Most of MSC's activity during 1967 and early 1968 was directed toward reducing the fire hazard in the command module. The spacecraft hatch was redesigned so that the crew could open it unaided in five seconds. Electrical systems and the plumbing that carried oxygen and combustible coolants were thoroughly examined and modified. New materials to replace flammable nylon were investigated. The advantages and disadvantages of atmospheres other than pure oxygen were weighed. Repeated testing gathered data to support recommended changes. A Senior Flammability Board, a Materials Selection Review Board, and a Crew Safety Review Board were established to oversee specific parts of the process, and a tough Configuration Control Board was set up to pass on all proposed changes in the command module. The spacecraft builder, North American Aviation, was prodded to supervise its subcontractors and vendors more closely to ensure on-time delivery of critical subsystems.1 The lunar landing module was less affected by the fire, but it had its own problems. As had happened two years earlier, its weight continued to creep upward, putting a squeeze on the scientific payload that could be landed on the moon. Stress corrosion - cracks in aluminum structural members - and fragile wiring caused delays and concern for reliability. Perhaps the most serious problem was combustion instability in the lander's ascent engine, which would blast the astronauts in the upper section back into lunar orbit after they had completed their lunar exploration. These were worrisome problems at this late stage, but concentrated effort by the lunar module contractor and two engine contractors produced enough progress by mid-1968 to give NASA managers reason for guarded optimism.2
Late in January 1968 flight tests resumed when MSC put an unmanned lunar lander through its paces in earth orbit. Designated Apollo 5 and launched on a Saturn I-B, this flight verified operation of the lunar module's propulsion and attitude-control systems and checked out the performance of the instrument unit on the launch vehicle's uppermost stage, the S-IVB. The success of this mission was more encouraging than the one that followed. On April 4 Apollo 6, the second "all-up" unmanned test of the Saturn V, tested launch- vehicle systems and the emergency detection system and allowed launch crews and vehicle engineers to rehearse their tasks once more. Along for the ride, more or less, was a Block I command module with some Block II* modifications; no mission objectives were to be satisfied by this spacecraft except verification of its performance during reentry from a lunar mission. Apollo 6 was trouble from the start. The first-stage burn produced intolerable "pogo" effects (longitudinal oscillations due to irregular fuel feed), and a section of the adapter that mated the spacecraft to the booster blew off during ascent. Two of the five engines on the second stage (S-II) shut down prematurely. Perhaps the most troublesome fault was the failure of the third stage (the S-IVB) to reignite in orbit - the maneuver that, on a lunar mission, would send the Apollo craft on its way to the moon. Marshall Space Flight Center immediately got to work on the problems; yet another unmanned Saturn V test might be needed unless Marshall's engineers could correct them.3
In spite of the difficulties with Saturn V and the lunar module, in mid-1968 it still seemed possible that manned flights could resume before the end of the year. Command and service module number 101, delivered to the Cape at the end of May, had fewer discrepancies on arrival than any previous spacecraft. It would fly on Apollo 7, the first manned earth-orbital test of the second-generation spacecraft, scheduled for the last quarter of the year. Since that mission would use a Saturn 1-B rather than a Saturn V and would not carry a lunar module, its prospects seemed good.4
While spacecraft and operations engineers worked toward getting Apollo flying again, their counterparts in the science programs were equally busy preparing for the first lunar landing. Of all the science-related efforts, the lunar surface experiments were in the best shape in early 1968. The lunar receiving laboratory with its complex scientific equipment, and the elaborate procedures for back-contamination control, had much farther to go before they would be ready to handle their part of the program.
* The two versions of the command module were designed respectively for earth-orbit and lunar-landing missions. They differed chiefly in onboard systems (guidance and navigation, docking, life-support, etc.).
1. 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), pp. 228-29, 237 41.
2. Ibid., pp. 244-47.
3. Ibid., pp. 241-53; Roger E. Bilstein, Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles, NASA SP-4206 (Washington, 1980), pp. 360-63.
4. Brooks, Grimwood, and Swenson, Chariots, p. 253.