Space Shuttle Ultra 1.25 Revision B development

[GLS]

As promised I did some checks on the SRBs and they look guilt free. I compared the thrust with some sources and the error barely gets above 1% at any moment during the burn.
That leaves mass evolution during first stage and thrust vector direction.

 

[Urwumpe]

What could also be: A too shallow pitch profile. We are 10 km lower and 100 m/s faster at the same total impulse, which suggests that we are maybe just pitching too aggressive. AFAIR, the splashdown of the SRBs was also about 50 km too far downrange.

 

[SiameseCat]

I tried using the new SSME position posted by DaveS, and it doesn't have a significant impact (the shuttle is actually 0.5km lower at SRB sep). Also, it seems to me the shuttle is too slow at SRB sep, not too fast. The stack should be 46.5 km high and travelling at 1271 m/s; it's actually 38.25 km high and travellling at 1200 m/s.

I took the pitch profile from a NASA training document, so I think it's correct. I think the aerodynamic parameters of the stack might be another problem - there might be too much drag, which will cause underperformance.

 

[DaveS]

I tried using the new SSME position posted by DaveS, and it doesn't have a significant impact (the shuttle is actually 0.5km lower at SRB sep). Also, it seems to me the shuttle is too slow at SRB sep, not too fast. The stack should be 46.5 km high and travelling at 1271 m/s; it's actually 38.25 km high and travellling at 1200 m/s.

I took the pitch profile from a NASA training document, so I think it's correct. I think the aerodynamic parameters of the stack might be another problem - there might be too much drag, which will cause underperformance.

What scenario are you using to test the launch?

 

[Donamy]

I seem to remember reading somewhere, that the later shuttle launches that flew a direct ascent, used a thrust vector that was in front of the CoG.

 

[GLS]

we are maybe just pitching too aggressive

That's what it looks to me. And because of the way first stage guidance works (and I agree with SiameseCat that it's correct), that would be caused by the vehicle accelerating too fast. What ever it is it starts early, because looking at the cue cards we already look low at 30s.

Also, it seems to me the shuttle is too slow at SRB sep, not too fast.

My first impression too, but then I noticed I was reading surface velocity instead of inertial velocity.

I seem to remember reading somewhere, that the later shuttle launches that flew a direct ascent, used a thrust vector that was in front of the CoG.

Actually, I was looking at some old things today and found something about that! No longer online but can be found here.

 

[SiameseCat]

According to the cue cards, the SSU pitch angle is consistently higher than it should be, not lower. I think we're accelerating too slowly for some reason.

As far as velocity goes, I've been comparing two surface-relative velocities. I think this is more reliable than inertial velocity, because that will change depending on the launch heading. BTW, I've been using the ET Attach Test scenario for testing the launch; this launches at a 90 deg azimuth.

 

[Donamy]

It also seems to pitch too soon to me. The real shuttle seems to roll first then a gradual arc over.

 

[DaveS]

That's what it looks to me. And because of the way first stage guidance works (and I agree with SiameseCat that it's correct), that would be caused by the vehicle accelerating too fast. What ever it is it starts early, because looking at the cue cards we already look low at 30s.

I noticed that the roll program starts too early. It should occur around T+10 seconds, in SSU it begins around T+5 seconds. Something I noticed about that is the vehicle seems to get an instant 15-30 m/s² acceleration upon SRB ignition and lift-off.

 

[Donamy]

I think that's why Columbia lofted on STS-1. Need to simulate the water cushion.

 

[DaveS]

I think that's why Columbia lofted on STS-1. Need to simulate the water cushion.

No, the lofting was due to hotter than expected SRBs which made the SRBs generate more thrust than expected. The water cushion generated by the Sound Suppression Water System (SSWS) is just to deaden the sound pressure waves from the SSMEs and SRBs. Without it, the pressure shock waves would tear the vehicle apart, which nearly happened on STS-1 due to improperly calculated ignition over-pressure waves from the SRBs.
They have nothing to do with the lift-off velocity.

 

[DaveS]

Any new discoveries been made on the launch problems?

 

[zerofay32]

Good day all. Just letting you all know I'm still here. I've been spending a lot of time in airplanes the last couple months and traveling a lot for work. I think I'm coming up on some free time so I would like to get back to working on the Docs. I saw a couple of posts ago that lots of stuff needs added. Looking over what I've done so far, I would like to revamp my whole scheme for it. :hmm: I'll work on it this week end and get back to you...

 

[DaveS]

With NTRS shut down, just how much does this affect SSU? I guess we won't be able to simulate the various systems with the desired accuracy.

 

[Urwumpe]

With NTRS shut down, just how much does this affect SSU? I guess we won't be able to simulate the various systems with the desired accuracy.

Well, we have a lot of material left to work with, I still have a few GB of NTRS files on my external HDD that I did not yet even put into the design.

The most important source for accuracy is the ODB anyway, which I did not get from the NTRS.

The closing of the NTRS is really really sad since it makes our research harder, but maybe it is soon online again.

 

[Donamy]

So, efforts on a release can be priority?

 

[Urwumpe]

So, efforts on a release can be priority?

Yes - but was that ever a question? :lol:

 

[Donamy]

Felix24 is working on some nice new "shiny" textures for the ISS modules, that will be a nice addition to the mission pack updates.

 

[Urwumpe]

Felix24 is working on some nice new "shiny" textures for the ISS modules, that will be a nice addition to the mission pack updates.

Do you know, if it would be possible to combine the reflective map feature of the DX9 client with the SSU radiators?

 

[DaveS]

Felix24 is working on some nice new "shiny" textures for the ISS modules, that will be a nice addition to the mission pack updates.

For me, I still need to complete the orbiter modifications. But a big problem is the wings. They're located too low according to schematics of Discovery which I found on NTRS before it was taken offline.

---------- Post added at 03:49 PM ---------- Previous post was at 03:48 PM ----------

Do you know, if it would be possible to combine the reflective map feature of the DX9 client with the SSU radiators?

Already done and the D3D9Client specific cfg file has already been checked in.