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Space Shuttle

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Re: Space Shuttle

Postby wlbragg » Tue Jul 25, 2017 6:26 pm

Tragedy! :(

It might help identifying the graphics card used.

I think in the case of SRB, it looks like the positional origin of the shader effect is not calculating correctly or is and this persons graphic card is either calculating the position differently or the strength is calculated differently.

The SSMA, is it really not there or no contrast allowing it to be visible. Or if it is shifted forward same as the SRB it may be hidden in the model. It's not as obvious and as large as the SRB flames.

I don't know the details of velocity of the shuttle VS the velocity of the effect and how or if it changes its position slightly.

Would have like to seen this against a dark atmosphere.

P.S. I am absolutely loving your comments about the FDM as I am sure Thorsten is. Even though I don't understand the half of it. It's really good reference for the uneducated.
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Re: Space Shuttle

Postby Thorsten » Tue Jul 25, 2017 6:34 pm

Is the ALS renderer on? The flame effect doesn't exist for the other renderers and the sky looks kind of non-ALS ish.

The SRB exhaust is a particle system timing effect - it seems vexingly impossible to get this completely right for all framerates and vehicle velocities. The OSG particle implementation sucks.

Usually the flame effect would (partially) hide the issue, but, see above, it seems to be off.
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Re: Space Shuttle

Postby GinGin » Tue Jul 25, 2017 7:53 pm

Thanks for your help guys and your kind word wlbragg ( I am a bit too much into Space Shuttle lately ahah)
I asked question to my friend.
So for SRB, depending on the frames, it can be correct or not, and it's game related?

Just to come back to my few questions Thorsten, are the max G/ EAS you implemented before break out those for contigency max limits LOC ( 4,1 G and 470 kts) ? By how far can we exceed them?
And do we do a forward RCS dump for RTLS also?
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Re: Space Shuttle

Postby Thorsten » Wed Jul 26, 2017 5:43 am

Thorsten, are the max G/ EAS you implemented before break out those for contigency max limits LOC ( 4,1 G and 470 kts) ?


The Nz hard limit assumed for breakage of a wing is 4.2 g. You may exceed it for fractions of a second, but not sustain any longer amount of time.

Actuator stall will gradually occur for qbar > 375 psf and degrade the effectiveness of the controls. There's no particular hard limit here - eventually (I think beyond 500 pfs?) control surfaces will be completely unable to move against the pressure, but if your attitude is 'good' at that point and your trajectory is rising into thinner air, the condition will resolve itself.

Whereas if your attitude is 'bad', the degraded effectiveness might mean you don't have enough authority to recover even way before complete actuator stall.

The structural limit of the orbiter against aerodynamical stresses is beyond 820 psf - you'll likely not get there before other bad things happen.

And do we do a forward RCS dump for RTLS also?


I haven't done it so far - I understood it's mainly a safety thing, the propellant won't be needed, rocket propellant is inherently dangerous so one gets rid of it.

It does affect trim in some way, but usually negatively (the OMS and MPS dumps make the Shuttle less tail-heavy, the forward RCS dump does the opposite - during an RTLS you have full aft RCS tanks, so you're quite a bit more tail-heavy than during a nominal entry) - it depends a bit on payload as well.
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Re: Space Shuttle

Postby GinGin » Wed Jul 26, 2017 5:50 pm

Very nice informations.

I see BFS is coming alive ahah, good good

Image

I found some old checklist from sts 1, nice to see difference with modern one, especially with gpc/crt interaction

At least radiator cold soaked procedure is still the same, almost

Image

Your sim allows us to follow check list close to the reality, love that.


Do you think it will be possible in the future to be able to do some IMU update with Star tracker etc, I find it pretty interesting and as you developped already very weel ST and Spec 33 it could be nice :)
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Re: Space Shuttle

Postby Thorsten » Wed Jul 26, 2017 6:16 pm

You can simulate an off-attitude condition in orbit, but the star tracker is largely an automated system, so if it is on and if the condition is not too far off, it'll be fixed automatically once the star tracker has a good fix in the camera.

You can watch that happen if you look very closely.

Only if the automatic system drifts too far off that a reliable camera fix can't be done, you need to perform a COAS.

So I'm not quite sure what procedure you want to see with the star tracker (you will get to experience bad things if the star tracker is off or broken).
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Re: Space Shuttle

Postby GinGin » Wed Jul 26, 2017 8:51 pm

I was thinking of spec 21 IMU and Spec 22 ST and update

To do some measure with ST with two stars, and see what is the difference with predicted position from IMU, then find a Delta angle torque on X, Y and Z M50 axis and Update IMU like in reality and have a more up to date State vector
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Re: Space Shuttle

Postby Thorsten » Thu Jul 27, 2017 3:30 am

Is there any halfway detailed documentation for this procedure? Seems easy enough to include it once we get a more detailed model of the IMUs.
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Re: Space Shuttle

Postby GinGin » Thu Jul 27, 2017 8:28 am

Yep, sent you a PM.
Thanks for considering :)

I was thinking of this because it's quite an important "normal" procedure and you implemented almost everything to allow it
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Re: Space Shuttle

Postby GinGin » Sat Jul 29, 2017 7:28 pm

Tried again RTLS with Failure just after SRB sep, works much better :)

Quick question on Spec 51, is it normal to see during ascent the ADTA value without atmosphere and probe deployed ?

Image
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Re: Space Shuttle

Postby Thorsten » Sat Jul 29, 2017 7:40 pm

Nope - it's a bug on my 'to fix' list, noticed the same thing trying to reproduce your last RTLS.
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Re: Space Shuttle

Postby GinGin » Sun Jul 30, 2017 5:29 am

Ah ok perfect if you saw it :)

I can't recall, is the same bug existing for normal entry OPS 3 or is it OPS 6 Specific ?
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Re: Space Shuttle

Postby Thorsten » Sun Jul 30, 2017 6:29 am

The forensics suggest that you would see air data always in OPS 3 and 6 regardless of whether the probes are deployed or not because the ADTA operational flag was not updated (the function calling it was never called).
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Re: Space Shuttle

Postby Thorsten » Mon Jul 31, 2017 11:51 am

@GinGin:

I realize if you're using the stable install, it'll be a while till you get to see bugfixes etc. because they all go to the devel repository (I fix only absolute mission-critical stuff on FGAddon).

In theory SourceForge should provide a tarball of the devel repository as snapshot if you want - otherwise you have to use GIT to grab a (preferably shallow) clone and updates:

http://wiki.flightgear.org/Howto:Start_using_git

Which takes some getting used to...

Otherwise I've now started on the IMU ALIGN page and simultaneously on the IMU system. Might still be a while, it's tedious...
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Re: Space Shuttle

Postby GinGin » Mon Jul 31, 2017 6:32 pm

Thanks for the update.

Ok, i am gonna give a look to the dev version.:) I hope to git good with Git ahah

No problem with IMU, it looks indeed quite tough, it s gonna be more realistic with the proper IMU align procedure combine with ST than to let ST update automatically the IMU and State Vector.
You plan to developp both Torque and Matrix alignement method ? I have to read again, dont understand really why there is two choice to align IMU. Two differents method but same results.

Anyway, thanks for always aiming for such a tremendous realism!!
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