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Space Shuttle - Bugfixes

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Re: Space Shuttle - Bugfixes

Postby wlbragg » Sun Jun 02, 2019 4:18 pm

That's up to Thorsten, I don't know all the weight specifications for the Shuttle or why the "Equipment" weight was added, The only other weights are the empty weight of 180,000, SRB's, ET, payload, OSM-kit and docked objects. Is the Shuttle 180,000 empty + installed equipment? Or was 1800,000 including any on-board equipment?
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Re: Space Shuttle - Bugfixes

Postby GinGin » Sun Jun 02, 2019 5:21 pm

180000 is the dry weight ( varying between 175000 and 185000 in my docs , might be the docking pod in addition )

So 180000 is perfect for dry weight.
40000 is too much for equipment like crying tanks etc ( max 5000 pounds )


I made the numbers and without those 40000 pounds .

Weight with payload and propellant is close by a few pour-cent to official datas from launch records
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Re: Space Shuttle - Bugfixes

Postby Thorsten » Sun Jun 02, 2019 5:42 pm

I'm fairly sure I had an idea why I put it in, so feel free to remove it on your own install, but unless I've re-examined the whole thing, we'll keep it (there might be all sorts of weird side effects, like the Shuttle blowing up since qmax is different...)
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Re: Space Shuttle - Bugfixes

Postby GinGin » Sun Jun 02, 2019 6:09 pm

Sure.
It seems a good idea.
That was just to let you know .

I made a lot of tests without it .
It was within the window for max q.

I will made deeper tests with and without it and replace the 40000 value by 40000 in the mission file to see if there is a difference in ascent profile with a same total Weight but coming from different input files
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Re: Space Shuttle - Bugfixes

Postby eatdirt » Sun Jun 02, 2019 7:50 pm

Talking about blowing-up, with --heading=90 from KTTS, I do blow up at qbar max for the AP targeting HST inclination. I've tried twice to check. It works fine with --heading=270 degrees though!
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Re: Space Shuttle - Bugfixes

Postby GinGin » Sun Jun 02, 2019 8:41 pm

If you do it again, could you note the angle of attack between Mach 0.9 and 1.6 ( or even take a small video )
You can try to widen the bucket in the mission file.
Start of throttle down at 30 seconds and throttle up at 60 seconds.
It will help to reduce the angle of attack

Also could you note the pitch rate in degrees during the Mach Swindon I mentioned ?
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Re: Space Shuttle - Bugfixes

Postby eatdirt » Sun Jun 02, 2019 9:47 pm

I'll do that, thanks Gingin!

Other things weird, sometimes, on OPS 105, when planning the OMS-2 burn, the predicted HA/HP after entering a proper VX and doing ITEM+22 are crazy. For instance, I could get a HP<0 while doing a prograde burn. If I simply cancel with ITEM+22 and load again with ITEM+22, without touching anything else, it usually becomes fine. So, sometimes, something gets seriously wrong. I suspect that might be related to the problem of nasal frames Thorsten was mentioning? Although I am throttling down to 60 fps.
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Re: Space Shuttle - Bugfixes

Postby GinGin » Sun Jun 02, 2019 9:55 pm

Weird indeed, never had that.
Could you take screens of ops page and nasal console?
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Re: Space Shuttle - Bugfixes

Postby Thorsten » Mon Jun 03, 2019 5:25 am

Talking about blowing-up, with --heading=90 from KTTS, I do blow up at qbar max for the AP targeting HST inclination. I've tried twice to check. It works fine with --heading=270 degrees though!


You're now supposed to edit the throttling plan yourself in the mission file according to your needs. :mrgreen: Simply command throttling down earlier.

So, sometimes, something gets seriously wrong. I suspect that might be related to the problem of nasal frames Thorsten was mentioning? Although I am throttling down to 60 fps.


Never seem this myself either - anyway, it's unlikely to be related to framerate, because this is the one bit of code that's actually threaded out of the FG loop and just executes at its own speed.

So I don't really know.
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Re: Space Shuttle - Bugfixes

Postby eatdirt » Mon Jun 03, 2019 6:44 am

Never seem this myself either


Thanks. I forgot to say I am seeing this only with 2019.2.0, with previous versions, I've indeed never seen it as well. I'll keep an eye on it and try to extract more information!

@gingin, here the videos aoa_hstlaunch.webm

It is not easy to really see on the ADI ball, but the Shuttle rotates very late and/or rotates too slowly, and has not finished rotating while reaching qbarmax. Any advice of which parameter to change welcome.
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Re: Space Shuttle - Bugfixes

Postby GinGin » Mon Jun 03, 2019 9:47 am

Sideslip angle is too high.
I had the same when launching at an inclination close to current latitude ( 28.45 here ?) and doing the roll after liftoff
Could you try the same with 31 degrees launch inclination?

You can take css control and null the sideslip angle while decreasing slowly the pitch to 70 degrees before Mach 1.
( smooth on the rates , 0.5 degrees is a good value to avoid aoa becoming too positive)
You can put the adi rate to minimum ( one degree for the scale )

I put some huge dead and on the joystick with target software ( you have the t 16000 ? ) it helps to avoid over controlling
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Re: Space Shuttle - Bugfixes

Postby eatdirt » Mon Jun 03, 2019 9:43 pm

Could you try the same with 31 degrees launch inclination?


It works with 31 degrees, exactly as you said, the Shuttle rotate enough to be in good AOA before qbarmax.

I have played with various things, and it even works almost down the the latitude of the launchpad (39A), which is 28.6274 (passed as argument --lat to fgfs). Now, looking into hst.xml, I see an inclination of 28.47. If I increase it a bit to 28.7, it works. If I set it exactly at 28.6274, it fails, the Shuttle does not even start rotating. If I set it at 28.65, the Shuttle rotates slowly, but has not yet finished the rotation within qbarmax. So it looks like the rotation rate is somehow related to the difference between target inclination and latitude. Is that possible Thorsten?

I'll try in manual, seems to be non-trivial, especially to read the screen when everything is shaking :) Concerning the "Terminator", I own a TWarthog instead of the T16000, it is very smooth, I just have to train...
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Re: Space Shuttle - Bugfixes

Postby GinGin » Tue Jun 04, 2019 10:38 am

Answered in help.
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Re: Space Shuttle - Bugfixes

Postby Thorsten » Wed Jun 05, 2019 9:05 am

So it looks like the rotation rate is somehow related to the difference between target inclination and latitude. Is that possible Thorsten?


The launch azimuth is a function of inclination and latitude, and the AP sets a rotation rate based on the current azimuth error (to get around singularities, it actually aligns the tail fin with the desired azimuth by maximizing the dot product, so there's nothing fragile in the AP itself).
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Re: Space Shuttle - Bugfixes

Postby eatdirt » Wed Jun 05, 2019 10:45 pm

The launch azimuth is a function of inclination and latitude, and the AP sets a rotation rate based on the current azimuth error ...


Ok, I have done my homework, I hope you'll forgive me swimming in unknown territory and making wild guesses... Don't flame me :)

But... I suspect this scalar product is "body-y[]. course-vector[]". In launches with inclination <= latitude (If I got it right, this situation lands back to inclination=latitude) , in the nasal console, I can see that course-vector[0]=10^(-17), while all along stage1 ascent the stage1-couse-error and the stage1-roll-cmd remain ridiculously small.

Within dialog.nas, I can see that launch_azimuth=90 degrees, which explains why course-vector[0] given by its cosine is vanishing. Now I suspect that in upward position, the roll attitude is body-y[0]? (wild guess), which then would explain why the Shuttle never rolls to correct attitude when starting with inclination=latitude, the dot product is independent on roll while the Shuttle is in upward position due to the vanishing of course-vector[0]. So this can only happen for inclination=latitude, which is what I do see.

In the console, I have forced a course-vector[0]=0.02, and starting with --heading=90, inclination=latitude, the Shuttle rotates as expected well before qbarmax. I don't know how to fix that properly, but I hope that could help!

Cheers,
Chris.
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