Apollo 16 LOPC-2 and Shape Questions

Wedge313

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Hi. Just completed the Apollo 16 flight, almost 50 years exactly from the actual mission. Casper is bobbing safely in the warm Pacific waters. I had a few questions about two maneuvers that were scheduled on the original Apollo 16 flight plan but were later scratched: LOPC-2 and the Shape burn.

First, what was the intended purpose of these maneuvers? I ask because TEI goes off just fine without them, in fact for me this was the best TEI of the four missions I've run (8, 11, 15, 16). MCC-5 and MCC-6 were scrubbed, and MCC-7 was only a 0.86 fps burp of the RCS that I conducted simply because I was getting nervous about the upcoming reentry with no MCCs. So why did they plan to do what appears to be two unnecessary maneuvers? Or were they only not needed because they did the TEI about one day early?

Second, how would I set up for LOPC-2? I tried to run two different scenarios during the flight, one that followed the original flight plan and one that followed the slightly altered plan (slightly? Yikes!) they actually ended up doing. But I didn't understand the purpose of the PC, and so I couldn't begin to try to plan it. We did a Shape burn on Apollo 15, so I understood that process. LOPC-1 sets the CSM/LM up to pass directly over the planned landing site. But I'm not clear on what LOPC-2 was for, or how we would do it.

Finally thanks again to everyone involved with the development of NASSP. It's an incredible simulation.

P.S. Landing at Descartes is great, but nothing to compare with the descent into Hadley.
 

MrFickles

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LOPC-2 is to set up the CSM to be in-plane with the landing site for ascent and rendezvous, but I'm not familiar with the new MFD interface to help you plan it.
 

indy91

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LOPC-2 is to set up the CSM to be in-plane with the landing site for ascent and rendezvous, but I'm not familiar with the new MFD interface to help you plan it.

No that is LOPC-1. LOPC-2 is after rendezvous and getting rid of the LM.

But targeting wise it should be very similar. "The CSM performs a second plane change on rev 61 to increase lunar surface photography coverage." What I did when flying Apollo 12, which also did a LOPC-2 for photography reasons, is change the landing site coordinates in the RTCC to one of the photo sites and then it's just a question of the 2nd threshold time for the LDPP when you want to fly over it. The difficulty is determining the coordinates and time to use there. I just tried a few things until it gave a similar DV to the flight plan.

EDIT: Interestingly the operational trajectory has LOPC-2 happening exactly at 0° latitude. Maybe then it is best to use the General Purpose Maneuver Processor. Let it find the TIG at an equatorial crossing and make it a plane change maneuver of 3°, or -3°, whichever makes your inclination larger than before the burn. That should get you a maneuver close to what was planned.

For the shaping burn, they want to be in a good orbit for launching the subsatellite, so that is has a long lifetime despite mascons. For Apollo 15 I know the exact constraints:

HA = 75 +/- 2NM
HP = 55 +/- 2NM
longitude of periapsis: 47°W with an acceptable range of 52°W to 37°W.

The Apollo 16 operational trajectory actually has a 55 x 85 orbit there instead. But I don't know about the longitude constraint. You can use the general purpose maneuver processor to achieve the HA and HP and if it's possible choose a TIG that is close to the flight plan and gets you into that window for the longitude of periapsis.
 
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Wedge313

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No that is LOPC-1. LOPC-2 is after rendezvous and getting rid of the LM.
Yeah, typo on my part. I meant LOPC-1.

Thanks for the explanation, changing the plane for photo coverage makes sense. And I forgot about the shape burn being for the subsatellite orbit, we did it on A15 but for some reason I was thinking it had something to do with setting up for TEI. And now that you pointed it out I do remember reading from the AFJ that they discussed that, how omitting the shape burn would affect the subsatellite.

Eventually it makes sense to me, it just takes me longer than most.
 
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