Space Shuttle Ultra 1.25 Revision B development

[Poscik]

In most cases during an actual entry of the shuttle, the vehicle dropped below mach 1 30 to 60 seconds before HAC intercept.

Dave

And that's normal, but for me, it happens shortly after TAEM, a lot of time before HAC, even without speedbrake and pitch around 0. I was watching some videos on youtube, and I'm doing it very similar.

 

[Donamy]

I had pitch between -5 and 0. This doesn't work so good, as I am too low (in spite of low speed). But TAEM is fully ok.

try dropping to -20, the extra speed will make you cover more ground quicker.

 

[SiameseCat]

I'v been flying reentries for 2 hours now, and indeed, drag works very fine, TAEM and 80kft, 2.5mach and 60nm to landing site. But I'm experiencing one problem. At TAEM I'm commanding final bank to "intercept" heading to HAC. But even with 0% speedbrake, I have very low speed. At 30kft I should start the HAC, breaking 1 mach then. But after TAEM speed drops very fast, and I'm breaking mach 1 very soon after TAEM. Any tips?

I think this might be a problem with the aerodynamics model. SSU seems to have too much drag at low speeds. I just tried flying through TAEM and had the same problem.

 

[DaveS]

One observation though, the first part of a fully AUTO entry was rock solid. It seems like the problem is always with the first roll reversal. It seems to get confused right when the roll is to be commanded.

I really think that if we just get this first roll reversal licked, everything will fall into place just nicely.

One way to wrangle it out is to fly ROLL/YAW CSS, but guidance calculated roll angles. That way we can gain good data.

 

[SiameseCat]

I'v been flying reentries for 2 hours now, and indeed, drag works very fine, TAEM and 80kft, 2.5mach and 60nm to landing site. But I'm experiencing one problem. At TAEM I'm commanding final bank to "intercept" heading to HAC. But even with 0% speedbrake, I have very low speed. At 30kft I should start the HAC, breaking 1 mach then. But after TAEM speed drops very fast, and I'm breaking mach 1 very soon after TAEM. Any tips?

I think this might be a problem with the aerodynamics model. SSU seems to have too much drag at low speeds. I just tried flying through TAEM and had the same problem.

I've been looking into this a bit more, and I think the problem might be with the range calculation, not the aerodynamics. The 60nm to landing site value includes the range around the HAC, which isn't taken into account by the current SSU code. You should be able to fly a straight-in approach without any problems.

 

[DaveS]

I really think that if we just get this first roll reversal licked, everything will fall into place just nicely.

One way to wrangle it out is to fly ROLL/YAW CSS, but guidance calculated roll angles. That way we can gain good data.

Any comments on this idea?

 

[SiameseCat]

I really think that if we just get this first roll reversal licked, everything will fall into place just nicely.

One way to wrangle it out is to fly ROLL/YAW CSS, but guidance calculated roll angles. That way we can gain good data.

IIRC, the existing AUTO guidance code tries to maintain a constant drag level throughout entry, which doesn't work very well. I remember trying your suggestion and having problems.

 

[DaveS]

IIRC, the existing AUTO guidance code tries to maintain a constant drag level throughout entry, which doesn't work very well. I remember trying your suggestion and having problems.

So what is different with the CSS guidance? No way to plug it into the AUTO code?

 

[SiameseCat]

I want to calculate the bank command based on the required vertical acceleration, instead of using a PID controller. Also, the CSS code tends to have spikes in the vertical speed, which may mess up the autopilot.

 

[DaveS]

I want to calculate the bank command based on the required vertical acceleration, instead of using a PID controller. Also, the CSS code tends to have spikes in the vertical speed, which may mess up the autopilot.

No way to tell it to ignore those spikes? Also, how about for now, going with the PID controller making the more advanced autopilot a WIP? This is so that people like me can get the vehicle through entry.

 

[Poscik]

I've been looking into this a bit more, and I think the problem might be with the range calculation, not the aerodynamics. The 60nm to landing site value includes the range around the HAC, which isn't taken into account by the current SSU code. You should be able to fly a straight-in approach without any problems.

And that could be the trick. Straight-in approach is easily achievable, but: "No HAC - no fun" :lol:

 

[SiameseCat]

Checked in a fixed range calculation. It should be possible to fly the HAC now.

 

[Donamy]

Checked in a fixed range calculation. It should be possible to fly the HAC now.

Could you update the dlls ?

 

[DaveS]

Any one here good with Lua scripts? If so, could someone write one that could be used to simulate ET tanking operations?

---------- Post added at 01:04 AM ---------- Previous post was at 12:28 AM ----------

Found a bug in SSUPad. When the ET is detanked the GOX venting from the GVA doesn't stop.

Further troubleshooting revealed that although the ET propellant resource is set to exactly 0, the equivalent propellant resource in SSUPad is only decreased to 0.0001 instead of exactly 0. This causes the GOX venting to never stop. Once set to exactly 0 through manual means(Scenario Editor) the GOX venting stops as expected.

 

[Poscik]

Checked in a fixed range calculation. It should be possible to fly the HAC now.

Tested it while ago. Works like a charm! Really fantastic! Now no problem with TAEM at all. Mach 1 broken about 10 seconds before HAC.

 

[DaveS]

Any one here good with Lua scripts? If so, could someone write one that could be used to simulate ET tanking operations?

---------- Post added at 01:04 AM ---------- Previous post was at 12:28 AM ----------

Found a bug in SSUPad. When the ET is detanked the GOX venting from the GVA doesn't stop.

Further troubleshooting revealed that although the ET propellant resource is set to exactly 0, the equivalent propellant resource in SSUPad is only decreased to 0.0001 instead of exactly 0. This causes the GOX venting to never stop. Once set to exactly 0 through manual means(Scenario Editor) the GOX venting stops as expected.

Checked in a scenario to test this bug and to be used to test other MPS and tanking related systems.

The scenario is set up to replicate the first STS-114 tanking test on April 14 2005 conducted at Pad B.

 

[SiameseCat]

How are you detanking the ET? I don't recall tanking being simulated at all.

 

[DaveS]

How are you detanking the ET? I don't recall tanking being simulated at all.

Through the Scenario Editor

 

[Poscik]

Loru created new SRB exhaust texture. If it's acceptable, I'm allowed to check it in.

 

[DaveS]

Loru created new SRB exhaust texture. If it's acceptable, I'm allowed to check it in.

Could you post one from the side for a general profile view?