From a technical standpoint, Apollo 10 could have landed on the moon. It probably would have - with some offloading of fuel to shed a little weight - had the flight been scheduled for the last few weeks of the decade. There were, however, good reasons for waiting until the next mission for a landing. Only two lunar modules had flown, and both those flights had been in earth orbit. NASA managers wanted to see how the lander's guidance and navigation system would behave in the moon's uneven gravity fields while the craft was within rescue range of the command module. Further, helium ingestion, which had caused Spider's descent engines to chug, would have to be investigated before a lunar module landed on the moon. Flight control also wanted a chance to review operation, tracking, and communications procedures of both vehicles while they were actually in the vicinity of the moon. The crews and controllers had been through many simulations, but it would take a real mission to give them the confidence they needed. Apollo 10 was to be a dress rehearsal, complete with a cast that included a lunar module capable of a lunar landing.35
The basics of the mission plan had been conceived in the spring of 1967. When, the next autumn, Low and his men outlined the alphabetical sequence of the route to the moon, Apollo 10 was assigned the "F" role, a lunar-orbit flight with all components. Toward the end of 1968, the mission planning and trajectory analysis people in Houston, led by John Mayer, Tindall, and Carl Huss (all veterans dating back to Mercury), buckled down to work out the refinements.
One feature was a two-phase lunar-orbit insertion maneuver introduced on Apollo8. The vehicle would begin the first revolution of the moon in an egg-shaped orbit, to avoid an unsafe pericynthion (known in earth orbit as a perigee - that is, the lowest point). If the service module engine fired too long and slowed the speed too much on the first burn, that part of the circuit must not be so low that the spacecraft would crash into the lunar surface. On Borman's mission the engine had fired for an excess of almost five seconds. On the next burn, to circularize the orbit, the duration of the firing was adjusted to keep the craft a safe distance above the moon. "Weren't we smart?" Tindall asked his colleagues, when this became a standing procedure for Apollo 10 and the lunar landing missions that followed.
As first planned, the lunar module on Apollo 10 would simply pull away from the command module and return for rendezvous and docking; but in December 1968 Tindall and the mission planners began campaigning to put the descent propulsion system through a real test down near the surface, where the landing radar could be fully checked. Moreover, they plotted the path so the lunar module crew could fly close enough to look for landmarks and take pictures of the site selected for the first landing. Tindall wanted them to go even farther - almost to touchdown - and then to fire the ascent engine to get back to the command module in a hurry, as though there had been an emergency. He had a fair hearing, he later said, but the mission planners did not think they had enough experience in the lunar environment to attempt this maneuver on the lander's first moon flight. Tindall reluctantly agreed. And there were many more procedures to be decided on and worked out before the flight plan became "final" in April 1969.36
When LM-4 arrived in Florida during October 1968 (the descent stage on the 11th and the ascent stage on the 15th), the Kennedy Space Center inspection team led by Joseph M. Bobik found it was a much better machine than LM-3; they had very little to grumble about. NASA was also quite satisfied with CSM-106* and with North American's performance in its checkout and delivery to the Cape on 25 November 1968.37
Although the contractors had shipped excellent spacecraft, preparations at Kennedy did not go lickety-split from the assembly building to the launch pad. Staying out of the way of Apollo 9 preflight activities delayed testing several days. And during maintenance to the Launch Control Center, the electrical power was cut off to replace a valve. The Apollo 10 launch vehicle's pneumatic controls sensed the power cutoff, opened some valves (the normal failure mode for these components), and dumped 20,000 liters of fuel (RP-1 - similar to kerosene) on the pad. Besides losing the propellant, the fuel tank bulkhead buckled. Technicians applied extra pressure to the tank, which removed all but a few wrinkles. Later the vehicle preparation team lowered a man inside to inspect the tank; he could find no further damage. Tests of the stage through the first week in May 1969 revealed no loss of structural integrity.38
Actually, neither spacecraft nor booster preparations held up the launch a single day, although adjustments in the launch date for other reasons probably helped the hardware teams to maintain schedules. On 10 January, NASA changed the anticipated sendoff from 1 to 17 May to fit the lunar launch window (optimum position of the moon in relation to earth for this mission) and to provide more time for crew training. Then on 17 March Phillips postponed the liftoff till the second day of the launch window (to 18 May), so the crew could get a better look at candidate landing sites.39
LM-4 and CSM-106 went through their flight readiness reviews on the same day, 11 April, with very nearly the same men passing on the lunar module in the morning and the command and service modules in the afternoon. During the lander review, a suggestion was made that the descent engine's chugging during McDivitt's flight might have been a form of pogo, but Low told Phillips that Faget's engineers had found no such indication. On 16 May, Phillips assured Mueller that all hardware would be ready for the mission two days later.40
On 13 November 1968, NASA had announced that the prime crew for Apollo 10 would be Thomas Stafford, John Young, and Eugene Cernan, with Gordon Cooper, Donn Eisele, and Edgar Mitchell as backups, and Joseph Engle, James Irwin, and Charles Duke as the support team. Coming from understudy roles on Apollo 7 in the leap-frogging crew selection methods that had evolved during Gemini, the Stafford group was the first all-veteran crew sent into space by the Americans.** Stafford had flown two missions (Gemini VI and IX), Young two (Gemini III and X), and Cernan one (Gemini IX).
The Apollo 10 crew had about 5 hours of formal training for each of the 192 hours it would spend on the lunar-orbital trip. Completely satisfied with the training program ("down to the nth degree," as Stafford later said) , the crew was especially pleased with the time spent in the simulators. Putting Stafford and Cernan in the lunar module simulator and Young in the command module trainer and then linking them with mission control provided situations remarkably like those faced during actual missions. They had four or five such sessions in the Houston simulators. When they arrived at the Cape, they would practice rendezvous maneuvers in no other way. During the more than 300 hours each man spent in the simulators, other tasks - such as reentry, launch abort, transearth injection, and translunar injection - were also studied. That this was a veteran crew was readily apparent in later remarks about such training aids as planetariums (Cernan said they had been looking at the stars for five years) and the centrifuge (Stafford said he had not been in one since Gemini III).41
Stafford's crew picked its flight patch in March. The patch displayed two craft flying above the lunar surface, with a Roman numeral X and the earth in the background. The astronauts also selected their call-signs, "Charlie Brown" for the command module and "Snoopy"*** for the lander. Julian Scheer, NASA's public affairs administrator, greeted these nicknames, as well as those of Spider and Gumdrop for Apollo 9, with raised eyebrows. He wrote Low that something a little more dignified should be picked for Apollo 11, the mission scheduled for the first lunar landing.42
* CSM-105 had been assigned as a ground test spacecraft in May 1968.
** During all phases of Apollo - seven more lunar flights, three Skylab missions, and one Apollo-Soyuz Test Project flight - there was only one other all-veteran crew: Neil Armstrong, Edwin Aldrin, and Michael Collins on Apollo 11.
*** These names - of a small boy and a beagle - were borrowed from the popular comic strip "Peanuts," created by Charles L. Schultz. Schultz' drawings were also used by NASA to promote manned space flight safety awareness. Persons making notable contributions in this field were given "Silver Snoopy Award" pins by the astronauts.
35. Low to NASA Hq., Attn.: Phillips, 26 Oct. 1968; Lewis R. Fisher, telephone interview, 10 Feb. 1976; Robert V. Battey, telephone interview, 5 March 1976; Owen G. Morris, telephone interview, 5 March 1976; NASA, "Project: Apollo 10," press kit, news release 69-68, 6 May 1969, p. 2; William J. Bennett memo, "Apollo Mission F Summary," 16 April 1968, with encs.; Michael Collins, Carrying the Fire: An Astronaut's Journeys (New York: Farrar, Strauss and Giroux, 1974), p. 326.
36. Carl R. Huss memo, "Abort considerations relating to LOI targeting for elliptical orbits," 20 Sept. 1967; MSC, "Apollo 10 Technical Crew Debriefing," 2 June 1969, pp. 18-l, 18-2; Albert P. Boysen, Jr., memo for file, "Notes of Apollo Flight Program Review at NASA Headquarters on September 21, 1967, Case 310," 24 Nov. 1967, with enc.; Low to Phillips, 8 Feb. 1969, with enc., Tindall, "Two-Stage LOI looks good after C'," 5 Feb. 1969; Tindall memos, "F Rendezvous Mission Techniques," 15 Nov. 1968, and "Proposal to add something nice to the F mission," 2 Dec. 1968; Tindall, telephone interview, 11 March 1976; Tindall memos, "Some decisions regarding lunar landmark tracking on the F and G missions," 10 Jan. 1969, and "F/G rendezvous Mission Technique - mostly F," 11 Feb. 1969; MSC, "Flight Operations Plan, Mission F," 30 Jan. 1969; Elvin B. Pippert, Jr., T. R. Lindsey, and W. M. Anderson, "Apollo 10; Apollo AS-505/CSM-106/LM-4: Final Flight Plan," MSC, 17 April 1969; Warren J. North letter, "Revision A to the Apollo 10 Final Flight Plan," 5 May }969, with encs.
37. Joseph M. Bobik to Chief, Apollo Spacecraft Office, KSC, "LM 4 Receiving Inspection," 20 Nov. 1968; Gay, Weekly Activity Reports for 9-15 Oct. and 20-26 Nov. 1968; Low memo for record, "Structural test program," 20 May 1968; Gilruth to Phillips, 16 Dec. 1968.
38. Mueller Reports, 10 March, 28 April, and 5 May 1969; Seaton, Weekly Status Report, 1 May 1969.
39. Seaton, Weekly Status Report, 10 Jan. 1969; Mueller Reports, 13 Jan. and 17 March 1969; Phillips TWX to MSC, MSFC, and KSC, Attn.: Low, James, and Middleton, 17 March 1969; NASA, "Apollo 10 Launch Date," news release 69-41, 17 March 1969; Phillips TWX to KSC, MSFC, and MSC, "Apollo 10 and 11 FRR Planning Dates," 17 Feb. 1969.
40. James A. York, secy., minutes of meeting, LM-4 FRR Board, 11 April 1969; Brendle, minutes of meeting, CSM 106 FRR Board, 11 April 1969; Low to Phillips, 12 May 1969, with encs., Maxime A. Faget to Mgr., ASPO, "Descent Propulsion System POGO possibilities," 12 May 1969, and Joseph N. Kotanchik to Dir., Engineering and Development, and Mgr., ASPO, "Spacecraft POGO," 13 Sept. 1968; Phillips to Apollo 10 FRR Board, "Confirmation of Flight Readiness for the Apollo 10 Mission," 16 May 1969.
41. MSC news release 68-81, 13 Nov. 1968; Apollo 10 press kit, pp. 3, 65; Gilruth to NASA Hq., Attn.: Mueller, "Flight crew training summaries," 12 May 1969; "Apollo 10 Debriefing," pp. 20-1 through 20-15.
42. Donald K. Slayton to Dir., MSC, "Proposed Apollo X patch," 13 March 1969, with enc.; NASA, "The Flight of Apollo 10, May 18-26, 1969," 2 June 1969, p. 3; Julian Scheer to Low, 18 April 1969.