Moonport: A History of Apollo Launch Facilities and Operations|
Apollo 16 Operations
While astronauts Scott and Irwin motored around Hadley Rille, KSC officials turned their attention to the Apollo 16 mission scheduled for March 1972. In early August, North American mated the command and service modules. Three weeks later Grumman joined the two LM stages for their altitude tests. September saw the start of lunar rover checkout and the erection of the S-IC stage. In October the launch vehicle team stacked the Saturn stages. Meanwhile the astronauts went through the crew compartment fit and functional tests and the altitude chamber runs. The spacecraft modules moved out of the chambers in November and landing gear was installed on the lunar module. In December the spacecraft team mated the Apollo spacecraft to the lunar adapter and moved the combination to the assembly building. Twelve days before Christmas Apollo 16 rolled out to the pad.19
The launch team had made relatively few changes to the Apollo 16 spacecraft during the first five months of launch operations. Malfunctions on Apollo 15 prompted two command module changes: replacing panel switches for the spacecraft propulsion system and replacing the main parachutes. One of the three main parachutes had failed to open for the splashdown of Apollo 15, and NASA officials suspected hydrogen embrittlement in the connector links of the suspension lines. After replacing the suspect parts with steel alloy links, North American shipped a new set of parachutes to KSC in mid-November. That same week the launch team replaced the water glycol accumulators in two fuel cells of the service module. When the fuel cells converted oxygen and hydrogen to electricity and water, considerable heat was produced. As it transferred this heat to a series of radiators, the glycol expanded and the excess liquid accumulated in reservoirs. The accumulators had been damaged in September when technicians overpressurized the glycol system during a vacuum-purging test.20
One of the few problem areas in the Saturn operations involved the engine actuators on the S-IC stage. These hydraulic actuators, 1.5 meters in length, swivelled the four outboard F-1 engines to change pitch, yaw, and roll. Actuator tests included the calibration of a recorder in the launch control center. As the actuators swivelled the F-1 engines, a potentiometer sent a voltage to the recorder indicating the direction and amount of movement. During November tests, excessive noise in one actuator interfered with the signal to the control center; the actuator was replaced on the 25th. The following week Boeing engineers inspected the S-IC LOX and RP-1 tanks for stress corrosion but found no problem.21
Early in the new year a spacesuit alteration and two spacecraft problems delayed the Apollo 16 launch to 16 April. Grumman engineers had increased the capacity of the lunar module batteries and wanted more time to gather test data. At Downey technicians discovered that an explosive device used to separate the command-service and lunar modules would malfunction under certain conditions; modification required additional time. The delay proved a godsend for KSC in late January when a fuel tank in the command module's reaction control system ruptured.22
The hypergolic propellants of the reaction control system, which controlled the attitude of the command module during reentry, were forced from their tanks by high pressure helium gas. Within each fuel tank, the fuel was inside a teflon bladder. As gas entered the tank, outside the bladder, rising pressure squeezed the bladder and forced the hazardous fuel from its tank. The flow of helium was tested during the integrated systems test. The primary and secondary regulators were checked to guarantee that an accurate flow was maintained, that the regulator shut off properly, and that after shutoff the pressure did not creep up, which would indicate internal leakage.
Problems with ground support equipment had put the launch team about two shifts behind schedule on 25 January when technicians completed the fuel-tank relief-valve checks and moved to the regulator tests. For these tests, the bladders were filled with helium gas instead of the hazardous monomethyl hydrazine. Human error brought the team grief: a technician failed to fully engage a quick-disconnect valve that controlled the flow of helium to a pressure regulator. Pressure inside a fuel tank, but outside the filled bladder, dropped quickly, and the bladder ruptured.23
The seriousness of the problem stemmed from its location. Replacement of the fuel tank involved removing the command module's aft heatshield, an operation that had to be conducted in the operations and checkout building. KSC faced a roll-back of the space vehicle from the pad to the assembly building - the first time this had happened since a hurricane threatened 500-F in June 1966. At first glance the accident seemed to preclude the April launch, and NASA officials announced a possible second month's delay; but after reviewing the work needed to replace the damaged fuel tank, Kapryan and Petrone concluded that the launch team could recover in time for the 16 April launch. The space vehicle was returned to the assembly building on 27 January. The following day the launch team transferred the spacecraft to the operations and checkout building where both fuel tanks were replaced, along with the descent propulsion system regulators. By working overtime and weekends,* KSC had Apollo 16 back on the pad in less than two weeks.24
While operations resumed their smooth course for most of the KSC team, the propellants section experienced more headaches. The spacecraft was undergoing another integrated systems test on 17 February when a leak developed in a quick-disconnect test point. A North American engineer closed off test points improperly and excessive pressure ruptured discs on both oxidizer tanks. While the launch team waited for replacements to arrive, the program office rescheduled the remaining propulsion tests. New burst discs were emplaced and x-rayed on the 22nd, and propulsion tests resumed the following day.25
* On 16 April 1972 the Washington Post noted that the damaged fuel tank had added an extra $200,000 to the cost of Apollo 16. Most of the money had gone for overtime pay at KSC.