See list belowMay 6, 196969-PA-T-72APA/Chief, Apollo Data Priority CoordinationComments on IMU compensation procedures
Attached is an MIT memo I thought you should see. It proposes that the MCC update the gyro compensation terms in the spacecraft computers whenever they are detectably wrong. One benefit, of course, is the possibility of eliminating a bunch of IMU alignments. But more important, it keeps the system right.
Incidentally, the threshold listed in the F and G Mission Rules beyond which the PIPA bias will be updated is twice too big. The Data Priority recommended value is .003 ft/sec². (See F Rules 15- 11 and 25-10, G Rules 15-11 and 24-3.) I'm sure you appreciate my calling your attention to this important matter! Seriously, I'd like to emphasize the significance of this on the LM during descent. Accelerometer bias is one of the two most undesirable LM IMU errors and should be minimized as much as possible. (The other, of course, is y-axis misalignment at PDI and that's a tough one.)
- May 15, 1969 – Some “improvements” in the Descent preparation procedures (3.9σ)
- Jul 23, 1968 – “C” Mission Retrofire and Reentry Mission Techniques meeting (4.3σ)
- Jul 17, 1969 – Gyro calibration and accelerometer bias update and redline values (3.8σ)
1969_tindallgrams.pdf
tindallgrams02.pdf
