Support Implementing AS-202

prawl

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Hi, newbie here.

I'd like to to implement AS-202 into NASSP 8, and to be frank I'm struggling. AS-202 is very similar to Apollo 7 for Orbiter, it is just an Apollo 7 like mission but with 3/4 of an orbit. I'm convinced that for anyone familiar with the addon, this endeavour is a matter of 1 hour.
Starting from the Apollo 7 scenarios, it appears to be much, much more difficult to implement a basic chain of events or trajectory.
I think the trajectory is stored in the "Saturn IB Default Flight Sequence Program.txt", but no documentation indicates what contains this file, what are those numbers, etc.
I have both the precise timeline and the precise trajectory of AS-202, and I never imagined that starting from Apollo 7 it would be such a pain. Do you have any suggestion about where to start ? Anyone feels like helping implementing this Apollo mission into NASSP ?

Thanks

NB: the only thing I successfully implemented was the update of the S-IVB stage that was painted different between AS-202 and Apollo 7.
 

indy91

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The flight sequence program is a sequence of scheduled commands from the LVDC to the stages (in this case IU, S-IVB and S-IB). They contain such things are commanding engine cutoff, engine starts, pressurization etc. So nothing to do with trajectory. It is badly documented, very sorry about that. You can only find what it does when digging in the NASSP code right now. An example of such a flight sequence program would be the second half of this document for Apollo 12: https://www.ibiblio.org/apollo/Docu...initionOfSaturnSA507FlightSequenceProgram.pdf

Each command is a time in the current time base, then a number for the stage and then the desired command. All that being said, I don't think you really need to change much in the flight sequence program to get a basic AS-202 going.

Some time last year I started an endeavour to get the Block I Virtual AGC emulator going in NASSP to be able to use the Apollo 4 and 6 software that we have for it. But because Block I and II CSMs were so different I had to make the decision to develop this in a branch that will never be part of the actual NASSP releases, as I deleted a lot of the Block II stuff and replaced it with Block I code. If I had tried to implement a full Block I CSM in parallel to our current CSM then I would have essentially needed to start from scratch, which would have been at least twice as much work. I did manage to make Apollo 4 and 6 work, made some videos about it and then tried to use the Virtual AGC to also fly AS-202, but the software was too different from 4 and 6 and it didn't really work right. The software for AS-202 (called Corona) is out there and there is some hope that we can eventually use it in NASSP, too. Should it become available I would return to my Block I branch and probably try to get a release version done.

Back to what you are trying to do, you can still profit from what I was trying there I think. I did add a AS-202 scenario: https://github.com/indy91/NASSP/blo...llo - NASSP/WIP Scenarios/AS-202 - Launch.scn

In the mainline version of NASSP you can probably only use the LVDC section from it. I also made a modified flight sequence program which you can try to use:


But it is mostly some differences in detail, not much in it that is strictly required.

So I guess my advice to you is use the Apollo 7 scenario as a baseline and plug the LVDC section from my AS-202 scenario into it and also use the updated flight sequence program. From there you will probably get to the suborbital insertion. The padload for the CMC is a whole other topic, that is still quite hand-crafted. I have a project to create these in a more automated way, but I am not quite done with it yet.
 

prawl

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Thank you so much for you help. I have tried what you said, and while the S-1B runs as expected, the S-IVB barely throttles for several seconds and shuts down, leading to a premature reentry in the Atlantic.
Maybe I missed something, I'll try pushing buttons and turning knobs, something useful might come out of it.
 

Urwumpe

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As I understand the logic, the S-IVB shall shutdown after T4+10 seconds if it did not achieve correct thrust. So, maybe there is a missing command in TB4. Maybe you also entered Timebase 4A instead - early staging.
 

indy91

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As I understand the logic, the S-IVB shall shutdown after T4+10 seconds if it did not achieve correct thrust. So, maybe there is a missing command in TB4.

Yeah this is what happened, although it is timebase 3 for the Saturn IB. The AS-202 file in my Block I branch is a bit dated, it's missing a critical command to allow the S-IVB engine to start. What you need is

3.2,3,11

under TB3 in the AS-202 flight sequence program. I can also update the file in my branch later if that helps. Should have just used the default Saturn IB file, that one would have worked :D

Maybe you also entered Timebase 4A instead - early staging.

No such thing on the Saturn IB. This timebase only exists on the Saturn V when you manually cause an early S-II/S-IVB staging.
 

Urwumpe

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Well, I am no Apollo expert at all, so I was just trying my worst. :)
 

prawl

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What you need is
3.2,3,11
under TB3 in the AS-202 flight sequence program.
Thanks, it worked like a charm !
I could note a ~10s difference between NASSP (~612s) and the planned (602.3s) S-IVB cutoff, even more compared to the actual (588.5s) cutoff.

A major difference is of course what happened just after the S-IVB cutoff: immediate S-IVB/CSM sep and start of the SPS for more than 3 minutes to the desired suborbital trajectory, as visible in the timeline below :
1670502248549.png


I guess this is the harder part to simulate in NASSP as this should use a Block 1 CSM, isn't it ?
 
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indy91

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I could note a ~10s difference between NASSP (~612s) and the planned (602.3s) S-IVB cutoff, even more compared to the actual (588.5s) cutoff.

Probably the Apollo 7 CSM being heavier than the AS-202 one or something like that.

A major difference is of course what happened just after the S-IVB cutoff: immediate S-IVB/CSM sep and start of the SPS for more than 3 minutes to the desired suborbital trajectory, as visible in the timeline below :


I guess this is the harder part to simulate in NASSP as this should use a Block 1 CSM, isn't it ?

Yeah the AGC software on AS-202, Apollo 4 and 6 had some special burn guidance to achieve desired semi-major axis and eccentricity for the orbit. See this document: https://www.ibiblio.org/apollo/Documents/R477-AS202-GSOP-Rev2.pdf

on PDF page 86. There is no equivalent burn guidance on the Block II CMC software so that would be difficult to replicate using the CMC. I guess you have to try and do it somewhat manually. I did try to use Solarium, the Apollo 4+6 software, in my Block I branch. The main issue is mission sequencing. The right burn guidance and all that exists, there just wasn't really a way to make it do the specific sequence of events of AS-202.
 

indy91

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Just to update this thread as well, we now have the software flown on this mission and it works in my Block I branch:

I don't plan to make any further updates for my branch at the moment: https://github.com/indy91/NASSP/blob/BlockI/

There is a lot that could be done in that branch, it's mostly a Block II CSM still. Well the code for the Block I Virtual AGC emulator, its connections to other systems and the Mission Control Programer are all properly implemented. So they might be useful in the future if someone tries to continue this project. But for now the branch is getting mothballed again. There is still the Apollo 1 software to find...
 
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