Airbrakes in Upper Atmosphere??

[Srpadget]

I finally got around to redesigning my Kerbin-SOI reusable infrastructure craft for V1.05.  Or, at least, I tried to.

I am having trouble with my nuclear-powered tug.  Specifically, I am having trouble aerobraking on return from Mun or Minmus. 

What I WANT is a ballute.  Ever since reentry heat became a thing in 1.0, I've been using the (overpowered, yes) airbrakes deployed in the very high atmosphere as a sort of stock ballute-substitute.  Airbrakes, of course, got nerfed in 1.05.  That 1.04 strategy seems to still work okay for lowish-mass craft in 1.05 -- at least, I've been using them to good effect with return trajectory direct to reentry from Minmus on a craft consisting of Hitchhiker, Mk 1 lander can, 2.5m heat shield, assorted low-mass science/utility gear, and 4 airbrakes.

Pile on the substantial added mass of 2 nuclear engines and added fuel tankage, though, and the technique fails spectacularly due to the airbrakes' low melting temperature.  Pulsing them does not help: they'll go from <350K to *kaboom* faster than the deploy/retract cycle.  I *assume* the issue is that the more massive vehicle gets lower into the atmosphere (and hence into a more challenging heat regime) without appreciably decelerating.

So has anyone had success with airbrake-assisted aerobraking of a 10-12-ish ton craft?  Do I just need to use more airbrakes in proportion to the higher mass?

I am tempted to ask for help bumping the airbrake temperature limit back up to 2000K, but would prefer to find a "stock" solution if a reasonable one exists....

[Phil deCube]

If you want a ballute, there's a mod for that.

http://forum.kerbalspaceprogram.com/index.php?/topic/121162-105-inline-ballutes-ib-v123-9122015/

 

[cantab]

What does your tug look like? I'm wondering if it would be possible to fly a lifting re-entry to reduce heating.

[Snark]

+1 to cantab's suggestion of a lifting re-entry.

Another option would be to have a not-fully-reusable infrastructure.  For example, you could have a big 100% reusable tug with a docking port on the front side, and dock a small ship on the front end that's basically just a heat shield.  You launch the heat-shield craft in batches like a stack of pancakes.  One heat shield would probably be good for a few reentries before using up all its ablator, depending on mass of tug.

Heat shields work really well, and a little ablator goes a long way.

[numerobis]

I re-enter at 52km or above from Mun without incident, just pointing my rocket normal (or radial). My 1200-degree parts survive at that rate, no heat shield needed.

It takes more than one orbit, is that acceptable?

[Srpadget]

Phil:

Historically I try to work with entirely stock parts/physics/etc.  (My only current mods are EVE, KAC, and Texture Replacer so I can give different suits to different professions and distinguish them by eyeball.)  However, that point is kind of moot now, as I've tweaked LFO tanks to LF-only for the current iteration of the tug in question, so I cannot truthfully claim it's a virgin stock craft anymore.  And that ballute is very pretty--plus the modder appears to have given thought to real-world-ish design considerations and compromises...

cantab/Snark:

I don't believe I have a picture of the tug handy, and my KSP time is about to be sharply curtailed (my son and his fiancee are flying in to town tomorrow for a week's visit).  If I can grab a few KSP minutes in the next few days, I'll grab a screenie and post it.  But I'm not optimistic re lifting reentry.

Snark:

I rather like your idea of a replaceable heat shield, and I may even be able to make it work with this design (likely have to rearrange a few parts to shift the CG appropriately, but that's not a big deal.

Numerobis:

I have no idea if the tug would survive a normal reentry rather than retrograde, I may have to try that.  (Though I must confess I do get impatient about aerobraking and would like to get it done in a single pass.  Which is kind of weird, given that this von-Braun-esque infrastructure requires three ships, two orbiting stations, and four docking operations (plus associated undockings, for a total of eight) just for a Munar round trip....