General Question Reentry Attitude Hold

[Snaps2010]

Ok so i have been using the Sierra Nevada Dream Chaser in Orbiter 2010 and when i get to reentry i cant hold a good Angle of Attack. i have tried both attitude mfd and aerobrake mfd with their attitude and AoA hold options but neither have been able to give me an AoA greater than 15 degrees once i hit the atmosphere. because of this i dont start slowing down very much until i get to the thicker parts of the atmosphere at witch point i have to roll on my sid or even upside down and pull a bunch of like 500g turns in order to avoid overshooting my target base. Is there any attitude or AoA autopilot that will fix this. What i am looking for is something like the attitude hold autopilot on the xr2. in the xr 2 if you try holding AoA manually you will get similar results to my Dream Chaser but when you use the attitude hold you can hold any AOA.

 

[dbeachy1]

in the xr 2 if you try holding AoA manually you will get similar results to my Dream Chaser but when you use the attitude hold you can hold any AOA.

to Orbiter-Forum!

If you want to hold AoA manually during reentry in an XR vessel you will need to adjust the center-of-gravity and/or elevator trim yourself in addition to RCS jets, which is what the XR Attitude Hold autopilot does for you. You can't do it with just RCS jets.

 

[Cras]

you got Attitude MFD.

Also Aerobrake MFD has an AoA hold autopilot, and Glideslope MFD does. No idea if the will work for you, but worth a shot I suppose.

 

[Tommy]

The problem you are having is that RCS alone isn't enough to maintain a high AoA in most Orbiter vessels. The XR vessels and the DGIV have attitude hold AP's that shift the center of gravity to assist in holding the AoA.

Unless a vessel has that ability to shift the COG, chances are it won't maintain a high AoA. One thing that MAY help is to ensure that you have a high AoA (at least 40 degrees) before you hit the atmosphere. AoAs lower than that are more difficult to maintain.

 

[DrSolidRocketMotor]

Reentry Techniques

Keep in mind that the real Space Shuttle did perform what were called roll reversals during its descent into the atmosphere. These were basically S-turns (often up to 90 degrees of bank angle, depending upon its range to the landing site) designed to bleed off speed and control its descent rate. This technique probably works in a similar manner for any winged spacecraft. I haven't flown the Sierra Nevada Dream Chaser yet, but it's worth a try -- Happy Landings!

 

[Snaps2010]

I have tried s turns and they help but when I get into the thicker atmosphere I am still goink like mock 15 so I my s turns are creating like 500 g turns.is their a way to add the ability to change cg and an autopilot to control the cg? I wonder how they did it with the space shuttle because I'm prity sure they can't shift the payload around to control the cg. How does the shuttle fleet add ons do it because they have an autopilot that will hold the right AoA.

 

[BruceJohnJennerLawso]

I have tried s turns and they help but when I get into the thicker atmosphere I am still goink like mock 15 so I my s turns are creating like 500 g turns.is their a way to add the ability to change cg and an autopilot to control the cg? I wonder how they did it with the space shuttle because I'm prity sure they can't shift the payload around to control the cg. How does the shuttle fleet add ons do it because they have an autopilot that will hold the right AoA.

Thats Mach, I think

I dont see any reason why they couldnt shift COG with payload, but not every shuttle landing would be carrying a payload at the time anyways. Im not entirely sure, but I think the Space Shuttle Ultra is able to vector its engines, probably low thrust, at just the right angle to hold it. Can anyone else confirm that for me?

 

[DaveS]

but I think the Space Shuttle Ultra is able to vector its engines, probably low thrust, at just the right angle to hold it. Can anyone else confirm that for me?

Not correct. It's a combination of aerosurfaces and aft RCS jets.

 

[BruceJohnJennerLawso]

Not correct. It's a combination of aerosurfaces and aft RCS jets.

hmm, I know I heard something about engine Gimbals, but Ive never flown SSU before. By aerosurfaces, you actually mean they can still adjust elevators/flaps in 300-400 degree temperatures?

 

[DaveS]

hmm, I know I heard something about engine Gimbals, but Ive never flown SSU before. By aerosurfaces, you actually mean they can still adjust elevators/flaps in 300-400 degree temperatures?

Yes. The aerosurfaces like the rest of the orbiter is covered with RSI. The engine gimballing is for the OMS and the SSMEs.