MSC-G-R-66-4
GEMINI PROGRAM MISSION REPORT
GEMINI VIIIPrepared by: Gemini Mission Evaluation Team
Approved by:
Charles W. Mathews, Manager, Gemini Program
George M. Low, Deputy Director
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
MANNED SPACECRAFT CENTER
HOUSTON, TEXAS
APRIL 29, 1966
UNCLASSIFIED
7.1.2.9 Control system problem. - At approximately 7 hours g.e.t., the two spacecraft were configured for the platform-parallelism test, which was to have provided a comparison of the spacecraft and GATV attitude reference systems. The GATV Attitude Control System (ACS) was active, and the TDA L-band transponder was off. The spacecraft attitude-control power-switch and maneuver-control switches were off. The radar was off, and the control mode switch was in PULSE.
Shortly after sending encoder command 041 (recorder ON), roll and yaw rates were observed to be developing. No visual or audible evidence of spacecraft thruster firing was noted, and the divergence was attributed to the GATV.
Commands were sent to de-energize the GATV ACS, geocentric rate, and horizon sensors, and the spacecraft Orbital Attitude and Maneuver System (OAMS) was activated.
The rates were reduced to near zero, but began to increase upon release of the hand controller. The ACS was commanded on to determine if GATV thruster action would help reduce the angular rates. No improvement was noted and the ACS was again commanded off. Plumes from a GATV pitch thruster were visually observed, however, during a period when the ACS was thought to be inactivated.
After a period of relatively stable operation, the rates once again began to increase. The spacecraft was switched to secondary bias power, secondary logics, and secondary drivers in an attempt to eliminate possible spacecraft control-system discrepancies. No improvement being observed, a conventional troubleshooting approach with the OAMS completely de-energized was attempted, but subsequently abandoned because of the existing rates.
An undocking was performed when the rates were determined to be low enough to preclude any recontact problems. Approximately a 3 ft/sec velocity change was used to effect separation of the two vehicles.
Angular rates continued to rise, verifying a spacecraft control-system problem. The hand controller appeared to be inactive. The Reentry Control System (RCS) was armed and, after trying ACME-DIRECT and then turning off all OAMS control switches and circuit breakers, was found to be operative in DIRECT-DIRECT. Angular rates were reduced to small values with the RCS B-ring. Inspection of the OAMS revealed that the no. 8 thruster had failed open. Some open Attitude Control and Maneuver Electronics (ACME) circuit breakers probably accounted for the inoperative hand controller noted earlier. All yaw thrusters other than number 8 were inoperative. Pitch and roll control were maintained by using the pitch thrusters.
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