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Author Topic: Apollo 8 vAGC TLI  (Read 3209 times)
AH
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« on: March 02, 2016, 05:15:02 PM »

Hi

I've been having a go at Apollo 8 for the first time in ages. I've tried TLI by the flight plan several times with IMFD and LTMFD, and the closest I seem able to get to a free return is dipping into the lunar soi before swinging away and returning to Earth. An MCC 1 burn of about 56 seconds and almost 10 percent SPS propellants then nails the free return about spot on.

Two questions: is this anywhere near what would be expected and, if not, will about 92% SPS propellants be enough to complete the mission or should I keep trying to fine-tune TLI?

Thanks
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indy91
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« Reply #1 on: March 02, 2016, 05:50:48 PM »

Realistic would be a very short burn with the SPS for MCC1, but LTMFD is usually good enough so that not even that is necessary. I think the Excel flightplan is a little bit outdated, there are better targeting parameter. Usually I target the lunar periapsis coordinates mentioned in the Apollo 8 mission report. These should be good enough so that the trajectory is close to free return, I don't know, maybe there is even a better way to ensure free return. Anyway, the parameters are:

Mod: Surface
TIG (manual): 2:50:31 GET
Frame: Moon Equ
PeT: 69:10:39 GET
PeA: 121.9k
TOA (does this even matter in Surface mode?): 69:10:39 GET
Latitude: 8.6S
Longitude: 172W

And you can just keep using the same parameters for any MCC.

But you are in luck, 92% after MCC1 is enough to continue with Apollo 8. Any mission with a LM this would be awefully close to not having enough fuel, I think.
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AH
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« Reply #2 on: March 04, 2016, 07:05:43 AM »

Hi

Thanks for that - I'll give those parameters a try  Happy

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AH
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« Reply #3 on: March 06, 2016, 06:33:02 AM »

Hi

I tried those numbers. but was still falling well short  Bangs Head

So I looked a bit more carefully at what was happening - turns out the S-IVB was running out of fuel a few seconds short, so I topped up the S-IVB tanks by 10% in Scenario Editor, and it worked perfectly Happy

Ok so perhaps Bormann, Lovell and Anders couldn't have found a gas station in EPO, but I'll go with what works  Very Happy

Thanks

AH
« Last Edit: March 06, 2016, 06:35:01 AM by AH » Logged
indy91
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« Reply #4 on: March 06, 2016, 07:07:23 AM »

Ah right, I know that issue, it happened to me before, too.

I think the problem is that our Saturn V has already been configured to work with the new autopilot, a simulation of the Launch Vehicle Digital Computer (LVDC). The new autopilot isn't used in the Apollo 8 scenario yet, because it can't do TLI yet. In the current configuration the old autopilot is very inefficient at doing the Saturn V ascent. So much so, that it spends too much S-IVB fuel on the ascent to still be able to perform the whole TLI maneuver. The LVDC can do the ascent much better and the old autopilot is still running in the background, so the TLI can still be done with it the "old way". LVDC for ascent and old autopilot for TLI is the only way of doing Apollo 8 at the moment without cheating and it doesn't really change all that much for the user. All you have to do to enable the LVDC pre-launch (preferably before T-20min) is add the line "USE_LVDC PLEASE" below the line "APOLLONO 8" or so.
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Vinny003
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« Reply #5 on: June 03, 2017, 11:14:19 PM »

Hi, guys!!

Question for you, I am using the VAGC apollo 8 in the latest version of NASSP (February 22,2017), how do i setup the SIV-B to burn out of earth orbit after once I get up to the parking orbit? Thanks!

                       Cheers,
                Vincent
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MrFickles
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« Reply #6 on: June 04, 2017, 12:47:31 AM »

You don't need to do anything to setup TLI in the latest version of NASSP. TLI is handled by the LVDC, you just need to monitor the burn.
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Thymo
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« Reply #7 on: June 04, 2017, 06:01:59 AM »

Like MrFickles said, you don't need to do anything for the TLI to initiate. Some things do need to be done to monitor the burn.
You can find all this in the procedures (Flightplan, checklist mfd, whatever you use) including the fact that TLI would automatically initiate.
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Vinny003
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« Reply #8 on: June 04, 2017, 10:30:53 AM »

Hi, guys!

Where do I find the TLI checklist on the project apollo MFD, and what does LVDC stand for? Thanks!

                 Cheers,
            Vincent
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indy91
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« Reply #9 on: June 04, 2017, 10:37:32 AM »

Hi, guys!

Where do I find the TLI checklist on the project apollo MFD, and what does LVDC stand for? Thanks!

                 Cheers,
            Vincent

It's the Project Apollo Checklist MFD that has the checklists. If you follow that step by step then you should be able to fly the complete mission with it. If you want to use the actually flown Apollo 8 Checklists (including the one for TLI) then you can download them here: https://drive.google.com/open?id=0BzUu_aREm1xSUlBQTW5Hclo4aFE

LVDC stands for Launch Vehicle Digital Computer. Our implementation in C++ (called LVDC++) replaced the old IU autopilot, which needed TLI burn data from TLMFD or IMFD to work, routed through the Project Apollo MFD. You might be familiar with that old procedure of using PAMFD for TLI. That is no longer necessary. Just like the real LVDC, it has all the TLI data stored onboard and calculate the time of ignition and the other burn data itself.
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Vinny003
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« Reply #10 on: June 04, 2017, 03:49:37 PM »

Hi, guys! Great! Thanks! I'll give it a try!
 
                 Cheers,
             Vincent
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Vinny003
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« Reply #11 on: June 10, 2017, 04:10:11 PM »

Hi, guys!

I now have the orbiter 2016 and the NASSP v8.0 alpha GIT build 547, I am now in orbit in NASSP v8.0, how do I do the TLI burn? Thanks!
 
                     Cheers,
                 Vincent
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rcflyinghokie
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« Reply #12 on: June 10, 2017, 06:06:38 PM »

Hi, guys!

I now have the orbiter 2016 and the NASSP v8.0 alpha GIT build 547, I am now in orbit in NASSP v8.0, how do I do the TLI burn? Thanks!
 
                     Cheers,
                 Vincent

TLI is computed and burns automatically using the LVDC.  If you follow the checklist MFD it will walk you through the times and procedures for preparing for the burn.
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rcflyinghokie
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« Reply #13 on: June 11, 2017, 05:23:24 PM »

Hi, guys! Great! Thanks! I'll give it a try!
 
                 Cheers,
             Vincent

How did your TLI go?
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