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Space Shuttle - Development

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Re: Space Shuttle - Development

Postby Thorsten » Mon Dec 31, 2018 3:03 pm

Seems I have a numerical Lambert solver running...

For specified ignition times TIG 1 and TIG 2 , this computes a 2-burn transfer solution via a numerical fit (i.e. J3 gravity and finite burn duration taken into account).

Here's a range of trajectories in target-relative coordinates for the interceptor starting on a phasing orbit 20 km lower using TIG 1 of 8150 s for different values of TIG 2.

Image

The first transfer is really quick and hence quite pathological - it uses large Delta v values to get there so quickly, so the deceleration burn isn't perfect and there's a residual relative motion with the target. The 11000 s solution already goes through a higher apsis and intercepts the target from the front.

The tool spits it out all nicely:

Code: Select all
Parameters of burn: Lambert_1
TIG             : 8150
Lambert 1
Dx (prograde)   : 6.93143
Dy (normal)     : 0
Dz (radial)     : -6.34362

TIG             : 12000
Lambert 2
Dx (prograde)   : 4.66364
Dy (normal)     : -0
Dz (radial)     : 11.8419


The fit is also able to null normal errors when this is possible - when not, the normal error can be disabled.

For too unreasonable transfer problems, the fit refuses to converge.
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Re: Space Shuttle - Development

Postby amalahama » Mon Dec 31, 2018 5:59 pm

Hi!

Is it implemented the Ku antenna use as rendez vous radar in the FG Shuttle?

Happy new year!
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Re: Space Shuttle - Development

Postby Thorsten » Mon Dec 31, 2018 6:05 pm

Yes - read the manual for how to do it :D
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Re: Space Shuttle - Development

Postby GinGin » Tue Jan 01, 2019 4:37 pm

Outstanding.
Can't wait to test that
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Re: Space Shuttle - Development

Postby amalahama » Tue Jan 01, 2019 8:14 pm

Thorsten wrote in Mon Dec 31, 2018 6:05 pm:Yes - read the manual for how to do it :D


Ah yes, I meant also the rates indicators and range display in the aft panel, close to the COAS.

The COAS would be a nice add for 2019, together with a functional CCTV :D

Image
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Re: Space Shuttle - Development

Postby Hooray » Tue Jan 01, 2019 10:23 pm

amalahama wrote in Tue Jan 01, 2019 8:14 pm:The COAS would be a nice add for 2019, together with a functional CCTV :D


FWIW, at least for the time being, exterior views rendered onto a cockpit screen are basically not possible to do, i.e. blocked by pending patches to be reviewed, i.e. either the original Canvas "camera-view" element prototyped by Icecode GL or the latest iteration of it, called the Compositor.

Fortunately, both, Stuart[1] and James[2] mentioned that they'd be willing to get those features reviewed for integration. Stuart specifically mentioned that he'd need this feature for his FG1000 PFD (which features synthetic vision support), but there are many other aircraft/developers that have some sort of external view support these days (tail-cams, gear view, FLIR/night vision), and even historical aircraft may benefit from that feature, because it could be used to implement support for "mirrors".


[1]: viewtopic.php?f=71&t=23929&&start=30#p317967
[2]: https://sourceforge.net/p/flightgear/ma ... /36355833/
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Re: Space Shuttle - Development

Postby wlbragg » Wed Jan 02, 2019 2:25 am

I just pushed a new bit of eye candy to development. At Thorsten's suggestion I created a very basic plasma burn texturing scheme to the exterior of the shuttle. Using the existing dirt map capabilities of ALS there is now code that uses the property fdm/jsbsim/systems/thermal/thermal-stress to place a dirt map over the exterior surface. There is five levels of discoloration possible. A "nominal" re-entry should be level one, and from there it gets progressively more discoloration as you put more thermal stress on the exterior.
One area I could stand some education in is what is nominal and what is the outside limit of that property.
During testing I saw an average of .8 as the final stress value but as high as 1.4 and still no failure. So if test pilots would please watch that property during their nominal and off-nominal re-entries and report back I would appreciate it.
As always the texture could be improved upon but is good enough for now.

To add to the discussion about automated flights and missions. Believe it or not, the re-entry startup variant is about as simple as it gets and gets you a nice long flight from entry interface to wheel stop.

All that is required to land at Vandenberg Air Force Base is to start the sim using the startup variant of "Re-entry".

In options add
--lat=0.0
--lon=-160.0
--heading=45

As soon as your in the Shuttle click on "Space Shuttle", "Entry Guidance", select "Vandenberg Air Force Base", "Activate". Then on panel F2 click on "Auto" pitch and "Auto" roll/yaw. The computers will do the rest all the way to the "Hack" (basically line you up facing the runway). It even switches you back to CSS when the time comes. From there it is your responsibility to land. The only other keys required to land are CTRL G for arming the landing gear and Shift G to drop the gear, the computer even tells you when to arm them. You should drop them late to reduce drag.
Don't be fooled by the approach and think you are not coming in correctly. You will cross in front of the runway (perpendicular) before making a 270 to line up out over the ocean.
This gives you a good deal of time to sit there and enjoy the ride. Absolutely fascinating!


Here are some shots taken during my testing.

Nominal burn discoloration
Image

Same from a different angle.
I also did some re-texturing to get rid of some heat glow in the wrong areas.
Image

While I was at it I added a lightweight interior shell to hide the interior side of the fuselage which was showing the heat glow where it shouldn't have been.
Image

You used to be able to see heat glowing in the interior from this angle. Also the forward jets used to incorrectly glow.
Image

I just thought this was a really cool picture, it also shows the discoloration from re-entry heat.
Image

Another angle.
Image

Finally, a successful landing, even though I used the entire runway, second attempt had a better outcome.
Image
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Re: Space Shuttle - Development

Postby Thorsten » Wed Jan 02, 2019 7:20 pm

Ah yes, I meant also the rates indicators and range display in the aft panel, close to the COAS.


I'd assume they're duplicates of the SPEC since there is no different information to be had. You can of course have those - but no CCTV image to go with them.

Still, I'd prefer to get the renderzvous math under control first.
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Re: Space Shuttle - Development

Postby Hooray » Wed Jan 02, 2019 7:58 pm

actually, thinking about it and for the sake of completeness: if someone really needs that CCTV image for some kind of home cockpit, it would still be possible to come up with a workaround: The Canvas system does support fetching imagery over http, i.e. Stuart's FG1000 is using that method to fetch tiled maps from a web server (slippy maps).

Also, FlightGear itself provides support for hooking up multiple fgfs instances in a master/slave, and a way to fetch screen shots over httpd (via Torsten's mongoose work) - in other words, a 2nd fgfs instance slaved to the master instance should be able to send live imagery of the corresponding view to the master instance, where it could be displayed via the Canvas system (LAN-only).

Again, it's a workaround obviously - but if someone really wants the feature, and is unable to patch/rebuild fgfs, it might still be a good compromise.
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Re: Space Shuttle - Development

Postby Thorsten » Wed Jan 09, 2019 3:33 pm

At least within a test suite, I have a lightweight version of the Lambert solver now in the Shuttle targeting manager. Still needs to be interfaced with the avionics and the actual orbiting object...
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Re: Space Shuttle - Development

Postby amalahama » Wed Jan 09, 2019 6:43 pm

Excelent! Is it a feature also included on the original shuttle? If negative, how do you envision the interface?
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Re: Space Shuttle - Development

Postby GinGin » Wed Jan 09, 2019 11:48 pm

Awsome work on both Lambert solver and 3 D external effects

@amalahama: It is a feature of the Shuttle, Spec 34 in GNC major function. You can have a look into the dps dictionary on the spec 34 to see the stuff.

It resolves Lambert équation for last part of rendez vous , fed by data coming from Star tracker and rendez vous radar that gives distance, azimuth , relative speed and acceleration relative to the target object ( ISS or satellites )
Those data are already available in Spec 33 page when approaching ISS in ISS scenario

It allows some burn for fine tuning on last orbits before rendez vous. ( horizontal distance less than 100 km from the target )

Some example of how work that display partially implemented in SSU ( last part of the sum up )

https://www.orbiter-forum.com/showthread.php?t=40283
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Re: Space Shuttle - Development

Postby Thorsten » Fri Jan 11, 2019 1:39 pm

The availability of on-board targeting reveals a rather knotty problem - it isn't exactly easy to target an object on an analytical orbit from a J3 orbit.

We do not have a second instance of JSBSim running that would provide a long-term stable orbiting object. away from the Shuttle. So the idea at some point was to let the object be computed analytically in the far zone and switch to a near-zone propagation that is corrected and stabilized by the Shuttle motion simulation.

Sadly, the y-targeting in that situation becomes very difficult because the J3 plane wobbles whereas the analytical plane does not - so dependent on circumstances there can be spurious 20 km gaps opening, which forces rather large and ugly DVY components in the burn solution.

I'm not quite sure how to solve this, have to sit down and think. I'm fairly sure it can be alleviated to some degree, but without a second FDM running probably not really solved (?)
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Re: Space Shuttle - Development

Postby GinGin » Fri Jan 11, 2019 4:42 pm

Wow, indeed, not easy problem to solve :/

And if we stick to a more basic Spherical Gravity model without Harmonics, is it easier for the calculations?
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Re: Space Shuttle - Development

Postby Thorsten » Fri Jan 11, 2019 5:18 pm

Sure, the calculation is easier. But in the end, JSBSim will move the Shuttle in J3 gravity :? So we have to deal with that.
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