Flight Question Need help for precision landing after KSC-Ascension suborbital flight

[tainanfish]

Dear fellow Orbiter users,

I am trying to fly a suborbital flight from KSC to Wideawake Intl on Ascension Island, but I have never been able to arrive exactly over the island like some other people have, even with the Aerobrake MFD (but I am not sure I use it well). Could someone help me answer these questions?

- I first put Wideawake as a target in the Map MFD and it gives me a heading to follow and the distance to Wideawake. I then take off, use main engine and scram engines to stabilize at about 70 km and Mach 20 and start my descent around 2000 km before Wideawake (as shown on the Map MFD). While in flight, I also use Aerobrake MFD to try to pinpoint my arrival (in the map configuration) but it is not very successful, the closest I came to Ascension island without using my engines was 200 km.

My questions are:

1. How do you know at what time/distance you should start your descent and what your AOA should be?
2. How do you manage to go in the exact direction of Wideawake? I follow the heading at the start but even a small deviation can have big consequences and once you have gained speed, it's almost impossible to correct.
3. At what moment do you try to correct your heading using Aerobrake MFD? As I said, I believe it is impossible at Mach 20, I tried using Normal/Antinormal too but it didn't work.
4. I also have Basesync MFD but it seems it works only when you start in orbit, can it be useful for the kind of suborbital flight I am trying to do (or any other MFD that you could recommand).
5. Also, at Mach 20, I have found it hard to break by raising your nose at around 40 deg, if I do that I usually start climbing into space. I also tried to burn retrograde with mixed results, the best results was when I first burned my main engines with my nose down, but quite often I then rebounded on the atmosphere once or twice, which I find annoying and nerve raking, especially as I fear going past 80 km into space.

In advance, thank you very much for your great help. Some of you are amazing pilots and it would be really awesome if I could also do the things they do. I don't want to go from KSC to Ascension as fast as possible so far, just to go there fast and accurately. Thanks for being as accurate and "down to earth" (if I may say ) as possible in your answers, with all the precise steps I need to follow, since I don't know all the MFDs functions very well in particular.

Philippe

 

[Jarvitä]

Try either going a little lower - at 60km, it's much easier to fly like a plane - or a little higher, just fire yourself into space on a ballistic trajectory towards Wideawake. Even if your re-entry is a little off, you should have plenty of scram and rocket fuel left to make it to the island. You're in the exact area where it's nigh-on impossible to maneuver because it's impossible to treat it as regular atmospheric flight or space.

 

[orbekler]

I don't know which is the vessel you're using, however you can lower your speed at about mach 15-17, and altitude at about 60km, as Jarvita said. Then use Aerobrake as usual.
If you're not able to stabilize AoA, you must use CoG to force that.
If you're out of path, use banking to correct, Aerobrake gives you the proper projection of the target.
I've just tried the trip, with the XR2, i depleted scram, and the speed was almost mach 20, however I safely landed on WdkI, in 43 mins.

 

[Tex]

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I've just tried the trip, with the XR2, i depleted scram, and the speed was almost mach 20, however I safely landed on WdkI, in 43 mins.
View attachment 7998

Sorry for off-topic, but where did you get the map like that for Aerobrake MFD? Is it this addon:

[ame="http://www.orbithangar.com/searchid.php?ID=2356"]Color Earth and Moon Maps for Map MFD[/ame] ?

Cheers!

 

[tainanfish]

Thank you for all your answers! Actually I flew the XR-2. I guess I will try to go either slightly in space then or around 60K. Do you also use Basesync or is Aerobrake enough? And do you know when to start your descent or do you just eyeball it/try it? (I usually started descending 2000 K before Wideawake, but that's totally random from me). Is there a way Aerobrake or Basesync or any other MFD can calculate that and tell you the right moment to descend, even if you are not in orbit and thus we are not talking of a deorbit burn proper? Thank you!

 

[orbekler]

Sorry for off-topic, but where did you get the map like that for Aerobrake MFD? Is it this addon:

Color Earth and Moon Maps for Map MFD ?

Cheers!

I don't remember clearly, but it seems not to me. I compared texture files for that addon and those in my Textures folder, and are NOT the same. I think maps came with the last AeroBrake MFD, though I'm not sure about it.

[ame="http://www.orbithangar.com/searchid.php?ID=2139"]http://www.orbithangar.com/searchid.php?ID=2139[/ame]

And, just in case, the map:
http://www.mediafire.com/?1f4hqo53xjvhx9p

 

[Tommy]

1. How do you know at what time/distance you should start your descent and what your AOA should be?

Practice and experience for this, it varies a lot with your actual speed and your ability to aerobrake.

2. How do you manage to go in the exact direction of Wideawake? I follow the heading at the start but even a small deviation can have big consequences and once you have gained speed, it's almost impossible to correct.

SuborbitalMFD can be used to get the initial heading - it is more accurate that MapMFD (takes planetary rotation into account - but not atmosphere.) Once up to a reasonable speed, AerobrakeMFD (in "grid" view - press MOD and PG, IIRC) can be used to fine tune your heading.

3. At what moment do you try to correct your heading using Aerobrake MFD? As I said, I believe it is impossible at Mach 20, I tried using Normal/Antinormal too but it didn't work.

It's best to make the corrections well before leaving the atmosphere. Once you get much above 4km/s velocity AerobrakeMFD should be showing your course well past AI. It's possible to make corrections using Normal/AntiNormal burns - but they will take a long time, and you want to be on course long before you leave the atmosphere - if you leave it at all.

4. I also have Basesync MFD but it seems it works only when you start in orbit, can it be useful for the kind of suborbital flight I am trying to do (or any other MFD that you could recommand).

SuborbitalMFD is best for finding your initial heading (before you even start the engines, make note of the heading shown in Suborb. Get on that heading as soon as you can - then just keep the wings level and ignore the fact that your heading will change during the flight (use Aerobrake as soon as it shows your trajectory far enough.)
[ame="http://www.orbithangar.com/searchid.php?ID=1367"]SuborbMFD v2.1[/ame]

5. Also, at Mach 20, I have found it hard to break by raising your nose at around 40 deg, if I do that I usually start climbing into space.

It's not uncommon to need an Angle of Attack higher than 40 degrees - even as high as 60 - 70 degrees. If you are "rebounding" it means your AoA is too low.

Here's a couple playbacks you may learn from:
[ame="http://www.orbithangar.com/searchid.php?ID=3669"]KSC to Ascension Island in 1000 seconds (17 minute[/ame]
[ame="http://www.orbithangar.com/searchid.php?ID=5138"]XR2 from KSC SLF to WIN under 18 minutes[/ame]

Both of these are "races", so not quite what you are looking for. It's easier if you aren't in such a hurry - you can keep the velocity down under orbital speed so you don't need to fly inverted to stay in the atmosphere.

I recommend using SuborbMFD, as noted above, for the initial heading. Then I ascend the same way as if I'm launching to orbit - but I stay under 7.5k velocity - and top out at around 65k altitude. By this time I have more than enough energy to get to AI, so I "coast" along at high altitude (around 65k) until I'm maybe 2k from AI. I'll have used AerobrakeMFD to stay on course, and at around 2k from AI I'll pitch up to at least 50 degrees (using the XR-2's attitude autopilot set to AoA - not pitch). Then I'll adjust the AoA so that the trajectory shown on AerobrakeMFD ends at AI - and from there it's pretty much the same as a re-entry.