Flight Question Help with capsule reentry

[SandroSalgueiro]

Hello everyone,

I'm opening this thread to look for some help in reentry procedures.

I'm new to Orbiter and lately I have been practicing a lot of flights from the Cape to the ISS and back. So far, I've had successful attempts with both the DGIV and the XR2.

As I wanted to step up in realism, I downloaded a Soyuz TMA add-on (included in ISS V3.2). After reading its documentation, I had no problem launching and docking to the ISS. When trying to reenter the atmosphere to land, however, problems quickly arose. Here's what has been happening: after properly separating the capsule and executing a de-orbit burn, the autopilot kicks in and takes control of the ship maneuvers. Because it starts a fixed pitch program, I can't correct trajectory during the descent for a pinpoint landing and end up landing too far from the designated landing site.

For comparison, on the XR2, I only use the Attitude Autopilot, being able to manage the AoA through the whole descent and keep my impact point constantly updated as drag and lift build up.

I did search for tutorials, but it seems that most of them are geared towards the Deltaglider. Finally, I ask for your help on how to land this Soyuz and capsules in general.

Any shared content is greatly appreciated.

Sincerely,
Sandro Salgueiro

---------- Post added at 04:02 PM ---------- Previous post was at 12:00 AM ----------

Here's what happened on my latest try: after the de-orbit burn, the ship got oriented heatshield-first. A few kilometers after passing the atmosphere interface, the capsule started climbing and bounced back to an orbit of 250K apoapsis. The HUD indicated that a Ballistic Entry program had kicked in, but, apparently, it didn't prevent lift from building up.

What's wrong?

 

[clickypens]

Sounds like you're coming in too shallow. Capsules like a much greater reentry angle than winged vessels, though I don't remember any exact others off the top of my head. If you have Basesync MFD you could just mess around with the numbers until you can get it every time.

 

[SandroSalgueiro]

How does a capsule reentry data differs from a winged vessel's one?

As an example, this is the set of data I usually use for reentry with the XR2:

Reentry interface 120km
Angular displacement during aerobrake 55deg
Angle 0.7deg

Also, I usually burn 'til PeA reads 60km.

 

[Tommy]

Capsules use a much steeper ReA. I'm not sure what it will be coming in from LEO, but I'd start by placing the PeA at zero altitude. They don't generate nearly as much lift, and have much higher G-forces during re-entry - so the Ant (angular displacement) will be much shorter - 20 to 30 degrees coming from LEO.

 

[SandroSalgueiro]

I've been using Aerobrake MFD for Reentry. Is there a more appropriate MFD to be used in a capsule for such procedure?

 

[Tommy]

Not really, just keep in mind that a capsule has very limited range compared to a winged vessel. AerobrakeMFD doesn't take aerodynamics into consideration until you are below 200k altitude. Above that it's showing a purely ballistic trajectory - which will be quite close to what the capsule actually does.

With a capsule, de-orbit timing is key to landing where you want.

 

[SandroSalgueiro]

It worked way better this time.