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Re: Space Shuttle

Postby Thorsten » Tue Mar 01, 2016 5:40 pm

We now have a viable docking code, and for those who have looked a bit into the manual, there's some of the relative position now displayed on SPEC 33. You can approach and dock ISS, and then undock and leave (there's no real simulation of ISS done when outside of the bubble around the Shuttle yet - it's just loaded into the same orbit when the scenario is selected). I've also started to make the radar ranging via the Ku-antenna usable.

The rest of SPEC 33 is... interesting. Basically it deals a lot with the state vector of the orbiter. It's basically continuously computed via the signal of the IMUs, but this is an error-prone procedure, so it needs to be updated regularly - which is what uplink information, star trackers and COAS are for.

I've started to (optionally) divorce navigation information of the Shuttle from reality to model this better. In this concept, the instruments will show what GNC thinks is the position of the vehicle and the AP tracking and pointing routines will be based on this (wrong) state vector, whereas JSBSIm computes the real state vector.

So it might be that the instruments show you zero meters to ISS whereas in reality you're three meters distant. This can be improved by improving the propagated IMU state vector via the measured and filtered data, e.g. from the ranging radar, which will have a much lower error.

The ultimate and cool goal would be to e.g. implement the COAS attitude fixing procedure correctly - you point the Shuttle at a known star in the sky, center the star in a HUD aiming pattern, select the ID of the star in the avionics and then press attitude reference button when it's really centered. You do this for two stars, and the inertial attitude of the orbiter is fixed. I think if I get this to work, it'd be an incredibly cool feature.
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Re: Space Shuttle

Postby wlbragg » Tue Mar 01, 2016 6:21 pm

it'd be an incredibly cool feature.

Outstanding!

Can we use "any" of the pictures on NASA's website to textures the station?
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Re: Space Shuttle

Postby Richard » Tue Mar 01, 2016 6:33 pm

wlbragg wrote in Tue Mar 01, 2016 6:21 pm:
it'd be an incredibly cool feature.

Outstanding!

Can we use "any" of the pictures on NASA's website to textures the station?


Last time I checked all photos etc published by NASA are public domain (unless otherwise stated).
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Re: Space Shuttle

Postby Thorsten » Wed Mar 02, 2016 6:14 am

There must be dozens of free textured ISS models around - I know Celestia has an ISS addon, so has Orbiter,... They seem to be all based on the NASA 3d models, so the most promising avenue to me seems to ask the authors of the texturing job whether we can have permission to use it under GPL.

I don't want to spend too much time with the lowres ISS version I'm using for flight testing - there's a higher res mesh in the repository which just needs to be moved to the coordinate origin - if we manage to strip a few vertices of it (seems to be a bit on the costly side) and get a texture pack, from somewhere, that'd be terrific.

If I remember correctly, there's also a 76 MB sized very hires version of ISS on the NASA 3d model page, but frankly, that seems an overkill for our purposes.
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Re: Space Shuttle

Postby wlbragg » Thu Mar 03, 2016 1:39 am

What property does [shift] + g set?

I think I understand most of the gear deploy except the key command shift+g.
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Re: Space Shuttle

Postby Thorsten » Thu Mar 03, 2016 6:34 am

Shift-g is the default key command of FG - it ends up in /fdm/jsbsim/gear/gear-cmd-norm and is processed in shuttle.xml, not as a system. There's a drag calculation associated with it.
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Re: Space Shuttle

Postby wlbragg » Thu Mar 03, 2016 8:26 am

I though that was what it was, turns out I had a typo. But I can't trigger /fdm/jsbsim/gear/gear-cmd-norm via property assign regardless. How do I trigger the shift+g key combination using a property-assign or a nasal assignment would work as well.

Following is the code I am trying to use.
Code: Select all
    <!-- Landing Gear Down Commander "Button" -->
    <animation>
        <type>pick</type>
        <object-name>landing_gear_down_cmd</object-name>
        <visible>true</visible>
        <action>
            <button>0</button>
            <repeatable>false</repeatable>
            <binding>
                <command>property-assign</command>
                <property>/fdm/jsbsim/gear/gear-cmd-norm</property>
                <value>1</value>
            </binding>
        </action>
        <hovered>
            <binding>
                <command>set-tooltip</command>
                <tooltip-id>beacon-switch</tooltip-id>
                <label>Deploy Gear</label>
                <property>landing_gear_down_cmd</property>
            </binding>
        </hovered>
    </animation>
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Re: Space Shuttle

Postby Thorsten » Thu Mar 03, 2016 11:07 am

Because it's set by the FG interface - try

Code: Select all
setprop("/controls/gear/gear-down",1);
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Re: Space Shuttle

Postby wlbragg » Fri Mar 04, 2016 8:13 am

The chute arm and deploy buttons are supposed to be pushed simultaneously to deploy the chute. As we don't really have a way to do that in the sim, I'm open for suggestions.

Some options ....

Make it so if you don't press each button within "X" seconds of each other it won't deploy?

Make it same as the gear, arm then deploy?

Make it deploy if either button is pressed?
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Re: Space Shuttle

Postby Thorsten » Fri Mar 04, 2016 8:24 am

Make it in sequence - arm first, then deploy.
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Re: Space Shuttle

Postby Thorsten » Fri Mar 04, 2016 3:07 pm

Proximity ops with semi-realistic state vector management is slowly coming into shape... Approaching ISS pointing orbiter -z direction towards the station.

Image

SPEC 33 shows the approach parameters - (list below SV SEL) for instance range (RNG) and approach rate (Rdot).

Image

However, this is based on internally propagated state vectors for the Shuttle and ISS which may or may not reflect the real state. Now the Ku-antenna is added into the fray, providing actual measurements for the range, approach rate, inertial angular position in the sky and apparent angular movement:

Image

It becomes apparent that measured range differs from propagated range. By switching the filter to use the radar ranging data we can provide information for a filtered state vector characterized by the various residuals displayed in the lower half of the screen.

The filter could now be used to be displayed in the approach data column rather than the propagated data, or it could replace the state vector if we believe it to be better.

Small charming detail - the antenna actually points, i.e. ceases to track the TDRS network and selects ISS instead.

Image
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Re: Space Shuttle

Postby wlbragg » Fri Mar 04, 2016 9:05 pm

Regarding the drag chute, can anyone verify exactly how the end of the animation works, as in when it gets cut loose?

Is it simply based on /gear/rollspeed-ms and automatically does a translate animation of the parachute model when a low enough speed is achieved?


I put the code in a test-bed that I could run quickly and change all the values, so I now know what it is doing. I'm refactoring it to make it work correctly.
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Re: Space Shuttle

Postby Thorsten » Sat Mar 05, 2016 6:27 am

I think the translation animation for the dropped chute is a bad idea (we inherited that from the Space Program Shuttle version) as one can observe when using the nose wheel steering - I'd like to replace it by a simple object placement at a definite location.

Also, I have entertained the notion of writing a deploy/fold shader for it to see an opening animation - but that's just for information, I haven't done anything on it yet.
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Re: Space Shuttle

Postby wlbragg » Sat Mar 05, 2016 6:45 am

I think the translation animation for the dropped chute is a bad idea


OK, I made a "deploy-button" activated timer to simulate the pilot chute for apps 6 seconds then the extended full sized until the jettison button is depressed. I can drop the chute (place the model) at that point. Later on, we could even get fancier and model the pilot chute separate from the main with some shader effects in the middle of all of it.

So I am removing the speed based translations as they aren't really appropriate anymore.

It will have some ground speed checks built into it to catch any anomalies (like trying to deploy the chute when the Shuttle isn't moving). Until you do some kind of shader effect, I think what I already have written will suffice.

Speaking of shader effects, you know what would be really cool, a better (stronger) touchdown vortex! That came to mind the other day while I was testing the gear deploy buttons.
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Re: Space Shuttle

Postby Thorsten » Sat Mar 05, 2016 7:49 am

Speaking of shader effects, you know what would be really cool, a better (stronger) touchdown vortex!


Remind me - why can't we do this with the techniques we have?
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