Problem Apollo 8 TLI Problems

[jarmonik]

The problem is that after requesting the burn data the first time, the S-IVB changes it’s attitude according to that. Because the S-IVB has attitude thrusters only at its rear end, there’s a rather huge “translational component” during that manoeuver, that means the S-IVB changes it’s orbit slightly. After the manoeuver, the S-IVB requests the burn data again with the hope to get new burn data w.r.t. it’s now-current orbit. Then it changes its attitude again according to that, requesting again and so forth for a couple of times.

It's possible to press [EXE] after S-IVB orientation to re-compute the data but I didn't do that in my test. Also set the TIg mode to manual before that. Also note that [EXE] shouldn't be pressed when time to ignition is less than 300 seconds. I'll try to remove that limitation from manual TIg mode.

 

[tomas2]

Wow thank you everybody! I will be retrying the scenario ASAP

 

[Tschachim]

I tested the scenario and couldn't find anything wrong. After TLI, altitude of lunar flyby was -260k when -240k was targeted.

I need to admit that I didn't do the burn actually but just saw that the burn data didn't change after the first attitude change of the S-IVB.

After actually executing the burn I can confirm your values, I had -240K target, -270k actual. I assume the difference is caused by the problem I mentioned, but it's not as big than I thought and not in the magnitude tomas2 is experiencing.

tomas2, what did you do exactly after you start the scenario YOU posted?

...and Jarmo just told me that the scenario I posted isn't working (CTD) with the latest beta modules, that's because of my work-in-progress, so please just ignore it, sorry...

Jarmo, despite the rather small error, would it be possible to change LTMFD to adress that problem, for example by "pressing exe automatically" when a burn data request is coming through the IPC interface or something like that?

Cheers
Tschachim

 

[jarmonik]

Jarmo, despite the rather small error, would it be possible to change LTMFD to adress that problem, for example by "pressing exe automatically" when a burn data request is coming through the IPC interface or something like that?

Yes, I suppose it's possible but the problem is that the computations are very heavy, meaning that if the burn data request comes for every time step the frame rate could easily drop below 10fps. Even if the burn data request comes for every MFD update it would still cause a peak impact in frame rate.

I am still working on some features those should reduce the flight plan update costs down to 1/10th.

 

[tomas2]

.tomas2, what did you do exactly after you start the scenario YOU posted?

After I start the scenario (which i believe is already set up) i press [Exe] [Dv] and than [Exe]. Then after a while when I was setting up for my first mid-course correction I used IMFD since I do not know how to use the Lunar Transfer MFD very well yet :embarrassed:. But when I set it up it says my PeA is like 22M (I could be reading this wrong), which most likley will result in zero fuel before I am done the correction burn.

P.S how do you use the Lunar Transfer MFD in the ProjectApollo MFD, like the IMFD? I couldn't figure that out (or should I just use the autoburn feature on the LunarTransfer MFD like before?)
Edit:

I tried your Scenario Tschachim but I CTD (sorry for bolding ).....oh wait ignore this comment

 

[jarmonik]

P.S how do you use the Lunar Transfer MFD in the ProjectApollo MFD, like the IMFD? I couldn't figure that out (or should I just use the autoburn feature on the LunarTransfer MFD like before?)

It would be better to let the ProjectApolloMFD to handle the TLI burn. Attitude controller of LTMFD doesn't work very well with S-IVB stack.
ProjectApolloMFD is used with LTMFD exactly the same way as with the IMFD. Just setup a burn in LTMFD and press [EXE]. Then press [IMFD][SIVB] from ProjectApolloMFD.

 

[tomas2]

Thank you very much jarmonik! I was trying to figure that out for the longest time!

---------- Post added at 05:39 PM ---------- Previous post was at 04:17 PM ----------

Since we are on the topic of the Lunar Transfer MFD, how do you do a correction burn with it? Do you just go back to the TLI program or is there a way of doing it with the Flight Monitor Program?

Thank you...again

 

[jarmonik]

Since we are on the topic of the Lunar Transfer MFD, how do you do a correction burn with it? Do you just go back to the TLI program or is there a way of doing it with the Flight Monitor Program?

TLI program is also used for translunar course corrections. Change FSt parameter from TLI to TLCC. Also read the lunar transfer tutorial that's distributed with LTMFD.

 

[tomas2]

LoL thank you!
I didn't see that tutorial :embarrassed: haha!

 

[Tschachim]

Yes, I suppose it's possible but the problem is that the computations are very heavy, meaning that if the burn data request comes for every time step the frame rate could easily drop below 10fps.

No, it shouldn't be that bad. The S-IVB is requesting once (i.e. until there are valid burn data) every 100 seconds at first, the last request (after the ullage burn) is about 4 seconds before the burn starts.

So if I understand you correctly the bigger problem is to get valid burn data 4 seconds before the burn in "auto TIg mode" (which especially "Quickstart Mode" users should/will use).

Cheers
Tschachim

 

[jarmonik]

So if I understand you correctly the bigger problem is to get valid burn data 4 seconds before the burn in "auto TIg mode" (which especially "Quickstart Mode" users should/will use).

Yes, that's true. I'll just need to think of something.

I suppose, one possibility is to switch automatically in manual mode if exe button is pressed multible times without altering any input parameters near the time of ignition.

 

[Tschachim]

I suppose, one possibility is to switch automatically in manual mode if exe button is pressed multible times without altering any input parameters near the time of ignition.

Yes, but I'd like to avoid that the users need to press the exe button multiple times, so perhaps it's possible to do this switch due to requests via the IPC interface, too?

Cheers
Tschachim

 

[jarmonik]

Yes, but I'd like to avoid that the users need to press the exe button multiple times, so perhaps it's possible to do this switch due to requests via the IPC interface, too?

Yes, of course it is. I suppose the user must press the exe when setting up the initial flight plan. After that the burn data could be updated automatically with automated exe press when IPC call comes in. If there is no flight plan in LTMFD in that case LTMFD would ignore IPC calls.

 

[Tschachim]

That sounds fine! :speakcool: