The command module reaction control system (RCS) selected by NAA was a dual system without interconnections. Either would be sufficient for the entire mission.
For the service module RCS, a quadruple arrangement was chosen which was basically similar to the command module RCS except that squib valves and burst discs were eliminated.
NAA completed attitude orientation studies, including one on the control of a tumbling command module (CM) following high-altitude abort above 125,000 feet. The studies indicated that the CM stabilization and control system would be adequate during the reentry phase with the CM in either of the two possible trim configurations.
The technique tentatively selected by NAA for separating the command and service modules from lower stages during an abort consisted of firing four 2000-pound-thrust posigrade rockets mounted on the service module adapter. With this technique, no retrorockets would be needed on the S-IV or S-IVB stages. Normal separation from the S-IVB would be accomplished with the service module reaction control system.
North American completed a study of CSM-LEM transposition and docking. During a lunar mission, after the spacecraft was fired into a trajectory toward the moon, the CSM would separate from the adapter section containing the LEM. It would then turn around, dock with the LEM, and pull the second vehicle free from the adapter. The contractor studied three methods of completing this maneuver: free fly-around, tethered fly- around, and mechanical repositioning. Of the three, the company recommended the free fly-around, based on NASA's criteria of minimum weight, simplicity of design, maximum docking reliability, minimum time of operation, and maximum visibility.
Also investigated was crew transfer from the CM to the LEM, to determine the requirements for crew performance and, from this, to define human engineering needs. North American concluded that a separate LEM airlock was not needed but that the CSM oxygen supply system's capacity should be increased to effect LEM pressurization.
On November 29, North American presented the results of docking simulations, which showed that the free flight docking mode was feasible and that the 45-kilogram (100-pound) service module (SM) reaction control system engines were adequate for the terminal phase of docking. The simulations also showed that overall performance of the maneuver was improved by providing the astronaut with an attitude display and some form of alignment aid, such as probe.
North American selected Bell Aerosystems Company to provide propellant tanks for the CSM reaction control system. These tanks were to be the "positive expulsion" type (i.e., fuel and oxidizer would be contained inside flexible bladder; pressure against one side of the device would force the propellant through the RCS lines).
The Marquardt Corporation received a definitive $9,353,200 contract from North American for development and production of reaction control engines for the SM. Marquardt, working under a letter contract since April 1962, had delivered the first engine to North American that November.
MSC defined the LEM terminal rendezvous maneuvers. That phase of the mission would begin at a range of 9.3 kilometers (five nautical miles) from the CSM and terminate at a range of 152.4 meters (500 feet). Before rendezvous initiation, closing velocity should be reduced to 61 meters (200 feet) per second by use of the ascent engine. The reaction control system should be used exclusively thereafter.
A design review of the CM reaction control system (RCS) was held. Included was a discussion of possible exposure of the crew to hazardous fumes from propellants if the RCS ruptured at earth impact. For the time being, the RCS design would not be changed, but no manned flights would be conducted until the matter had been satisfactorily resolved. A detailed study would be made on whether to eliminate, reduce, or accept this crew safety hazard.
At a North American-Grumman interface meeting on September 23-24, two possible relative role alignments for CSM-active docking were agreed upon. The major item blocking final selection was the effect of the SM's reaction control system engines upon the LEM antennas. ASPO requested Grumman to investigate the problem, to analyze the design penalties of the two-attitude docking mode, and to report any other factors that would influence the final attitude selection.
Dalmo-Victor studied thermal-demanded weight increases for the LEM's steerable antenna. Investigators reported to Grumman and RCA that, in the plume of the CSM's reaction control engines, 1.18 kg (2.5 lbs) was necessary merely for the survival of the antenna; another 1.18 kg would be required for tracking during this impingement.
A mission planning presentation was given to ASPO Manager Joseph F. Shea, Assistant Director for Flight Operations Christopher C. Kraft, Jr., and Assistant Director for Flight Crew Operations Donald K. Slayton covering missions AS-201, AS-202, and AS-203. Shea said he wanted either a natural decaying orbit of proper lifetime or reaction control system deorbit capability for the first manned missions. It was decided not to put a C-band beacon on the SM for the post CM/SM separation tracking. This decision came back to haunt the program much later.
A LEM/CSM interface meeting uncovered a number of design problems and referred them to the Systems Engineering Division (SED) for evaluation: the requirement for ground verification of panel deployment prior to LEM withdrawal; the requirement for panel deployment in earth orbit during the SA-206 flight; the absence of a backup to the command sequencer for jettisoning the CSM (Flight Projects Division [FPD] urged such a backup signal); and Grumman's opposition to a communications link with the LEM during withdrawal of the spacecraft (FPD felt that such a link was needed through verification of reaction control system ignition). SED's recommendations on these issues were anticipated by April 22.
Grumman was requested to attend a meeting at MSC and to present their reasons as to why the LEM reaction control system (RCS) propellant tanks could not be of common technology with the CSM RCS propellant tanks. Grumman was to also say why an additional development program was required for the LEM tanks.
Technical personnel at MSC became concerned over an RCS oxidizer tank failure that occurred in February 1965, during propellant exposure and creep tests. The failure had previously been explained as stress corrosion caused from a fingerprint on the tank shell before heat treat. NASA requested that the test be repeated under tighter controlled procedures.
MSC approved North American's concept for thermal control of the valves in the CM's reaction control system (essential for long-duration missions). The crew could electrically heat the valves for about ten minutes before CSM separation and before the system was pressurized, thereby forestalling possible freezing of the oxidizer when it contacted the valve.
An RCS oxidizer tank failed during a test to demonstrate propellant compatibility with titanium tanks. This was the first of seven tanks to fail from a group of ten tanks put into test to investigate a failure that occurred during February 1965. These results caused an intensive investigation to be undertaken.
NASA's office at Downey, Calif., approved the contract with the Marquardt Corporation for the procurement of Block II SM reaction control system engines. Estimated cost of the fixed price contract would be $6.5 million. Marquardt was supplying the Block I SM engines.
A series of tests were run to determine the cause of stress corrosion of the reaction control system titanium tanks. Results showed that tanks exposed to chemically pure nitrogen tetroxide (N2O4) oxidizer suffered stress corrosion cracking, but tanks exposed to N2O4 containing small amounts of nitric oxide did not fail. The qualification testing program would soon resume.
The MSC Structures and Mechanics Division reported to ASPO Manager George M. Low that additional verification of the spacecraft 020 reaction control system (RCS) pressure vessels would not be required. Using pressure vessel histories received March 14 and the previous propellant temperature restriction of 297 kelvins (75 degrees F) maximum, fracture mechanics analyses showed:
To support the Apollo 13 Review Board, an MSC Apollo 13 Investigation Team, headed by Scott H. Simpkinson, was established with the following panels: spacecraft incident investigation, flight crew observations, flight operations and network ; photograph handling, processing, and cataloging ; corrective action study and implementation for the CSM, LM, and government-furnished equipment; related system evaluation; reaction processes in high-pressure fluid systems; high-pressure oxygen system survey; public affairs; and administration, communications, and procurement.