C’ Mission Techniques – mostly Entry

See list attachedNovember 20, 196868-PA-T-254APA/Chief, Apollo Data Priority CoordinationC’ Mission Techniques – mostly Entry

On Friday, November 15, we had the last C' Mission Techniques meeting I expect we will ever have. It was mostly devoted to entry although, of course, some other odds and ends were discussed.

Before getting into the results of the meeting I would like to report two minor adjustments we have made in maneuver monitoring. Specifically, we have changed the time limit the crew uses in protecting against over- burn on TLI by manually shutting down the S-IVB from ten seconds to six seconds past nominal. We have changed the equivalent time on the TEI burn from three seconds to two seconds.

The MCC-H will uplink the entry REFSMMAT shortly after TEI. We intend to use the same REFSMMAT all the way back and no adjustments will normally be made to it prior to entry even though dispersions could cause it to deviate slightly from its nominal 0, 180, 0 values at entry interface.

In the event of communication loss, the crew will use the return-to-earth program (P37) for midcourse maneuver targeting and entry initialization. In a nominal mission this would not be necessary, of course, but the crew does intend to play games with it just to see how it works. It is to be emphasized that P37 must not be used after three and one-half hours before entry interface when the MCC 7 update is uplinked, because to do so will cause the External ΔV target load and the landing point location to be revised based on P37 computations and we don't want this to happen.

As noted previously, at EI-15 hours, the MCC-H will inform the crew that MSFN state vectors are adequate to complete the mission in the event of subsequent communication loss. It is to be emphasized that all other information required for carrying out the final midcourse correction and entry must also be supplied at the same time. This includes the complete entry PAD voice message and reentry reference time (RRT). The RRT value will not be changed after this voice message.

Flight Analysis Branch reports there is no recontact problem following CM/ SM separation providing the ΔV is at least 3 fps. Of course, it should be substantially more than that.

In all cases, both with and without communication, the crew will hold lift vector up until .05 g's. This makes all the entry procedures standard, which considerably simplifies things.

Non-G&N constant g entries will all be flown with the lift vector toward the north in order to provide the best horizon view. With the EMD working, it was agreed that the crew will hold four g's until crossing the circular velocity line on the EMS. If the EMS is not working, they will maintain four g's as long as it is possible to do so. It is to be noted that it will not be possible to reach the 1350 n/m/ target by following this procedure since by the time the crew starts ranging with the EMS they will probably not be able to fly more than 1200 n.m. with the remaining lift capability. Without EMS ranging at all, which is what they get by flying the g meter, a four g entry range is about 1100 n.m. It was decided after considerable discussion to use four g's since that it the center of the acceptable range (i.e., three to five g) and it is impossible to reach 1350 safely using the EMS alone. That would require flying a constant 1.5 g entry and this value is considered entirely too small to positively preclude skipping out. If Claude Graves' people are able to develop a chart for the MCC-H flight controllers to use in determining the time the spacecraft should achieve circular velocity, assuming a four g entry, they will do so and this quantity will be added to the entry PAD message. It will be used as part of the EMD performance evaluation and in the event of a g meter entry it will give the crew some idea when skip-out is no longer possible.

While reviewing the PAD messages, a number of minor adjustments were made. One item which should be reported is that the MCC-H will always include their best estimate of spacecraft weight on the maneuver PAD. The flight controllers recommend that the crew always load this value into the DAP data load routine (R03) regardless of how small the change from what is already presently in memory. You recall that COLOSSUS automatically updates weight during maneuvers. We expect that the crew will exercise some judgment when applying this procedure.