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Author Topic: What needs done?  (Read 74502 times)
dseagrav
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« on: July 18, 2015, 09:03:34 AM »

For the moment I have the ability to get some work done, but given my medical situation I am unsure of how long this situation will persist. It could be weeks or months, or it could be only a handful days. It is therefore my intention to get as much done as I can manage.

To this end, what needs done other than completing the LM? What prevents us from making a release that can fly Apollo 7 and 8? I was working on the LM because the CSM was under rapid development at the time, but I consider such a release to have priority. This thread is for determining what to do and what order to do them in.
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indy91
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« Reply #1 on: July 18, 2015, 02:54:12 PM »

Others are probably more qualified to answer this, but the two things that were mostly worked on or prevented a release so far were the LVDC++ and a good method for the Apollo 7 phasing and rendezvous. The latter is pretty much solved and Meik84 was occasionally working on the LVDC++ when he was around the last time. I'm not sure if the LVDC++ is needed for a release.
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eddievhfan1984
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« Reply #2 on: July 18, 2015, 10:24:08 PM »

IMO, the LVDC++ is the most important part prior to a release. Indy's work on the RTCC MFD has gone a long way to solving the issue of ground targeting for the AP7 rendezvous. We just need to clean up the LVDC++.

Here's some of the issues I've seen:

  • No provision for leaving the LVDC++ code in the discarded SIVB stage: If sep is initiated, the LVDC continues with the CSM, or causes a crash. I had to code the LVDC to "destruct" after sep to prevent crashing.
  • SIVB retrograde maneuver after phasing not modeled.
  • Abort handling/sequencer handling: As far as I can tell, the LVDC timestep loop does not return control back to the rest of the Saturn IB/Saturn V code, or does it such a way that the abort sequencer does not properly function. Ideally, this shouldn't be a problem for running a simulated mission, but if someone wanted to do an abort scenario...

That's all I can think of for the moment.
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dseagrav
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« Reply #3 on: July 19, 2015, 12:59:51 PM »

It was odd that aborts got broken; IIRC it worked in the LVDC before it worked otherwise. Anyway, that was trivial to fix (of a sort), and I cleaned up the formatting of the LVDC code while I was there.
Once sourceforge comes back I can commit it and people can fly abort scenarios again.

Next is arranging for the LVDC++ to survive CSM staging.

Edit: I just realized there are actually two completely separate (and incompatible) instances of the LVDC++ code, one for the Saturn V and one for the Saturn 1B. I'm going to have to merge them.
« Last Edit: July 20, 2015, 04:01:26 AM by dseagrav » Logged
dseagrav
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« Reply #4 on: July 24, 2015, 02:21:01 AM »

Can someone please take this scenario and test whether or not the 3-MFD TEI planning procedure in the Apollo 8 Excel checklist actually works?
When I try it, it fails to read data from IMFD, saying either "NO DATA" or "IMFD NOT IN P30 MODE" (when I am certain it is)

If the procedure given in the spreadsheet is incorrect I would appreciate having the correct one so I can fix it.

* Apollo 8 Virtual AGC - 65 TEI.scn (158.15 KB - downloaded 107 times.)
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indy91
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« Reply #5 on: July 24, 2015, 05:50:31 AM »

I can remember from my own Apollo 8 mission, and I also just tried it again, that I had the same issue. I manually put the numbers IMFD had calculated in the AGC, but that didn't 100% work out. Either because the displayed numbers were in a different coordinate system or not in the format the AGC needs (the AGC compensates the finite maneuver time to a certain degree). Anyway, I needed very long MCCs to correct the wrong trajectory.

If we can't find the issue, LTMFD might be the better choice. It's more accurate and doesn't require a procedure with 3(!) MFDs. We would just have to figure out the correct input values. I am no expert on the use of IMFD and LTMFD though.
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jalexb88
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« Reply #6 on: July 24, 2015, 12:31:37 PM »

IMHO I think LTMFD is the way to go. I have been using it exclusively since it was first released by jarmonik and it is far simpler to use than IMFD and can do everything that is needed for TLI, LOI, TEI on all lunar missions. Also I have no problems with uploading LTMFD data to the PAMFD.
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dseagrav
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« Reply #7 on: July 24, 2015, 12:51:34 PM »

How do you get LTMFD to target the correct reentry location? Or do you just ignore that and correct it with the MCC burns?
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jalexb88
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« Reply #8 on: July 24, 2015, 01:10:59 PM »

How do you get LTMFD to target the correct reentry location? Or do you just ignore that and correct it with the MCC burns?


RTCC MFD is quite good and targeting the splashdown location. What I found works with LTMFD is a TiG of 89:19:16, ReT: ~146:58:00, ReA: 6.5. Adjust heading so as to have the minimum dV for the burn. For the MCCs I use the RTCC MFD and target the correct longitude, -165. If everything was done correctly prior the MCC-5 should only be about ~5-10 fps, if not it can be up to 100 fps (which will still work but not as historically correct)
« Last Edit: July 24, 2015, 01:15:44 PM by jalexb88 » Logged
indy91
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« Reply #9 on: July 26, 2015, 04:31:15 AM »

There are two things that probably should be changed about the vAGC launch scenarios.

For Apollo 7 the time from final pass through P35 to the TPM burn (ATIGINC) should be 3 minutes instead of 90 seconds. Sundisk used 90 seconds, but Colossus needs a longer time for the calculation of the maneuver and I'm fairly confident that I know what causes that. The change would be setting

EMEM2022 43120

and that's it.

For Apollo 8, I once calculated the correct values to have the pseudo landing site stored in the AGC. See this post for the explanation: http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=2725.msg22524#msg22524
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eddievhfan1984
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« Reply #10 on: July 26, 2015, 04:58:33 PM »

A remembered issue with the abort sequencer: during the Launch checklist, the abort sequencer/sequential logic is supposed to be tested with a click of the ABORT button—if you do that in LVDC++ mode, the launch discrete is sent to the computer. DX
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dseagrav
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« Reply #11 on: July 31, 2015, 04:20:55 AM »

OK, so, back to the LVDC, where we were when all this sourceforge mess started: What maneuvers does the S4B need to do after CSM separation? I don't know about Apollo 7, but I do know that some of the later missions deliberately crashed them into the moon to create seismometer data.

It turns out that the S4B alone (after being separated from the CSM) is not a Saturn-class-derived vessel, so my choices for giving it more brains are to make it Saturn-derived so it can be driven by the LVDC++ code (if it needs to be complicated enough to warrant that) or just write code to do whatever in the existing class (if the maneuvers are simple)
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eddievhfan1984
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« Reply #12 on: July 31, 2015, 09:00:36 PM »

The Apollo 7 SIVB maneuver was a retrograde burn using the engine purge system. You know how we have a 2.5 fps separation burn after sep? Originally, it was supposed to be 7.5 fps retrograde, and the SIVB would also vent retrograde for 5 fps delta-V. After that the LVDC can be shut down or allow its batteries to die out, depending on the preferred method.

The TLC burns of the spent booster would be of a similar method, using the venting/purge thrust. Most likely have to either calculate predetermined maneuver information, or work on that IU uplink feature...
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indy91
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« Reply #13 on: August 01, 2015, 04:15:35 AM »

The Apollo RTCC MFD usually comes up with a 1.7 fps phasing burn, was the SIVB maneuver supposed to happen just after the phasing burn? Then simply burning 6.7 fps retrograde will work just fine.
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meik84
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« Reply #14 on: August 01, 2015, 08:00:13 AM »

@dseagrav: Good to see that you've the same problems I have. I thought that it would be as simple as "copy data from the old LVDC to the new one, kill the old one". Won't work, as the 'stand-alone' SIVB has different engine handles and stuff. Changing that is a pain in the...well!
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The Apollo 7 SIVB maneuver was a retrograde burn using the engine purge system. You know how we have a 2.5 fps separation burn after sep? Originally, it was supposed to be 7.5 fps retrograde, and the SIVB would also vent retrograde for 5 fps delta-V. After that the LVDC can be shut down or allow its batteries to die out, depending on the preferred method.
Neg. After sep the SIVB simply went retrograde and that was it. Engine purging wasn't possible, as the vents remained open after the dump with the CSM still attached. There was nothing to dump left. The LVDC remained active until its batteries died, which was after the APS fuel had been depleted. That's why the astronauts faced a tumbling SIVB during the rendezvous: the APS fuel one one pack had been consumed before the other, so the LVDC wasn't able to stop the rotation.
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