NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Apollo navigation
From: Paul Hirose
Date: 2013 Nov 03, 10:22 -0800
From: Paul Hirose
Date: 2013 Nov 03, 10:22 -0800
The Apollo 13 air to ground voice transcription can be found here: http://www.jsc.nasa.gov/history/mission_trans/mission_transcripts.htm The emergency technique that used the Earth and Sun to establish a known attitude is described on this page: http://www.universetoday.com/62763/13-things-that-saved-apollo-13-part-6-navigating-by-earths-terminator/ The link to the "navigation report" didn't work for me. I got only a partial file. But the report is also available here: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090026451_2009026278.pdf "Gimbal lock" is frequently mentioned in the report. Because the inertial measurement unit's gyro and accelerometer platform was supported by only three gimbals, there were forbidden attitudes where it was unable to maintain a fixed orientation independent of spacecraft motion. Grumman, the Lunar Module contractor, had insisted on four gimbals to assure total freedom of maneuver. But the designer of the navigation system, MIT, said that wasn't necessary. A system with three gimbals would have a size, weight, and reliability advantage. As recounted in "Digital Apollo" (David A. Mindell, 2008), in early 1964 NASA got both parties together in a meeting and demanded the issue be explored until one side admitted defeat. MIT came very well prepared and the decision was for three gimbals. But when Apollo began flying, everyone soon realized Grumman had been right. The requirement to avoid gimbal lock imposed an irritating workload on mission control and the astronauts. Sometimes winning an argument merely proves you're the more skillful arguer. --