Challenge Mid-Air Docking Challenge.

jangofett287

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Backstory:
On the OMP server the main cause of people stopping flying is running out of fuel. I set out to solve this problem through the employment of an aerial dock which could fool the XR2's refueling system into allowing pilots to refuel without actually landing. I threw together a sphere mesh in blender, whipped up a quick config file for it and UCD'ed it to a hovering arrow. After turning wind off I came to the conclusion that a stationary dock wasn't terribly practical, what with the need to hover to dock to it and all. I thought that if the dock was flying forward, it would be much more simple to dock with it.

Boy was I wrong...

The challenge:
In this scenario there are 2 XR2s. The 2nd one has my fuelsphere UCD'ed to its back. The sphere has no mass and causes no drag, so the XR2 is capable of flying perfectly straight. (with wind off at any rate) It is controlled entirely by airspeed and attitude autopilots. You are in the first XR2. It is also currently controlled entirely by airspeed and attitude autopilots. Your job is simple, dock with the docking port on the sphere atop the 2nd XR2.

Requirements:
Scenario requires the XR2 Ravenstar and Universal Cargo Deck.
You also have to turn damage off in the XR2's config, or your nose cone will be instantly destroyed by the airspeed.

I reckon this one is actually humanly impossible, but since I know people on this forum will manage it anyway, I included 2 scenarios, one with both XR2s moving at 200m/s, one with both moving at 300m/s. I tried for 1/2 and hour at both and couldn't do it. As is obvious from reading above I made this in the Orbiter 2010-p2 beta, but theres no reason it will not work on 2010-p1. If you want a real challenge get the beta and turn wind on. The challenge in that state should be considered like the secret secret boss of a Touhou game.
To all those who dare to attempt this, I have only one thing to say;
GOOD LUCK!
Your gonna need it...
 

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dgatsoulis

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I remember I had done something similar a few years ago.

XR2midairrefueling.jpg


IIRC it was @ ~8 km altitude with a speed of about 180 m/s.
Damage was on but at that altitude and speed the dynamic pressure was pretty low, so the XR2 didn't even give off a warning call-out.

EDIT: Here is the thread
The speed was 170 m/s and I had used FuelMFD for the transfer.
The only change was the addition of a docking port on the 747, exactly where the extended fuel line is.
 
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dgatsoulis

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I had some time to try out the challenge today. I had done midair refuelings in the past, so for me, it wasn't an extremely hard mission to perform.

The problem is that the setup doesn't really work. The dock on the child attachment (sphere→XR2) is possible but it doesn't affect the physics of the docked vessel.

For it to work, the dock should be on the XR2, not the sphere.
A lua script check that adds the docking port to the XR2 should be enough for it to work, without the need to change the config file of the XR2 that refuels the target vessel.

Here is a video of a successful "docking"

 

jangofett287

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That's some mighty fine flying there. I think we may have found a bug in the Orbiter core...
 

dgatsoulis

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Also, once you docked, did you undock immediately on purpose? Or is that a bug?

I did not undock. As far as Orbiter was concerned the XR2 was docked to the sphere the whole time. It isn't exactly a bug, since the sphere is attached to the XR2 via a child attachment.

A better way to do it is to have the sphere (with no docking port) for eye-candy and add a docking port to the XR2, but that means that you have to overwrite the default cfg of the XR2.


Or... you can grab the attached file from here.
I liked the idea for a scenario, so I wrote a script that handles the refueling a little bit better.

The "Tanker" is a Vanguard. The more the mass, the more the inertia, making the flight steady while docked.

I added a "fuel-line" mesh, an animation and a docking port on the Vanguard, so the refueling looks slightly better.

Everything, including the animation is accessed via lua script, no changes to the XR5Vanguard.cfg or to the XR5Vanguard.msh.

I added an autopilot script, so flying the XR5 is automatic. All you have to do is to set the autopilot to the prefered altitude and speed, switch focus to the XR2 and approach the "XR5-TANKER"

Once the distance to the XR5 is less than 1 km, an auto-sequence kicks in.
1. Cheesy dialogue with text/sound.
2. Addition of fuel-line mesh to the Vanguard and a 10 second animation to "extend" the fuel-line
3. Addition of a second docking port to the XR5, exactly where the extended fuel line is.

All you have to do is target the XR5-TANKER's dock2 (which was created after the animation) and dock.

Here is the whole sequence:

1. In the modules enable the LuaMFD (otherwise the autopilot doesn't work) and run the "Midair-Refueling(XR2-XR5)" scenario.

2. You begin inside the XR5 and the APU is on. Press INP on the left MFD and type: run('ap')

3. You just loaded the autopilot, now you need to enter two variables.
First the altitude. Press INP again and type: ap.alt(x)
x can be any number you want. I recommend a value from 7000 to 15000, but that doesn't mean that you can't go lower or higher than that.

4. Now the second variable is the speed.
Press INP again and Type: ap.spd(x)
Again x can be any number you want, I recommend a value between 250 and 350.

5. As soon as you hit ENTER the autopilot will start and it will take the XR5 at the chosen altitude and velocity. Everything is automatic, even the stow of the gear. Wait until the gear is fully stowed and switch focus to the "XR2-REFUEL-01".
(If you change focus before the gear is stowed, the APU will shut down and the gear will remain down).

6. Launch and catch up with the XR5. You can look at the text on the upper-right corner for some helpful info.
As soon as you are within 1 km, the auto-sequence will kick in (dialogue/animation/docking-port addition) and then you will be able to dock with the XR5 on the (just created) dock No2.

Here is a vid with the whole thing.


All the files are attached here. Unzip in your Orbiter directory and maintain directory structure. If you already have ProaudioRT.dll and lua51.dll from one of my previous challenges, simply overwrite (or skip) those two files.

Run the "Midair-Refueling(XR2-XR5)" scenario.

Additional notes:
-The XR2 and XR5 have their own config override .xrcfg files. They are set to default ISP settings.
-You will also find a playback of a successful docking in the playbacks folder.

Have fun
:cheers:
 

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Max Pain

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This is really hard. I tried it two times and both times run out of fuel. Unfortunately the autopilot of the xr5 gets a bit unstable (maybe when the fuel is low?) and it starts to oscillate up and down making everything even more complicated.

I have a question: Is it possible to control linear rcs while using the attitude hold autopilot of the xr2? Maybe this would help.
 

dgatsoulis

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This is really hard. I tried it two times and both times run out of fuel. Unfortunately the autopilot of the xr5 gets a bit unstable (maybe when the fuel is low?) and it starts to oscillate up and down making everything even more complicated.

I have tested the autopilot for a wide range of speeds and altitudes and it has been relatively steady for me. The oscilation is less than 20 cm and it works until the XR5 completely runs out of fuel.
I have even performed a supersonic refueling (~Mach 2.4) with no problems.

The way I have set it up, the XR2 should run out of fuel long before the Vanguard.

What altitude and speed combination are you using?

I have a question: Is it possible to control linear rcs while using the attitude hold autopilot of the xr2? Maybe this would help.

Yes... and no. Linear RCS helps a lot, but when you press 2 or 8 on the numpad you will change the attitude AP of the Ravenstar.
The way I do it, is to handle left-right with linear RCS and up-down with ALT-2 and ALT-8 (0.5° steps) on the attitude AP.

Don't forget to shut down the AF-Control surfaces when you are close.

Hope this helps.
:cheers:
 

Max Pain

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Thx a lot, that actually helped :)!



Although, after some fiddling, I found it easier to control up-down with the trim function.

About the autopilot: I used the combinations in your vid (alt 7000 m, spd 250 m/s). The instability might come from high framerate? This time I couldn't reproduce it.
 

dgatsoulis

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About the autopilot: I used the combinations in your vid (alt 7000 m, spd 250 m/s). The instability might come from high framerate? This time I couldn't reproduce it.

Could be. I don't think that my mediocre setup could ever be responsible for "high frame-rate" , but hyperphany is a dangerous thing.

Thanks for bringing up that to my notice. I'll try my best to make these challenges, accessable to the world.
 
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