Opinions on stock re-entry heat (as of 1.0.5) ?

[Francois424]

Okay so I've started playing KSP more seriously (tired of waiting for 1.1), but I'm wondering if this is on purpose or just plain out broken ?

Last week, I make a ship to go to the Jool system, carrying a Vall Exploration Rover.  I set-up aerobreaking @ Laythe. POOF...  Okay I did not have a heatshield, but I was exploding 3 seconds after touching the outer layer.   Thankfully, I had enough Delta-V (barely) to do a manual break using a close Tylo approach and coming back to Laythe. Quite expensive.

Yesterday I decide to go to EVE.  Learning from my Laythe experiences of last week, I put a 2,5m heatshield AND keep my fairing over the rover.  Entering atmosphere...  BOOM !  **again** and the heatshield got consumed/destroyed in about 1 sec.

I mean fine that you need to build with a heatshield and all, it works really well on Duna and Kerbin (coming back from Mün and Minmus anyways).
But having to drop re-entry heating to 20-40%, if not straight out kill it to 0% is kind of a bummer. I like the extra challenge but it's ridiculous now.
Are there any fixes being done in 1.1 or is that the 'way it's gonna be' ?  Because right now I have to budget a lot of dV to manually break entering a SoI

 

[Armisael]

I'm not aware of any major bugs with re-entry right now. How fast were you moving when you hit Eve's atmosphere? I've hit it at ~4.6 km/s surface velocity with a half-full heatshield and been just fine. If your heatshield is blowing up instantly you must be going fast enough to push it over the critical temperature despite the ablator, which means that you were doing 5-6 km/s - or perhaps that your ship tilted and parts of it were exposed and they went first. 

Edited January 27, 2016 by Armisael

[m4v]

Making straight aero capture practical by just adding a heatshield isn't extra challenge. You kinda have to get a capture before dipping in the atmosphere, otherwise reentry heat would be negligible in all the other less extreme cases.

Edited January 27, 2016 by m4v

[Benoit Hage]

In reality, peak heating happens at the beginning of the reentry as shown below with the Orion reentry

youtube

Edited January 27, 2016 by Benoit Hage

[Evanitis]

Reentry got tougher, but nothing unmanageable. Though aerobraking with interplanetary velocity is kinda' asking for a superheated discombobulation. These days I wouldn't attempt it without using a local moon's gravity to decrese my speed first. Also, keep in mind that Laythe is a moon too, so the rules of gravity assisting also apply. So if you are attempting aerobraking on it's 'retrograde' side, you'll -gain- speed in the atmo instead of bleeding it. And poof.

My recent Laythe flights indicate that a 35-40km PE on the planet's prograde side safely eats up 3600 m/s of velocity without a heatshield, while trying the same on the other side sends your charred remains on a Jool escape trajectory. Of course, coming from Kerbin means that you'll need Tylo anyways to slow you down, but it can capture a craft coming from Kerbin with a hohmann transfer in itself..

Edited January 27, 2016 by Evanitis

[Francois424]

In both cases I was coming from an interplanetary transfer at about 8k orbital speed.  

7 minutes ago, m4v said:

You kinda have to get a capture before dipping in the atmosphere

Answers my question.  I just wanted to make sure I had gotten this right.  Definitely less fun than previous versions of KSP.  But there's the difficulty slider so might as well use it.
Still... with default settings, blowing up in 3 seconds in KSP is right-off broken in my book, looks like no more Aero Braking maneuvers of any kind anymore...

Thanks for answering.

Edited January 27, 2016 by Francois424

[Armisael]

I don't think that the problem is with re-entry heating here - you're apparently setting your transfers such that your trajectory intercepts the target's trajectory at a pretty serious angle. Aerocapture works just fine at reasonable speeds.

Edited January 27, 2016 by Armisael

[Evanitis]

I also remeber times when I could splash into Jool with 9k m/s... though it was really really long ago. Maybe 0.9?

But the dV required to sling infront of Tylo is minimal if you fine-tune your approach right after the transfer burn. I kinda' like it better - slingshooting is awesome.

Though I'm concerned about Eve. I have less experience with that planet in the newer versions. Gilly isn't much of a help when slowing down, the atmo is thick there and you can't sling while the entry. Guess that's the place where one goes with maxium ablator.

[Guest]

18 minutes ago, Francois424 said:

In both cases I was coming from an interplanetary transfer at about 8k orbital speed.

Yeah, shallow aerocapture into an elliptical orbit is the way to go.  You can then aerobrake to circularize.  Break your energy transfer to the planet into smaller chunks to avoid damage.

More tedious?  I suppose, but Space Is Hard.

[LordKael]

19 minutes ago, Francois424 said:

looks like no more Aero Braking maneuvers of any kind anymore...

The above replies have given a couple different instances in which an aerobraking maneuver is perfectly viable. I'm not sure you can really say "of any kind" if the only type of aerobraking maneuver is a ridiculously aggressive one. I personally have managed to bring my velocity down considerably with aerobraking, even at Eve. 

[cjdrover]

Yeah, 8 km/s is way too high.

A low energy Kerbin->Eve transfer has an optimal velocity of 4.8 km/s at atmospheric interface.

FWIW, I have been playing with the Kerbin 365 rescale and routinely coming back to Kerbin at ~6 km/s with stock heatshields, the reentry corridor is just a lot tighter. (Side note, in some ways the rescale helps aerocapture because a shallow trajectory gives you a lot more time in atmosphere without dipping too low, and you have a deeper gravity well to work with. Stock scale is somewhat funky because any reasonable grazing path through the atmosphere takes you way too deep into the dense air...)

Edited January 27, 2016 by cjdrover
spelling

[Francois424]

47 minutes ago, regex said:

Yeah, shallow aerocapture into an elliptical orbit is the way to go.  You can then aerobrake to circularize.  Break your energy transfer to the planet into smaller chunks to avoid damage.

More tedious?  I suppose, but Space Is Hard.

This will be the way to go.  Less delta-V spent on capturing, just the minimum required for that high-Orbit.  Then let the many passes slow you down.
Or just bring loads of fuel for deceleration... some assembly may be required (in orbit) but I don't mind.  And even a THR of 0.1 is enough given you have almost infinite time to get the orbit right before dipping in.
I guess I just had to get used to the fact that Atmospheric worlds have to be respected like non-atmo ones are, treating their atmosphere like hard ground (Not good for braking at high speeds).

[Guest]

13 minutes ago, Francois424 said:

This will be the way to go.  Less delta-V spent on capturing, just the minimum required for that high-Orbit.  Then let the many passes slow you down.

Well, KSP is less punishing than IRL, once you're in an elliptical orbit you could probably get away with one aerobrake pass, depending on how tough your ship is.

13 minutes ago, Francois424 said:

Or just bring loads of fuel for deceleration... some assembly may be required (in orbit) but I don't mind.  And even a THR of 0.1 is enough given you have almost infinite time to get the orbit right before dipping in.

This is what I do anyway.  IMO, no sane space agency would subject a potentially reusable interplanetary tug to the rigors of an atmosphere.  For probes and the like, aerocapture and braking and perfectly fine maneuvers.