Encyclopedia Astronautica
1968.06.10 - Flight combustion stability monitor on Apollo 7

ASPO Manager George M. Low met with Christopher C. Kraft, Jr., and Donald K. Slayton, Directors of MSC Flight and Flight Crew Operations, and several members of their staffs (including astronaut Walter M. Schirra, Jr.) to discuss using the flight combustion stability monitor (FCSM) on the Apollo 7 flight.

(The FCSM was a safety device to shut down the service propulsion system (SPS) automatically in the event of rough combustion or instability.) At the insistence of the Propulsion and Power Division, they agreed to use the FCSM for all SPS burns on Apollo 7. On all "noncritical" burns, two attempts to start the engine would be made with the FCSM active. Should the stability monitor shut down the engine on both those attempts, a detailed review of the situation would be made before again attempting to start the engine. On "critical" burns (i.e., the abort-to-orbit and reentry burns), should the FCSM halt the burn the SPS engine would be restarted immediately with the FCSM inactive on the assumption that the shutdown was caused either by an FCSM malfunction or by an engine instability that would not reoccur on the next start.

Low, Kraft, and the others unanimously wanted to eliminate the FCSM before a lunar mission, because on this mission lunar orbit and transearth insertion burns were highly critical and inadvertent shutdowns would cause major trajectory perturbations. Representatives from the Propulsion and Power Division (PPD) contended that, because of the relatively small number of bomb tests carried out on the Block II SPS engine, flight-testing of the engine before the lunar mission would be inadequate to demonstrate engine stability under all conditions. Low therefore asked Engineering and Development Director Maxime A. Faget and PPD Chief Joseph G. Thibodaux, Jr., to plan a ground test program that would give sufficient confidence in the SPS engine to eliminate the FCSM before undertaking lunar missions.

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