Problem XR-2 Ravenstar Re-entry trouble

[SpecialKaye87]

I've been beating my head against a brick wall with this one. I can't get this Ravenstar to re-enter on target.
Here's the steps I've taken

Indocked from ISS, base alignment (this part's a piece of cake).
Once I've gotten my alignment with cape canaveral I do my de-orbit burn using basesync MFD.
Here's where I encounter the problem, I determine my re-entry angle using the Map program on IMFD. I retro-burn when the basesync mfd tells me to and i burn until my re-entry angle on the aforementioned map IMFD says .5, .3, 1.0 (i've tried them all).
I go prograde until I hit about 80km, then start maintaining an AOA of about 40*, on several attempts I've let the Aerobrake MFD hold my aoa and bank, regardless, one of two things happens 1) i burn up, 2) i skid off the atmosphere and eventually re-enter way beyond my target ( I aimed for Cape Canaveral and I ended up in Castro's back yard some where over Cuba).

I've checked my fuel level (kept it around 25% after retro burn) so I know I'm not too heavy. I've run this same attempt probably 30+ times now with no success. Can some one tell me what I'm doing wrong? I've nailed everything from ISS intercept and docking to landing on the moon, but I cannot get this ship to re-enter successfully! >:-(

 

[TerraMimic]

You should observe the behavior of the Auto Reentry autopilot on the DG-IV-2. It does not maintain a constant AOA. I believe it does, however use 40 degrees as a starting point and then adjusts accordingly depending on the actual conditions during reentry.

I could be wrong, but I believe it increases or decreases AOA depending on your rate of descent.

 

[MaverickSawyer]

FYI: the smilie you're looking for is : beathead : without the spaces...
:beathead:
Post the .scn files, and we'll see what we can do.
Oh, and check Tex's tutorials... Probably something there.

 

[SpecialKaye87]

.scn files? :beathead: <----like that?

 

[Shinrar]

.scn files?

Do all the above you've mentioned, and right after you go to *40 AOA @ 80km alt - close orbiter. Then post the contents of the current scenario file, which will end in .scn, here.... (I forget the exact name for the moment, for some reason...)

Use [CO.DE][/CO.DE] (without the periods) to keep it readable.

This allows us to plug your same exact situation into our games, and give you better instructions on what we would do in your situation.

 

[Spacethingy]

If you look in "C:/..../yourorbiterinstall/scenarios/" you'll find a load of .scn files that represent the scenarios you see in the Orbiter launchpad.
When you double click on one to try and open it, it'll probably say can't find the right program; you just need to select Wordpad or Notepad. That'll do it.

 

[Tommy]

This question has been asked (and answered) countless times on this forum. Please make use of the "search" feature BEFORE creating new threads. We get tired of answering the same question over and over again.

For instance:
http://www.orbiter-forum.com/showthread.php?t=18561&highlight=AerobrakeMFD


First, the XR vessels have a perfectly good attitude hold auto-pilot built in. It works MUCH better than the one in AerobrakeMFD. Read the XR Operations Manual for instructions on how to use it, and make sure it's set to hold AoA - not Pitch.

Second, read this tutorial to understand why you are bouncing off or burning up:

[ame="http://www.orbithangar.com/searchid.php?ID=3428"]Tutorial: Concepts for atmospheric reentry[/ame]

Third, read this entire thread:

http://www.orbiter-forum.com/showthread.php?t=18671&highlight=basesyncMFD

 

[Grover]

as far as i can tell, youve programmed your basesync de-orbit wrong, you should set ALT to 80km, ANT to between 40 and 50 (depending on how fast you want to descend) and ANG to between 0.7 and 1

that gives you a deorbit almost exactly on the far side of earth, once you hit the atmosphere, check your attitude AP is holding AoA NOT pitch )theres a button on the top right of that panel)

aim to hold a descent speed, not your AoA, that should change throughout the descent, starting from 42-45 and ending about 30 (read on)

holding 80m/s is my usual target, but you can go higher without burning up, and lower to extend your re-entry (but dont go too low, or youll lose too much speed and then burn up after a kinda secondary stall)

once your speed gets below 2.3k, you can roll out of the high AoA, and use aerobrake mfd to set your traget impact point about 100k ahead of your target (1/2 to 2/3 of a square on the zoomed map)

then you should pass a few kms over your target, just descend like a glider (in a descent spiral a couple of km after the end of your target runway, and move in for landing when you can descend to it without losing control

if you find yourself way too short (we've all done it, dont worry) you can open your scram doors if you have any fuel left, or use your mains, prefferably early on in the higher atmosphere where they have a greater ISP, but save some for your final approach if you need it

alternatley you can read through this tutorial of mine, it focuses on the DGIV, but the concepts are the same

good luck man!

 

[Cras]

My current procedure for XR2 re-entry is this:

Left MFD set to Aerobrake, Right MFD set to Base sync

Both set to the base I want to land at, either Edwards AFB or Kennedy Space Center

Base Sync deorbit set to Ang 2, Ant 65, Alt 80KM, burn when it says to burn, but do not burn the entire time Base sync says to. Look at the left MFD and watch where it says you will end up. Want it to be a bit long, not much, but a little long.

At 150 KM, I close up the bay doors, and the nose cone, then activate the AoA autopilot (XR2s autopilot), and set it for AoA 40.

Do some small adjustments with either RCS translations, retro engines, or very little main engines.

Then at 105km, I perform the reentry check, close up the radiator, the retro doors, leave the APU on for the rest of the flight, and make the small adjustments to ensure that the dot falls right before the base in Aerobrake. I want it right before because the XR2 has amazing lift and is able to fly level with little speed loss, so I can fly a HAC if needed, and not worry about landing short like in the Shuttle. I also try to get the ship flying as slow as possible, landing at around 150 velocity.

Now my method requires the de orbit burn done later than at the half way around the world like most people like to do. Mainly because the APU is needed for the AoA autopilot to function under 90km in altitude or there abouts, and I run with a quick APU burn. If I de orbit and leave the APU on, it will run out before I land, so I go with a sharper deorbit burn, and I get more effects during re-entry that the shuttle used to see. It is certainly possible to re-enter with the XR2 and not ever see a bit of re-entry plasma, but that is a goal I am not interested in. I need the re-entry to be quicker so I have APU left over for the control surfaces.

The deorbit this way results in a little skip. The ship will re-enter quickly and temps will rise to about 800-900 degrees and then skip up around 60km, then re-enter for good, which is when you will see temps hit 1700 degrees and the re-entry fire effects. Then will subside, and at about 95,000 feet, kill the AoA down to about 20 degrees, then turn off the RCS, switch to full air surfaces, and take manual control for a nice smooth landing back on Earth.

I never fire the engines one in the atmosphere. Most of the time, I will burn the remainng main engine fuel to lower the cross range needed after the deorbit burn and aim for a more straight in, as I find roll reversals not very useful in the XR2 until deep in the atmosphere.

 

[SpecialKaye87]

Well, it took some studying, lots of coffee, and a lot of reading, but I've gotten the hang of it. Thank you EVERYONE for all the insight. You all have been more than helpful!

Now I can fly launch, scram ascent, sync and dock with ISS, and fly to the moon! the next challenge: MARS!