Tindallgrams

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Although most of the things discussed in our Friday, July 19 "C" Rendezvous Mission Techniques meeting are not of general interest, there were a couple of things I would like to let you know about.

First of all, in an effort to reduce the probability of having to make the NCC2 maneuver, which would be an extra SPS burn, it has been decided to trim the NCC1 ΔV residuals if they are less than 10 fps. In addition, the time of the NSR maneuver will be adjusted in real time by as much as 30 seconds thereby changing the differential altitude. These two new things together should be adequate to maintain the nominal TPI time, which is the primary objective in targeting these maneuvers. The nominal differential altitude, you recall, is about 7.8 n.m. on the low side to 9 n.m. on the high side. These adjustment limits give us a capability of adjusting the TPI time by about 20 minutes to account for dispersions. Using these procedures, it will only be necessary to make the NCC2 burn if we encounter dispersions far in excess of those expected.

Something else which has been changed is that the elevation angle at TPI is considered more sacred than any lighting limits at all and should be retained at the nominal value at all cost even though the so-called lighting limits are violated. Previously the elevation angle was to be changed if the lighting limits could not be met.

Another important mission rule adopted now is that the rendezvous exercise will be terminated if the G&N fails prior to NSR, and probably will be terminated any time the G&N fails. This is to conserve SM RCS and permit flying a full duration mission.

The changes to the mission techniques are relatively minor and it is probable that it will not be necessary to reissue the entire document. Rather than that, we will probably distribute change pages of some sort.

Terms & Abbreviations

G&N

Guidance and Navigation.

NSR

Co-elliptical, an orbital maneuver originally used in the Gemini program.

RCS

Reaction Control System.

SPS

Service Propulsion System, the large engine of the Service Module that was used to enter and exit lunar orbit, as well as make course corrections while going to and from the moon.

TPI

Transfer Phase Initiation (also known as Terminal Phase Initiation). One of the maneuvers performed by the LM after ascent from the lunar surface to rendevouz with the CSM.