Apollo Expeditions to the Moon|
DETECTIVE WORK ON THE TELEMETRYWhat had happened? Ferreting out clues from mission records and the reams of data recorded from telemetry was a fascinating story of technical detective work. More than a thousand engineers and technicians at NASA Centers, contractor plants, and several universities were involved in establishing causes and designing and testing fixes.
The solution for pogo was to modify the pre-valves of the second-stage engines so that they could be charged with helium gas. This provided shock-absorbing accumulators that damped out the thrust oscillations.
Finding the culprit that cut off the J-2 engines involved long theorizing and hundreds of tests that finally pinpointed a six-foot tube, half an inch in diameter, carrying liquid hydrogen to the starter cup of the engine. This line had been fitted with two small bellows for absorbing vibration. It worked fine on ground tests because ice forming on the bellows provided a damping effect. But in the dryness of space - eventually simulated in a vacuum chamber - no ice formed because there was no air from which to draw moisture, and there the lines vibrated, cracked, and broke. The fix: replace the bellows with bends in the tubes to take up the motion.
With careful engineering analysis and extensive testing we satisfied ourselves that we understood the problems that plagued Apollo 6 and that the resulting changes were more than adequate to commit the third Saturn V to manned flight.
At this point we planned that the next Saturn V would be the D mission, launching Apollo 8 in December with Astronauts McDivitt, Scott, and Schweickart. Their main objective would be to test the spider-like lunar module then abuilding at the Grumman plant on Long Island. Early in 1968 we had set the objective of flying the D mission before the year was out. It was a reasonable target at the time, considering progress across the program, and would put us in an excellent position to complete the preparatory missions and have more than one shot at the landing in 1969.
Meanwhile, the command and service modules, after almost two years of reworking at the North American Aviation plant in Downey, Calif., would have their crucial flight test on Apollo 7, the C mission, after launch in October 1968 by the smaller Saturn IB. On board this first manned Apollo mission would be Astronauts Schirra, Eisele, and Cunningham.
By midsummer it was apparent that Apollo 7 would fly in October, but that the lunar module for the D mission would not be ready for a December flight. Electromagnetic interference problems were plaguing checkout tests, and it was obvious that engineering changes and further time-consuming tests were needed. After a comprehensive review in early August, my unhappy estimate was that the D mission would not be ready until March 1969.