dcn@ihuxl.UUCP (Dave Newkirk) (11/08/86)
Young caught sight of the lunar module at a distance of 120 kilometers; Snoopy appeared to be running across the lunar surface like a spider. At other times, using a sextant, he spotted the craft as far away as 550 kilometers. An hour after the first descent burn, Stafford and Cernan fired the engine again to shape the trajectory for their return to the command module. ... After Stafford's camera failed, he and Cernan had little to do except look at the scenery until [it was] time to dump the descent stage. Stafford had the vehicle in the right attitude 10 minutes early. Cernan asked, "You ready?" Then he suddenly exclaimed, "Son of a bitch!" Snoopy seemed to be throwing a fit, lurching wildly about. He later said it was like flying an Immelmann turn in an aircraft, a combination of pitch and yaw. Stafford yelled that they were in gimbal lock - that the engine had swiveled over to a stop and stuck - and they almost were. He called for Cernan to thrust forward. Stafford then hit the switch to get rid of the descent stage and realized that they were thirty degrees off from their previous attitude. The lunar module continued its crazy gyrations across the lunar sky, and a warning light indicated that the inertial measuring unit was about to reach its limits and go into gimbal lock. Stafford then took over in manual control, made a big pitch maneuver, and started working the attitude control switches. Snoopy finally calmed down. For this first lunar module flight to the vicinity of the moon, the pilots were supposed to use the abort guidance system instead of the primary guidance system, to test performance in the lunar environment. The abort system had two basic modes: "attitude hold" and "automatic." In automatic mode, the computer would take over the guidance and start looking for the command module, which was certainly not what the crew wanted to do just then. In correcting for a minor yaw-rate-gyro distur- bance, the pilots had accidentally switched the spacecraft to the automatic mode, and the frantic gyrations resulted. From Cernan's startled ejacula- tion to Stafford's report that everything was under control took only three minutes. Flight control told the crewmen that they had made an error in switching, but the system was fine. They could fire the ascent engine. After the firing, the lander flew what Stafford called a "Dutch roll," yawing and pitching and snaking along. When the engine shut down, however, to the crew's surprise the attitude and flight path to the command module were correct. From a maximum distance of 630 kilometers, the thrust from the ascent engine moved the lunar module to within 78 kilometers of the mother ship. ------------------------------------------------------------------------ From "Chariots for Apollo: A History of Manned Lunar Spacecraft", NASA SP-4205, available from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402, stock number 033-000-00768-0, $12. -- Dave Newkirk, ihnp4!ihuxl!dcn