D Maneuver Monitoring Mission Techniques

See list attachedNovember 12, 196868-PA-T-248APA/Chief, Apollo Data Priority CoordinationD Maneuver Monitoring Mission Techniques

On November 4 we had our first-and-last D Maneuver Monitoring Mission Techniques meeting. In addition to all interested MSC organizations, it was attended by MIT, NR, TRW, and GAEC. We spent the day going through all of the SPS maneuvers both docked and undocked, except for those associated with the rendezvous and the docked DPS burn, and discussing the pre-burn systems checks and the actual burn monitoring techniques. I believe we established procedures which should do the job and I feel they can be considered firm. The crew and the flight controllers intend to use these techniques in the forthcoming simulations and changes will only be considered to those which simulations show to be unacceptable.

Following is a list of final agreements which apply to all SPS maneuvers:

1. It is intended to use the onboard computed weight and SPS trim gimbal angles stored from the previous burn in the DAP, unless they differ from the MCC-H ground values by more than 10 percent and -5 degree res- pectively. If any of the three parameters exceed the limit, all three will be updated.

2. Except for retrofire, it is intended to use the onboard computed REFSMMAT for all maneuvers as determined by using the “preferred” alignment option. The MCC-H will compute and compare REFSMMAT with the onboard values primarily as a check for some procedures or communications error. This will be done by determining the angular difference between them, which should be zero. If it is in excess of .5 degree, the G&N should be considered no go.

3. It was concluded that the check of onboard computed apogee and perigee heights (ha and hp) is unnecessary and will be dropped from the procedures. In addition, these values will be dropped from the maneuver PAD message.

4. Prior to each maneuver, the crew shall make a maneuver attitude check using a sextant star. The shaft and trunnion angles of the star must agree with the PAD values to within five degrees or the burn is no go. If the crew is unable to see any stars, that check will be dropped for that burn.

5. In place of the previously proposed P40 VG test, we are substitu- ting a check on the ΔV_R. This parameter must agree with the PAD value to within 10 fps.

6. Another CMC pre-burn check is through use of the Ground Track Determination program (P21). The crew will check latitude, longitude, and altitude against the PAD values to determine that they are within limits in order to give a G&N go. The limits are .02 degree and .2 n.m. respectively.

7. An attitude excursion limit of 10 degrees has been established for all SPS burns. Five degrees a second is the attitude rate limit. If the crew ascertains that either of these limits have been exceeded as indicated by two independent data sources (primarily the BMAGS and visible cues), they will takeover using SCS MTVC to damp rates and will shutdown the engine. An exception to this is that during the initial start transient, an attitude excursion beyond 10 degrees will be considered acceptable if, in the crew's judgment, it is truly due to the start transient and GNCS control of the spacecraft is still acceptable. (G&CD has the action item of approving this MTVC takeover procedures for safety when applied to docked burns. I have been told by Ken Cox that studies are underway, the results of which so far indicate this procedure is acceptable.)

8. The EMS ΔV counter will not be used as part of the crew monitoring procedure to avoid overburn. That is, for purposes of simplicity it was decided to backup the GNCS engine cutoff based on burn duration only. The procedure is for the crew to manually shutdown the engine if the GNCS has not done so within five seconds of the nominal burn time for docked SPS burns and within one second of the nominal burn time for undocked SPS burns. The nominal burn time is included on the maneuver PAD for each burn.

9. Although the EMS will not be used to monitor against an overburn, it will always be set up to provide an automatic cutoff if the crew switches to SCS. Accordingly, it is intended to slew into the ΔV counter that value (ΔVC) which would cause it to provide as accurate a cutoff as possible. In other words, tailoff and known accelerometer bias will be taken into account when computing the ΔVC included on the maneuver PAD.

10. Except for retrofire, the crew will not trim any ΔV residuals following any SPS maneuver.

11. Since the first SPS burn is made before adequate checks of the G&N can be carried out to insure proper GNCS operation, we propose to utilize some special techniques for that one burn. Essentially we intend to evaluate the GNCS performance during the launch phase on the D mission exactly as we do as part of our TLI go/no go procedure on the C' mission. The procedure involves comparing the performance of the spacecraft GNCS with the SIVB IU during the launch phase. If the differences do not exceed certain pre- established limits (which incidentally are the same as. C') no further special checks are required to declare the GNCS go for SPS₁. If the limits are exceeded, the crew will perform an additional platform align- ment (REFSMMAT Option) to the pre-launch orientation just prior to the aligning to the burn REFSMMAT. If the gyro torquing angles indicate that the drift rate has been less than .6 degree/hour since the fine alignment while docked to the SIVB, the GNCS is declared go for the burn. Incidentally, the GDC is also checked during the same period. Its no go limit is 10 degrees/hour on all three axes.

Obviously, special procedures are required for the docked DPS burn. This maneuver is extremely unusual and provides the greatest chances of screw- ing up procedurally. Prior to the maneuver, the following steps are taken:

1. The LGC E-memory will be dumped to the ground and checked by MCC-H. If any of the critical E-memory values are in error, they must be updated prior to the burn.

2. MCC-H will compute and relay to both spacecraft that REFSMMAT which is consistant with the LM x-axis aligned along the velocity to be gained by the maneuver and the y-axis shall be horizontal. Both spacecraft will utilize the same REFSMMAT.

3. The MCC-H will update the state vectors for both vehicles. The same external ΔV targets will be uplinked to both vehicles. (There is some question as to how the CSM will monitor the maneuver. One proposal is to call up the SPS thrust program (P40), which would be operated just as though it was controlling the maneuver. However, we're not sure how it will perform when the ΔV targeted and achieved is in the negative x direction. MIT was asked to advise us on this matter.)

4. The CSM will maneuver the two spacecraft to near burn attitude using onboard computed gimbal angles. The LM completes this attitude maneuver using R60.

5. Both spacecraft will perform burn attitude checks, the command module using a sextant star and the LM using an AOT star while the LM controls attitude during the last darkness period prior to the burn. Five degrees has been established as the go/no go limit.

6. The DPS trim gimbals will be moved prior to the maneuver to verify they are operating properly and will be reset to align the thrust vector through the c.g. taking into account engine mount compliance at 40 percent thrust. Assistance by MCC-H is required since there is no onboard indica- tion of engine gimbal angle. The technique will involve iterative attempts to align the engine which will be continued until they are within a 0.1 degree of the desired values.

7. The AGS will be initialized and used in the follow-up mode exactly as it is for the undocked DPS burns. Of course, there is no consideration given to taking over with the AGS.

8. We established an attitude limit of 10 degrees and an attitude rate limit of five degrees per second. However, this maneuver is likely to include some pretty wild attitude excursions, particularly as the thrust level is varied, which could easily exceed those limits. During these transient periods, it must be left to the crew's judgment whether a diver- gent situation is occurring or not. We did establish that a 45 degrees attitude excursion is an absolute limit. This should be coincident with the “VG increasing” alarm. If these occur, the DPS should be manually shut- down. The trim gimbal light is essentially ignored throughout the burn since it cannot really be trusted for anything.

9. Following manual shutdown, attitude control is turned over to the CSM. If a malfunction occurs requiring premature burn termination with excessive attitude rates, they will be damped using the LM y and z-axis RCS translation jets.

As noted previously, the above techniques do not necessarily apply to the maneuvers during the rendezvous or rendezvous abort situations. These techniques will be discussed at our next rendezvous meeting on November 18, at which time any special procedures for those maneuvers will be identified, agreed to, and documented.