#Using ACG to create V37 N15 Program 15 Manually doesn't work?

1 messages · Page 1 of 1 (latest)

midnight harbor
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For TLI Apollo Guidance Computer I don't want to use the planner I want to input my own numbers into ACG

V06 N33 -> V22 for min and V23 for seconds WORKS

But V06 N14 -> V21 for dV does NOT work.

When I put in for instance +10448 then when executing V37 N15 and running P15.

I get the correct countdown but the dV becomes 00104.

Representing 2 missing values I can't seem to input.

IS THIS USER ERROR?

Using the V21 and V22 commands in Program 15 as should be able also doesn't seem to work or change any program parameters. Will try again.

acoustic beacon
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Not sure exactly how Reentry presents P15, but in reality its not used to input new burn parameters, but rather a backup monitoring of the TLI burn, running average g to keep the state vector updated during and to provide a backup source for the tb6 signal if needed

cedar ore
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The only way I know how to use it is through the TLI planner I don’t think there’s another way because it’s an uplink so you can’t change it manually have to use the planner.

patent cedar
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I have never tried manually inputting values, it’s possible it is broken. But you are very much intended to use the planner not load it yourself

patent cedar
acoustic beacon
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you mean in reentry

patent cedar
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the IU is pretty much just a fixed attitude sequence in Reentry

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Yes

acoustic beacon
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I would have hoped that was fixed by now

midnight harbor
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In follow up I did research and it's a different program. P24 I believe - that enters burn parameters. The reason when V06 N14 is used to enter example 10448fps it turns to 00104 fps is because P24 (the input program) truncated values that are not as precise as what is uploaded by Mission control.

P15 is preset or uploaded by mission control with 15bit integer giving you 10448fps.

P24 is onboard input in 10ths of fps and only good for up to 999.9fps total.

The behavior of inputting fps through the DSKY therefore might actually be expected. Because P15 was never meant to be used that way ever. If burn parameters needed to be entered in DSKY they'd likely have aborted the entire mission because TLI could be off by hundreds of miles if the burn was inaccurate as little as 0.01fps.

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That being said the SIVB burn planner is like using mission control to upload the required fps dV for TLI. Per real life.

The GETI time input does work as expected because in all cases its the same register value as is used by P15 or any other burn programs.

It's only the TLI burn and presumably the P02 burn dV that need much more precision and were therefore preloaded

DSKY isn't a big enough computer to input the values

patent cedar
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...no lol

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you normally input values to P15, and P24 is not a burn program, it's for landmark tracking

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you are thinking of P30

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P15 has VI targets in whole fps for the reason you stated, though

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P15 as a whole is a backup method to the IU in the Saturn V, that is what normally guides TLI

midnight harbor
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Well my response is from stuff I was reading earlier today so could have the wrong P## but regardless there doesn't seem to be any way to upload actual burn dV with enough precision into P15. That was done from the ground or preloaded into the program on the ground

The backup you mention doesn't seem to be actually available in the real program?

patent cedar
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the backup is P15

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the primary is the Saturn launch vehicle computer

midnight harbor
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What I mean is like...if needed to input 10448 the crew would need to ask mission control to re-upload a value

patent cedar
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that has a very precise target loaded pre-launch that can also be uploaded from the ground

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P15 doesn't have automatic steering, so you couldn't actually fly it that precisely anyway

midnight harbor
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Right by back up are you just meaning a redundant computer?

patent cedar
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yes it is a program in the AGC to monitor TLI and do it if necessary

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it is just a normal burn monitor program with an ignition and cutoff signal, nothing else

midnight harbor
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OK yes that makes sense to me. But therefore that seems to be the case that it would never have been possible to input a large enough dV value into the computer to run TLI through the DSKY. It simply wasn't built to do it.

patent cedar
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not in the P30 register format no

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but P15 has its own separate format specifically intended for TLI

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it uses whole fps so you can input >10000 values, since the nominal input is about 36200 ft/s (it's velocity at cutoff, not delta v irl)

midnight harbor
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I looked for it and it just didn't seem to be the actual case. My reading suggested P15 V6 N14 should allow 10448 to be input. But then the actual v06 n14 behaves like the aforementioned truncated 10ths of fps.

patent cedar
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Reentry is not accurate to irl with some of these things

midnight harbor
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Yeah it'd be a monumental undertaking by one guy to do it all. But it's cool to see whether or not it is accurate.

But even so not sure why you'd want to manual input because the last 0.00fps is crucial. 10448 is not close enough without adjustments later?

patent cedar
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there are planned adjustments throughout translunar coast, so it doesn't have to be perfect

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in fact usually there is a >15 ft/s midcourse even with the automatic IU guidance

midnight harbor
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Not perfect but then the 10th of fps which works out to that prior example only gets 0.0 accuracy. Was that enough?

patent cedar
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yes

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and again you have to steer yourself with no help except a cue card, so it's not going to be precise enough for that to matter anyway

midnight harbor
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Well darn. I'd hope this part of P15 gets fixed then cuz it'd be fun to use it that way haha. But I'm ok with it not being used that way too

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Well the precision problem is why? Because the only register in P15 v06 n14 is dV(x)?

patent cedar
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yeah - if you'd like to have a study-level simulator there is NASSP for Orbiter that implements all of this very realistically

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the precision problem, like you said, is because you can't input decimal ft/s

midnight harbor
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The only problem I have with NASSP is the asshole graphics. I would much rather enjoy something visual before fidelity. NASA isn't hiring me for "knowing shit".

patent cedar
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and because there is no automatic steering so your directional accuracy is dependent on the commander's Mk1 eyeball

patent cedar
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not as good as reentry certainly, but serviceable

midnight harbor
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It needs to be star citizen good. Even the window view of REENTRY is starting feel dated lol.

What would be awesome is to take simulators like these and slap them into engines like star citizen and make a somewhat realistic space-trucker game.

patent cedar
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look I wish I had a perfect space game too but unfortunately we live in the real world lol

midnight harbor
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So without automatic steering how bad would P15 as the only burn program get you off course? Lll

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Lol

patent cedar
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I think the estimate was a 50-100 ft/s MCC

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that is within budgets, but much larger than usual

midnight harbor
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Well cool. I haven't played reentry in a bit. So I'm not sure how much more development it's done in the last couple years. But still seems about right for what I want out of a Sim. Can be better. But definitely good enough with the movie feel.

The deviation when time elapsing is still a bit annoying though. Advice on minimizing that?

patent cedar
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not much, don't timewarp super fast and it usually deviates less

midnight harbor
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Right. So it'll deviate some even at 2x? Or is there a cutoff?

patent cedar
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I haven't played in a minute either

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but yeah I think it will deviate some at even 2x

midnight harbor
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Good to know. Well thanks for the prompt deeper dive!

slow crow
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yeah you need to use the burn planner to calculate the burn, and P15 is used to monitor it. I still have a logic enabled that requires you to use P15 to execute the burn (it would be easy to remove it too, as long as you use the TLI/SIVB burn planner), but even in Reentry, P15 does not do much except for monitoring the burn and dV. The TLI planner inserts the parameters into the SIVB and the SIVB is in control of the burn