| Apollo Expeditions to the Moon|
Getting lt All Together
By GEORGE E. MUELLER
The Apollo 9 and 10 missions were the learning phase of the program, coming as they did between the first tests of the command module in deep space on Apollo 8 and the lunar landing of Apollo 11.
Apollo 9 and 10 were missions designed to rehearse all the steps and reproduce all the events of the Apollo 11 mission with the single exception of the lunar touchdown, stay, and liftoff. The command and service modules and the lunar module were used in flight procedures identical to those that would later take similar vehicles to the Moon and a landing. The flight mechanics, the mission support systems, the communications, the recording of data - all these techniques and components were tested in a final round of verification.
We learned from those two missions how to develop our flight procedures. They are complex, at best, and for future missions we wanted to know exactly what alternatives we would have under a wide variety of circumstances to assure the safety of the astronauts and the success of the missions, in that order. Fortunately we had very few problems on both missions. Three reasons for that good fortune were the extensive ground tests, the simulation exercises which provided the crews with high-fidelity training for every phase of the flight, and the critical design review procedures.
The crews rehearsed and re-rehearsed their movements in ground simulators and in conditions of inflight weightlessness produced by parabolic flights in a converted Air Force KC-135 tanker and by neutral buoyancy simulations. They had started this kind of training as a crew months before the flight, gradually working toward proficiency and a degree of automatic response to the checklists, the pilots' shorthand notes that were developed simultaneously. By the time they were ready for their actual missions, they had run through all the normal routines many times, and had thoroughly rehearsed emergency procedures for every imaginable trouble or failure.
The critical design reviews were fundamental to the testing and simulation programs. What we actually did was to go over every single part of the spacecraft to make sure that we understood how it worked, how it might go wrong, and what alternative procedure or backup system we had in case it did go wrong. The overriding consideration was, of course, crew safety; there always had to be at least one way back from orbit or from the Moon if something went wrong. These design reviews were done by a number of task groups, because there were too many spacecraft systems for any single group to consider, let alone understand to the required degree.
One of my areas of special interest lay in what we called software - the computer programs that provided the intelligence and control functions onboard the spacecraft and at the ground stations. General Phillips asked me to form a special software review group that met for several months and initiated some disciplines which, I believe, finally made it possible for the Apollo 11 lunar landing to take place when it did.
An interesting point about the Apollo 10 flight is that it did fail to do one of the steps that was later done on the Apollo 11 and which caused some brief moments of tension just before the lunar landing. On Apollo 10, the landing radar and the rendezvous radar never were operated at the same time. They are used for two different procedures, and at two different altitudes, so that there didn't seem to be any need for simultaneous operation of the pair. But on Apollo 11, they wanted to check the operation of the high-altitude gate radar as they approached the surface of the Moon, and so it was left on. That radar and the landing radar were feeding information directly into the onboard computer in the Apollo 11 lunar module. Although the data from the altitude radar was not being used, it nevertheless was driving the input registers of the computer and thus forcing the central processor to decide at each cycle that the radar data were not germane.