'll be coming up in a minute or so as the Apollo spacecraft goes on full internal power on the fuel cells on board. Up to this time in the countdown, an external power source also has been applied to conserve those fuel cells. The external power source is removed. The astronauts will take a look at the status of their power system onboard and report it back to the Spacecraft Control Center. Both - The astronauts also will arm their hand controllers on board the spacecraft, and we will be ready to proceed to also place the Emergency Detection System on its automatic mode. Our countdown is still proceeding very satisfactorily as we come up on the 15-minute mark. The flight azimuth is the same. About 5 minutes ago there was an update given to the spacecraft computer. No changes were required because our countdown is right on time. 14 minutes, 53 seconds and counting; this is Kennedy Launch Control.
The crew is checking the final status of the electrical system and the setup of the FDAI (Flight Director Attitude Indicator). This instrument, often called the "8-ball", is similar to the ball-style artificial horizon found on many aircraft and, likewise, allows determination of the spacecraft's attitude with respect to a desired frame of reference, usually this will be the IMU (Inertial Measurement Unit) though it may be the GDC (Gyro Display Coupler), a device which displays the spacecraft's attitude based on a separate set of gyros. The FDAI will also show attitude errors and the rates of change of attitude.
This is Kennedy Launch Control. T minus 10 minutes, 55 seconds and counting. Countdown still running smoothly as astronaut Dave Scott on board the spacecraft checks out a key abort circuit. [This is probably the Astro Launch Operations Voice Check at the bottom of the CSM Boost Preparation checklist.] This is a special communications system with only about 3 or 4 people on it. These are the people who could recommend an abort to the spacecraft commander if required. These people include the Launch Operations Manager Paul Donnelly, the spacecraft communicator here in the [Launch] Control Center, astronaut Vance Brand, Spacecraft Test Conductor Skip Chauvin, and Houston Flight Director Gerry Griffin. We've checked out this special communication system and Dave Scott confirms that all is well.
Astronaut Vance Brand, the back-up CMP, communicates with the spacecraft from the LCC (Launch Control Center), five kilometres from the launch pad. In Mission Control, Houston, astronaut Gordon Fullerton is designated the CapCom for the first part of the mission and is awaiting the moment when the ascending vehicle will clear the tower it has stood next to and control of the mission transfers from the LCC to Houston.
The countdown [is] proceeding. Jim Irwin [is] now reading off some checks on the status of the fuel cells as we continue to go. We'll go on an automatic sequence here in the countdown starting at the 3-minute, 7-second mark in the count. From that time down, we will be automatic, with the countdown driven by the computer. This will wind up with ignition of those five engines in the first stage at the 8.9-second mark in the countdown. The engines will build up to their full thrust, the computer will make a determination that we have 90 per cent thrust in all 5 engines and that will be the signal for commit, or to release the vehicle. Our countdown still proceeding; 9 minutes, 33 seconds and counting. This is Kennedy Launch Control.
The third stage of the Saturn V, called the S-IVB for historical reasons, could be described as a smaller version of the S-II stage in that it also consists of a single tank structure with a common bulkhead between the LH2 and LOX compartments. These propellants, which are stored at the same supercold temperatures as for the S-II, are burned in a single J-2 engine which yields a thrust of 890 kN (a shade over 200,000 pounds). The engine's capability for restarting is utilised for the boost out of Earth orbit to the Moon. The construction of the S-IVB's propellant tank differs from the S-II stage by having the insulation on the inside of the tank's metal skin, a detail which made manufacture easier by not having to develop a bonding system which had to work at only 20 degrees above absolute zero. With the insulation between it and the propellant, it would be substantially warmer. About 8 hours before launch, the cryogenic systems of the S-IVB stage are purged, including the engine feeds and pump cavities. At T minus seven and a half hours, the LOX tank is precooled by pumping LOX onboard at 31.5 litres per second and allowing its conversion to a gas to take away heat from the tank. When enough liquid remains to fill the tank to 5 per cent, the fill rate goes to 63 litres per second, the fast fill rate, until the tank is 98 per cent full. Finally the tank's total capacity of about 77,000 litres is reached at a slow fill rate of up to 19 litres per second, and after that, replenished at a rate of up to 2 litres per second. The LOX tank filling takes about 25 minutes. Loading the fuel tank with about 250,000 litres of LH2 follows a similar process beginning 4 hours and 11 minutes before launch. Tank precooling and filling to 5 per cent is achieved with a fill rate of 31.5 litres per second, before the fast filling of the tank at 190 litres per second takes the tank's quantity to 98 per cent three and a half hours before launch. The slow rate of fill is re-established to top off the tank and keep it replenished. LH2 tank pressurization is maintained, during initial flight, by the boil-off of the fuel, then later with helium from a collection of spheres mounted on the exterior of the thrust structure at the base of the stage. The LOX tank is pressurised from heated helium fed from cold storage tanks within the LH2 tank.
This is Kennedy Launch Control; T minus 5 minutes, 55 seconds and counting. We're still Go. Just - we're about to come up with some status checks now to determine the final status. In the meantime, the Lunar Module test conductor, Fritz Widick has come in over the circuits, and informed the spacecraft commander Dave Scott, that Lunar Module Falcon and the Rover are Go. Dave Scott thanked him for this and then also received a report from Spacecraft Test Conductor Skip Chauvin that the command ship, which will be - have the call sign Endeavour, also is Go. We've just completed our status report and the Launch Operations Manager Paul Donnelly, the Launch Director Walt Kapryan and the Mission Director Chet Lee, all have given their Gos. We're standing by for the swing arm to retract to its full fallback position. It's moving now as we approach the 5-minute mark in the count. Coming up on the 5-minute mark. Mark: T minus 5 minutes and counting. We're Go on Apollo 15. This is Kennedy Launch Control.
The Saturn V launch vehicle is assembled, transported on, and launched from the Mobile Launcher. This structure consists of a base platform 48.8 x 41.1 metres and 7.6 metres high with a 13.7-metre square hole over which the vehicle is mounted. (The platforms were later converted for use by the Space Shuttle.) Sprouting from one end of this platform is the LUT (Launch Umbilical Tower). This 116-metre tower bears nine swing arms which provide the ground crew with access points to the vehicle, and a wide range of services including fuel, LOX, hydraulics, electrical power and various gases for purging and pressurization. These arms are articulated so they can swing away from the vehicle to give it clearance as it rises, and to protect them from the rocket's white hot exhaust gases. The crew enter the spacecraft via the top, or ninth, arm, which carries an environmentally controlled room at its end. Known as the "white room", it covers the CM hatch until the crew is aboard. 43 minutes before launch, it is swung away from the spacecraft by 12°. Five minutes before launch, it completes its retraction to 180°, on the opposite side of the tower from the Saturn V.
The Flight Plan indicates that in the CM, the five launch vehicle indicator lights are illuminated at T minus 4 minutes, 10 seconds. Throughout powered flight, these lights, arranged to resemble the pattern of the engine clusters on the S-IC and S-II stages, will provide the commander with cues about the progress of the boost and the status of each engine in each stage. Readers can familiarize themselves with this subpanel through the movie Apollo 13. Two events in the film that focus on this panel are when Tom Hanks (as Jim Lovell, Apollo 13's commander) manually jettisons the Launch Escape Tower, and when the inboard engine of the S-II stage prematurely shuts down. Then we see one of the few flaws in this movie, otherwise known for its incredibly high standards of accuracy. The central light is shown to blink on and off. In reality, it simply changes from on to off or vice versa.
Dave Scott, from 1998 correspondence: "In Apollo 13, the movie, the light was purposely made to blink to get the viewer's attention - the movie-makers knew the actual operation, but chose to take this license for dramatic effect (actually a pretty good license, as otherwise, the viewer would have missed the point!)."
This is Kennedy Launch Control. We just passed the 3-minute, 30-second mark in the count. The terminal sequencer has been armed and we are Go. Launch Operations Manager Paul Donnelly just wished the crew good luck and 'God speed' and received an expression of thanks from all three crew members. We'll be coming up shortly on the automatic sequence. 3 minutes, 10 seconds; firing command enable, firing command On. We have the firing command. We're now on the automatic sequence and the tanks in the 3 stages of the Saturn V, that contain those propellants, will begin to pressurize. The countdown is still proceeding and we're at now 2 minutes, 50 seconds and counting. We understand that there was an estimate that there are more than a million people in the area here to view the launch. The traffic has been heavy since 2 o'clock this morning. The beaches are packed and the roads are packed. 2 minutes, 35 seconds and counting. We're monitoring our status board here in Firing Room 1. Our ready lights are on concerning the spacecraft. Our Emergency Detection System Instrument Unit preparations are complete, and the automatic sequence is continuing. 2 minutes, 20 seconds and counting. We now have second stage liquid oxygen and third stage liquid oxygen supplies pressurized as the countdown continues.
At T minus 2 minutes, 15 seconds; glycol coolant is routed to bypass a radiator on the surface of the Service Module. The radiator will be heating up from aerodynamic friction during the passage through the atmosphere and therefore will not work as a cooling device. Coolant flow to the radiator will be reinstated once the spacecraft is in Earth orbit.
Coming up on the 2-minute mark. We'll be standing by for the Q-ball cover to be retracted shortly, atop the Saturn V vehicle.
The Q-ball cover is not unlike a pitot tube cover on an aircraft, it covers and protects eight openings at the top of the Launch Escape Tower. These openings lead to instruments which gauge air pressure. As well as providing dynamic pressure (known as "Q") information during powered flight, they help determine the angle of incidence of the tower during an abort event.
Mark: T minutes 2 minutes - T minus 2 minutes and counting. Still going well. Propellants stable on board the vehicle. The crew here in the Firing Room monitoring more than 300 redline values, watching temperatures and pressures to ensure they do not go above nominal. In the case that it did, any one of these key people could call in to hold the countdown. 1 minute, 36 seconds and counting; still going well. The pressurization sequence is still continuing in the vehicle. We're now 90 seconds away from lift-off. All still going well. We'll go on internal power with the vehicle at the 50-second mark in the count. We now get indications from our status board that all is still going well, and the third stage is now completely pressurized. Coming up shortly on the 1-minute mark, we're now 70 seconds and counting.
The CM batteries are connected across the two main power busses in the spacecraft to supply the extra power required during this particularly busy period. They also ensure that systems will continue to be powered in the event of a fuel cell failure during powered flight. The batteries will be recharged later, once the mission settles down to a lower power regime.
Second stage tanks are pressurized as our countdown continues. Mark: T minus 60 seconds and counting on Apollo 15. The astronauts are Go. Launch vehicle and spacecraft components; all Go as our countdown proceeds.
In preparation for the higher noise level during launch, the volume of the radio in the astronauts' headsets is increased.
Now 50 seconds; we have the power transfer. The [launch] vehicle [is] now on the battery power on the vehicle and all is still going well. Lunar Module Pilot Jim Irwin making some final checks now.
The FDAI is aligned so the vehicle's attitude can be monitored. The attitude of the launch site at the time of launch and with respect to the stars, is the frame of reference used for this alignment. At launch, the FDAI will display roll, 178° (launch azimuth of 88° plus 90°); pitch, 90°; yaw, 0°.
Passing the 40-second mark. Spacecraft Commander Dave Scott now has made his final check; that is, aligning the guidance system. 30 seconds and counting. The guidance system will go internal at the 17-second mark."
Now 25 seconds. We have complete clearance to launch. We are Go. 20.
At T minus 16.94 seconds, the Saturn's inertial guidance platform is released from the systems which have up to now been holding it in the correct orientation for the flight.
The ignition sequence of an F-1 engine is a complicated affair with many interrelated events happening almost simultaneously.
Diagram of the F-1 rocket engine
First, a description of the engine. A large combustion chamber and bell have an injector plate at the top, through which, RP-1 fuel and LOX are injected at high pressure. Above the injector is the LOX dome which also transmits the force of the thrust from the engine to the rocket's structure. A single-shaft turbopump is mounted beside the combustion chamber. The turbine is at the bottom and is driven by the exhaust gas from burning RP-1 and LOX in a fuel-rich mixture in a gas generator. After powering the turbine, the exhaust gas passes through a heat exchanger, then to a wrap-around exhaust manifold which feeds it into the periphery of the engine bell. The final task for these hot gases is to cool and protect the nozzle extension from the far hotter exhaust of the main engine itself. Above the turbine, on the same shaft, is the fuel pump with two inlets from the fuel tank and two outlets going, via shutoff valves, to the injector plate. A line from one of these 'feeds' supplies the gas generator with fuel. Fuel is also used within the engine as a lubricant and as a hydraulic working fluid, though before launch, RJ-1 ramjet fuel is supplied from the ground for this purpose. At the top of the turbopump shaft is the LOX pump with a single, large inlet in-line with the turboshaft axis. This pump also has two outlet lines, with valves, to feed the injector plate. One line also supplies LOX to the gas generator. The interior lining of the combustion chamber and engine bell consists of a myriad of pipework through which a large portion of the fuel supply is fed. This cools the chamber and bell structure while also pre-warming the fuel. Lastly, an igniter, containing a cartridge of igniter fluid with burst diaphragms at either end, is in the high pressure fuel circuit and has its own inject point in the combustion chamber. This fluid, often described as hypergolic but more accurately known as a pyrophoric substance, is triethylboron with 10-15 per cent triethylaluminium.
At T minus 8.9 seconds, a signal from the automatic sequencer fires four pyrotechnic devices. Two initiate combustion within the gas generator while another two cause the fuel-rich turbine exhaust gas to ignite when it enters the engine bell. Links are burned away by these igniters to generate an electrical signal to move the start solenoid. The start solenoid directs hydraulic pressure from the ground supply to open the main LOX valves. LOX begins to flow through the LOX pump, forcing it to rotate, then into the combustion chamber. The opening of both LOX valves also causes a valve to allow fuel and LOX into the gas generator, where they ignite and accelerate the turbine. Fuel and LOX pressures rise as the turbine gains speed. The fuel-rich exhaust from the gas generator ignites in the engine bell to prevent backfiring and burping of the engine. The increasing pressure in the fuel lines opens a valve, the igniter fuel valve, letting fuel pressure reach the hypergol cartridge which promptly ruptures. Igniter fluid, followed by fuel, enters the chamber through its own ports where it spontaneously ignites on contact with the LOX already present.
Engines On. 5, 4...
Rising combustion-induced pressure on the injector plate actuates the ignition monitor valve, directing hydraulic fluid to open the main fuel valves. These are the valves in the fuel lines between the turbopump and the injector plate. The fuel flushes out ethylene glycol which had been preloaded into the cooling pipework around the combustion chamber and nozzle. The heavy load of ethylene glycol mixed with the first injection of fuel slows the build-up of thrust, giving a gentler start. Fluid pressure through calibrated orifices completes the opening of the fuel valves and fuel enters the combustion chamber where it burns in the already flaming gases. The exact time that the main fuel valves open is sequenced across the five engines to spread the rise in applied force that the structure of the rocket must withstand.
...3,...
As fuel and LOX flow increase to maximum, the rise in chamber pressure, and therefore thrust, is monitored to confirm that the required force has been achieved. With the turbopump at full speed, fuel pressure exceeds hydraulic pressure supplied from ground equipment. Check valves switch the engine's hydraulic supply to be fed from the rocket's fuel instead of from the ground.
...2, 1, all engines running.
NASA image KSC-71PC-543 shows the vehicle on the pad as the engines build up to their full thrust.
One second to lift-off, the five launch vehicle indicator lights in the spacecraft have gone out, announcing to the crew that the thrust is OK and the stack is about to be let go of the hold-down clamps. Another lamp is illuminated at the point of lift-off as a verification for the crew.
Launch commit.
The stack is held onto the pad two ways. Four hold-down arms clamp the base of the S-IC, each with a force of 350 tonnes, anchoring the vehicle until full thrust is confirmed. A pneumatic device, backed up by an explosive, collapses the lever linkage to allow the arm to rise. Additionally, a number of controlled-release mechanisms (up to 16, depending on the mission) prevent the vehicle from accelerating too rapidly in the first moments of motion. These consist of tapered pins mounted to the pad which are pulled through dies mounted on the vehicle. The deformation of the pins controls the initial acceleration for the first 150 mm of flight; a simple and ingenious arrangement.
Lift-off. We have lift-off at 9:34 am Eastern Daylight Time.
The Flight Plan is an overarching document that defines the intended progress of the mission. After some preliminary notes, its major section consists of a timeline that shows flight events on pages covering up to 120 minutes or as little as 30 minutes of the mission. Where necessary, the activities of the three crewmembers are separately defined and there is a column for Mission Control's tasks that directly relate to the spacecraft; computer uploads for example. Symbols and lines are added to indicate important astronomical alignments; darkness, sub-Earth and subsolar points. The Flight Plan does not usually carry detailed steps. These are left to the checklists. Where an operation requires the crewman to be concentrating on the instrument panel, a set of cue cards carries a subset of steps.
Once the launch vehicle begins to rise, even fractionally, it cannot safely settle back onto the pad. Intentional engine shutdown will not occur, so of the nine access arms, the five which have remained attached up to this point, must now detach their umbilicals from the vehicle and swing clear. The first two centimetres of travel trigger the release of the umbilical connector plates which in turn triggers retraction of the arms.
At lift-off, one of the most important areas of the main display console that the commander must monitor is the subpanel which annunciates the progress of the launch. From top to bottom, this subpanel contains the Abort light, Mission Event Timer, Launch Vehicle Engine lights, lift-off light and critical switches (with safety covers) that are used to override the automatic abort sequences.
000:00:01 Scott: And the clock is running.
With a line that has come from crews since Alan Shepard's first flight for America, Dave Scott is confirming that the MET (Mission Event Timer) has begun counting. The timer receives a signal that the vehicle has lifted off, begins incrementing and the Flight Plan calls for this to be reported.
000:00:02 Brand: Roger. [Pause.]
000:00:04 Worden (onboard): Okay. [Garble] lift-off [garble].
On this, and all Saturn V launches, the stack can easily be seen leaning away from the LUT as it ascends from the launch pad. This yaw, begun 1.35 seconds after lift-off, manoeuvres the vehicle 1.25° from vertical in a direction away from the tower to ensure clearance in case a gust of wind pushes it back or a swing arm doesn't fully retract. Then nine seconds into the flight, almost as the rising rocket clears the tower, the stack is brought vertical again. To those who were not prepared for it, this fully intended yawing of over 110 metres of metal, filled to the brim with exotic fuels and oxidisers, could sometimes cause some consternation. The launch checklist for the CSM calls for the initiation of this yaw to be reported to the ground but the transcript does not carry it.
Scott, from 1998 correspondence: "The approved, required, authorized, etc. procedures during launch were on the cue cards. For A-15, there were 45 "CSM Cue Cards," all of which were prepared (in a single book) by the Crew Procedures Division. The Cue Cards represent the proper crew procedures when applicable. During launch, the A-15 CDR Cue Card indicated :00 - lift-off, and then next :11 - Roll. Therefore, in summary, there was no "yaw" transmission to the ground. How this got into the "checklist" I do not know, but as the missions wore on, "interested parties" were able to get into the loop. During the early days of Apollo, the crew only prepared the "checklist," which was later approved by the Crew Procedures Change Board. An interesting part of the Apollo 'culture.'"
All Saturn V launches were extensively photographed from every conceivable angle.
The Apollo 15 space vehicle rising past the Launch Umbilical Tower. From Kipp Teague's Apollo Image Gallery.
Eric Jones, editor of the Apollo Lunar Surface Journal was one of those lucky enough to witness the launch.
Jones, from 1999 correspondence: "I was on the beach about 10 miles from the pad for Apollo 15 and I will never forget listening to PAO as the excitement built and then seeing the engines fire and then feeling - more than hearing - that incredible noise as the Saturn V began to rise. I was screaming 'Go, go, go', completely unable to hear myself. Awesome!"
Woods, from 1999 correspondence with Jones: "I never knew you were actually there at launch. Care to tell us more about your experience that morning - for the Journal, of course?"
Jones, from 1999 correspondence: "Actually, I don't remember a great deal about it other than the magnificence of the spectacle. I made the mistake of trying to take pictures which actually detracts. I do remember that it was an interesting mix of middle-aged Middle Americans in their campers and hippies. There was a lovely girl with a kitten on a string wading in the shallow water while we also listened to the countdown via the many radios that folks had with them. And the traffic leaving afterwards was incredible."
000:00:12 Scott: Roger dede [sic]. Clear the tower.
The tower is clear.
Once the ascending vehicle has cleared the Launch Umbilical Tower, control of the mission is transferred to Mission Control in Houston, Texas. Gordon Fullerton assumes the role of CapCom from Vance Brand.
Scott, from 1998 correspondence: "The 'Tower Clear' call is made by the Launch Director - this is a very critical transmission in terms of both safety and responsibility: (1) safety, of course, at the instant of the call, and by visual observation of the Launch Director, the Saturn is clear of a major obstacle (such failures as an engine hardover would probably be catastrophic prior to Tower Clear); and (2) this is the official transfer of mission responsibility from the LCC (Launch Control Center) at the Cape (the Launch Director) to the MCC in Houston (the Flight Director). The Flight Director would have acknowledged this over the comm link with the Launch Director. This is very important topic, as few people seem to realize the significance of the call."
Dave has reported that a guidance program in the Saturn V's Instrument Unit (IU) has begun to manoeuvre the stack in roll. According to the AS-510 Flight Evaluation Report, both a roll and a pitch manoeuvre begin at 12.2 seconds into the flight.
The launch pads at Launch Complex 39, Kennedy Space Center, are aligned to the points of the compass with the LUT north of the vehicle. Therefore, at launch, the vehicle's frame of reference, its azimuth, is 90° east of north and the purpose of this roll manoeuvre is to align the launch vehicle with the desired trajectory, with an azimuth 88.088° east of north. The vehicle's manoeuvres will place the spacecraft into a "heads down" attitude.
Scott, from 1971 Technical Debrief: "My evaluation, compared to Apollo 9 [on which he flew as CMP], was that the lift-off itself was softer and quieter. When the tiedowns went, we could feel definite motion, but it didn't seem like as much as it was on Apollo 9."
Woods, from 1998 correspondence with Scott: "Could the difference between your perception of Apollo 9's and Apollo 15's lift-off be due to the greater weight of the stack in the latter mission?"
Scott, from 1998 correspondence: "Unlikely - there are probably many other variables with greater influence on the 'feel' of a launch - each launch seemed to have its own unique characteristics, even each mission. The crew reports after each mission were, among other uses, factored into the simulators - which to subtle, but perceptible, degrees were changed in some form after each mission - like sounds of thrusters, sometimes louder and sometimes softer. Also, the added mass in per cent was probably less than temperature and wind changes in percent - on any given launch."
000:00:18 Fullerton: You have good thrust on all five engines.
000:00:21 Scott: Thanks, Gordo. Roll's complete.
000:00:24 Fullerton: Roger.
At 20.5 seconds into the flight, the four outboard engines cant outwards in order to direct their thrust more towards the centre of mass of the vehicle. This is so that if one of those engines fail, the resultant turning moment from the other engines would be less than if they were all aimed along the X-axis.
000:00:27 Scott: And we have a pitch program.
000:00:28 Fullerton: Roger. Pitch. [Pause.]
KSC-71PC-547 shows the vehicle well into its vertical flight.
Scott, from 1998 correspondence: "During launch, all transmissions between the spacecraft and MCC are made to and from the Commander and the CapCom, only. This is essential to maintain continuity, clarity, command, and control of the existing situation as well as potential and actual abort situations. In the spacecraft, just as in MCC, only one person communicates during time-critical situations."
Ascent has been nearly vertical up to now, except for the yaw manoeuvre for tower clearance. The vehicle has rolled to the required azimuth and, under control of the IU, is pitching over to begin gaining horizontal velocity.
The guidance of the launch vehicle is monitored and controlled by the Launch Vehicle Digital Computer in the IU and its programs, and not by the CM guidance and control system, which only monitors for now. The value of this arrangement was dramatically demonstrated on Apollo 12 when, during the early seconds of the flight, lightning temporarily knocked out the CM's electrical system, causing the CM's Inertial Measurement Unit (IMU) to tumble and lose its pointing reference. The IU, clearly unaffected by the enormous pulse of electricity which passed through the vehicle, continued to faithfully guide the Saturn towards orbit while the crew worked to reset the CM's guidance system.
000:00:39 Fullerton: Stand by for Mode One Bravo.
000:00:42 Fullerton: Mark. One Bravo.
000:00:43 Scott: Roger. One Bravo. [Long pause.]
The role of Public Affairs Officer has also transferred to Houston.
Booster Systems Engineer reports to Flight Director that S-IC stage [is] looking good.
'Booster' is one of the posts on the front row of Mission Control. After the Saturn V finishes its task, and Apollo 15 is on its way to the Moon, the three booster consoles are vacated.
Throughout the powered ascent of the launch vehicle, there are various modes of aborting the mission, each of which are appropriate to the current height and speed. For the first two of these modes, IA and IB, the Flight Plan defines the safe range of vehicle motion rates as not exceeding ±4° per second in pitch and yaw, ±20° per second in roll. Motion rates exceeding these limits will entail an abort.
The initial 42 seconds, to an altitude of about 3,000 metres (10,000 feet) are flown in abort Mode IA (one alpha). If a dangerous situation occurs within this period, the CM would separate from the SM, and the LET (Launch Escape Tower, or just 'tower'), which is the solid-fuelled rocket mounted on top of the CM, would carry it up from the wayward launch vehicle while a small 'pitch control' motor at the top of the LET steers the assembly east out over the ocean and away from a possibly exploding booster below. The tower would be jettisoned only 14 seconds after the initiation of the abort. While this is going on, the highly dangerous hypergolic propellants of the Command Module's RCS would quickly and automatically be dumped overboard as they would be harmful to the recovery forces. The CM would then descend on parachutes to a normal splashdown.
Abort Mode IB extends from 42 seconds into the flight to an altitude of 30.5 km (16.5 nautical miles) as defined by the abort checklist. With the vehicle being further downrange and tilted over, the pitch control motor would not be required in the event of a IB abort. However, it had been discovered during hypersonic testing, that the CM/LET stack could be aerodynamically stable in a tower-first as well as a base-first attitude so a pair of canards were added which would be deployed automatically to force the combination into an attitude where the base of the CM is facing the direction of travel, ready for the safe deployment of the drogue and main parachutes. While the canards have little effect in a low altitude abort, they become increasingly important as the Saturn V gains speed through the IB mode.
Scott, from 1998 correspondence: "The 'abort' function was so very critical in terms of success/failure that many people thought there should be no crew function, and it should all be automatic (which in turn would introduce other more consequential failure modes). The most difficult simulations during the entire training process were 'launch aborts' - even more so than lunar landings (the landing itself was more difficult than launch, but not for 'aborts'). More crews 'bought it' during launch sims than any other area, by far!"
000:00:45 Worden (onboard): Propellant Dump, RCS Command, Dave.
000:00:46 Scott (onboard): Okay.
000:00:54 Scott (onboard): Okay. Going through the air. (Laughter)
000:00:56 Worden (onboard): Cabin pressure decreasing.
000:00:57 Scott (onboard): Okay. Good.
000:00:58 Irwin (onboard): Looks good over here.
000:01:00 Worden (onboard): High at 20,000.
000:01:01 Irwin (onboard): Dead.
000:01:02 Worden (onboard): One minute.
000:01:03 Irwin (onboard): Here [garble].
000:01:03 Fullerton: 15, Houston. Everything looks perfect down here.
000:01:06 Scott: Okay. Looks cleared up here, Gordo. [Long pause.]
000:01:09 Scott (onboard): Okay, the altimeter is six zero.
000:01:12 Worden (onboard): Well, how about that?
Going through maximum dynamic pressure at this time.
The aerodynamic forces acting on the launch vehicle have been rising as the vehicle gains speed. However, the air around it is thinning rapidly with increasing altitude. The interaction of these two changing values results in a maximum degree of pressure on the vehicle's skin at 1 minute, 22 seconds; at a speed of about Mach 1.7 and an altitude of 13.7 km. This moment of maximum dynamic pressure is also often described as Max Q.
Scott, from 1971 Technical debrief: "The noise was relatively low-level, and none of us had any trouble with the comm at all. We had vibrations within the S-IC which were just about the same frequency as the noise you hear standing on the ground. You hear the reverberations from the engines - or the S-IC vibrations were about the same frequency, low amplitude - just something you could feel. Going through max Q was noisy, but we still had good comm. And it didn't seem to me that that was as loud as it was on Apollo 9 either. I could hear Jim call 'cabin pressure relieving' very clearly. You could hear pretty well all the way through there, too."
Irwin, from 1971 Technical debrief: "Yes, I thought the comm was excellent."
Worden, from 1971 Technical debrief: "I guess the shaking of the S-IC was a little bit more than I expected. More lateral shaking, a little more vibration than I expected right at lift-off. When we got away from the tower and got away, maybe from some ground effects, whatever it was, it smoothed down."
Scott, from 1971 Technical debrief: "During the launch phase we went right into the Sun. At one point during launch, I put my hand up to shield my eyes so I could see the ball [the FDAI]. I was surprised."
During the ascent through the atmosphere, it is important that the rocket points straight into the direction of its motion, and avoids flying sideways, even slightly, lest aerodynamic forces overload its structure. This is achieved by flying the first stage, and the start of the second stage, according to a carefully calculated, preprogrammed tilt schedule.
000:01:28 Irwin (onboard): Exciting!
000:01:30 Scott (onboard): Okay. We're through Max Q.
000:01:34 Worden (onboard): Okay. 1:32. Program looks good, Dave. Out at 11 miles.
000:01:40 Scott (onboard): Okay. Good shot. Two and a half g.
000:01:44 Irwin (onboard): Roger.
000:01:47 Scott (onboard): Pitch profile looks good.
000:01:50 Irwin (onboard): Roger.
000:01:52 Worden (onboard): 1:50.
9 [nautical] miles [16.6 km] downrange, 13 - 14.5 [nautical] miles [24 - 26.8 km] height.
000:01:54 Fullerton: Stand by for Mode One Charlie.
000:01:57 Fullerton: Mark. One Charlie now.
000:01:58 Scott: Roger. One Charlie.
Mode IC is used for aborts occurring between 30.5 km (16.5 nautical miles) and the jettison of the tower. As the air is now very thin, the airflow around the pair of canards at the top of the tower would have little aerodynamic effect during an abort. Instead, the tower and BPC would be jettisoned and the Command Module's RCS used to control the orientation of the spacecraft. The safe range of vehicle motion rates are now defined as not exceeding ±9° per second in pitch and yaw, ±20° per second in roll.
Each of the S-ICs...
000:02:01 Scott: EDS Auto to Off.
000:02:03 Fullerton: Roger. [Long pause.]
As the S-IC nears the end of its burn, Al Worden is inhibiting the EDS (Emergency Detection System) with a switch directly below the computer keypad. The EDS is only needed for flight through the thickest part of the atmosphere where high aerodynamic forces and the structural load they impart to the vehicle could cause loss of control to turn catastrophic too quickly for the crew to react in time. With EDS switched off, any required aborts must be initiated by the crew.
000:02:06 Scott (onboard): Okay, we're at 3g's. Stand by for inboard.
000:02:14 Worden (onboard): Okay. The program's looking good.
Each of the five S-IC engines [are] gulping 3 tons of fuel [means propellant] per second.
Expressed in SI units, each F-1 is consuming about 0.8 metric tons of fuel and about 1.8 metric tons of oxidizer each second. Across the five engines, the stage was consuming 13.5 tonnes of propellant each second.
Towards the end of the S-IC's boost phase, two factors serve to gradually increase the acceleration experienced on board. First, the atmosphere is becoming essentially a vacuum, reducing the backpressure that the exhaust gases have to fight against when compared to the air pressure at sea level. This improves the efficiency of the engines so that from launch to cut-off, S-IC thrust rises 19 per cent from 34,250 kN to about 40,700 kN. Second, the S-IC tanks are emptying, lightening the launch vehicle and presenting less inertia to the thrust. At 1,500 metric tons, just the quantity of LOX in the first stage was more than half the mass of the entire space vehicle before the engines started. To alleviate the rising acceleration forces and the shock of all five engines shutting down simultaneously, the centre engine of the cluster is shut down 23.5 seconds earlier than the outboard engines. The outboard engines cut off at 2:39.6, staging occurs at 2:40.7 and the second stage ignition command is at 2:41.8.
Another effect of the reduced air pressure on the S-IC is visible on movie coverage of the launch as the base of the vehicle appears to be progressively consumed by the conflagration. Near the ground, the plume is constrained by air pressure into a narrow flame extending rearwards. With decreasing air pressure, the hot gases are able to expand into an ever widening plume. Towards the end of the S-IC's flight, the air is so thin and the slipstream so negligible that a small amount of exhaust is able to expand forwards up the side of the rocket's structure giving the appearance, on TV coverage, of the rocket's base being consumed by the plume.
000:02:30 Irwin (onboard): A little high hum, there.
000:02:31 Worden (onboard): Yes.
000:02:32 Scott (onboard): Okay, 10 seconds to staging. Hang on.
000:02:34 Worden (onboard): Okay.
000:02:36 Scott (onboard): Five seconds.
Flight Dynamics reports Go for staging.
The spent S-IC has lifted the vehicle to about 70 km; above most of the atmosphere. The S-II will continue the ascent to the orbital height of about 170 km, as well as accelerating the vehicle to about 90 per cent of the velocity required to achieve a stable orbit. Staging occurs at 000:02:41.2.
000:02:43 Worden (onboard): Man, you aren't kidding.
000:02:44 Irwin (onboard): Boy.
000:02:46 Scott: Good stage.
000:02:47 Fullerton: Roger. [Pause.]
The term "Good stage" is used to mean that one stage of the stack is spent and has been separated from the rest of the rocket to allow the stage above it to take over the task of acceleration. The tilt sequence, which has defined the trajectory throughout the flight so far, has brought the rocket's slow, pre-programmed tilting motion to a halt so that during staging, the attitude is stable which avoids complicating the event with unwanted rotation of the vehicle.
The S-IC/S-II staging sequence for AS-510 differed markedly from earlier missions. On previous flights, the interstage, or skirt, a 4.9-metre tall ring matching the 10-metre diameter of the S-IC and S-II that it sits between, carried solid-fuel rockets which fired shortly after the first stage separated to settle the S-II propellants in their tanks. AS-501 had eight of these ullage rockets, while AS-502 to AS-509 had four. They were deleted from the Apollo 15 launch vehicle, along with four of the eight retro rockets built into the conical engine fairings around the base of the S-IC, in order to save weight and increase payload. Ullage is a brewers' term for the portion of a barrel occupied by air, not liquor. The separation did not quite go according to plan. After the F-1 engines were shut down, the thrust they generated during the tail-off period was greater than expected. The engines don't instantly stop thrusting when they receive their cut-off command. After a quick drop to about 2 per cent thrust, they take over four seconds to decay to zero. As the engines expired, the acceleration imparted to the, now separate, empty and therefore light S-IC stage was above the predicted value. Despite deliberately coasting for longer than usual between separation and S-II ignition, the distance between the two stages was less than engineers had planned and the blast of hot gases from five J-2s against the top of the empty stage disabled a telemetry package with which the S-IC was to be monitored until its impact with the Atlantic Ocean.
Staging of the S-IC and S-II is technically described as a "dual plane separation," as the vehicle is cut across two geometrical planes. The first plane is between the skirt and the S-IC, with the S-II engines starting 1.1 seconds later. The second plane separation, when the second stage loses the skirt, occurs at 3 minutes, 10.7 seconds; 30.0 seconds after the S-IC separation. This time allows the S-II's attitude to stabilise because if either part of the launch vehicle were to be yawing or pitching excessively, there would be a danger of the engine bells striking the S-IC and skirt as the two great metal cylinders coast along before ignition of the S-II. The skirt provides clearance above the first stage's LOX tank for the five J-2 engines of the S-II stage.
000:02:55 Fullerton: 15, Houston. You have good thrust on the S-II. All five are good.
000:02:58 Scott: Okay. [Long pause.]
73 [nautical] miles [135 km] downrange, 47.9 [88.7 km] altitude.
Scott, from 1971 Technical debrief: "The staging was as we expected, I guess. It was what I'd call violent when the S-IC shuts down and everything recoils there, and that was almost identical to Apollo 9. It was really just a big bang. We saw the fireball come up to the BPC [Boost Protective Cover]; I saw it in my left side window. I saw the fireball out the front window, too."
000:03:00 Worden (onboard): Okay, Dave. You got TFF 3:26.
000:03:02 Scott (onboard): Good show. We'll go on time.
The Boost Protective Cover over the Apollo 15 CM had windows in it to allow visibility through both the CM hatch window (window 3) that the CMP could look through, and the left-hand rendezvous window (window 2).
Scott, from 1971 Technical debrief: "Right after, or just prior to, the S-II ignition, there was a lateral motion, attitude-wise, in the vehicle. Sometime in this staging sequence, we got a slight yaw."
Worden, from 1971 Technical debrief: "After being briefed several times of what to expect at separation, it didn't seem as violent as I was really expecting it to be."
Scott [speaking to Worden], from 1971 Technical debrief: "Which one?"
Worden, from 1971 Technical debrief: "The first one."
Scott, from 1971 Technical debrief: "I thought you agreed that it was pretty violent."
Worden, from 1971 Technical debrief: "It was pretty violent, but I guess I was expecting something even more than that."
Irwin [speaking to Scott], from 1971 Technical debrief: "You had us so well briefed, Dave, that we were expecting it."
The S-II stage carries five J-2 uprated engines which burn LH2 and LOX to produce up to 1,041 kN (234,000 pounds) thrust each. They are capable of being restarted in flight but this feature is only implemented in the engine used in the S-IVB.
Labelled diagram of the J-2 engine.
The thrust chamber and bell of each engine is fabricated from stainless steel tubes brazed together in a single unit. Supercold LH2 is pumped through these tubes to cool the thrust chamber and simultaneously prewarm the fuel, turning it to a vapour in the process. The engine carries two separate turbopumps, both powered in turn by the exhaust from a gas generator which burns the stage's main propellants. The hot gas exhaust from the gas generator is fed first to the fuel turbopump, then to the LOX turbopump before being routed to a heat exchanger and finally into the engine bell where it aids combustion. The fuel and LOX outputs of both turbopumps are fed, via main control valves, to the thrust chamber injector via the LOX dome. Unlike the solid steel, copper-faced injector of the F-1, the J-2 injector is fabricated from layers of stainless steel mesh sintered into a single porous unit. A solid LOX injector behind this carries 614 posts which pass LOX through the injector face and into the combustion chamber. Each post has an annular fuel orifice around it through which gaseous hydrogen passes, atomising and mixing with the LOX as it does. The fuel delivery is arranged to ensure that about 5 percent seeps through the injector face to cool it, the rest passing through the annular orifices.
In the centre of the injector face is the ASI (Augmented Spark Igniter) which is fed with propellant. it provides a flame to initiate full combustion. Valves are provided to bleed propellant through the supply system well before ignition to chill all components to their operating temperatures otherwise gas would be formed which would interfere with the engine's use of propellant as a lubricant in the turbopump bearings. A tank of gaseous helium is fabricated within a larger tank of gaseous hydrogen. This is the Start Tank. The helium provides control pressure for the engine's valves while the hydrogen is used to spin up the turbopumps before the gas generator is ignited. A PU (Propellant Utilization) valve on the output of the LOX turbopump can open to reduce the LOX flowrate. This adjusts engine thrust down to 890 kN (200,000 pounds) during flight to optimise engine performance. Although it reduces the thrust, it increases the efficiency of the engine.
To start the J-2 engine, spark plugs in the ASI and gas generator are energised. The Helium Control and Ignition Phase valves are actuated. Helium pressure closes the Propellant Bleed valves, it purges the LOX dome and other parts of the engine. The Main Fuel valve and the ASI Oxidiser valves are opened. Flame from the ASI enters the thrust chamber while fuel begins to circulate through its walls under pressure from the fuel tank. After a delay to allow the thrust chamber walls to become conditioned to the chill of the fuel, the contents of the Start Tank are discharged through the turbines to spin them up. This delay depends on the role of the engine. A one second delay is used for the S-II engines. Half a second later, the Mainstage Control Solenoid begins the major sequence of the engine start. It opens the control valve of the gas generator so that combustion can begin. The exhaust supplies power for the turbopumps. The Main Oxidiser valve is opened 14° allowing LOX to begin burning with the fuel which has been circulating through the chamber walls. A valve which has been allowing the gas generator exhaust to bypass the LOX turbopump is closed allowing its turbine to build up to full speed. Finally, the pressure holding the Main Fuel valve at 14° is allowed to bleed away and the valve gradually opens, building the engine up to its rated thrust.
The interstage ring or skirt is jettisoned at 000:03:11.2, thirty seconds after staging. It has been kept with the S-II for this time to allow the stage's operation to smooth out before it is dropped. This is to reduce the possibility of contact due to the small clearance between the engine bells and the skirt. Since the vehicles is essentially being cut across two planes, above and below the interstage, Dave describes this as the second plane separation.
000:03:12 Scott: Second plane sep.
000:03:14 Fullerton: Roger.
A single, small, solid-propellant motor near the top of the tower fires for one second, jettisoning the entire LES (Launch Escape System) and the checklist moves to abort mode II. The time for this event is 000:03:15.9.
000:03:17 Scott: Tower Jett.
000:03:18 Fullerton: Roger. We confirm the Skirt Sep. You're Mode II.
000:03:21 Scott: Roger. Mode II.
The LES consists of the tower, with all its rocket motors, instrumentation and canards; and the BPC (Boost Protective Cover), which is a shroud over the entire Command Module which protects the spacecraft from the friction generated heat of ascent, and from the exhaust of the Launch Escape Motor should the tower be used for an abort. The BPC includes two windows to allow visibility through the left hand and central windows of the CM. The central window is mounted in the main hatch of the CM. Only when the LES is jettisoned are the other three windows uncovered.
The main rocket motor of the LES, if used, would burn for eight seconds, generating 654 kN (147,000 pounds) through four nozzles which are angled to direct the exhaust away from the CM.
Abort Mode II lasts from the jettisoning of the tower to the decision to stage from the S-II to the S-IVB. In a Mode II abort, the Command and the Service Modules will separate from the launch vehicle and the SM main engine or its RCS engines will be used to get the spacecraft away from the launch vehicle. Then the CM and SM will separate before the CM completes a normal splashdown on the ocean.
At 000:03:22.6, the IU begins the IGM (Iterative Guidance Mode). Up to now, the IU has been steering the vehicle according to a predetermined trajectory which minimises sideways movements though the air while tilting it along its flight azimuth. It has not been using any information about its position and velocity to alter its flight path. The control is "open loop" and there is essentially no active guidance taking place. What Dave calls "Guidance initiate" is when the control loop is closed as the IU begins using position and velocity data to help it guide the vehicle to where it wants to get to - an accurate Earth orbit.
000:03:26 Scott: Guidance Initiate.
000:03:28 Fullerton: Roger. [Long pause.]
Scott, from 1971 Technical debrief: "The S-II was very smooth, and all the way through the S-II burn, we had a very light - I'd guess in talking about it - we figured 10- to 12-cycle-per-second vibration, something in that range, low-amplitude, something you could just feel, but it was continuous all the way through. There was no pogo, no change in the oscillation. Tower jett was smooth and came away very cleanly."
Being a huge, long, metal structure in a very dynamic environment, with large quantities of fluid moving inside at speed, the stack is prone to vibrations along its length. This lengthwise stretching and squeezing is known as "Pogo" from its similarity to the spring action of the "Pogo stick," a contemporary child's toy. The structure itself vibrates at particular frequencies which, as the fuel tanks empty, sweep through a substantial range. Other variables, such as vehicle and payload mass, and propellant characteristics, make it exceedingly difficult to predict the frequency and magnitude of these pogo oscillations.
Many launch vehicles suffer pogo problems during development and the Saturn V was never completely free of it. The S-II, in particular, exhibited severe pogo which plagued the early flights. One partial cure for this is to shut down the centre engine earlier than the others.
Coming up on 10,000 feet per second [3,000 m/s] mark. Down range 131 [nautical miles, 243 km], altitude 66 [nautical miles, 122 km].
000:03:37 Scott (onboard): How we doing, Al?
000:03:38 Worden (onboard): We're doing fine; 63 miles [117 km].
000:03:41 Scott (onboard): Good.
000:03:48 Irwin (onboard): Everything looks good over here.
000:03:50 Scott (onboard): Okay.
000:03:51 Worden (onboard): Just - looks just about a hundred feet per second [30 m/s] down on the H-dot, but everything else looks fine.
000:03:56 Scott (onboard): Okay, I got the big fireball going by at staging. I don't know whether you saw it or not. That beauty really goes.
000:03:59 Worden (onboard): Yes...
000:04:01 Fullerton: 15, Houston. At 4 [minutes], the guidance has converged. The CMC is Go and everything looks good.
000:04:06 Scott: Okay, Gordo. Looks good up here. [Long pause.]
The CMC (Command Module Computer) will be closely involved in computation of the spacecraft's trajectory throughout the mission. However, during launch and ascent, the IU handles trajectory computation and vehicle control. The CMC is accessed by the crew via two DSKYs (Display and Keyboard), one of which is on the main instrument panel, the other being on the LEB (Lower Equipment Bay). The LM carries a computer of very similar design.
Since they left the pad, the CMC has been running Program 11 for two main purposes. It lets the crew monitor the progress of the ascent, and it gives Dave the option of having the CMC control the ascent instead of the IU, even with crew input.
Scott, from 1998 correspondence: "The CMC computed the entire launch profile such that if the IU failed (at any time) the entire Saturn V, or subsequent stages, could be flown into orbit manually by using primarily the FDAI and DSKY displays and one of the two RHCs [Rotational Hand Controllers]. This is a little-known, but very important capability; and we spent a fair amount of time training for this. The DSKY display also provided a monitor of the IU performance, and if deviations were too large, [you could] disengage the IU completely and proceed with a manual launch insertion."
There is a note in the Launch Checklist, page L2-8, that gives the simple procedure for changing to manual control of the booster. The LV Guidance switch at the bottom left of Panel 2 is switched away from IU to CMC, then Verb 46 in the computer is executed, allowing control signals from the Rotational Hand Controllers to be processed and routed to the Saturn V.
000:04:09 Irwin (onboard): Man, I got the Moon in my window.
000:04:11 Worden (onboard): Yes, sir. It's out there.
000:04:19 Scott (onboard): Thrusters are stable; the ball's stable.
000:04:23 Worden (onboard): We're at a VI of 11,000 and right on the money.
000:04:27 Scott (onboard): Good show. Let me check here at 4:30 just to make sure.
000:04:36 Worden (onboard): That sucker's right on - right on.
000:04:45 Worden (onboard): Little high on altitude. I bet you they're going to give you the [garble] here in a minute.
000:04:53 Scott (onboard): I hope so by now.
Now at 35 per cent of the velocity needed to orbit. Downrange 190 [nautical] miles [352 km]. Altitude 79 [nautical miles, 146 km].
Apollo 15 has just about reached the correct height for its Earth parking orbit. This orbit will be very low and would not be sustainable over the long term, but it is sufficient for the two hours and fifty minutes that the crew and Mission Control require to check all the vehicle's systems before they leave for the Moon. The stack is travelling almost horizontally, skimming through the upper atmosphere and accelerating towards an orbital velocity of 7.8 kilometres per second.
000:05:12 Worden (onboard): Yes siree, looks good.
000:05:20 Scott (onboard): See, we're getting just a little teeny bounce. You feel it now?
000:05:23 Worden (onboard): Uh-huh.
000:05:24 Irwin (onboard): Every once in a while?
000:05:25 Worden (onboard): Yes.
000:05:30 Scott (onboard): Very low amplitude.
000:05:41 Scott (onboard): Okay, be watching for the S-IVB for COI.
000:05:44 Irwin (onboard): Okay.
Predicting nominal shutdown on the S-II stage.
000:05:43 Fullerton: 15, Houston. Times are nominal. The level sense arm will be 8 plus 34, and S-II cut-off at 9 plus 09. Over.
This method of relating GET (Ground Elapsed Time) is a common shorthand used throughout the mission. To some extent, the context determines whether the first figure is hours or minutes. These times are 0 hours, 8 minutes and 34 seconds; and 0 hours, 9 minutes and 9 seconds.
Each propellant tank in the S-II has five sensors near the bottom which signal when they are uncovered by the draining liquid. When it receives two such signals from the same tank, the IU computer begins a sequence which will lead to engine cut-off. However, this engine cut-off system is not armed until the measured level has fallen below a certain threshold so as to inhibit the possibility of a false shutdown. Fullerton is telling the crew when Mission Control expects the cut-off system to be armed, based on current consumption, and when the engines will subsequently be shut down.
000:05:52 Scott: Roger; 8 plus 34 and 9 plus 09.
000:05:57 Fullerton: And stand by for S-IVB to COI.
COI stands for Contingency Orbit Insertion. This is another way of saying "abort Mode III". The S-IVB now has the capability to take the stack to a point where the Service Module's large SPS engine can ignite and place the CSM into Earth orbit. However, in the event of such an abort, and without the S-IVB, the spacecraft would not be able to depart for the Moon, instead embarking on a planned for, but hopefully unrequired Earth orbit mission.
000:05:57 Scott (onboard): Okay, Jimmy; gimbal motors.
At the base of the Service Module behind them is the Service Propulsion System engine with its large nozzle. It is mounted on gimbals to allow a degree of steering and in case it is used in an abort, the electric motors that drive it are powered up. The engine can be steered in the pitch and yaw axes, two degrees of freedom, and each axis has two motors for redundancy, four in all.
000:05:59 Fullerton: Mark. You have S-IVB to COI now.
000:06:22 Scott (onboard): Okay, we're right - right down the line.
000:06:26 Irwin (onboard): Okay.
000:06:27 Worden (onboard): Coming up on 15,000 VI, 260 H-dot. That's right where we ought to be, and that gives us an SCS COI.
000:06:32 Scott (onboard): Okay. Keep your eye up for S-IVB to orbit.
000:06:38 Worden (onboard): Yes.
380 [nautical] miles [704 km] downrange, altitude 94.5 [nautical miles, 175.0 km], velocity 15,000 feet per second [4,572 m/s].
Apollo 15 is now above their nominal orbital height and for a time, the attitude of the vehicle will be slightly nose down.
The crew is at the top of page 2-9 of the CSM Launch Checklist. Communication with Mission Control is through a ground station in Bermuda and is via one of four antennas spaced around the Command Module at 90° intervals, designated A, B, C and D. The Flight Plan calls for Omni(directional) antenna D to be used if the launch azimuth is less than 96°, antenna C if greater than 96°. The actual launch azimuth was 88.088° so antenna D should be used.
The four flush mounted S-band antennas are used for near Earth communication and as a back-up to deep space communication. There is a capability for the ground to switch between antenna D and one which has been manually selected by the crew. Normally, the crew would select antenna B, which is on the opposite side of the spacecraft to D. Then, as one antenna goes away from line of sight of Earth, the other will come into view and the ground can take care of antenna selection. However, if the crew manually selects antenna D, then the ground effectively lose control of which antenna is being used at any particular time.
000:06:40 Fullerton: Stand by for S-IVB to orbit capability.
000:06:46 Fullerton: Mark. You have it now.
000:06:48 Scott: Rog; S-IVB to orbit. [Long pause.]
Should the S-II cut out early, the S-IVB now has the ability to place itself, the CSM and LM into a safe orbit. Of course, there would not then be sufficient propellant onboard to boost to the Moon. However, the crew would switch to an alternate mission plan.
Scott, from 1998 correspondence: "There were several Alternate Mission Timelines in Section 6 of the Flight Plan to be used in the event there was no TLI. They were very straightforward and were essentially an extension of the pre-TLI timeline. We spent very little time on them, only to be aware that they were there and the general nature of the requirements. Although Al Worden did probably work on the non-lunar-return reentry to ensure that he was proficient in that area too."
Downrange 479 [nautical] miles, [887 km], altitude 96 [nautical] miles, [178 km], now approaching 65 per cent of velocity needed for orbit. The velocity now, 16,700 feet per second [5,090 metres per second]. Official time of lift-off [9 hours] 34 minutes, 00 seconds .79. [Eastern Daylight Time]
000:07:01 Scott (onboard): How's our cabin pressure, Jim?
000:07:03 Irwin (onboard): Holding at 6 [psi, 41 kPa].
000:07:04 Scott (onboard): Very good.
000:07:18 Worden (onboard): Feels like we get a little vibration out of that thing.
000:07:21 Scott (onboard): Well, it seems to be pretty steady though.
000:07:24 Worden (onboard): Yes.
000:07:25 Scott (onboard): We're about 1.7g, somewhere around there. Okay, 10 seconds to inboard.
000:07:34 Worden (onboard): VI's 18,000 [fps, 5,486 m/s]. [Garble] We're at 96 [nautical] miles [178 km].
Downrange 660 [nautical] miles [1,222 km], altitude 95 [nautical] miles [176 km], velocity 78 per cent velocity required for orbit.
As with the first stage, the centre or inboard engine of the S-II is cut-off early. However, the reason is entirely different. In early Saturn V flights, it was found that the centre engine, mounted on a crossbeam, was prone to pogo vibrations late into the burn. Rather than strengthen the beam, engineers elected simply shut the centre engine down early. The inboard engine cut-off was at 7:39.5; 1 minute, 29.5 seconds before the outboard engines.
000:07:48 Scott (onboard): Okay, about 10 seconds to PU shift.
000:08:03 Worden (onboard): Didn't even feel it. There it goes, 8:03.
At 8:03.9, the PU (Propellant Utilization) valves open, reducing the LOX flowrate and therefore the mixture ratio to the engines from 5.5:1 to 4.8:1 LOX to fuel. This reduction in the flow of oxygen results in a perceptible change in the g-forces felt by the crew as the thrust drops. It is part of a strategy to make sure that as little propellant as possible is left in the tanks when the second stage has done its work. The AS-510 Saturn V Flight Manual explains that this changeover occurs when the S-II stage has achieved a predetermined velocity change, or Delta-V. Earlier flights of the S-II used the readings from onboard sensors to calculate the most appropriate time for PU shift.
Counter-intuitively, although the thrust has been reduced, the efficiency of the engine has actually increased. The reason for this is that there is more unburnt hydrogen in the exhaust. Since H2 is a light molecule, it can more easily be accelerated by the heat of reaction, increasing the overall exhaust velocity. Since the efficiency of a rocket engine is directly related to the exhaust velocity, this reduction in mixture ratio improved the amount of momentum imparted by each kilogram of propellant burned.
000:08:10 Scott (onboard): A little bit.
000:08:11 Worden (onboard): Yes.
000:08:12 Fullerton: 15, Houston. 15, Houston. Go ahead. Say again, 15?
000:08:25 Scott: Houston, 15. We didn't call. You got something?
000:08:29 Fullerton: You've had PU shift, and the thrust looks good.
000:08:32 Scott: Okay.
CapCom Gordon Fullerton had thought he heard the crew speak. With the situation clarified, he informs Dave that PU valves have operated to ensure optimal stage performance.
Scott, from 1971 Technical debrief: "We didn't notice the PU shift; when we went through it, I couldn't feel anything ... I remember on Apollo 9, we also didn't feel the PU shift, but I guess other crews have felt it."
000:08:40 Fullerton: You've had level sense arm now?
Fullerton is informing the crew that the "level sense arm" signal has been sent to the IU. The engines will be shut down once two probes in one of the tanks have been uncovered by the dwindling propellant. They can expect shutdown shortly.
000:08:42 Scott: Roger. [Long pause.]
About 6 seconds to staging.
The outboard engines cut off at 000:09:09. S-IVB separation from the S-II occurs one second after outboard cut-off. Ignition of the S-IVB's single J-2 engine then occurs a tenth of a second later.
The sequence of events for the first ignition of the single J-2 engine in the third stage is essentially the same as for the engines in the S-II (see 000:02:58). The main change is that the supercold fuel is allowed to flow through the walls of the thrust chamber to condition it for three seconds, instead on one, before the Start Tank discharges through the turbines, spinning them up in preparation for operation. The difference is due to the fact that the five engines in the S-II created a colder environment for pre-chill than the single engine of the S-IVB.
000:09:11 Fullerton: Stand by for Mode IV capability.
000:09:15 Fullerton: Mark. You have Mode IV now.
Mode IV is the abort mode where the crew have been given a Go decision to continue to orbit using the S-IVB, and should that stage deviate from its allowed limits, the CSM will separate from the Saturn and use the SPS (Service Propulsion System) to continue into Earth orbit.
000:09:16 Scott: Rog. And a good stage.
Although it was built as part of the S-IVB, the conical interstage at its aft remains with the S-II at separation. Unlike the earlier staging, this is a single plane separation as the vehicle is essentially outside the effects of the atmosphere. Also, as there is only one engine, there is much more clearance and essentially no possibility of an unbalanced thrust across a cluster of engines skewing the S-IVB's attitude.
Scott, from 1971 Technical debrief: "The S-II to S-IVB staging was about a quarter to a fifth the force of the S-IC staging. It was again a positive kind of feeling, but it wasn't a violent crash like we felt on the S-IC; I didn't think. We had the same light 10- to 12-cps vibration on the S-IVB all the way into orbit. The shutdown was smooth. All the sequences throughout the launch were nominal and as expected. All the lights worked good; controls and displays were good; comfortable."
Irwin, from 1971 Technical debrief: "The noise and the vibration were less than I was expecting; it was much less. I was impressed about the lateral vibration on launch. It was much greater on the S-IC than it was on the S-II. Just a shaking, back and forth, lateral vibration all the way through the launch. It was a pretty smooth ride."
000:09:18 Fullerton: Roger. [Pause.]
Booster reports thrust okay on the S-IVB stage.
000:09:24 Fullerton: 15, Houston. You've had - you have good thrust on the S-IVB.
000:09:28 Scott: Roger.
Comm break.
960 [nautical] miles [1,778 km] downrange, 94.7 [nautical miles, 175.4 km] altitude. Velocity 23,230 [feet per second, 7,081 m/s].
000:10:46 Fullerton: 15, Houston. Everything's looking perfect. Predicted [S-IVB engine] cut-off time [is] 11 plus 37. Over.
000:10:54 Scott: Roger; 11 plus 37. [Long pause.]
1,281 [nautical] miles [2,372 km] downrange, 93.4 [nautical miles, 173.0 km] altitude, 97 percent of velocity - 98 percent of velocity required. [Current velocity is] 25,143 feet per second [7,664 m/s].
000:11:36 Scott: Okay. Cut-off. 11 plus 34.
000:11:39 Fullerton: Roger. [Long pause.]
Booster confirms the S-IVB has shutdown.
This first burn of the S-IVB was 3.8 seconds shorter than was predicted. This was due to the over-performance of the previous stages, and higher than expected thrust from the S-IVB's J-2 engine. For sixty seconds during its burn, the engine has been refilling the spherical Start Tank with gaseous hydrogen derived from feeds of both gaseous and liquid hydrogen from the engine's high pressure lines. This gas will be used to respin the turbines when the engine is restarted for the boost out of Earth orbit. The helium tank within the Start Tank does not need to be refilled as there is sufficient in it for three or four restarts.
The crew are now experiencing prolonged weightlessness for the first time in the mission after a ride that has subjected them to loads of up to 4g.
Graph of g-forces during the Saturn V's ascent into Earth orbit.
The above graph was derived from the Apollo 15 AS-510 Saturn V Flight Evaluation Report. It displays how the acceleration of the vehicle changed throughout the boost, from about 1g on leaving the launch pad to weightlessness 11½ minutes later. The key events in the graph are:
Launch with ignition of the S-IC. Note how the acceleration rapidly rises with increasing engine efficiency and reduced propellant load.
Cut-off of the centre engine of the S-IC.
Outboard engine cut-off of the S-IC at a peak of 4g.
S-II stage ignition. Note the reduced angle of the graph for although the mass of the first stage has been discarded, the thrust of the S-II stage is nearly one tenth of the final S-IC thrust.
Cut-off of the centre engine of the S-II.
Change in mixture ratio caused by the operation of the PU valve. The richer mixture reduces the thrust slightly.
Outboard engine cut-off of the S-II at a peak of approximately 1.8g.
S-IVB stage ignition. Note again the reduced angle of the graph caused by the thrust being cut by a fifth.
With the cut-off of the S-IVB's first burn, the vehicle is in orbit with zero acceleration.
The 4g reached during boost is not the highest that will experienced during the mission. Entry through Earth's atmosphere decelerates the Command Module by about 6½g.
The moment of orbital insertion is about 10 seconds after the engine shut down in order to allow for any tail-off in the thrust. There, it is stated as occurring at 000:11:44.
000:11:53 Scott: Okay, Houston. [SPS engine] Gimbal Motors are Off, and the S-IVB oxidizer is 40 [psi, 276 kPa], and the fuel's about 31 [psi, 214 kPa].
000:11:59 Fullerton: Roger; 40 and 31.
During firing, pressurisation of the LOX tank comes from eight helium spheres in the LH2 tank which, via a heat exchanger in the engine, feed helium into the ullage space above the LOX. 40 psi is within the range of normal operation but between now and the restarting of the engine, the LOX pressure will be allowed to decay. During ascent on the previous stages, the S-IVB's LH2 tank pressure is maintained by boil-off of the liquid hydrogen itself.
After S-IVB ignition, GH2 (gaseous hydrogen) is generated by the engine for tank pressurisation. 31 psi is within allowable limits. From the end of the first burn to the time of S-IVB restart, the CVS (Continuous Vent System) will regulate tank pressure at 19.3 psi [133 kPa]. The GH2 generated by boil-off of LH2 is vented propulsively in order to provide a force to settle propellants in the tanks.
000:12:06 Worden: Okay, Gordo. We got ourselves in a 93.7 [nautical miles, 173.5 km] by 88.9 [nautical miles, 164.6 km, orbit]; [engine] shutdown [was] on a VI [inertial velocity] of plus 25595 [fps, 7,801 m/s]; H dot, plus 00008 [fps, 2.4 m/s], altitude plus 00932 [93.2 nautical miles, 172.6 km].
000:12:46 Fullerton: 15, Houston. IU shows you in a 92.5 by 91.5 [nautical mile orbit, 171.3 by 169.5 km]. Radar confirms that. And the booster is safed.
The crew is consulting their computer's DSKY (display and keyboard), as required by the checklist, which tells them that they have achieved a slightly eccentric orbit of 93.7 nautical miles (173.4 km) by 88.9 nautical mile (164.5 km) and their velocity is currently 25,595 feet per second [7,801 m/s]. H dot is the derivative of height with respect to time - essentially the rate of change of height - and, at 8 feet per second, is small as would be expected for a nearly circular orbit. The current altitude is 93.2 nautical miles (172.6 km). The IU is giving a slightly different answer which Mission Control have observed through telemetry and which has been confirmed by radar. This is a very low orbit and one which cannot be sustained for long due to the friction with the tenuous air at this altitude. Indeed, there is significant heating on the skin of the vehicle due to atmospheric friction. However, this is considered acceptable for the three hours duration of the parking orbit and the low altitude allows the Saturn to carry a greater payload.
000:12:55 Scott: Okay, Gordo; good job. That was a very smooth ride all the way.
000:13:01 Fullerton: Roger. [Long pause.]
000:13:28 Fullerton: 15, Houston. The booster is configured for orbit. Over.
000:13:35 Scott: Roger.
Comm break.
On attaining orbit, the APS (Auxiliary Propulsion System, the S-IVB's own attitude control system), begins a manoeuvre to rotate the vehicle from the 18° pitched down attitude it had at shutdown of the S-IVB, to be parallel to the local horizontal (i.e. with respect to Earth's surface below). This manoeuvre is greater on Apollo 15 than the 6° to 10° noted on previous flights, due to the lower altitude of the final orbit, and is carried out at a rate of 0.3° per second. However, the large size of the manoeuvre helps develop a slosh wave within the nearly three quarters full LOX tank and about 220 kilograms of LOX is lost through an intentionally open vent. Future missions would rotate the stack at only 0.14° per second to minimise propellant sloshing.
The APS then sets up a slow pitch rotation at a rate which matches the vehicle's rate of rotation about Earth (therefore called 'orb rate') so that throughout the orbit, the same side keeps facing Earth. In this case the crew is in a 'heads down' attitude and the vehicle is pointing in the direction of travel.
diagram to illustrate the difference between a stellar inertial attitude and an 'orb rate' attitude.
There seem to be a number of interrelated reasons for the orb rate manoeuvre during Earth parking orbit. As we have seen, making large attitude changes to the very full S-IVB is to be avoided to inhibit sloshing in the tanks. Already, nearly a quarter of a metric ton of LOX has been lost. They entered orbit nearly "pointy-end-forward" and will boost to the Moon (the TLI or Translunar Injection burn) in a similar attitude. Staying in that same attitude, relative to the local horizontal, avoids excessive attitude changes. Also, this attitude presents a small cross section to the extremely thin atmosphere that the spacecraft and S-IVB is still moving through, and this minimises aerodynamic heating. The small thrust resulting from the venting of LH2 pushes the vehicle in the same direction as orbital motion, keeping propellants toone end of their tanks. Finally, keeping the CSM in a 'heads down' attitude ensures that the spacecraft's optics, mounted on the opposite side of the Command Module from the hatch, are facing towards the stars so Al can sight on them during the upcoming navigation tasks.
Woods, from 2004 mission review: "There was a propulsive vent going on the whole time while you were in Earth orbit. They were venting the boil-off as a propulsive vent, partly to settle the propellants. And I wondered if you had any sense of there being a microgravity, a drift to the aft end of the spacecraft?"
Scott, from 2004 mission review: "No."
Woods, from 2004 mission review: "Was it too small?"
Scott, from 2004 mission review: "Don't remember it. I'm not sure I didn't stay strapped in the whole time. Al was the only guy that got out, wasn't he?"
000:14:46 Fullerton: 15, Houston. I have your Z torquing angle.
000:14:53 Worden: Okay; go ahead.
000:14:55 Fullerton: Minus decimal 1 degrees. One tenth of a degree, minus.
000:15:02 Scott: Ah, Rog. Minus .1.
000:15:06 Fullerton: That's correct.
Woods, from 2004 mission review: "As soon as you get to orbit, you're given a Z-torquing angle. What is that?"
Scott, from 2004 mission review: "That torques the CSM guidance platform to your nominal orientation - the orientation you want after insertion because it may have drifted during launch. Before launch, you gyrotorque down to the last minute so that everything's aligned. And then you go through the launch and you get all this vibration and all that stuff. I think what they do when you get into orbit is to torque it again to null again all the drift and bias built up during launch."
Communication is about to be lost through the Bermuda ground station but will be reacquired in about a minute through a station on Gran Canaria, one of the Canary Islands just off the coast of North Africa.
