Flight Question Aero-braking

cr1

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I'm trying to achieve this: Assuming my Deltaglider (the default one) is in a geostationary orbit around Earth (35'786km * 35'786km), I want to decrease the orbit size into (300km * 300km). What I want to do is to perform a deorbit burn at some point to decrease my PeA to somewhere in the atmosphere, so that at periapsis I would use the atmosphere to decrease my ApA to somewhere similar to 300km (aero-brake). Then I would fire again at apoapsis to raise my periapsis to 300km.

Does anyone know how I could do the aero-braking manoeuvre with the AeroBrake MFD?
 

Tommy

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I'm not sure AerobrakeMFD is going to be much help with this. Aerobraking in a glider usually requires flying inverted to stay in the atmosphere long enough to loose the velocity. Delta Gliders don't have much negative lift, but you can try using the Alt autopilot while upright and see if that will keep you in the atmosphere. Aerobrake won't show an ApA prediction while you are inverted, it assumes you'll stay inverted and thus stay in the atmosphere. You can areobrake untill your V is about 7.6 K, then roll upright and control your ascent using OrbitMFD to tune your ApA to 300k, or after you're upright, AerobrakeMFD will help with the ApA prediction. Press the <MOD> button until you see the line "Apo Alt" and when it gets to 300, start increasing pitch to maintain the 300k prediction until you're high enough that the drag doesn't matter, about 90k to 100k. Then just coast up to the ApA and circularise your orbit.


For an aerobrake, you'll want a PeA of 65k to 70k.
 

cr1

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OK, I'll definitely try that. Meanwhile, if I want to try the same thing with some "flammable" spaceship like the DGIV, wouldn't this make the ship explode? Going at ~9km/s (my guess) at 65km altitude sounds scary for a DGIV pilot...
 

RisingFury

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OK, I'll definitely try that. Meanwhile, if I want to try the same thing with some "flammable" spaceship like the DGIV, wouldn't this make the ship explode? Going at ~9km/s (my guess) at 65km altitude sounds scary for a DGIV pilot...


That's a bit extreme... try 70 km first... and keep an AOA of over 40°.
 

Tommy

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I'd try 70k alt first, but I suspect you can get a little lower. Haven't had a chance to check. If you come in inverted (and at that speed you'll skip out if you don't) start with a zero AoA, and use elevator trim to hold at 70k.

If you want to try a higher AoA, start with about 55 or 60 degrees inverted, otherwise you'll have too much lift and get pulled down into the atmosphere and burn up. There's a trick to getting both RCS and aerodynamic control surfaces working simultaneously - you'll need to do that to maintain the high AoA. First, while in Panel View, set the controls to AF. Then switch to "glass cockpit" mode using <F8>, and click on the RCS ROT button on the top left of the screen. As you get down to 70k, lower the AoA to increase lift so you can stay at 70k. Watch your VS and VACC closely. Expect to burn up a few times until you get this right.

I recommended the zero AoA and low AoA during the initial braking phase because it's easier to do, and easier to transition to upright when you get down to suborbital speeds. It does take longer - you get much less braking that way.

If you do go with the higher AoA, drop as low as you can until you get to about 8.25 Km/s, then start climbing back up to 70k. You'll want about 100 m/s of positive vertical speed when you transition to the low AoA before turning upright since you'll be passing through the DGIV's maximum lift AoA and it will pull you down.

You may want to check out my Home Direct tutorial, it shows the inverted aerobraking in an XR2. It'll be a little harder in a DGIV since you cant shift the COG, but the principle is the same.
[ame="http://www.orbithangar.com/searchid.php?ID=3660"]Home Direct[/ame]
 

Tommy

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If you don't want to use the DGIV (a great ship, don't know why you wouldn't) you can install Delta Tweak, which adjusts the stock DG's aerodynamics allowing for better re-entry:

[ame="http://www.orbithangar.com/searchid.php?ID=2648"]DeltaTweak 0.2[/ame]
 
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