Results of the February 18 Apollo Spacecraft Software Configuration Control Board (ASSCCB) meeting

See list belowFebruary 20, 196969-FM-T-30FM/Deputy ChiefResults of the February 18 Apollo Spacecraft Software Configuration Control Board (ASSCCB) meeting

This is just a short note to inform you of the most significant actions taken at the subject meeting.

1. PCR 268 for both LUMINARY 1A and COLOSSUS 2A was approved. As a result, these programs which will be used on the G mission will be modified to speed up Programs P34 and P35 as recommended by Ed Lineberry, Bob Regelbrugge, etc. Specifically, this change to the TPI and MCC tar- geting programs is to use a Kepler prediction rather than the precision numerical integration since it is so much faster with no appreciable decrease in accuracy. It is estimated that about 80 seconds is saved each time these programs are called up. Since the command module runs through P34 three times between CDH and TPI, this represents a saving of about four minutes in that extremely crowded timeline. MIT intends to implement this such that it normally operates in the fast mode but they are providing a crew option to override that logic and use the old pre- cision integration if it is deemed necessary. [Incidentally, no change is being made to the Stable Orbit rendezvous program (P38).]

2. PCR 273 to put the jerk limits used on the descent abort programs into erasible memory was disapproved. However, we were given the action item of determining the values which we feel are best to be put in fixed memory. These must be relayed to MIT on or before February 21.

3. PCR 274 for LUMINARY 1A and COLOSSUS 2A to modify the lunar potential was disapproved based on George Cherry's estimate that the impact would be substantial. MIT was asked to start a parallel effort in developing the formulation for the expanded lunar potential model for their programs but not to plan to implement it for the G mission. This obviously means we will have to develop workaround procedures for DOI and descent targeting to be used in the MCC-H/RTCC.

4. PCR 732 LUMINARY 1A to add rendezvous radar bias to the W-matrix input/output display was approved. As you recall, the crew was already given a convenient way to readout and update the position and velocity terms of the W-matrix but had to go through a special procedure for load- ing the rendezvous radar term. This change merely added that parameter to the standard display. There was considerable discussion regarding units of these terms. MIT was given the option of changing them for crew convenience at no impact if they could do it to both COLOSSUS and LUMINARY. It should be emphasized this is just a nicety.

5. Several changes have been approved to the Descent programs of LUMINARY 1A. Probably the most significant deals with providing the crew with the capability of taking over manual control of spacecraft attitude and then returning to automatic control while in the terminal descent programs. If you are interested in this sort of thing I suggest you contact the experts to learn precisely what is being done. As I under- stand it, if the crew does take over attitude control, it is important that they maintain the computer recommended attitude as displayed in the FDAI error-needles, otherwise the throttle control by the LGC will get screwed up. Also, there is some concern that if the crew does not respond fast enough they may create an unstable situation.

Finally, I would like to confess a mistake I have been making, which I am going to try to avoid in the future. Namely, in the interest of expediency, I have been signing MPAD's PCR's which are not written up accurately or completely enough. From now on I am going to be looking for much more detail specifically describing the change and the advantages to be accrued.