The Ninth Mission:
The Fourth Lunar Landing
26 July-7 August 1971
Apollo 15 was the first of the three Type J missions, consisting of extensive scientific investigations of the Moon on the lunar surface and from lunar orbit. It was designed to conduct exploration of the Moon over longer periods, over greater ranges, and with more instruments for scientific data acquisition than on previous Apollo missions. Major modifications and augmentations to the basic Apollo hardware were made. The most significant was the installation of an instrument module in one of the service module bays for scientific investigations from lunar orbit. Other hardware changes consisted of LM modifications to accommodate a greater payload and permit a longer stay on the lunar surface, the provision of a lunar rover vehicle (LRV), and a scientific subsatellite to be deployed into lunar orbit.
Planned to be used on this and the next two lunar missions, the LRV was a four-wheeled, lightweight vehicle designed to greatly extend the area that could be explored on the lunar surface. The LRV had five major systems: mobility, crew station, navigation, power, and thermal control. Auxiliary equipment included the lunar communications relay unit with high and low gain antennas, ground control television assembly, a motion picture camera, scientific equipment, astronaut tools, and sample stowage bags. It was 122 inches long and 44.8 inches high with a 90-inch wheelbase and 72-inch tread width. Two 36-volt batteries provided power, although one alone would provide enough power for all LRV systems. Earth weight was 462 pounds, with a payload capacity of 1,080 pounds, including two astronauts and their life support equipment (about 800 pounds), communication equipment (100 pounds), scientific equipment, photographic gear (120 pounds), and lunar samples (60 pounds). For the flight to the Moon, the LRV was folded and stowed in Quad 1 of the LM descent stage. After landing, the astronauts would manually deploy the vehicle and prepare it for cargo loading and operation. The LRV was designed to operate for 78 hours during the lunar day, and could travel a cumulative distance of 35 nautical miles, within a five-mile radius from the LM.
The chosen landing site was an area near the foot of the Montes Apenninus (Apennine Mountains) and adjacent to Hadley Rille.
The primary objectives for Apollo 15 were:
The all-Air Force crew included Colonel David Randolph Scott (USAF), commander; Major Alfred Merrill Worden [WARD-in] (USAF), command module pilot; and Lt. Colonel James Benson Irwin (USAF), lunar module pilot.
Selected as an astronaut in 1963, Scott had been pilot of Gemini 8, the first docking of two vehicles in space, and command module pilot of Apollo 9, the first flight test of the LM. Born 6 June 1932 in San Antonio, Texas, he was 39 years old at the time of the Apollo 15 mission. Scott received a B.S. from the U.S. Military Academy in 1954 and a M.S. in aeronautics and astronautics from the Massachusetts Institute of Technology in 1962. His backup for the mission was Captain Richard Francis “Dick” Gordon, Jr. (USN).
Worden and Irwin were making their first spaceflights. Worden was born 7 February 1932 in Jackson, Michigan, and was 39 years old at the time of the Apollo 15 mission. He received a B.S. in military science from the U.S. Military Academy in 1955, a M.S. in astronautical and aeronautical engineering and a M.S. in instrumentation engineering from the University of Michigan in 1963, and was selected as an astronaut in 1966. His backup was Vance DeVoe Brand.
Born 17 March 1930 in Pittsburgh, Pennsylvania, Irwin was 41 years old at the time of the Apollo 15 mission. He received a B.S. in naval science from the U.S. Naval Academy in 1951, and a M.S. in aeronautical engineering and an M.S. in instrumentation engineering from the University of Michigan in 1957, and was selected as an astronaut in 1966. His backup was Harrison Hagan “Jack” Schmitt, Ph.D.
The capsule communicators (CAPCOMs) for the mission were Joseph Percival Allen IV, Ph.D., Major Charles Gordon Fullerton (USAF), Karl Gordon Henize, Ph.D., Commander Edgar Dean Mitchell (USN/Sc.D.), Robert Alan Ridley Parker, Ph.D., Schmitt, Captain Alan Bartlett Shepard, Jr. (USN), Gordon, and Brand. The support crew were Henize, Allen, and Parker. The flight directors were Gerald D. Griffin (first shift), Milton L. Windler (second shift), and Glynn S. Lunney and Eugene F. Kranz (third shift).
The Apollo 15 launch vehicle was a Saturn V, designated SA-510. The mission also carried the designation Eastern Test Range #7744. The CSM was designated CSM-112, and had the call-sign “Endeavour.” The lunar module was designated LM-10 and had the call-sign “Falcon.”
The terminal countdown was picked up at T-28 hours at 23:00:00 GMT on 24 July 1971. Scheduled holds were initiated at T-9 hours for 9 hours 34 minutes and at T-3 hours 30 minutes for 1 hour.
At launch time, the Cape Kennedy launch area was experiencing fair weather resulting from a ridge of high pressure extending westward, from the Bermuda High, through central Florida. Cirrus clouds covered 70 percent of the sky (base 25,000 feet), the temperature was 85.6° F, the relative humidity was 68 percent, and the barometric pressure was 14.788 lb/in2. The winds, as measured by the anemometer on the light pole 60.0 feet above ground at the launch site, measured 9.9 knots at 156° from true north. The winds at 530 feet above the launch site measured 10.5 knots at 158° from true north.
Apollo 15 was launched from Kennedy Space Center Launch Complex 39, Pad A, at a Range Zero time of 13:34:00 GMT (09:34:00 a.m. EDT) on 26 July 1971. The planned launch window for Apollo 15 extended to 16:11:00 GMT to take advantage of a sun elevation angle on the lunar surface of 12.0°.
Between 000:00:12.21 and 000:00:23.02, the vehicle rolled from a launch pad azimuth of 90° to a flight azimuth of 80.088°. The S-IC engine shut down at 000:02:39.56, followed by S-IC/S-II separation, and S-II engine ignition. The S-II engine shut down at 000:09:09.06 followed by separation from the S-IVB, which ignited at 000:09:13.20. The first S-IVB engine cutoff occurred at 000:11:34.67, with deviations from the planned trajectory of only -2.0 ft/sec in velocity and only 0.4 n mi in altitude.
The maximum wind conditions encountered during ascent were 36.2 knots at 63° from true north at 45,110 feet and a maximum wind shear of 0.0110 sec-1 at 36,830 feet.
Parking orbit conditions at insertion, 000:11:44.67 (S-IVB cutoff plus 10 seconds to account for engine tailoff and other transient effects), showed an apogee and perigee of 91.5 by 89.6 n mi, an inclination of 29.679°, a period of 87.84 minutes, and a velocity of 25,602.6 ft/sec. The apogee and perigee were based upon a spherical Earth with a radius of 3,443.934 n mi.
The international designation for the CSM upon achieving orbit was 1971-063A and the S-IVB was designated 1971-063B. After undocking at the Moon, the LM ascent stage would be designated 1971-063C, the descent stage 1971-063E, and the subsatellite 1971-063D.
After inflight systems checks, the 350.71-second translunar injection maneuver (second S-IVB firing) was performed at 002:50:02.90. The S-IVB engine shut down at 002:55:53.61 and translunar injection occurred ten seconds later at a velocity of 35,579.1 ft/sec after 1.5 Earth orbits lasting 2 hours 44 minutes 18.94 seconds.
At 003:22:27.2, the CSM was separated from the S-IVB stage, transposed, and docked at 003:33:49.5. The onboard color television camera covered the docking. The docked spacecraft were ejected from the S-IVB at 004:18:01.2, and an 80.2-second separation maneuver was performed at 004:40:01.8.
At 005:46:00.7, the S-IVB tanks were vented and the auxiliary propulsion system was fired for 241.2 seconds to target the S-IVB for a lunar impact. An additional 71-second maneuver was made at 010:00:01, about 30 minutes later than planned. The late burn provided additional tracking time to compensate for any trajectory perturbations introduced by liquid oxygen and liquid hydrogen tank venting. The S-IVB impacted the lunar surface at 079:24:42.9. The impact point was latitude 1.51° south and longitude 11.81° west, 83 n mi from the target point, 192 n mi from the Apollo 12 seismometer, and 99 n mi from the Apollo 14 seismometer. At impact, the S-IVB weighed 30,880 pounds and was traveling 8,465 ft/sec.
Two minor CSM midcourse corrections were required during translunar flight to assure proper lunar orbit injection. The first was a 0.8-second maneuver at 028:40:22.0 that produced a change in velocity of 5.3 ft/sec.
The second midcourse correction was performed with the service propulsion system bank A in order to provide better analysis of an apparent intermittent short. Because power could still be applied to the valve with a downstream short, bank A could be operated satisfactorily in the manual mode for subsequent firings. The redundant bank B system was nominal and could be used for automatic starting and shutdown.
The LM crew entered the LM at 033:56 for checkout, approximately 50 minutes earlier than scheduled. LM communications checks were performed between 034:21 and 034:45. Good quality voice and data were received even though the Goldstone tracking station in California was not yet configured correctly during the initial portion of the down-voice backup checks. Approximately 15 minutes later, the downlink carrier lock was lost for a minute and a half; however, because other stations were tracking, data loss was reduced to just a few seconds.
A television transmission of the CSM and LM interiors was broadcast between 034:55 and 035:46. Camera operation was nominal, but the picture quality varied with the lighting of the scene observed. During the checkout of the LM, the crew discovered the range/range rate exterior cover glass was broken, thus removing the protective helium barrier. Subsequent ground testing qualified the unprotected meter for use during the remainder of the mission in the spacecraft ambient atmosphere.
Intravehicular transfer and LM housekeeping began at 056:26, about an hour and a half earlier than scheduled. The crew vacuumed the LM to remove broken glass from the damaged range/range rate meter. LM checkout was completed as planned.
Based on the first midcourse correction burn test data, it was decided to perform all service propulsion system maneuvers except lunar orbit insertion and transearth injection using bank B only. The insertion and injection maneuvers would be dual bank burns with modified procedures to permit automatic start and shutdown on bank B. The second midcourse correction, using this propulsion system, was made at 073:31:14.81 for 0.91 seconds and changed the velocity by 5.4 ft/sec.
The scientific instrument bay door was jettisoned at 074:06:47.1. The lunar module pilot photographed the jettisoned door and visually observed it slowly tumbling through space away from the CSM and eventually into heliocentric orbit.
At 078:31:46.70, at an altitude of 86.7 n mi above the Moon, the service propulsion engine was fired for 398.36 seconds, inserting the spacecraft into a lunar orbit of 170.1 by 57.7 n mi. The translunar coast had lasted 75 hours 42 minutes 21.45 seconds. During the burn, bank A was shut down 32 seconds before planned cutoff to obtain performance data on bank B for future single bank burns.
Lunar Orbit/Lunar Surface Phase
At 082:39:49:09, a 24.53-second service propulsion system maneuver was performed to establish the descent orbit of 58.5 by 9.6 n mi in preparation for undocking of the LM. A 30.40-second orbit trim maneuver was performed at 095:56:44.70 and adjusted the orbit to 60.3 by 8.8 n mi.
During the 12th lunar revolution on the far side of the Moon at about 100:14, the CSM/LM undocking and separation maneuver was initiated; however, undocking did not occur. The crew and ground control decided that the probe instrumentation LM/CSM umbilical was either loose or disconnected. The command module pilot went into the tunnel to inspect the connection and found the umbilical plug to be loose. After reconnecting the plug and adjusting the spacecraft attitude, undocking and separation were achieved approximately 25 minutes late at 100:39:16.2 at an altitude of 7.4 n mi. A 3.67-second maneuver at 101:38:58.98 circularized the CSM orbit to 65.2 by 54.8 n mi in preparation for the acquisition of scientific data.
The powered descent engine firing began at 104:30:09.4 at an altitude of 5.8 n mi and ended 739.2 seconds later, just 0.7 seconds before landing at 22:16:29 GMT (06:16:29 p.m. EDT) on 30 July at 104:42:29.3. The spacecraft landed in the Montes Apenninus (Apennine Mountains), adjacent to Hadley Rille at latitude 26.13222° north and longitude 3.63386° east, and 1,800 feet northwest of the planned landing point. Approximately 103 seconds of engine firing time remained at landing.
At 106:42:49, two hours after landing, the cabin was depressurized and the commander opened the LM top hatch to photograph and describe the landing site area. During this “stand-up EVA” (SEVA), which lasted 33 minutes 7 seconds, he took a series of panoramic photos of the area immediately surrounding the LM landing site.
The first lunar surface extravehicular activity was initiated at 119:39:17 when the cabin of the LM was depressurized.
On the way down the ladder, the commander deployed the modularized equipment stowage assembly (MESA). The television in the MESA was activated and the pictures of the commander’s remaining descent to the lunar surface were excellent. The lunar module pilot then exited to the surface. While the commander removed the television camera from the MESA and deployed it on a tripod, the lunar module pilot collected the contingency sample.
At 120:18:31, the crew offloaded the LRV and deployed it 13 minutes later. They unstowed the third Apollo lunar surface experiments package (ALSEP) and other equipment, and configured the LRV for lunar surface operations.
Some problems were experienced in deploying and checking out the LRV but these problems were worked out. During checkout of the LRV, it was found that the front steering mechanism was inoperative. Additionally, there were no readouts on the LRV battery #2 ampere/volt meter. After minor troubleshooting, a decision was made to perform the first extravehicular activity (EVA-1) without the LRV front wheel steering activated.
At 121:44:55, the crew drove the LRV to Elbow Crater, collected and documented samples and gave an enthusiastic and informative commentary on lunar features.
The mission control center provided television control during various stops. After obtaining additional samples and photographs near St. George Crater, the crew returned to the LM using the LRV navigation system.
The crew then proceeded to the selected Apollo lunar surface experiments package deployment site, 360 feet west-northwest of the LM. There, the experiments were deployed essentially as planned, except that the second heatflow experiment probe was not emplaced because drilling was more difficult than expected and the hole was not completed.
The crew entered the LM and the cabin was repressurized at 126:11:59. The first EVA lasted 6 hours 32 minutes 42 seconds, about 27 minutes less than planned because of higher than anticipated oxygen usage by the commander. The distance traveled in the lunar rover vehicle was 5.6 n mi (10.3 km), vehicle drive time was 1 hour 2 minutes, parked time was 1 hour 14 minutes, and 31.97 pounds (14.5 kg) of samples were collected.
Between the first and second extravehicular periods, the crew spent 16 hours in the LM. The second period began at 142:14:48 when the cabin was depressurized.
After the crew left the LM for the second EVA, they checked out the LRV and prepared it for the second traverse. During the checkout, they recycled the circuit breakers on the vehicle and the front steering became completely operational.
The crew started their traverse at 143:10:43, heading south to the Apennine front, just east of the first traverse. Stops were made at Spur Crater and other points along the base of the front, as well as at Dune Crater on the return trip. Television transmission was very good.
The return route closely followed the outbound route. Documented samples, a core sample, and a comprehensive sample were collected, and photographs were taken.
During this period, the lunar module pilot performed soil mechanics tasks. The commander also tried to drill for a deep-core sample but terminated the effort because of time constraints.
After reaching the LM at 148:32:17, the crew returned to the experiments package site where the commander completed drilling the second hole for the heat flow experiment, emplaced the probe, and collected a core tube sample. The drill core stems were left at the ALSEP site for retrieval during EVA-3.
The crew then returned to the LM and deployed the United States flag. The sample container and film were stowed in the LM.
The crew entered the LM and the cabin was repressurized at 149:27:02. The second extravehicular activity period lasted 7 hours 12 minutes 14 seconds. The distance traveled in the lunar rover vehicle was 6.7 n mi (12.5 km), vehicle drive time was 1 hour 23 minutes, the vehicle was parked for 2 hour 34 minutes, and 76.94 pounds (34.9 kg) of samples were collected.
The crew spent almost 14 hours in the LM before the cabin was depressurized for the third extravehicular period at 163:18:14. The third extravehicular activity began 1 hour 45 minutes later than planned due to cumulative changes in the surface activities timeline. Because of this delay and later delays at the ALSEP site, the planned trip to the North Complex was deleted.
The first stop was the ALSEP site at 164:09:00 to retrieve drill core stem samples left during EVA-2. Two core sections were disengaged and placed in the LRV. The drill and the remaining four sections could not be separated and were left for later retrieval.
The third geologic traverse took a westerly direction and included stops at Scarp Crater, Rim Crater, and “The Terrace” near Rim Crater. Extensive samples and a double-core-tube sample were obtained.
Photographs were taken of the west wall of Hadley Rille, where exposed layering was observed. The return trip was east toward the LM with a stop at the ALSEP site at 166:43:40 to retrieve the remaining sections of the deep-core sample. One more section was separated, and the remaining three sections were returned in one piece. During sample collecting, the commander tripped over a rock and fell, but experienced no difficulty in getting up.
After returning to the LM, the LRV was unloaded and parked at 167:35:24 for ground-controlled television coverage of the LM ascent. The commander selected a site slightly closer to the LM than planned in order to take advantage of more elevated terrain for better television coverage of the ascent.
The crew reentered the LM and the cabin was repressurized at 168:08:04, thus ending the fourth human exploration of the Moon. The third extravehicular period had lasted 4 hours 49 minutes 50 seconds. The distance traveled in the lunar rover vehicle was 2.7 n mi (5.1 km); vehicle drive time was 35 minutes and it was parked for 1 hour 22 minutes; 60.19 pounds (27.3 kg) of samples were collected.
For the mission, the total time spent outside the LM was 18 hours 34 minutes 46 seconds, the total distance traveled in the lunar rover vehicle was about 15.1 n mi (27.9 km), vehicle drive time was 3 hours 0 minutes, the vehicle was parked during extravehicular activities for 5 hours 10 minutes, and the collected samples totaled 170.44 pounds (77.31 kg; official total in kilograms as determined by the Lunar Receiving Laboratory in Houston). The farthest point traveled from the LM was 16,470 feet.
While the LM was on the surface, the command module pilot completed 34 lunar orbits, conducting scientific instrument module experiments and operating cameras to obtain data concerning the lunar surface and the lunar environment.
Some scientific tasks accomplished during this time were photographing the sunlit lunar surface, gathering data needed for mapping the bulk chemical composition of the lunar surface and for determining the geometry of the Moon along the ground track, visually surveying regions of the Moon to assist in identifying processes that formed geologic features, obtaining lunar atmospheric data, and surveying gamma ray and x-ray sources.
High-resolution photographs were obtained with the panoramic and mapping cameras during the missions. An 18.31-second CSM plane change maneuver had been conducted at 165:11:32.74 and resulted in an orbit of 64.5 by 53.6 n mi.
Ignition of the ascent stage engine for lunar liftoff occurred at 17:11:23 GMT (01:11:23 p.m. EDT) on 2 August 1971 at 171:37:23.2. The LM had been on the lunar surface for 66 hours 54 minutes 53.9 seconds.
The 431.0-second firing achieved the initial lunar orbit of 42.5 by 9.0 n mi. Several rendezvous sequence maneuvers were required before docking could occur approximately two hours later.
A 2.6-second terminal phase initiate maneuver at 172:29:40.0 adjusted the ascent stage orbit to 64.4 by 38.7 n mi. The ascent stage and the CSM docked at 173:36:25.5 at an altitude of 57 n mi. The two craft had been undocked for 72 hours 57 minutes 9.3 seconds.
After transfer of the crew and samples to the CSM, the ascent stage was jettisoned at 179:30.01.4, and the CSM was prepared for transearth injection. Jettison had been delayed one revolution because of difficulty verifying the spacecraft tunnel sealing and astronaut pressure suit integrity.
At 181:04:19.8 and 61.5 n mi altitude, the ascent stage was maneuvered to impact the lunar surface by firing the engine to depletion, which occurred 83.0 seconds after ignition. Impact occurred at latitude 26.36° north and longitude 0.25° east 03:03:35 GMT on 3 August (11:03:35 p.m. EDT on 2 August) at 181:29:37.0. The impact point was 12.7 n mi (23.5 km) from the planned point and 50 n mi (93 km) west of the Apollo 15 landing site. The impact was recorded by the Apollo 12, 14, and 15 seismic stations.
In preparation for the launch of a subsatellite into lunar orbit, a 3.42-second orbit-shaping maneuver at 221:20:48.02 altered the CSM orbit to 76.0 by 54.3 n mi. The subsatellite was then spring-ejected from the scientific instrument module bay at 222:39:29.1 during the 74th revolution into an orbit of 76.3 by 55.1 n mi at an inclination of -28.7°. The subsatellite was instrumented to measure plasma and energetic-particle fluxes, vector magnetic fields, and subsatellite velocity from which lunar gravitational anomalies could be determined. All systems operated as expected.
Following a 140.90-second maneuver at 67.6 n mi altitude at 223:48:45.84, transearth injection was achieved at 223:51:06.74 at a velocity of 8,272.4 ft/sec after 74 lunar orbits lasting 145 hours 12 minutes 41.68 seconds.
At 241:57:12, the command module pilot began a transearth coast extravehicular activity. Television coverage was provided for the 39-minute 7-second extravehicular period during which he retrieved panoramic and mapping camera film cassettes from the scientific instrument module bay.
Three excursions were made to the bay. The film cassettes were retrieved during the first two trips. The third trip was used to observe and report the general condition of the instruments, in particular the mapping camera.
The command module pilot reported no evidence of the cause for the mapping camera extend/retract mechanism failure in the extended position and no observable reason for the pan camera velocity/altitude sensor failure. He also reported that the mass spectrometer boom was not fully retracted. The EVA was completed at 242:36:19. This brought the total extravehicular activity for the mission to 19 hours 46 minutes 59 seconds.
A 22.30-second midcourse correction of 5.6 ft/sec was performed 291:56:49.91 to put the CSM on a proper track for Earth entry.
The service module was jettisoned at 294:43:55.2, and CM entry followed a normal profile. The command module reentered the Earth’s atmosphere (400,000 feet altitude) at 294:58:54.7 at a velocity of 36,096.4 ft/sec, following a transearth coast of 71 hours 7 minutes 48 seconds.
The parachute system, with two main parachutes properly inflated and one collapsed, effected splashdown of the CM in the Pacific Ocean at 20:45:53 GMT (04:45:53 p.m. EDT) on 7 August. Mission duration was 295:11:53.0. The impact point was about 1.0 n mi from the target point and 5 n mi from the recovery ship U.S.S. Okinawa.
The collapsed parachute contributed to the fastest entry time in the Apollo program, just 778.3 seconds from entry to splashdown. The splashdown site was estimated to be latitude 26.13° north and longitude 158.13° west.
After splashdown, the CM assumed an apex-up flotation attitude. The crew was retrieved by helicopter and was aboard the recovery 39 minutes after splashdown. The CM was recovered 55 minutes later. The estimated CM weight at splashdown was 11,731 pounds, and the estimated distance traveled for the mission was 1,107,945 n mi.
The mission accomplished all primary objectives and provided scientists with a large amount of new information concerning the Moon and its characteristics.
The Apollo 15 mission was the fourth lunar landing and resulted in the collection of a wealth of scientific information. The Apollo system, in addition to providing a means of transportation, excelled as an operational scientific facility. The following conclusions were made from an analysis of post-mission data:
 Irwin, who had a history of heart trouble, died of a heart attack on 08 August 1991 in Glenwood Springs, Colorado.