Apollo 16 LM Aborts

Wedge313

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I tried two aborts, one using the PNGS and one using the AGS. This might turn out to be fun.....

As a starting point I picked a time right after P64 pitchover. I only did one of each so it's a small sample size, but few questions:

The PNGS abort resulted in an orbit 9.9 x 67.4 which seems to be setting me up for a direct rendezvous, while the AGS ended up in an 10.6 x 43.8 orbit which seems to be setting up for a coelliptic method. Is this the case? Is the PNGS programed to give me a different orbit than the AGS, or did these maneuvers just not work as planned?

I noticed using the AGS guidance the ascent stage had much less "wobble" and the RCS seemed to be firing much more rapidly. This is my first attempt at using the AGS as primary guidance, so is that how it works? The down side was after engine shutdown using AGS guidance the RCS kept firing steadily, it sounded like a stuck nozzle or two, in both Auto and ATT HOLD, and the only way I could figure out how to shut it off was by turning off the AGS Mode Control after nulling out the rates. What might be causing the constant RCS firing?

I will be playing around with this more, but after achieving orbit what would we do? I need to get the RR radar fired up and start figuring out the rendezvous. Could you guide me to the documents that discuss the various abort situations that might arrive? I'm just working off the LM AOH, the G&C checklist and the timeline. I would guess there's an explanation/discussion of aborts somewhere?

Thanks
 

indy91

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I tried two aborts, one using the PNGS and one using the AGS. This might turn out to be fun.....

As a starting point I picked a time right after P64 pitchover. I only did one of each so it's a small sample size, but few questions:

The PNGS abort resulted in an orbit 9.9 x 67.4 which seems to be setting me up for a direct rendezvous, while the AGS ended up in an 10.6 x 43.8 orbit which seems to be setting up for a coelliptic method. Is this the case? Is the PNGS programed to give me a different orbit than the AGS, or did these maneuvers just not work as planned?

Hmm I think they should be compatible. Did you enter the values in the Timeline Book for the AGS abort constants (page 2, DEDA 224 etc)? Those look quite the same as in the padload for the LGC for Apollo 16.

You will find the second half of the timeline book quite useful, starting on page 19. It has tables, charts and graphs for aborts. If you aborted when P64 starts (about PDI + 9:20?) then I would expect an apolune of about 50 NM. So both PGNS and AGS are a bit off??? But not a lot. For the rendezvous profile, there never is a direct rendezvous with any non-nominal situations, always coelliptic, sometimes with an additional phasing or height adjustment maneuver thrown in.

How up to date is your CSM state vector in the LGC. That gets used to determine the insertion conditions.

I noticed using the AGS guidance the ascent stage had much less "wobble" and the RCS seemed to be firing much more rapidly. This is my first attempt at using the AGS as primary guidance, so is that how it works? The down side was after engine shutdown using AGS guidance the RCS kept firing steadily, it sounded like a stuck nozzle or two, in both Auto and ATT HOLD, and the only way I could figure out how to shut it off was by turning off the AGS Mode Control after nulling out the rates. What might be causing the constant RCS firing?

Yes the wobble is also referred to as a propellant saving maneuver. It lets the attitude rates build up and then does one longer firing of the RCS. The DAP is smart enough to do that. The AGS has no digital autopilot, only an analog one, so all it can do is try to hold the desired attitude in a certain deadband like during any other maneuver. And that leads to quite a bit off rapid RCS firing. That's where you really want to use the APS-RCS propellant interconnect to use APS instead of RCS propellant. I don't know why it keeps on firing like that after shutdown though. Maybe it's still in the smallest deadband and it can't deal with so much RCS thrust with so little LM weight? I'm sure they would change the configuration after shutdown, like max deadband and such.

I will be playing around with this more, but after achieving orbit what would we do? I need to get the RR radar fired up and start figuring out the rendezvous. Could you guide me to the documents that discuss the various abort situations that might arrive? I'm just working off the LM AOH, the G&C checklist and the timeline. I would guess there's an explanation/discussion of aborts somewhere?

Thanks

The second half of the timeline book already has a lot of necessary procedures. The time when you aborted probably fell in the category of 8 < PDI-1 < 10 (minutes). That would actually be a somewhat normal rendezvous, with CSI and CDH and then you are coelliptic and do TPI. You would start on page 24 in the timeline book after insertion. CSI happens at 55 minutes after insertion, TPI at time with specific lighting roughly 2 hours after insertion (use TPI time calculation in the RTCC MFD).

For more documentation read the LM rendezvous procedures (slightly incomplete document): https://www.ibiblio.org/apollo/Documents/lm_rendezvous_procedures_j2_j3_final_rev1.pdf
 

Wedge313

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Thank you. I realize you guys are pretty busy answering questions (I see others working on Apollo 12 and Apollo 10) so I appreciate your time. I'm trying to keep my question/maneuver ratio as low as possible.
 

rcflyinghokie

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Thank you. I realize you guys are pretty busy answering questions (I see others working on Apollo 12 and Apollo 10) so I appreciate your time. I'm trying to keep my question/maneuver ratio as low as possible.
Honestly don't sweat it! You aren't asking too much by any means.

Please feel completely free to keep them coming!
 
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