Eve aerobraking at 5000m/s

[OhioBob]

6 hours ago, FancyMouse said:

5km/s isn't a problem - I've done 5.5km/s reentry on Eve in 1.0.4, which is even harder than 1.0.5. The trick is to make sure heat shield covers the whole ship, and the ship is capable of pointing prograde.

I ran a bunch of tests up to about 5 km/s.  In addition to making sure the heat shield covers the whole ship, we need to make sure we don't overload the heat shield with too much mass behind it.  I tested a 2.5m heat shield loaded up with anywhere from 6 to 38 tonnes of mass behind it.  With a small loading (below about 20t), aerocapture was easy, even at 5 km/s.  At the highest loadings, aerocapture was still possible, but it was also likely I'd overheat and explode if I came in too deep.  At 38t the safe entry corridor was very narrow.  I wouldn't recommend it.

 

Edited December 31, 2015 by OhioBob

[Foxster]

1 hour ago, Snark said:

I gotta say I'm with @FancyMouse on this one.  It feels like an exploit to me.

At hypersonic speeds in the upper atmosphere, the craft isn't slipping through the air; it's punching a hole in it.  There's not laminar flow around the craft, or even turbulent.  It's just slamming the air aside, leaving a vacuum behind it.  The air doesn't curve back behind the craft, because it doesn't have time to-- the gas molecules only move at the speed of sound, and the craft is traveling many times that.  The gas is already far behind the craft by the time it has a chance to flow back into the hole the craft is leaving.

So if you've got any airbrakes (or anything else) that are completely in the shadow of the heatshield, they're basically in a vacuum.  They shouldn't experience any drag at all.

In any case, at those speeds, "drag" in the usual sense is fairly meaningless-- what you have is dynamic pressure from the air slamming into the front of the craft.  Any component on the craft is either exposed to that air flow-- in which case it experiences drag, and bow-wave-compression, and heating-- or else it doesn't, in which case it has neither heat nor drag.  There's not a scenario in which you get to have drag without heating.  (If you could, wouldn't NASA be using it?)

By all means, use this trick if you enjoy it, that's what KSP is all about.    But I won't be using it myself, it just feels like cheating to me.

I'll just think of it as a "feathered" or shuttlecock-like reentry, as has been tried on various craft including SpaceShip Two. That's good enough for me . 

[Foxster]

On 15/12/2015 at 2:14 PM, Galinette said:

Dear all,

I am passing close to Eve and would like to loose as much speed as possible using aerobraking. My speed at atmosphere edge is 5000m/s and I can adjust the angle to as low as needed. However, as soon as I pass 90km and the barometer is starting to move to the right, I explode in a few seconds. The speed barely decreases, which means that few energy was dissipated.

Isn't this a bug / non realistic behavior?

My ship has a heat shield (3.5m) and a cylindrical interstage fairing (3.5m too). It has 8 AIRBRAKES at the back for stability. So I can't do much better. Does the shield need to be much larger than the ship beneath?

I know 5000m/s is a lot, and I did not expect to loose all speed in one shot without exploding, but here even if I make a very high pass and loose a couple of m/s, I explode...

Thanks in advance!

The heat shield needs to be the same part size or larger as any round parts coupled above it and any other bolt-on parts on the craft must not protrude further than the diameter of the heat shield. Or you can use multiple heat shields.  

You must keep the craft tightly prograde and the Pe at reentry is vital. 65km works good for my craft that tend to be around 50-100t. You will likely need a couple of passes to get the speed down enough to land.