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Space Shuttle - Development

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Re: Space Shuttle - Development

Postby Thorsten » Mon Jan 21, 2019 11:07 am

Meh... the ISS close-range simulation is apparently not stable against unusual frame delays (such as Earthview at high res might cause)... Need to do something there.
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Re: Space Shuttle - Development

Postby GinGin » Mon Jan 21, 2019 1:41 pm

Argh, What happens ? ISS is flickering with fps?

Very nice addition for Rinc and Imperial units :)
I have a lot of fun trying to tweak launch window.
In my scenario, Shuttle is on the ground with a LAN around 254 °

I set ISS to 254,40 ° LAN, 51 ° INC

Launch when ISS is almost above us with the Lan guidance target ( which works quite well, Inc is almost spot on, and LAN plus or minus a degree after MECO)

My best launch so far
Lan Guidance was perfect on that one, it depends of the launch :)


Image

I would say not even 0.05 ° of Rinc :)
The Y off set on canvas map is pretty useful to find the next node with two orbits

After the Launch, ISS was 20 ° in front of us. Good position for a fast rendez vous in a couple of orbit


@Thorsten: I pulled the last dev version, I have the rendez vous Canvas which seems to be freeze ( since yesterday)
Did you encounter the same?

Image
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Re: Space Shuttle - Development

Postby Thorsten » Mon Jan 21, 2019 1:53 pm

It probably writes an error when it freezes up, and that's probably because I didn't push something that's required (?)
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Re: Space Shuttle - Development

Postby GinGin » Mon Jan 21, 2019 3:19 pm

I have that since the pull of yesterday ( the one introducing Rinc)

I got those Nasal errors ( first one seems to be linked to rendez vous canvas)

Image

Image
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Re: Space Shuttle - Development

Postby Thorsten » Mon Jan 21, 2019 3:38 pm

The display (like the avionics) communicate with the orbital target - which is simulated by $FGData/Nasal/orbital_target.nas - if you have a stable FG install, that won't provide the required interfaces yet, so you could get just that file from the FGData repository and replace it.

Probably that's the issue.
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Re: Space Shuttle - Development

Postby eatdirt » Mon Jan 21, 2019 3:52 pm

Meh... the ISS close-range simulation is apparently not stable against unusual frame delays (such as Earthview at high res might cause)... Need to do something there.


That may not be relevant, but I mention it in case it is.

I still do observe satellite drifting much faster than they should at high altitudes. It also seems to me that when the ET tank separates at high altitude, there is a "jump" in position between the tank attached to the Shuttle and the tank separated just after. I do not see this in nominal orbits, such as starting with --aircraft=SpaceShuttle-orbit. In the nominal case, everything goes smooth. And indeed, rendering the full Earth at high altitude is tough, sometimes framerate drops to 0 for a few seconds!
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Re: Space Shuttle - Development

Postby Thorsten » Mon Jan 21, 2019 4:27 pm

I still do observe satellite drifting much faster than they should at high altitudes.


I stubbornly hold on to my explanation - the approximation being used is derived for low orbits, it doesn't work overly well at 2000 miles out. I'm aware of the issue, but it's not flagged as important.
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Re: Space Shuttle - Development

Postby GinGin » Mon Jan 21, 2019 6:36 pm

Thanks, you mean FG DATA from the dev branches of FG here: https://sourceforge.net/projects/flightgear/files/unstable/ ?
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Re: Space Shuttle - Development

Postby Thorsten » Mon Jan 21, 2019 6:39 pm

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Re: Space Shuttle - Development

Postby GinGin » Mon Jan 21, 2019 6:57 pm

Fixed, thanks again.
Weird it only appears with the pull of yesterday, it was working before.
Is it the only file that is important in the unstable version?
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Re: Space Shuttle - Development

Postby legoboyvdlp » Mon Jan 21, 2019 7:21 pm

The ET seems to have gone mad:
Image

I did a rapid pitch around to get a photo in the overhead window; after turning another 270 deg back to prograde, the ET is climbing away and I am behind it...?

I am quite low, so descending, but I don't think I'm descending that fast. Am I?
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Re: Space Shuttle - Development

Postby GinGin » Mon Jan 21, 2019 8:56 pm

@Thorsten: You really made a great work on Rendez Vous. It is really working already well.
Starting from your scenario, I am playing with small burn and spec 34 to get close, trying some delayed final rendez vous with negative catchup by increasing apogee etc.
Really nice.
I am quite close to Nasa Rendez vous schedule data :)


I have got one or two things to clarify.
Mainly the conventions taken for ISS LVLH frame.

I know we discussed already the Z axis ( which is inverted with the +Z), but no worries with that ( we know it)
I have a question with the +X Axis ( which for me is normally positive in the prograde velocity vector of the object from which it is based)

Just to confirm, the frame you constructed is orientated like this:

Image


Item 7 for downrange at ignition time and item 18 should have positive value if we want to be right ( behind) ISS, it is correct ?

I
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Re: Space Shuttle - Development

Postby Thorsten » Mon Jan 21, 2019 8:56 pm

Weird it only appears with the pull of yesterday, it was working before.


No, it wasn't - SPEC 34 wouldn't have worked (that needs inertial speed as well).


I did a rapid pitch around to get a photo in the overhead window; after turning another 270 deg back to prograde, the ET is climbing away and I am behind it.


Rapid may be the keyword - the Shuttle doesn't do 'pure' rotations or translations, so doing a rapid rotation could potentially give you net momentum (and you feel more drag than the ET of course...)

But I don't know for sure.
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Re: Space Shuttle - Development

Postby GinGin » Mon Jan 21, 2019 9:51 pm

Trying some phasing

Image

Hello ISS

Image


Lot of stuff to learn with LEO still.
Non spherical gravity makes the rendez vous quite challenging, like it :)
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Re: Space Shuttle - Development

Postby Thorsten » Tue Jan 22, 2019 7:21 am

I have a question with the +X Axis ( which for me is normally positive in the prograde velocity vector of the object from which it is based)


I guess the signs are done to re-produce the visuals of the relative motion plots I've seen - somehow there the chaser comes typically from the lower left, so if I plot that into a normal coordinate system with a plot program, that's the region of negative Z and positive X.

The +X axis remains the normalized velocity vector - just what is subtracted from what to get a distance is flipped. But the normal axis is the dot product of prograde forward and radial outward unit vectors.

NASA made a royal mess of the whole thing in my opinion... if you're used to just doing math, it's really weird what they define and plot.

But the offsets should pretty much follow the sign convention in the rendezvous dialog plot - a positive X will get you 'behind' ISS, a negative Z should get you 'below' ISS, and I suspect a positive Y should get you 'right' of ISS.
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