Flight Question Earth ReEntry

jambooger

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Open to suggestions from you veterens. Im trying to perfect my Earth Reentry and land at KSC. This is what Ive been doing in my DGIV.

Starting from a 395 km circular orbit

I first align my plane with KSC using BaseSync.

Then I use Aerobrake and when I am 180 degrees of KSC I burn retrograde untill my reentry angle is 1.2 degrees according to my DGIV display.

I then use the DGIV Auto-Reentry Auto Pilot and manually adjust bank angle to direct toward the KSC target on my HUD.

When the Autopilot completes I can be anywhere from 100 km's to 500 km's away from KSC.

Is there a more precise way to do this?

Thanks!
 
Open to suggestions from you veterens. Im trying to perfect my Earth Reentry and land at KSC. This is what Ive been doing in my DGIV.

Starting from a 395 km circular orbit

I first align my plane with KSC using BaseSync.

Then I use Aerobrake and when I am 180 degrees of KSC I burn retrograde untill my reentry angle is 1.2 degrees according to my DGIV display.

I then use the DGIV Auto-Reentry Auto Pilot and manually adjust bank angle to direct toward the KSC target on my HUD.

When the Autopilot completes I can be anywhere from 100 km's to 500 km's away from KSC.

Is there a more precise way to do this?

Thanks!

Things to try:
  • Wait until you are closer.
  • Higher entry angle < 2.0°
  • Make sure your cross track distance is as close to zero as possible.
  • Fly the reentry manually(takes practice)
 
Is itpossible for the DGIV to survive a 2° reentry?
(Edit: ahhh, you mean less than 2°, sorry^^)

@Jambooger: If the range is to big of your reentrys try to reentry with the same weight at all times ... I don't know exactly but maybe Orbiter takes your Vessel mass into account.

Greetings!
 
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You can directly get it from Base-SyncMFD ;) It is the white Number, which should be under 1k for a spot-on-Path ;)

Greetings!
 
You can directly get it from Base-SyncMFD ;) It is the white Number, which should be under 1k for a spot-on-Path ;)

Greetings!


Oh ok, thanks. Ive got that very low. Im not having a problem with side to side distance. I get that spot on. I just want to be able to calculate my altitude when Im very close to the base.
 
The only reliable way for me to hit the spot is manual or at least realtime-controlled reenty (it is possible for XR vessels to gradually change AOA during reentry, DGIV has the same ability but with lesser precision).
 
yes i do manual reentry as well, actually I don't use base sync, I use an equation program i developed on my calculator. I managed to accomplish accurate reentries by doing some test runs and taking data points on velocity and altitude to get the reentry profile for my dgiv which i standardized for my missions. then I just made a calculation of distance from the base to reenter at combined with a delta v number and voila!

also if you get more experienced, and you can tell that you are coming up short while you are reentering, lower your AoA a bit so that your wings begin to lift, this will flatten out your trajectory and let the vessel keep some speed. be careful though, if you lift too much you will come up short from what i can only compare to a kind of reentry stall. also if you are going too fast, raise angle of attack so that your vessel falls faster and receives more friction, it should help a little, but i've found overshooting is much more difficult to remedy than trying to keep some speed by easing your deceleration.

---------- Post added at 07:24 PM ---------- Previous post was at 07:22 PM ----------

also it is easy to burn up trying to slow down faster, of course
 
Also one of projections of graph/map program of AerobrakeMFD can show you a nice overview of your reentry profile and how it changes according to your actions in realtime. It also show you distance between your projected impact point and defined target base, so if your trajectory passes right over the base you don't even need to use that map projection where digits are messing up with map background.
 
The DGIV's fully automatic re-entry auto-pilot isn't accurate enough for the kind of precision needed for a "dead-stick" landing. While you have some contrl over direction, you don't have any control over distance.This means de-orbit is the only chance to get the distance right. The de-orbit burn would need to be perfect. It would need to be the right distance from the base(and keep in mind that 1/10 of one second either way means missing by over 700km. The burn would also have to leave the ReA perfect to within 1/100 degrees. The location and duration of the burn would depend on both your altitude and your vessels mass.

It's actually much easier to use the "Manual Re-entry AP". This can be much easier than you may think. I'll outline a re-entry profile that takes most of the worries away - even an overweight DGIV will survive this - so you don't have to worry so much about heat.

1: Initial alignment. Use BaseSync (in direct mode) and see which orbit gives you the closest approach. One or two orbits before that, reduce the closest approach to 50k if it is higher.

2: De-Orbit. The burn should be opposite the target base, but doesn't need to be exact. Lower the PeA to 50k altitude. IIRC, this will be about 0.8 degrees Re-Entry Angle.

3: Final alignment. When we de-orbited, we changed our velocity, and thus our period. Our groundtrack has changed. 1/4 orbit before the target make another base alignment burn with BaseSync. This time be precise.

4:Entry. After the final alignment begin orienting for re-entry. Use Aerobrake in the mode that shows the map. At 120k altitude, engage the re-entry AP set to 35 degrees AoA (spec 35). Now, see where Aerobrake predicts you will land. It it's short of the base, lower the AoA. If it shows you will be long, increase the AoA. Usually, 35 of 40 degrees wi be close. Since the DGIV only changes AoA in 5 degree increments, chances are you will have to choose between a setting that leaves you short or a setting that leaves you long. Choose the setting that leaves you short for now. Every once in a while, during the re-entry, try the other setting to see if it's changed. Eventually, the setting that used to be too long will be perfect. Later, when you are under 35k altitude, start aiming a a tiny bit long to ensure you have speed to manuever. You should end up within a few kilometers by the time you are down to 20k altitude, around 850 m/s velocity. Disengage the AP and fly it in.

The same method works with the XR vessels. Better, actually, since the XR's have a 0.5 degree increment for AoA hold compared to the 5 degrees for the DGIV. You will "bounce" a bit, it's more of a rollercoaster than an even slope. Just maintain the AoA as per Aerobrake. Unless you are seriously overwieght, you shouldn't even come that close to overheating. That's one of the advantages to de-orbiting at 180 degrees, it allows a slower descent which means more time to loose velocity which results in lower temps.

As you gain practice, experiment with de-orbiting later, say 17.5 M from the base. Aim for a Re-Entry Angle of one degree. Start with an AoA of 40 degrees. Here's the trick. You need to get the VS above -80m/s by the time you reach 65k altitude. In fact, that's how the full auto AP works. It adjusts the AoA to maintain a VS of -80m/s. Doing this manually is a bit tricky. You need to pay attention to the VACC.

How hot your hull gets has to do with how quickly you are descending and how quickly you are slowing down. The quicker you slow down, the faster you can descend. With a DGIV anywhere near the "re-entry max" weight, 80 m/s is a safe descent rate. The trick now becomes anticipation. There is no perfect AoA that will hold a steady descent rate throughout the re-entry. Also, there is a lag between action and effect. Changing the AoA (which takes a second) changes the VACC which changes the VS (which takes time) which changes the Hull Temps. Keep the VACC as small as possible, either one click to high, or one click to low. Try to sstay close to -80m/s, never more than -90ms. If the hull starts getting really hot, slow the descent to about -50m/s for a bit to allow it to cool. As your skill increases, you'll find that you can hold a smoother descent, which means you can reduce the margin a bit and use a quicker descent rate. Don't be afraid to make some gentle S turns - the bank can help you tune the VACC.

Once you get settled in at a VS of -80m/s, take a look at Aerobrake. You should be showing up as short of target. If not, use more aggressive S turns. If you are more than 100k short, reduce your descent rate. After you've slowed some, and the hull temps start dropping, use the AoA that comes just short of target, and gradually reduce AoA a bit as you lose velocity.
 
I Did It! With you all urging me to do it manually gave me the confidence to try it. Aerobrake used to scar me but now I see how great it is for a controlled ReEntry. That is so much better. Cant wait to try again tomorrow. Thanks Tommy for the very detailed response.

Thanks to all. :tiphat::cheers:


hail :probe:
 
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