Lunar rendezvous shaping up

See list attachedJUL 2 196868-PA-T-147APA/Chief, Apollo Data Priority CoordinationLunar rendezvous shaping up

1. On June 26 we took another wack at the “G” Rendezvous Mission Techniques. I think we now have most of the basic things squared away so that we can get into the detail with some confidence. The most significant decisions were:

a. To make the new plane change maneuver discussed in the last report with the LM as long as RCS propellant is adequate.

b. To add IMU fine alignments into both the LM and CSM timelines right after LM insertion.

c. To increase the time between LM insertion and the CSI maneuver to 50 minutes.

d. Since that decreases the CDH/TPI Δt and increases the CSI/CDH Δt, to move the new plane change maneuver from 30 minutes after CDH to 30 minutes before CDH.

2. It is interesting to note that the timeline now is very similar to the second half of the “D” mission rendezvous and not so darned crowded as it used to be. It looks like this now:

| 50 | 20 | 30 | 47 | INS CSI PC CDH & TPI PC | | | | 50 70 100 147

3. Ed Lineberry and his guys have done some good work since our last meeting, which led to their proposal to make CSI 50 minutes after LM insertion into orbit. This not only reduces the timeline crowding in that busy period, but improves the CSM rendezvous navigation. You see, since we moved TPI about 45 minutes later (to midpoint of darkness), the relative range at insertion increased to about 320 nautical miles. By delaying CSI, we maintain the range at about 150 nautical miles at CSI as it was before. This also makes it possible to add the IMU alignments of both the LM and CSM into the nominal timeline after insertion. We feel this is quite an advantage since the LM really needs one after Ascent, prior to rendezvous navigation – and the CSM alignment would have been over four hours old at TPI. And we would have been forced to add it in as a contingency procedure if the LM crew couldn't see stars through the AOT in the lunar surface.

4. Shifting CSI later forces CDH to move also, as shown above. This leads to the “final” change – moving the plane change to before rather than after CDH. Although we had previously been inclined toward making this burn with the CSM, everyone agreed that as long as the LM has the fuel it can do it with the least impact on everything. This is because the LM lateral thrusters are pretty well aligned through the c.g. at this time in the mission so we can use them making an IMU alignment unnecessary. In fact, we are so anxious to avoid realigning that CSM three gimbal IMU we concluded that if the LM fuel becomes marginal we should do CSI, CDH, and TPI all with the CSM if that permits the LM to do the plane change. Tradeoff of CSM maneuvering rather than the LM will be based on LM RCS propellant remaining, red line values established pre-flight. (Action item for Guidance and Performance Branch)

5. Some associated ground rules follow:

a. The plane change will be made by the LM no matter how small – i.e., there is no minimum threshold.

b. The CSM does mirror image targeting for all LM burns except the planechange (to avoid the out-of-plane alignment).

c. If the LM becomes passive before CSI, the CSM will use the maneuver sequence illustrated above including an out-of-plane alignment for the plane change.

d. If the LM becomes passive at the plane change, the CDH will be targeted to force a node 20 minutes after CDH to insure adequate time for TPI preparation. This is a little more expensive than 30 minutes, which is the “natural node,” but is worth it to avoid a jam up at TPI.

6. MPAD will prepare and distribute a memo defining the many parameters of interest based on this new timeline. At our next meeting we'll review that and the rendezvous navigation tracking schedule. We will also start the tradeoff of the various guidance systems. You know – shall we put rendezvous radar data in the AGS? etc.