Eve EDL issues...

[MaverickSawyer]

I'm starting work on a Grand Tour, and I am currently ramming my head against a wall over the Eve ascent vehicle. No matter how hard I try, using the inflatable heat shield results in the ship tumbling, burning, and breaking up at ~30km altitude. I've festooned the upper portion of the vehicle with ejectable airbrakes in an attempt to pull the center of drag aft of the center of mass, but that still doesn't stop the flip.

Is there a trick to the inflatable heat shield? I've seen people use it with great success, but it's been nothing but grief for me in the entire time I've had access to it.

In the meantime, I'm going to trial a TweakScaled rigid shield to see if that clears the problem, or if it persists.

[Foxster]

Could you post a picture of the craft?

How many air brakes?

[Snark]

1 hour ago, MaverickSawyer said:

No matter how hard I try, using the inflatable heat shield results in the ship tumbling, burning, and breaking up at ~30km altitude. I've festooned the upper portion of the vehicle with ejectable airbrakes in an attempt to pull the center of drag aft of the center of mass, but that still doesn't stop the flip.

Is there a trick to the inflatable heat shield? I've seen people use it with great success, but it's been nothing but grief for me in the entire time I've had access to it.

You've got the right idea, just haven't carried it far enough.

• You want the CoM of the ship to be really close to the heat shield.  As close as you can possibly make it.
• Sticking airbrakes at the other end is a great idea... but you need lots of them, and they need to be really far back.  The distance from your CoM to the airbrakes needs to be a significantly big multiple of the distance from your CoM to the heat shield.
• Alternatively, put an inflatable heat shield at each end of your ship. 
• Another option is to put the inflatable shield on the back end of the ship, like a big heavy parachute.  Then put a smaller heat shield on the ship itself.

 

 

[MaverickSawyer]

Well, some quick tests have revealed that the inflatable heat shield is NOT alone in the flipping problem... but rigid heat shields that have been suitably scaled up are less prone to flipping. However, replacing the airbrakes with the Kerbal Reusability Expansion pack's grid fins have proven to be highly successful. The ascent vehicle has landed safe and sound, and was more than capable of achieving orbit without a passenger.

Consider this one solved, gang, but keep it around as a reference for future mission planners.

[Foxster]

Which goes to show you can get around any difficult problem by taking the easy way of throwing mods at it.

[Aegolius13]

One idea: put a big flat fuel tank on the bottom of your lander, right above the heat shield.   Launch with some of your lander tanks empty or plan to use some fuel in your transfer to Eve.  You want just enough fuel in the tanks to eventually fill the ascender portion. 

At some point before reentry,  pump as much fuel as possible from your ascender to the lower tank,  starting from as high on the ascender as possible.   This will help get your COM lower.  

Once you land,  pump the fuel back and leave the tank when you leave. 

[fourfa]

In actual practice, I find the simplest and most effective way to deal with this in stock is to have two inflatables, one at each end. You can fit a reasonable lander between them directly, or use a fairing between. The forces generated by the inflatable are simply colossal, and even the heat shield sandwich seems to tumble fairly often. So I like a fairing just for safety. 

If the intention of this part was as a re-entry/landing heat shield, I don't think it's really working as intended. If it's meant more for aerobraking from interplanetary transfers into orbit - that seems easier to achieve without extraordinary measures.