C’ Lunar Orbit – Navigation and Block Data

See list attachedNovember 15, 196868-PA-T-251APA/Chief, Apollo Data Priority CoordinationC’ Lunar Orbit – Navigation and Block Data

On Thursday, November 7, we gathered with the C' Flight Crew and everyone else who was interested in the lunar orbit Operations On that flight. At this meeting we cleaned up a lot of loose ends primarily dealing with the lunar orbit navigation and with block data. This memo is to report the new things accomplished at that time.

Landing Site Lighting Evaluation

As you recall, one pass over the pseudo-landing site prior to marking with the optics will be made to permit the crew to evaluate lighting. The space- craft will be oriented with a five degree pitch up attitude and will be torqued at orbit rate. The optics will be fixed at zero. The MCC-H will compute and inform the crew of the time at which the optics crosshairs will be viewing the lunar surface location experiencing a 10 degree sun elevation angle. The crew will use this time primarily as a check point to key in their verbal description of what they are actually looking at. Although, it had been proposed as an option that the crew would mark on the pseudo-landing site if it became visible, we dropped this option in favor of continuing the lighting evaluation beyond the terminator and into the region of earth lit lunar surface. It was emphasized that if any difficulty were experienced in finding the control points, forget'em and press on since a continuous evaluation of lighting conditions as the sun angle varies is the important thing on this pass.

Landmark Sightings

The only information the crew desired of MCC-H associated with the land- mark sighting exercise is the GET of closest approach to the initial point (IP). This time viii be relayed to the crew for every pass by the pseudo-landing site, but only for the first approach to the other three control landmarks on the back of the moon.

In order to avoid excessive shaft angle rates during the observational pass, the crew will roll the spacecraft to insure that the trunnion angle never gets less than 10 degrees. (This value is MIT's recommended minimum.)

The P22 initialization value of the W-matrix shall be 0, 0, 10,000 meters which will prevent the state vectors from being updated, but will permit onboard determination of the landmark location. It should be noted, how- ever, that the updated location of the landmarks are not stored and each time the spacecraft comes over a landmark of interest it is necessary for the crew to key in the values of latitude, half-longitude, and altitude prior to the pass if auto optics are to be used. This obviously means that it is necessary for the crew to record these values following each pass.

Since the pseudo-landing site is being chosen specifically to provide the proper lighting conditions during the tracking exercise, it is necessary to have a bunch of pseudo-landing sites to cover the entire C' mission launch window. In fact, four have been selected for each launch day. The nominal is included in the pre-launch E-memory load. However, if the launch occurs at any other time, it will often be necessary for the MCC-H to uplink the proper pseudo-lending site at some convenient time during translunar coast. It was recommended to the crew that for the pseudo- landing site they do not use the onboard determined location on successive passes but rather always use the “01” option to operate with the old stored values.

In order to insure that all of the data is properly stored on the tape recorder, the crew has been requested to delay proceeding from the ΔR, ΔV display for at least one minute. This applies not only to back side observations but also to the pseudo-landing site where the data will be coming to the ground on low-bit rate via the omnis.

State Vector Updates

While in lunar orbit, state vectors will be transmitted once per revolu- tion via the command program (P27) except no state vector updating will be done from the ground during the revolutions immediately following each of the two LOI burns. To be consistent with the rest of the mission, it was decided to update CSM state vectors only into the LM slots of computer memory. The only exception is immediately prior to a maneuver at which time both LM and CSM slots will be loaded – LM slots first.

Block Data

Attached to this memo in a list of the block data updates to be supplied associated with lunar orbit. As you will note, two maneuvers are supplied to get out of lunar orbit prior to LOI₁ and during each of the first three revolutions. Thereafter only one TEI maneuver per revolution is relayed to the spacecraft.

Regarding the TEI burns, which all take place with approximately the same earth-moon geometry end approximately the same targeting objective, the question arises as to how much the TEI ΔV components vary from one revo- lution to the next. Some of us simple-minded cats have a feeling that given a few TEI maneuvers you could probably extrapolate and get a pretty good maneuver to breakout of lunar orbit if it were necessary. We will get the answer to this question but it will only be for background knowledge, not to change the operational procedures we have established.

Enclosure

TEI BLOCK DATA ASSOCIATED WITH LUNAR ORBIT

Pre-LOI₁

a. TEI₁ assuming LOI₁

b. TEI₂ assuming LOI₂

Rev 1

a. TEI₁ updated based on GNCS

b. TEI₂ updated based on GNCS

Rev 2

a. TEI₃ assuming LOI₂

b. TEI₃ assuming LOI₂

Rev 3

a. TEI₃ updated based on GNCS

b. TEI₄ based on GNCS

Rev 4⟶Rev 10

TEI₅⟶TEI₁₁

Definition TEI₂ “2” means end of Rev 2