Chariots for Apollo: A History of Manned Lunar Spacecraft|
Some Special Considerations
NASA officials used only a dozen words to list the primary objectives of Apollo 11: "1. Perform a manned lunar landing and return. 2. Perform selenological inspection and sampling."2 They had worked many years to be able to write these objectives for a mission rather than a program. Ever since Apollo was named in 1960, groups scattered throughout the country had studied and planned the segments of that mission. Through 1965, this planning had helped design the hardware. After that, with the exception of rework caused by the fire in 1967, the mission planners had analyzed the spacecraft capabilities and used this information to draft the most minute details of the flight plan, which appeared in "final" form on 1 July 1969, to be followed by "revision A" seven days later.3
Chris Kraft's flight operations team in Houston designed and evaluated most of the mission techniques. When the lunar landing flight became the letter "G" on the chart of the progressive steps to land the first men on the moon, Rodney G. Rose had already presided over 21 monthly meetings on how the crew would operate when it reached its goal. The Rose team held 20 more meetings before being satisfied that it had done all it could to smooth operations for what turned out to be Apollo 11. The 41st and final (summing-up) session was held in April 1969, after a flight operations plan had been issued to outline in detail the duties and actions to be performed at precise times.4
Rose's group served two specific purposes. First, its members were observers, acquiring and passing on information about the spacecraft, about flight crew operational procedures tried and either adopted or rejected, and about engineering and development progress in qualifying the suit and backpack for the lunar walk. The committee was, second, a forum before which the mission planning and analysis team could air computer-checked trajectories and techniques that affected the interactions of hardware, crew, and fuel. Mission planners relied not only on theoretical plans run through the computers, but also on actual experience. Apollo 8, for example, needed only 2 periods of onboard navigation during translunar and transearth coasting, rather than the 10 previously planned. But past experience was set aside in one case. As far back as Mercury, the crews had dumped any remaining fuel before landing, as a safety precaution. What should be done about the propellants in the lander's descent and ascent propulsion systems? Should one be burned to depletion before lunar touchdown and the other before redocking with the command module? The Apollo office objected to this. It would be safer for the lunar module pilots to land as soon as they reached the selected site than to cruise around burning up fuel, with the possibility that they might have to touch down in an undesirable site as a result. And it would be much better to go ahead and dock than to fly around until they were low on fuel and then find, if an emergency arose, that they had no way to return to the command module. Firing to depletion in either case would be a last-ditch action to ensure crew safety.5
Rose's team also helped Donald Slayton's support personnel decide how many lunar revolutions should be flown before undocking and descent, to make sure a well-rested crew would land on the moon with the sun angle at 6 to 20 degrees, for the best lighting. Apollo 10 supplied the answer to this question. But the planners and trajectory plotters could not set a specific flight path in concrete. With the possibility that delays could cause them to miss a launch window (determined by the moon's position in relation to the earth), they had to plan for one mission in July, for another in August, and for a third in September.6
Closely allied with Rose's work were the activities of Bill Tindall. Long an associate of John Mayer in mission planning, Tindall had guided Gemini efforts while Mayer had concentrated on early phases of Apollo planning. When Gemini ended in 1966, Tindall had jumped in to help out on the complex Apollo task, first as Mayer's deputy and then as data coordination chief in the Apollo office. After 16 January 1968, the day he assumed his new duties, his barrage of "Tindallgrams" continued to enliven interoffice mails. Although he was now the liaison between spacecraft and operations people, Tindall had been and still was a mover of information and an assigner of tasks to specialists, either to devise or to solve some mission technique. His memoranda, sometimes addressed to hundreds of persons, often contained admonitions to one, such as, "Bob Ernull please take note."7
Three areas of the mission demanded the toughest scouting by Tindall, Rose, and other mission planners: descent, surface operations, and ascent. Judged by the sheer weight of paperwork, descent seemed to be the engineers' chief worry. Yet nobody wanted to set mission rules so narrow that the crew could not land. Tindall and astronaut Harrison Schmitt even discussed whether it was absolutely necessary for the pilots to see exact landmarks. A touchdown outside the targeted area might be quite satisfactory. They decided to leave the pilots some options: "quit and come home, go another revolution and try again, or don't worry about it and press on with the landing."8
Much of the concern about hitting a precise spot stemmed from uncertainties about trajectory dispersions caused by the moon's strange gravity fields. As more information was gathered about the mass concentrations, called mascons, the Landing Analysis Branch fed the data into computers for run after run (205 on just one study), trying to evaluate fuel use and the probability of mission success based on varying degrees of mascon influence on the descent trajectory. Tindall's group also found guidance system faults that might result in unwanted excursions. Flight controllers would have to help the crew decide whether to go on or return to the command module. But returning to the mother ship would be tricky, Tindall said. Dispersions had to be severely contained to prevent the crew from flying a "dead man" curve - an aimless trip across the lunar sky far out of range of the command module's rescue capability.9
Constantly looking for clear explanations of how to guide a spacecraft safely down to the moon, Tindall pounced on a lucid description by George W. Cherry of the Massachusetts Institute of Technology and arranged to have it reproduced and distributed to flight controllers, managers, and astronauts. Cherry numbered each step of the descent phase and outlined the guidance in finite detail, including how the spacecraft should react and what the pilots should do. Cherry said that, during "program 63 (P63)" (braking), the crew should steer out any errors in attitude. During P64, as the lander tipped over to give the crew a first look at the landing site, the thrusters that turned and tilted the spacecraft should be carefully checked to make sure they were working properly for the landing. From there to touchdown - P65, 66, and 67 - a maze of procedures would take the pilots through this most critical step in the mission.10
When the Sea of Tranquility appeared the possible target for Apollo 11, Tindall alerted planners to some unusual conditions in that location. Although the lunar module would begin its descent from an orbital station 18,300 meters above the mean surface of the moon, its altitude above the landing zone would be much less than that. Tranquility, he said, was 2,700 meters above the mean average, and even more in its hilly area. So the landing approach would start low. Moreover, it would be uphill because there was a one percent upward grade in the direction of the flight path. These numbers, too, were fed into the computers to check the crew's responses as they flew the trajectories in the lunar module simulator. All through June and early July, memoranda and notes about descent-propellant margins, use of the guidance system, and even the views to be seen out the windows - continued to flow.11
In March 1969, Tindall had reminded his colleagues that the "lunar surface stuff [was] still incomplete." Even the proper terminology had not been decided. For example, Tindall said, the past practice of continuing or aborting a mission by making a "go/no go" decision seemed inappropriate; once the lander had settled on the lunar surface, this might confuse the pilots. Tindall suggested something like "stay/no stay," and that phrase became standard.12
There were other lunar surface worries. Suppose the vehicle landed at an angle? That possibility did not worry the planners very much, because the LM was designed to take off with as much as a 30-degree list, but the guidance system did not know that. In flight, the attitude thrusters fired automatically to keep the lander on an even keel, and they would do the same thing on the ground. But nobody wanted these engines to fire while on the lunar surface. George Cherry had the answer. "Just joggling the handcontroller will not necessarily . . . stop the firing," he said; the crew would have to cycle the guidance switches to off and then to attitude hold to prevent the thrusters from doing their programmed job.
The two hours after landing were critical. The pilots - who would act as their own launch crew - had to go through a countdown after landing to be prepared to leave the moon in a hurry if anything went wrong. They would do the same thing the last two hours before their scheduled departure. One crucial task in both these exercises was aligning the guidance system's inertial platform. Most mission planners agreed that the moon's gravity could be used for this reading, but Tindall worried that the lander might be so near "one of those big damn lumps of gold" that the alignment might be wrong and the lander might take off on an incorrect course. Two days before launch, however, he reported that "the various far-flung experts predict that mascons should have no significant effect."13
Ascent from the moon also raised questions about trajectory dispersions. Fairly small deviations could cause the lunar module to crash back into the moon or miss the rendezvous with the command module. That was not as big a worry, however, as the possibility of a failure in the guidance system. The chances of the crew's taking off in the lunar module and finding the command module would be extremely poor if all the guidance equip ment failed.* Planners had been studying manual takeover and steering of the lander even before Grumman was selected to build the machine in 1962; in 1969 the computers were still grinding away, trying to find a satisfactory solution. The consensus appeared to be that controlling the lunar module manually was only slightly better than doing nothing.
And a launch from the moon had to be exactly on time. If the crew fell behind in the schedule, it would have to delay the launch until the command module circled the moon again. It was also important that the command module's path be precisely in line with the lunar module's ascent trajectory (that is, "in plane"). The command module pilot was responsible for tasks such as altering the command ship's flight path - not just watching from his window. He would participate actively by keeping a close eye on the lunar spacecraft while it was on the surface and by being ready to help deal with whatever contingencies the lander might encounter. To be prepared for any abort situation, the command module pilot had a "cookbook" of 18 different two-page checklists to cover all envisioned rescue operations.14
Landing, surface work, and ascent were going to be difficult, complex, and demanding tasks. George Mueller, the manned space flight chief in Washington, had therefore urged in mid-1968 that the first lunar landing crew be selected as soon as possible.15
* Mission planner Carl Huss had talked with the astronauts (especially Russell Schweickart) during the early days about manual control. At that time, however, his group thought the lander had enough redundancy and backup systems to do the job. As the landing flight drew near, astronaut interest in manual control naturally heightened.
2. NASA OMSF, "Mission Implementation Plan for Apollo 'G' Mission," 1 Oct. 1968, pp. 3, 4, 13, 15; append. 5, "Flight Primary Objectives (Apollo-Saturn 201 through Apollo 17)," in Ivan D. Ertel and Roland W. Newkirk, with Courtney G. Brooks, The Apollo Spacecraft: A Chronology, vol. 4, January 21, 1966-July 13, 1974, NASA SP-4009 (Washington, 1978).
3. L. J. Riche, G. M. Colton, and T. A. Guillory, "Apollo 11, Apollo AS-506 CSM-107/LM-5: Final Flight Plan," 1 July 1969; Warren J. North memo, "Revision A to the Apollo 11 Final Flight Plan," 8 July 1969, with 2 encs.
4. MSC, minutes of 22nd Lunar Landing Mission (G Mission) Flight Operations Plan (FOP) Meeting, 27 Oct. 1967; MSC, "Results of 41st G-1 Mission FOP Meeting," 10 April 1969.
5. "Results of 38th G Mission FOP Meeting," 16 Jan., and ". . . 39th G Mission FOP Meeting," 13 Feb. 1969.
6. "Results of 35th G Mission FOP Meeting," 24 Oct. 1968; "Results of 38th G Mission FOP Meeting"; Donald K. Slayton to Mgr., ASPO, "Shortening of the G Mission lunar orbit timeline," 13 Jan. 1969; Low to Slayton, "G mission lunar orbit timeline," 24 Jan. 1969.
7. Howard W. Tindall, Jr., interview, Houston, 16 Dec. 1966; Tindall memos, "AGS accelerometers may not work," 16 Jan. 1968, and "External Delta V for LOI," 16 Jan. 1968. Tindall signed one of these memos as Deputy Chief, Mission Planning and Analysis Div. (MPAD), and the other as Chief, Apollo Data Priority Coordination.
8. Tindall memo, "Maybe lunar landing site observations arc not needed to land," 2 Oct. 1968.
9. Gilbert L. Carman and Moises N. Montez, MSC, "Project Apollo Preliminary Lunar Descent Dispersion Analysis," Internal Note 69-FM-20, 30 Jan. 1969; Tindall memo, "Descent monitoring at MCC," 10 April 1969.
10. Tindall memo, "What's descent all about?" 30 April 1969, with enc., George W. Cherry to MSC, Attn.: William R. Kelly and Tindall, "Lunar Landing Guidance and Control Modes," 21 March 1969; Charles O. Lewis, "LM Descent Ascent Summary Document, Mission G & Subsequent: Final," MSC Internal Note MSC-CF-P-69-16, 22 May 1969, pp. 2-3.
11. Tindall memo, "G mission lunar descent is uphill all the way," 12 May 1969; George M. Low to Lt. Gen. Samuel C. Phillips, 26 June 1969, with enc., John P. Mayer to Dir., Flight Ops., "Review of Bellcomm's recommendations concerning Apollo 11 Lunar Module (LM) descent propellant margin/manual landing interactions," 20 June 1969; Mayer memo, "Views from the CM and LM during the flight of Apollo 11," 11 June 1969; Alfred N. Lunde, "Views from the CM and LM During the Flight of Apollo 11 (Mission G)," MSC Internal Note 69-FM-168, 12 June 1969; Tindall memo, "Some new ideas on how to use the AGS during Descent," 3 July 1969.
12. Tindall memo, "G Lunar Surface stuff is still incomplete," 7 March 1969.
13. Tindall memo, "G Lunar Surface Phase Mission Techniques," 11 Feb. 1969; idem, "There will be no VHF ranging data collected while tracking the LM on the lunar surface," 28 Feb. 1969; idem, "AGS alignments in lunar orbit and operations on the lunar surface," 4 April 1969, with enc., "First 2 Hours on the Lunar Surface After Touchdown anti First Stay Decision," 2 April 1969; idem, "PGNCS operations while on the lunar surface," 1 April 1969, With enc., "LM IMU Alignment Sequence"; MSC, "Apollo Mission Techniques, Mission G, Lunar Surface Phase: Revision A," Internal Note S-PA-9T-050, 12 May 1969, pp. 3-7, 20; Tindall memo, "How we will handle the effect of mascons on the LM lunar surface gravity alignments," 14 July 1969; General Electric, "Study of the Postlanding Tilt Angle of the LEM," TIR 545-S64-03-006, 21 May 1964; Courtney G. Brooks and Ivan D. Ertel, The Apollo Spacecraft: A Chronology, vol. 3, October 1, 1964-January 20, 1966, NASA SP-4009 (Washington, 1976), p. 175.
14. Tindall memo, "Manual Steering for LM Ascent," 12 May 1969; idem. "Let's drop one of the lunar surface RR tests," 15 April 1969; idem, "Some things about Ascent from the moon," 8 April 1969; Tindall memo, 11 Feb. 1969; idem, "CSM Rescue Mission Techniques are complete and clean," 11 June 1969; Carl R. Huss to JSC History Office, "Comments on Draft Copy of 'Chariots for Apollo: A History . . . ,' " 2 Nov. 1976.
15. George E. Mueller to Robert R. Gilruth, 5 June 1968.