Add 68-PA-T-49A

68-PA-T-49A.md

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+---
+layout: tindallgram
+date: Mar 01 1968
+from: PA/Chief, Apollo Data Priority Coordination
+serial: 68-PA-TR-49A
+subject: "Fifth \"D\" Mission Rendezvous Mission Techniques meeting---don't miss Paragraph 5: It's great"
+---
+
+1. We spent just about the entire February 26 meeting discussing 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 mssion 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 objects, they would be considered.
+
+2. Nominal situation: PNGCS seams to be working properly and is prime; 
+   AGS must be maintained in optimum state to take over in the event the 
+   PNGSCS 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 the CSI and CDH, 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 the 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) where given the 
+   action item to determine if this assumption is reasonable. Our 
+   alternative plans for TPI---PNGCS out, radar working---are as 
+   follows:
+
+   (a). Compare the onboard chart solution for TPI with the MSFN. If the 
+   comparison is favourable, 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 AGS state vectors *with rendezvous radar data inputs*. 
+   Proceed using GS 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 makes 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 henderences 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 reached 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 our 
+   recommendations 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 assuming ourselves the 
+   capability of making a good *midcourse correction* subsequent to TPI  
+   which is extremely important since with not 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, of 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 
+   procedure 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 these maneuvers would require a great deal of coordination and 
+   communication between spacecraft crews in real time which is 
+   undesirable. And, it avoids having to prepare procedures and training 
+   for this special situation.
+
+8. In was stated by FCOD that the command module pilot will be unable to 
+   computer onboard chart solutions 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 bey loading a zero magnitude maneuver into its External Delta V 
+   processor which zeros 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