Interfaces with the First SIM

Apollo 15 launch operations got off to a slow start, impeded by spacecraft modifications. Checkout of the lunar module began in mid-June 1970, about the time the Apollo 13 review board announced its findings. Service module modifications, recommended by the board, delayed the launch date by five months. The September decision to enlarge the final missions brought further hardware changes. Spacecraft operations resumed in November with the arrival of the modified stages of the lunar module. Initial testing concentrated on the propulsion systems. Early in the new year Grumman engineers added three equipment pallets to the descent stage and brackets for the lunar rover. The new command-service module arrived in midJanuary and went almost immediately into the altitude chambers.5

January also brought the first instruments for the scientific instrument module. By that time the Experiments Section had been at work on the SIM for more than a year. Preparations for the lunar orbiting experiments included the construction of a laboratory in the operations and checkout building and development of ground support equipment. When testing began, the 7-man Experiments Section supervised 25 engineers representing 8 contractors. An occasional visit from an experiment's scientist-author further complicated the three-shift operations. The contractor representatives proved invaluable from a logistical standpoint, securing minor design changes and spare parts. They did not always, however, seem to appreciate the need to meet a launch date.

From the very beginning the test engineers faced a familiar problem - hardware designed for use under conditions of zero gravity could not stand up to the rigors of earth gravity. The 7.5-meter extendable booms, which would deploy the mass and gamma-ray spectrometers, were built by North American for zero gravity. They could not support the spectrometers on Merritt Island, Earth. North American designed a long rail to help carry the load for test purposes. The operation was generally unsatisfactory, however, since it introduced problems that would not occur in zero g.

The SIM work crew joined North American's spacecraft operation in late February and placed the SIM, with its eight experiments, inside the service module. Interface problems between the scientific instruments and the service module appeared almost immediately. The alpha spectrometer's data stream failed to synchronize with the spacecraft data-relay system. The Experiments Section had more trouble with the gamma-ray and mass spectrometer booms. When the engineers extended the boom, they received no indication that signals were being received. Investigation indicated that diodes in the boom circuitry were blocking the signal. North American subsequently modified the spectrometer booms.6

Test procedures caused nearly as much trouble as the hardware:

The SIM bay complicated the checkout flow in every major procedure we ran. In some cases the vendors got the scientific instruments to us late. In other cases they would want to conduct a last-minute check at a very inconvenient time. Every time we powered up the ship for a major test somebody would come down with a special requirement for their instrument.7

The initial requirements for the calibration of the gamma-ray spectrometer called for halting all motor vehicles within 16 kilometers. NASA and the contractor negotiated the matter for several weeks, agreeing finally to a late night test with a traffic ban in nearby parking lots and roads. Following the weekend calibration exercise, the Experiments Section tested all SIM systems on 15 March and returned them to the factory for a month's rework by the responsible contractors.

The instruments arrived back at KSC in mid-April. While there were some minor problems, e.g., the mapping camera would not turn off, the test team closed out the SIM bay temporarily in late April for the move to the pad. When the subsatellite arrived a month later, the Experiments Section installed its batteries, checked out the transmitter, and tested the interface with the mechanism that would eject the subsatellite into a lunar orbit. Technicians entered the space vehicle stack on 9 June and added the subsatellite to the SIM bay.8

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