This discussion is based primarily on NASA Technical Note TN D-7112, "Apollo Experience Report Simulation of Manned Space Flight for Crew Training," by C. H. Woodling, Stanley Faber, John J. Van Bockel, Charles C. Olasky, Wayne K. Williams, John L. C. Mire, and James R. Homer, March 1973.

Even before Project Mercury began, the value of high-fidelity simulation as a training procedure was well established through aircraft flight experience. But whereas aircraft pilots can obtain much of their training during actual flights, the crews for space missions must receive all their training in flight tasks before the mission, because a manned space flight is fully committed to its entire mission at liftoff and the crew must be proficient in all anticipated flight operations at the time of launch. Aircraft experience was used in the development of the first space flight simulator, the Mercury Procedures Simulator; subsequent programs drew heavily on experience in actual space flights to design the simulators.

Lack of experience with the environmental factors of space flight gave rise to considerable concern in the early stages of Project Mercury; hence training concentrated on acclimating astronauts to the high acceleration forces of launch and reentry, zero-gravity conditions, heat, noise, and spacecraft tumbling. Once it was established that crews could perform normally under these conditions, subsequent training programs focused more narrowly on the complexities of operating the spacecraft systems.

For Project Apollo (and Gemini before it) a very large effort was devoted to the development of simulators that would duplicate as closely as possible the sights, sounds, and sensations of space flight. It was not possible to produce all these effects simultaneously - in particular, zero gravity or weightlessness could not be sustained for any length of time on earth - hence simulators were broadly divided into two classes: moving-base, in which the crew station could be moved to simulate expected conditions, and fixed-base, in which no motion was imparted to the crew. An outstanding example of a moving-base simulator was the lunar landing training vehicle [see Chapter 9], a free-flying device providing six degrees of freedom and designed to approximate the performance of the lunar module in its final approach to landing on the moon in reduced gravity. Others included the translation and docking simulator, the dynamic crew procedures simulator, and the lunar landing research facility, which allowed training for specific phases of a mission ("part-task trainers"). Most of the astronauts' training time, however, was spent in the fixed-base command module simulator (CMS) and the lunar module simulator (LMS).

Both the CMS and the LMS were built around mock-ups of the respective spacecraft, fully equipped with controls and displays, crew couches, and storage compartments as nearly like the mission-specific spacecraft as possible.* An elaborate optical system projected realistic out-the-window scenes for each stage of the mission, using either films or hand-made mock-ups photographed by high- resolution television cameras. (The preparation of three-dimensional scale models of the lunar surface for use in the simulators was a factor that had to be considered in meeting an assigned launch date.) For solving navigation problems, a star field was projected in the field of vision showing all stars of magnitude 5 or less that appeared in the vicinity of the stars used for determining the spacecraft's position. Switches and controls were designed to have exactly the same "feel" as flight articles and produced responses exactly like those that would be generated during a mission. The CMS system was controlled by four large digital computers and a program of 750,000 words. The analogous LMS required three computers and a 600,000-word program. At the computer control panels, instructors could create every conceivable type of emergency for the astronauts to cope with.

Because two or more crews might be in training at the same time, three command module simulators were provided, one at the Manned Spacecraft Center and two at Kennedy Space Center, where astronauts spent much of their last few weeks of preparation before flight. One lunar module simulator was located at each center. At the height of preparations for Apollo 11 some 175 contractor personnel worked on the development and control of the simulator software; 200 more were assigned to hardware operations and maintenance.

Not only the crews, but also the flight controllers who manned the consoles in the Mission Control Center (MCC) had to become proficient in real-time management of all the systems involved in a flight. Much of their training was conducted independently of the crew, using computer-generated "math models." In the later stages of preparation Mission Control and the spacecraft simulators (either or both) were linked in integrated network simulations requiring both crews and flight controllers to respond to normal and contingency situations. The time devoted to these integrated simulations varied with the complexity of the mission and with experience.

Besides their use in crew and flight controller training, the spacecraft simulators were invaluable in working out new operational procedures. During Apollo 13, for example, procedures improvised by flight control teams were checked in real time by astronauts in the simulators before being sent to the crew in the crippled spacecraft.

Zero-gravity training was accomplished in two ways. Short periods (up to about 40 seconds) of partial to null gravity can be achieved in an airplane by flying what was called a "Keplerian trajectory" - a carefully defined parabolic path during part of which centrifugal force offsets gravity. An Air Force KC-135 (the military version of the Boeing 707), structurally reinforced to take the strain of these maneuvers, flew regular missions during which critical operations were evaluated in zero gravity. The alternative method used the buoyant effect of water. By attaching weights to various parts of the body of a suited astronaut it was possible to achieve "neutral buoyancy" in a large tank. Many tasks were rehearsed and procedures modified in the neutral-buoyancy facilities at MSC and at Marshall Space Flight Center. The method had the advantage of providing all the time needed; its major disadvantage was that it was less realistic than the aircraft flights on account of the viscosity of the water, which hampered movement. Still, it had its place in zero-gravity training, and astronauts generally found that it gave a conservative estimate of the difficulty of a task. Anything that could be done in the neutral-buoyancy tank could usually be done in space.

Lunar surface simulations were conducted at a site off to one corner of the Manned Spacecraft Center, where a few acres of ground had been pocked with craters and strewn with rocks and gravel to simulate the moon's surface. Here astronauts checked out deployment of the lunar surface experiments and practiced sampling. No attempt was made to approximate the reduced gravity of the moon, although NASA engineers devised a suspension system that offset five-sixths of the astronaut's weight, which was valuable for evaluating techniques of locomotion and manipulation.

Field geology was another important phase of astronaut training. No terrestrial site duplicates the lunar surface, but the rugged conditions expected to be found on the moon have many counterparts on earth. Among the areas visited by astronauts and their instructors were the Grand Canyon in Arizona; volcanic areas in Iceland, Mexico, New Mexico, Alaska, and Hawaii; and the Ries Crater area in West Germany. Each site had specific features applicable to lunar geology, and each provided the opportunity to conduct surface operations analogous to those to be used on the moon.

Besides such "hands-on" rehearsal of mission operations, astronauts sat through many hours of classroom-type work - lengthy briefings on the spacecraft systems, principles of propulsion, guidance and navigation, and orbital mechanics. They also spent many a day in design reviews, crew compartment fit-and-function reviews, and all the other reviews that punctuated the progress of spacecraft from design to delivery and played important roles in the formulation of flight plans.

This discussion does not by any means exhaustively cover the effort that went into simulation and training, but it may indicate the complexity of the simulation program and its importance to the Apollo project. The tables that follow give an indication of the amount of time required to prepare for lunar missions.

* In the early days of the project, details of spacecraft design changed so rapidly that it was difficult to keep the simulators up to date. At one point during training for the first manned mission (AS-204), Gus Grissom became so disgusted with the discrepancies between the simulator and the spacecraft that he hung a lemon on the trainer. Courtney G. Brooks, James M. Grimwood, and Loyd S. Swenson, Jr., Chariots for Apollo: A History of Manned Lunar Spacecraft, NASA SP-4205 (Washington 1979), p. 209.

Table 1.

Apollo Astronaut Training Summary

*Tables adapted from C. H. Woodling et al., "Apollo Experience Report - Simulation of Manned Space Flight for Crew Training," NASA TN D-7112, March 1973.

Type of Training                         No. of hours

Command module                                
 Command module simulator                      17,605
 CM procedures simulator                        1,204
 Simulator briefings                            1,195
 Contractor evaluations                           866
 Dynamic crew' procedures simulator               741
 Other simulators                                 156
 Rendezvous and docking simulator                  87
 Centrifuge                                        58
 MIT hybrid simulator                              48

                           Subtotal            21,960

Lunar module
 LM simulator                                  13,317(c)
 Lunar landing training vehicle                 1,130(d)
 LM procedures simulator                          770
 Simulator briefings                              533
 Full mission engineering simulator               179
 Translation & docking simulator                   64
                           Subtotal            15,993

                           TOTAL               37,953

Mission techniques                              2,730
Checklist                                       2,334
Flight plan                                     1,987
Mission rules                                   1,039
Design, acceptance                              1,011
Test reviews                                      814
Team meetings                                     541
Training meetings                                 393
Rendezvous                                        288
Extravehicular contingency transfer                88
Flight readiness reviews                           48

                           TOTAL               11,273

Lunar science                                  11,408(a)
Water immersion facility checkout               1,248
Stowage                                           993
Extravehicular mobility unit checkout             919
Egress                                            820
Bench checks                                      802
Walkthroughs                                      719(b)
Medical                                           601
Water immersion facility (zero gravity)           516
Planetarium                                       448
Fire                                              174

                           TOTAL               18,698

Command and service module                      4,060
Guidance and navigation                         2,397
Lunar module                                    2,130
Lunar topography                                1,458
Launch vehicle                                    656
Photography                                       405

                           TOTAL               11,106

Command and service module                      3,332
Lunar module                                    1,759

                           TOTAL                5,091

                   PROGRAM TOTAL               84,071

(a) Includes briefings, geology field trips, lunar surface simulations, and lunar roving vehicle trainer operation.

(b) Related to zero-gravity flight operations.

(c) Includes lunar roving vehicle navigation simulator.

(d) Includes lunar landing training vehicle flights (2 hr. per flight), vehicle systems briefings, lunar landing research facility and lunar landing training vehicle time.

Table 2.

Apportionment of Training According to Mission Type

Missions before first lunar landing (a)

Training Category           Hours   Percent of total
Simulators                 11,511                 36
Special purpose             4,023                 13
Procedures                  7,924                 25
Briefings                   5,894                 18
Spacecraft tests            2,576                  8

Total                      31,928                100

Early lunar landing missions (b)

Training Category           Hours   Percent of total
Simulators                 15,029                 56
Special purpose             5,379                 20
Procedures                  2,084                  8
Briefings                   3,070                 11
Spacecraft tests            1,260                  5

Total                      26,822                100

Final lunar landing missions (c)

Training Category           Hours   Percent of total
Simulators                 11,413                 45
Special purpose             9,246                 36
Procedures                  1,265                 5
Briefings                   2,142                 9
Spacecraft tests            1,255                 5

Total                      25,320                100

(a) Apollo 7, 8, 9. 10

(b) Apollo 11, 12, 13, 14

(c) Apollo 15, 16, 17

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