See list attachedOctober 20, 196969-PA-T-129APA/Chief, Apollo Data Priority CoordinationWhat can be done about the AOT?
One of the largest error sources affecting precision landing on the moon is the LM platform alignment accuracy at PDI. The AOT is adequate to fly an Apollo 11 type mission but it is simply not designed to support precise landings; AOT alignments, as currently carried out, leave something to be desired. The result is we must depend more on the LPD to get us where we want to go – that is, to correct the terminal descent trajectory for errors built up during the braking phase. This is undesirable, of course, particularly in the crossrange direction. Another unfortunate fact is that the lousy alignment accuracy obscures inflight IMU drift determination and virtually forces us to depend on the preflight compensation for any- thing but gross changes. This is good enough for flight safety (i.e., abortability) but can also screw up the precision landing. (Here are some numbers: 0.1° out-of-plane alignment error at PDI causes a 2,000 ft. cross- range error. A 3 sigma PGNCS drift will cause this misalignment. AOT align- ments experienced in flight haven't been much better than that either.)
Aside from making sure you are aware of the situation, I am writing this snowflake to solicit any ideas you might have to improve this business. Is there some way we can improve the AOT? Or its alignment in the LM? Or the way we get and use the marks in the computer program? Or should we ask the crew to make more marks – (Note: without a DOI burn, the crew timeline is tolerant)? – or something?
If you think of something, do it – or give me a call and I'll put your name in lights, Baby!
- May 15, 1969 – Some “improvements” in the Descent preparation procedures (3.4σ)
- Apr 17, 1969 – Reduction in Number of P52 Alignments During Apollo Missions (3.0σ)