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Re: Space Shuttle

Postby Hooray » Thu May 12, 2016 6:13 pm

does the --trace-read/write thing still work, what is it saying for you when you run the shuttle displays with --trace-writes=/canvas ?
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Re: Space Shuttle

Postby Thorsten » Fri May 13, 2016 4:36 am

Sorry, I know my numbers reasonably well (and I haven't seen any from you). I don't want to spend more time for refined benchmarks I'm not really interested in just to know who's king of the hill of property access:-)
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Re: Space Shuttle

Postby Hooray » Fri May 13, 2016 9:55 am

no need to apologize - the parameter I suggested, didn't work for me when I tried it - too bad, it would have been useful for other things, too ...
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Re: Space Shuttle

Postby Thorsten » Sat May 14, 2016 2:36 pm

The avionics now supports ATO and AOA aborts - technically these are mostly particular versions of OMS burns, and the corresponding targets are guesstimated by a script when using the abort target function on OPS 104 via item 35.

The targets are

1: apoapsis raising OMS-1 burn aiming at 105 miles

3: circularization burn for ATO
4: nominal entry trajectory burn for AOA
5: shallow entry trajectory burn for AOA (untested)

The abort procedure wiki article has some more information, but in general this is not the easiest subject and I recommend a look into the manual.

(Don't ask me how to know what abort to fly under what conditions - in reality that wasn't computed aboard the Shuttle but by mission control and there were mission-specific cue cards aboard in case there's no communication. It depends on payload and ET version, launch azimuth, launch site latitude and the time of engine failure making the abort necessary. There's probably tools or tables available somewhere, but I don't actually have them... so you need to experiment a bit...)
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Re: Space Shuttle

Postby Thorsten » Mon May 16, 2016 5:26 pm

Image

We've got company in orbit...

(I've made the orbital motion code such that you can instance several objects aircraft-side with their orbital elements - the actual close-up sim and interaction model then has to reside aircraft-side, but the far-away dynamics is generic. So we could also do this for Vostok.

There'll eventually be rendezvous planning software and the handover, so you can specify a mission to launch to ISS or HST and rendezvous with it eventually.
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Re: Space Shuttle

Postby wlbragg » Mon May 16, 2016 5:40 pm

:Applause:
Kansas(2-27-15)/Ohio/Midwest scenery development.
KEQA (2-27-15), 3AU, KRCP Airport Layout
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Re: Space Shuttle

Postby Hooray » Mon May 16, 2016 5:50 pm

Nice, note that, if there is any sort of "meta information" that would be useful while developing/debugging this (without necessarily having the property browser visible), you can register a tooltip to display a popup when hovering over, or clicking, the ISS/shuttle symbols using something along the lines of:

Code: Select all
CanvasElement.addEventListener("mouseover", func() {
  gui.popupTip("mouseover tooltip says", getprop("/sim/fg-root") );
});


Such a popup could then display element specific information (altitude, speed etc)

(whereas CanvasElement should be referring to the group of the symbol you're using to render the shuttle/ISS symbols)

http://wiki.flightgear.org/Tooltips
http://wiki.flightgear.org/Canvas_Event_Handling

PS: There seem to be plenty of ISS icons available online in the form of public domain SVGs (e.g. see wikimedia commons)
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Re: Space Shuttle

Postby Thorsten » Thu May 19, 2016 5:34 pm

Been standardizing coordinate systems today such that longitude of ascending node means the same thing for Shuttle and ISS. I think I'll code all in JSBSim inertial and just make the instruments show M50 on request - otherwise it's close to impossible to debug.

If there's anyone who has a solid understanding of how SPEC 34 (orbital targeting) works in reality, please speak up. My current plan is to make this a Hohmann transfer orbit calculator with some additional support for faster, not that propellant efficient transfers and inclination corrections, but from the description, the real thing appears to do a lot of which I'm not quite sure how I'd use it.

(Come to think of it, the Shuttle avionics is definitely the wrong place to learn the basics of orbital mechanics... it's all not very visual)
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Re: Space Shuttle

Postby Hooray » Thu May 19, 2016 6:04 pm

Thorsten wrote in Thu May 19, 2016 5:34 pm:(Come to think of it, the Shuttle avionics is definitely the wrong place to learn the basics of orbital mechanics... it's all not very visual)


I cannot comment on the specifics of the shuttle, let alone the physics/maths involved in all this, but I am more than willing to help you come up with a visual representation of it all, e.g. by extending the existing trajectory map that you have created already.

As you may remember, that was one of the original reasons for me getting involved in the discusssion, i.e. creating a reusable "trajectory map" that could help people develop these features, regardless of the aircraft/spacecraft in use - I think, we actually discussed the Vostok/SpaceShip One specifically back then.

However, I don't know what an "ideal" representation would look like - i.e. it would probably be something to support spatial awareness ?

Maybe there's something in Orbiter that we could learn from ? Any screenshots of orbiter maps ?

For instance, something like the following should be possible to re-create using Nasal and Canvas, animating it using trajectories of actual FlightGear objects:

https://www.eeb.ucla.edu/test/faculty/n ... ensors.htm
Image

Here's a related discussion I found online, which specifically mentions visualization of space trajectories:
http://space.stackexchange.com/question ... lar-system
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Re: Space Shuttle

Postby Thorsten » Fri May 20, 2016 5:04 pm

Ideally you would visualize it in 3d space, with the orbits as lines projected around Earth and the ability to turn and zoom.

Otherwise the two most useful projections are groundtrack (for inclination, node crossing and what you should see looking out of the window) and the projection orthogonal to the orbital plane (basically the plot you show).

There's no technical issue preventing me from doing the projections at least (Orbiter uses a series of similar generic MFDs), but my priority with the Shuttle really is to re-create the original avionics. I was more commenting on the fact that the avionics makes it hard to really know your orbital state - there's no moving map, inclination isn't displayed at all, node crossing time is on a different display than apoapsis and periapsis - the Shuttle doesn't seem to have a single summary display 'this is my orbit'.

Of course, it doesn't also have any real capability to change orbit, so your orbit is always the one you launched into modulo small corrections.

So from a pedagogical POV the Shuttle is a poor vehicle to learn the basics of orbital mechanics, and the Orbiter Delta Glider with it's vastly higher Delta v reserves is much better for learning (Vostok is even less suitable, it hardly has any maneuvering capability).
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Re: Space Shuttle

Postby Hooray » Sat May 21, 2016 10:51 am

Thorsten wrote in Fri May 20, 2016 5:04 pm:Ideally you would visualize it in 3d space, with the orbits as lines projected around Earth and the ability to turn and zoom.


I think I mentioned this previously in this thread when Richard was talking about animating the PFD (sphere): I actually have experimental code that also allows Canvas to be used on conjunction with arbitrary 3D models.

Basically, what it will do is add a new Canvas "element type", called "model", where you can specify a filename of a 3D model, and then it will add the whole thing under a osg::PositionAttitudeTransformMatrix, so that you can freely position/scale and tranform the whole 3D model arbitrarily by accessing a few properties (that are then mapped to the osg::PAT methods to rotate, scale etc) - several elements can be added to the same "scene"

http://wiki.flightgear.org/Howto:Extend ... _3D_models
ImageImage

For now this may be a little offtopic, but it may make sense to keep this in mind, especially given bugman's "directional moonlight" effort, i.e. conceptually you could even load your EarthView models/textures into the same scene, and "animate" it using a handful of properties (obviously, there are not the conventional FG light sources (sun) or the skydome etc)
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Re: Space Shuttle

Postby erik » Mon May 23, 2016 9:43 am

Thorsten,

I've pushed the latest JSBSim code to git.
In the change log there was one suspicious change which might affect the solid rocket booster separation of the space shuttle.

Could you check that after separation they still have zero fuel?

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Re: Space Shuttle

Postby Thorsten » Mon May 23, 2016 11:12 am

I'll keep an eye on this.

It will probably be a few days till I pull the latest FG since I'm currently in the middle of some nasty orbital targeting problem that turns out to be a mess since analytical expressions aren't good enough to the desired accuracy, and I don't want to complicate my life by version troubles...

Do you mean at regular separation (aka when they're actually empty) or premature separation?
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Re: Space Shuttle

Postby erik » Mon May 23, 2016 11:29 am

I think we discussed premature separation on the mailing list, so that one.

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Re: Space Shuttle

Postby Thorsten » Thu May 26, 2016 5:31 pm

Yay, the nitty-gritty details of orbital mechanics really suck...

I'm still trying to compute transfer orbits. In theory (i.e. starting from a circular orbit on point mass gravity) it's all a piece of cake,

Unfortunately JSBSim neither uses point mass gravity nor do we necessarily have a perfectly circular orbit. The corrections (even for apoapsis and periapsis the same within 5 km) are large enough such that you miss easily by 100 km. That's not much by normal orbital distances, but too far to 'just' fly over.

So it requires a numerical prediction of the trajectory. This needs to be done at high temporal resolution to avoid numerical drift and hence be split across multiple frames (I'm forwarding some 5 seconds per frame). Then the calculation takes time... perhaps some 4 seconds. What I figured out today is that computing distance to target without taking the calculation time into account causes an offset of some 40 km in the result - because stuff in orbit moves fast.

Now the code latches onto the wrong solution - it gets the closest distance when the Shuttle on the rising trajectory passes right underneath ISS, rather when it reaches apoapsis and ISS comes from behind 15 minutes later. So the whole aim has to be refined.

All that before messing with the lateral dynamics when the inclination isn't 100% perfectly matched.

Okay, I wonder if anyone will ever actually use the orbital targeting screen at all, because it's really about as non-intuitive as it gets...
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