All about F APS burn to depletion and landmark tracking

See list attachedFebruary 19, 196969-PA-T-27APA/Chief, Apollo Data Priority CoordinationAll about F APS burn to depletion and landmark tracking

On February 14 we had a Mission Techniques meeting to pin down F lunar orbital operations between the end of rendezvous and TEI. Aside from a rest period, this consists of two exercises – the APS burn to propellant depletion and landmark tracking with the optics. I think we have a good understanding of how to do both of these things. We are recommending the addition of an extra rev in lunar orbit in order to complete them and to obtain one pass of strip photography on the sunlit part of the moon prior to TEI. This will make the time between wakeup and TEI approximately 12 hours which does not seem unacceptable, and does not increase total mission time.

1. APS Burn to Depletion

Although we went into considerable detail in planning this exercise I will only list here several of the most significant items. The detailed procedures, of course, will be documented elsewhere.

a. As you know, the APS burn to depletion is initiated at approxi- mately zero degrees longitude in a horizontal, posi-grade direction. It occurs about l¼ rev after docking.

b. After docking, the command module will be used for controlling attitude of the docked configuration. As soon as convenient after docking, the command module will reorient to near the burn attitude based on gimbal angles computed pre-flight and included in the flight plan.

c. The only data required from MCC-H is as follows:

(1) A P27 command load to the LM PGNCS of LM state vectors.

(2) Voice PAD message to the LM for PGNCS and AGS targeting. This will be the standard P30 PAD with a number of parameters omitted, which are only applicable to a manned burn.

(3) Voice to the CSM of the gimbal angles for the burn attitude. Having obtained these, the CMP is able to orient the CSM/LM accurately in burn attitude based on real time data and the LM crew is able to orient the steerable S-band antenna to achieve maximum signal strength with MSFN.

d. Just prior to LOS, about 3/4 rev before TIG, the LM crew will update the state vectors in the AGS and will align it to the PGNCS. They will already have run through the SPS pre-thrust program (P30) and will leave the PGNCS in Program P00.

e. The CSM will jettison the LM ¼ rev before TIG and will null the relative velocity. They will then execute a 2 fps separation burn in a radially upward direction which will place the command module above and behind the LM at the time of the burn.

2. Landmark Tracking

Before C' we thought we knew how the optics tracking and MSFN orbit determination capability should be used for a lunar landing flight. Unfortunately we are worse off now since C' has proved we really don't know. At this time – with incomplete post-flight analysis, we have a dilemma. The optics data seems to indicate that spacecraft altitude was not changing while in lunar orbit; on the other hand, the MSFN data clearly shows a continuous change in altitude which was more or less what was expected based on Lunar Orbiter data. These two systems disagree with each other and yet both appear to be operating right. It may be possible eventually to figure out what is happening by further analysis of the C' data but unfortunately we are at a point when we must pin down the F mission flight plan. So what we were trying to do at this time, based on what we know now was to develop an exercise which we feel will give us the greatest opportunity to resolve our difficulties in time to support the G mission descent tar- geting accurately and dependently. Simply stated, we need as much data as we can obtain. Essentially, we are asking for a repeat of the C' lunar landmark exercise with some minor modification. Since the thing we are most concerned about is trends (i.e., the change in altitude) – it seemed that tracking on four successive revs is the minimum that would provide any kind of confidence in the results. I think everyone in attendance agreed with that. Secondly, although MPAD was asking for observation on four landmarks on each of these revs, we all agreed that three are probably adequate and so our proposal is to do landmark tracking on three sites on each of four successive revs.

To be a little more specific, we are currently recommending:

a. One of these be the same pseudo-landing site landmark we used on C'. It is called Bl.

b. The first backside landmark as the spacecraft enters daylight (CP1) should probably be chosen by the CMP in real time at about 20 degrees passed the terminator, the same as Lovell did.

c. The third landmark (CP2) can probably be moved closer to the sub- solar point than on C'. We are recommending a landmark about 25 degrees prior to local high noon.

Of course, we are specifying that all observations be made with the sextant and that they be spaced as far apart as possible – in the order to 25 seconds. It appears that it should be possible to use lunar orbit rate torquing during the landmark tracking period if that is easiest for the crew.

It is possible to include the exercise as described here in the current F mission timeline without affecting the rest period or the TEI burn currently scheduled at about 127:50. However, this would preclude obtaining strip photography desired on one pass over the entire sunlit lunar surface. In order to include that it will be necessary to delay TEI one rev to about 129:50. This will increase its magnitude by about 100 fps but does not change Pacific landing time. Of course, it is possible to retain the earlier original TEI as an optional maneuver time in the event of crew exhaustion to be utilized based on a real time judg- ment, if necessary. It appeared advantageous to us to put the strip photography after the more strenuous landmark exercise since it is less demanding on the crew, interferes less with TEI preparation and is of lower priority. The ASPO mission engineer, Bob Ward, will submit a Trajectory Change Request for this extra rev and everyone else I think will begin now to include it in their planning and documentation on the assumption that it will be approved.

Except for odds and ends, this pretty well finishes off the main line F Mission Techniques work.