Eve rescue/return in 1.0.4 (re-entry super-heating)

[ringerc]

TL;DR: How do you manage to get anything big enough to take off again to survive Eve re-entry in 1.0.4, keeping it stably behind a heat sheld without being instantly annihilated?

Hi all

I'm attempting an Eve rescue mission in 1.0.4, with the tweaked thermals. I'm finding that anything beyond a capsule with a heat shield that I try to drop into Eve's atmosphere is just obliterated by heat, even if I enter on a pretty gentle angle (Pe = 76k).

Anything tall enough for a couple of stages just gets anihilated at about 70k, with heating seeming to go almost exponential so that most of the craft explodes at once. It's not the usual gradual burning up of pieces of craft and disintegration, it's more like the whole thing gets hit by a bomb. From intact craft to drifting fragments so suddenly that the graphics seizes up for a few seconds on my poor laptop trying to render all the simultaneous explosions.

I've even tried putting the whole craft in a faring with a heat sheld on the bottom of the faring, hauling the whole monstrosity from Kerbin, and injecting it into a shallow Eve atmosphere-skimming orbital trajectory where it makes 20+ orbits before finally going suborbital and begining final descent. So it's moving at low-circular-orbit speeds for its final entry. The faring is shaped like a rivet with a wider head so it self-orients retrograde, which made it a nightmare to launch but means the craft is oriented with all the heat shields pointing the correct direction when the faring is discarded or destroyed. No matter what I do ... kaboom - the faring overheats and is destroyed, and then the craft within is instantly obliterated by heat.

The only things that survive are landing gear, struts, capsules, engines, and heat shields. So I have a cluster of fragments gently drifting down to the sea through the soupy atmosphere.

I can't even rocket-brake down effectively because exposed rockets (solid boosters, or fuel tanks of liquid rockets) get obliterated by heat before even reaching 80km.

This doesn't seem right.

Happy to follow up with craft files, screenshots, etc.

Happens with or without any mods.

Ideas?

Edit: Getting similar results if I do tests at Kerbin by launching the vessel into a high Kerbin orbit and power-diving toward a Pe of 32k or so at 4.3km/s re-entry velocity (to simulate Eve's greater gravity and atmospheric density). Near-instant obliteration. The vessel sometimes survives to 34k or so, but well before the heat shield is depleted the craft lands up tipping slightly out from behind the heat shield and being instantly annihilated.

I guess the question is then: How does one keep anything but a very small craft behind an heat shield in 1.0.4, given that the point at which all drag is applied is the heat shield? I can't use aerodynamic effects because anything exposed to the airstream is instantly obliterated. SAS doesn't have the power without absurd reaction wheels and batteries. I can't make the vessel conical behind a bigger heat shield, since there are only up to 3m heat shields in KSP.

Here's a series taken with a Kerbin re-entry simulation. Used MechJeb for testing purposes to make sure I was 100% dialled into the surface velocity vector, entering the atmosphere at zero degrees angle-of-attack. Re-entering a small-to-medium stack suitable for Eve surface escape inside a cigar-shaped faring. If I use a rivet-shaped faring (with a "T" top) then the faring is not occluded by the heat shield so it gets obliterated early in re-entry.

If I discard the faring and deploy airbrakes the vessel fares better, rather counter-intuitively. Until the airbrakes overheat and the whole thing explodes in an instant.

(I'm finding that these harsh Kerbin re-entries seem to simulate gentler re-entries to Eve, e.g. many aerobraking passes then an aerocapture at ~3.2km/s, Pe=80km, given the higher low orbit velocity around Eve and its denser atmosphere. It's easier to test different vessels this way. Nothing survives, though.)

Edit: OK, I think part of the issue is that Eve's atmosphere ends at 90km, but is incredibly deadly by 70km. There's just not much margin for orbiting within the upper atmosphere bleeding off speed, especially since fuel tanks tend to be instantly destroyed on contact with the upper atmosphere so it's difficult to achieve really flat trajectory. The steeper re-entry angle on Kerbin that I'm using to simulate Eve is having a similar effect. However, there seems to be no margin at interplanetary encounter speeds, even on Kerbin, between enough aerobraking to lead to aerocapture and total destruction.

Edited July 8, 2015 by ringerc
More info

[Foxster]

One word: airbrakes.

Slap a bunch of these on the top (to help with orientation during re-entry too) and it should come down fine. Mount them along with the landing gear and any other disposable items for decoupling before liftoff.

This landed fine without overheating:

[Streetwind]

Indeed, airbrakes are pure magic. They look small, but they have a hugely disproportionate effect on your drag. They're like drogue chutes that you can open anytime (even have them opened before entering the atmosphere) without them tearing off.

Works great for aerobraking too, you can get more braking force without dipping as deep into the atmosphere, so you don't have to worry as much about heat.

[Sharpy]

I wonder what kind of ladder you need to get from that to the ground and back. I mean, in that gravity you can't dream of flying to the capsule.

[selfish_meme]

You put a capsule at the bottom of course, you can leave it behind.

[Signo]

In my experience I had to combine fairings with airbrakes and "rocket-braking".

I doubled the airbrakes in the designs I use lately to obtain a better stability.

Beware the "too fast too low" borders - depending on the drag and shape of the craft the limit speed you will experience may vary.

EDIT: I always try to go for a common almost circular orbit before the descent. The best way I found is to make the atmo do the most of the job slowly braking from a 95x80 orbit or similar. I constantly burn a little bit to control my speed and there are a few "gateways" I try to keep as a standard (I try to brake as much as needed to approach 90000m @roughly 2800m/s, then depending on the craft, approaching 45000m @roughly 2000m/s; below 45000m I try to "rocket-brake" as much as I can, saving a few of the fuel for the touchdown). Mammoth engines are the best heatshield available IMO, their skin temperature will be as low as 750° while a 3.75m heatshield in a comparable place will have around 1750°. However they will not avoid the turbulent convection overheating.

Edited July 8, 2015 by Signo