Heat Shields

[More Boosters]

Hey, I know they're rated for Eve but I rarely seem to need them on re-entry.

Can you share your experiences with Heat Shields? I once attempted a very aggressive return to Kerbin (like straight down) from the Mun with the front completely covered in heat shields hoping I would survive with spending most/all of my Ablator, but it didn't get rid of the heat quickly enough and exploded.

What are they good for? Should I take them for Jool aerocaptures or stuff?

[Javster]

I think they're meant to be used for shallower re-entries

[Varsi]

I tried aerobraking with a heat shield at Eve and exploded very fast... To me it seems the heat shield only helps at a very narrow area between "not heating enough to need one" to "exploding even with a heat shield".

[Xyphos]

Heat shields aren't required if you know what you're doing.

Heat shields just let you be more aggressive during atmospheric re-entry.

[cantab]

The ablator will quite happily boil away in deep space, whether because you've flown close to the Sun (a trip to Moho will do it) or because your ship is being hit by heating bugs.

[KerikBalm]

keep in mind that heat shields wont help if parts behind them are still exposed to the airstream.

I have a jool/laythe probe on the way with a 2.5m heat shield and 1.25m parts + some radially attached stuff right at the base where the heat shield connects, I already tested it on kerbin, and it appears to be aerodynamically stable (like a proper capsule), with no heating from very aggressive re-entry in 1.02.... I hope the 1.04 update doesn't break it (doing other stuff while its on its long journey)

[Varsi]

Heat shields will happily explode as a first part if you give it a chance to heat enough

//Edit

Actually. Now that I thought about this it could be that the ablator just vanishes instantly if you're going too fast which is why it explodes. Think I'll have to do some testing once I get home.

Edited August 4, 2015 by Varsi
afterthought

[Mystique]

I made return from Minmus to ~40 km Kerbin periapsis and it went totally ok (I had 2,5 m heatshield with about 60 or 70 units of ablator). Main idea is to keep heatshield strictly in front (pointing at surface prograde marker) and it should be wide enough to cover all other parts (could be easily visually checked in VAB). The only downside was that after this aerobraking I was at altitude of about 10 km and speed of about 500-600 m/s (mostly vertical, i.e. going down fast), which isn't best cause for chute deployment. But anyway I had enough time to aerobrake below 300 m/s, deploy chutes and even decouple propulsion module of craft for separate landing (I tend to build fuel tank+heatshield (without engine) as separate module for missions that require landing on other bodies and use landing module's engine as main propulsion).

[Varsi]

Tested now, heat shields can definitely explode due to overheating before running out of ablator. At Kerbin you need to do something ridiculous to achieve this but at Eve and Jool it will be much easier due to interplanetary speeds.

[Streetwind]

A part will explode when either its internal temperature or its skin temperature exceeds the part's rated max temperature.

Slow, shallow reentries keep the skin from getting too hot, but will take very long, and therefore tend to overload internal temperature via conduction. This generally kills spaceplanes that don't bleed off speed quickly enough.

Steep, fast reentries are too fast to heat up the part internally very much because conduction is sluggish, but they can overload the skin. This is generally what happens when you try to aerobrake out of an interplanetary transfer a Jool. Because the skin has next to no thermal mass, this overheating happens near-instantaneously, giving people the impression that they explode just by touching the atmosphere. And in a way, that's true.

Ablator on the heatshield is a consumable that carries skin heat away. Think of it as "every point of ablator is worth X heat energy". That means the skin of the heatshield stays cooler than it usually would be as long as it has ablator to spend. It doesn't die immediately after running out of ablator either; it simply behaves like any other part at that point. However, ablator can only be consumed so fast. It is possible to overheat the skin of the heatshield even when you have ablator left, because it simply cannot spend ablator fast enough to carry the heat away.

[Captain Sierra]

Meanwhile on MatoroIgnika's stream ... a heat shield survived two hours of aerobraking passes at Jool with zero ablator before finally exploding (when it did the rest of the craft went up almost instantaneously).

Heat shields may need a tiny bit of work.

[Streetwind]

That's exactly what I wrote... when running out of ablator, heatshields simply work like any other part in KSP. I.e. they explode when either their internal temperature or their skin temperature exceed their maxTemp value.

As long as temperatures don't get that high, you can aerobrake with it just fine for all eternity. Just like you can with a service bay, or an engine, or any other particularly heat resistant part. Of course, pulling that off at Jool is quite a feat, and a testament to M.I.'s piloting skill (or dumb luck ).

The rest of the ship then goes almost instantly because the maxTemp value for heatshields is very high. If the situation is such that the heatshield passes its threshold, then by definition it is also enough to easily overload all other parts that remain after the heatshield is gone.

Edited August 4, 2015 by Streetwind

[Warzouz]

I must say I don't understand how the heat systems works. Once I blew up in Kerbin sky coming from Minmus with a ultra shallow 5 or 6 pass even using air-brakes and heating shield.

And once I aerobraked a 100tons space station in Eve and only blew up the lower big docking ring. The space station wasn't even designed specifically to do so.

Aero braking was fun. Now it seems random and I chose to pack up some more fuel and so some boring retro burn at PE. The heating system puzzles me...