Upthread: Fourth Mission “D” Rendezvous Mission Techniques meeting (Feb 18, 1968)
Downthread: Seventh “D” Mission Rendezvous Mission Techniques meeting (Mar 13, 1968)
See list belowMAR 1 196868-PA-T-49APA/Chief, Apollo Data Priority CoordinationFifth “D” Mission Rendezvous Mission Techniques meeting—don’t miss Paragraph 5; it’s great!
1. We spent just about the entire February 26 meeting discussion the way the AGS and PNGCS should be used during the “D” Mission rendezvous. I feel as though we have accomplished quite a lot in this area having reached agreement on how the AGS should be used throughout that mission phase, with one minor exception. It is all based on the ground rule that on this mission the AGS should be maintained in that state which makes it most useful to perform the rendezvous in the event of PNGCS failure. It was noted that if, after having established the preferred techniques in accordance with that ground rule, it is possible to include some AGS systems tests without jeopardizing crew safety or other mission objectives, they would be considered.
2. Nominal situation: PNGCS seems to be working properly and is prime; AGS must be maintained in optimum state to take over in the event the PNGCS fails. This applies to all maneuvers—CSI, CDH, TPI.
(a) Checking of the PNGCS will be by comparison with the ground computed solution only. That is, comparisons of maneuver targeting from other sources, such as the AGS, backup charts or the CSM, will not be made to commit to the PNGCS. The PNGCS solution will be used providing it is within acceptable limits of the MSFN solution. One possible exception here is that, since the CSM optics provide very strong solutions to the TPI delta V components perpendicular to the line of sight, comparison with them may be advantageous.
(b) The state vectors in the AGS will be updated each time PNGCS is confirmed to be acceptable. This will likely be at each time it is committed to make the next maneuver using the PNGCS.
(c) AGS alignments will be made each time the PNGCS is realigned and each time the state vector in the AGS is updated from the PNGCS.
(d) No radar data will be input into the AGS as long as the PNGCS is working. In effect, it is obtaining benefit of the radar via the PNGCS state vector updates since the PNGCS is processing the radar data.
(e) There is no need to prepare or learn to use backup charts for CSI and/or CDH maneuvers for this mission. Terminal phase charts are essential in the LM.
3. In the event of a PNGCS failure: CSI and CDH only.
(a) For CSI and CSH, use the AGS in almost the identical manner in which the Gemini spacecraft was flown. That is, use ground targeted maneuvers executed with the AGS External delta V mode.
(B) No radar data would be input into the AGS prior to CSI and CDH.
4. By far the most extensive discussion dealt with the Terminal Phase Initiation (TPI) maneuver and subsequent midcourse maneuvers in the event of a PNGCS failure, but with the radar still working. This was the one area still lacking agreement. It is all based on the assumption that a rendezvous radar failure is obvious as opposed to insidious. Clarke Hackler (GCD) and Al Nathan (GAEC) were given the action item to determine if this assumption is reasonable. Our alternate plans for TPI—PNCGS out, radar working—are as follows:
(a) Compare the onboard chart solution for TPI with the MSFN. If the comparison is favorable, execute the chart solution and, if not, use the MSFN delta V's and the maneuver execution time based on the onboard solution. The maneuver would be made using the AGS external delta V mode—this procedure to be amplified later in this memo. Do not input radar data into the AGS. OR…..
(b) As soon as PNGCS failure is apparent (but not sooner than CDH) start updating the AGS state vector with rendezvous radar data inputs. Proceed using AGS in place of PNGCS. That is, compare TPI solution with MSFN (and maybe CSM for components perpendicular to the line of sight). Use AGS solution if acceptable. If not, execute MSFN delta V's using AGS External Delta V mode. The argument for inputting rendezvous radar in the AGS and using its solution is that it is a closed loop system which analysis shows should work well using rendezvous radar and more analysis is on the way to prove it further. In addition, Flight Crew is concerned that the arithmetic associated with the charts make its solution more susceptible to crew error, whereas the AGS does the arithmetic for them. The arguments against use of radar in the AGS for TPI is that to attempt to maintain both the AGS and charts solutions is likely to create an excessive work load upon the crew, particularly when considering the hinderances of the spacesuits and the zero g environment. Furthermore, we have considerable confidence in the charts and expect that if the charts and AGS (with radar) solutions differ we would be inclined to believe the charts and use that solution instead of the AGS anyway.
5. The following is the most startling conclusion reach today! If the LM PNGCS is working but rendezvous radar has failed, we have a serious problem with the LM since no external data will be input to the spacecraft systems—PNGCS, AGS or charts. In this case, it is our recommendation that the command module execute the TPI and subsequent midcourse correction maneuvers and the LM do the braking— maneuvers.
(a) The command module would compare its TPI solution with the MSFN. If the comparison is favorable that maneuver would be executed; if not, the command module would execute the MSFN delta V's using its own time of ignition.
(b) The command module would voice relay to the LM the maneuvers it has executed in order that the LM crew could update the command module state vectors in the LGC using the Target Delta V program.
6. I would like to present here the rationale for making the command module active for TPI and midcourse when only the rendezvous radar has failed. The justification is based on assuring ourselves the capability of making a good midcourse correction subsequent to TPI which is extremely important since with no ranging device the braking maneuver is going to be very difficult for the LM to do. The whole point is that only the command module is able to maintain a closed loop knowledge of the situation (with its sextant) and maintain an up-to-date set of state vectors in the computer to target the midcourse correction maneuver. Furthermore, it is only able to do this well if it makes the TPI maneuver, so that its PNGCS senses that too. It should be noted that this does not use a great deal of CSM RCS propellant. Nowhere near that budgeted for LM rescue. All of the other maneuvers are carried out by the LM and the really large RCS drinker—braking—will also be carried out by the LM. The reason for that, or course, is that since the LM will be coming in from below, viewing the command module against a star background, it will be in a much better position to do the braking maneuver. In addition, we would prefer to save CSM fuel where possible.
7. An obvious additional advantage to this is that it keeps the procedures as simple as possible in this critical situation. In fact, it is a standard CSM TPI for which a great deal of planning and training will have been carried out. On the other hand, for the LM to make those two maneuvers would require a great deal of coordination and communication between the spacecraft crews in real time which is undesirable. And, it avoids having to prepare procedures and training for this special situation.
8. It was stated by FCOD that the command module pilot will be unable to computer onboard chart solution for TPI due to the press of other activity and so they will not be available as a data source.
9. The manner in which the AGS can be used to execute LM chart solutions is by loading a zero magnitude maneuver into its External Delta V processor which zeroes the registers and permits it to be used like the PNGCS Average G program (P-47). The crew would thrust sequentially along each of the three body axes, probably burning the largest component first. The sequential operation is necessary since there is only one digital readout on the DEDA register.
10. I expect that at the next meeting we will review all this and tune it up a little. We should then probably apply these techniques to the earlier “pseudo-TPI” maneuver which occurs half way through the exercise including special considerations associated with a TPI maneuver that we do not really intend to execute.