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Bleach

Ablator degradation on low sun orbit

Question

Hi all! When I flying near Sun (1000000 km) ablator on heat shield was evaporate. How I can protect it? I tested thermal control system and panel, heat shield 10 m, but its don't help me.

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Ok guys, re: stock radiators. They aren't going to protect an ablative heat shield from heating up to its ablation point because they don't even kick in for that part until it meets or exceeds a threshold based on its max temperature. Its ablation point is considerably lower than that. The entire craft will heat up past the shield's ablation point before the radiators kick in no matter which kind of radiator you use.

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First, just to confirm:  your radiators are the folding variety that auto-rotate to stay edge-on to the sun, yes?  Because that's what you need to have-- the fixed, static radiator panels can actually make your problem worse, because unless you can keep the whole ship manually rotated to keep them perfectly edge-on to the sun, they can easily end up absorbing more heat than they radiate.

So, assuming that you're using the folding radiator panels:  Have you tried just spamming them?  Put lots of radiator panels.  If you're skimming to within a million kilometers of the sun, that's a lot of radiant heat-- Kerbin's at over 13 million km, so you're getting hit with nearly 200 times the radiant heat as at Kerbin.  Each radiator can only pump a certain amount of heat.

(The good news is that it doesn't matter where on the ship you place them.  The folding radiator panels pump heat from the entire ship, regardless of placement, so you don't need to worry about where they go.  Just have lots of them.  Your ship should look like a sea urchin with radiators for spines.)

Another thing to consider... could you just design the ship to get by without ablator?  You mention that you're going 5000 m/s when you hit Kerbin.  If you can build a bit more dV into your ship, so you can cushion the blow a bit-- i.e. reduce it down to 3500 m/s or so before you hit atmosphere-- then the inflatable heat shield (which has no ablator to start with) can handle it just fine.  So if you can just build another 1000-1500 m/s or so of dV into your ship (for slowing down prior to hitting atmosphere), then you can stop worrying about ablator completely.

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If you use one of the extendable radiators, they automatically turn to be out of the sun.

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You could try reducing the heat shield's heatConductivity... in the actual part config (preferably with a Module Manager patch; don't edit part files directly)

Default value is 0.12 and you would want it 1/1000th of that or lower. How much lower I don't know. 

When the heat shield is exposed and no longer shielded (because you decoupled the rest of the craft) it will automagically change the part's heatConductivity to whatever the heat shield's reentryConductivity is set to. (default is 0.01)

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Accept that you're going to lose ablator while you're close to the Sun with focus, and only have focus on the craft long enough to do the science you need to.

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Point the other end of your rocket at the Sun?

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Yes, it not help. Beside this I tried overshadow craft from sun by 10m heath shield as an umbrella. It also not work.

Edited by Bleach

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Were your thermal control systems deployed in the shadow of your spacecraft? I have no idea if that actually affects heat transfer or not, but they do have tracking motors that make them turn edge-on to sunlight, so it may make a difference.

Maybe try putting your heatshield inside a fairing or cargo bay? If it's still losing ablator in those cases, you should probably file a bug report.

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1 hour ago, Allocthonous said:

Were your thermal control systems deployed in the shadow of your spacecraft?

 

Thermal control system was attached to decoupler near heat shield, because I don't know how attache it on heat shield edge. I think pats transfer heat. Isn't it?

 

PS. I can't attach radiator panel to heat shield directly..

Edited by Bleach

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Try putting a nose cone over the heat shield, make it the same size as the heat shield itself (so 1.25m cone on a 1.25m heat shield).  should protect the ablator until things get really critical. when the nose cone explodes, the hs can finally do its thing.

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2 minutes ago, AeroGav said:

Try putting a nose cone over the heat shield, make it the same size as the heat shield itself (so 1.25m cone on a 1.25m heat shield).  should protect the ablator until things get really critical. when the nose cone explodes, the hs can finally do its thing.

I tried this. And engine to sun oriented variant, and overshadow craft from sun by 10m heath shield .. Ablator all time degradate.

PS. Mission consist in ecliptic orbit on sun with periapsis ~990000 km (dV 4000m/s) and apoapsis on Kerbin orbit, take scientific data (x11), fly 3 times around sun (synchronize rendezvous point), correct this point (dV 20 m/s) and reentry Kerbin atmosphere on ~5000 m/s (2 times to break). All good, but ablator to this time degradate to 0.

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@Snark. Thanks for very useful reply! And, would You be so kindly, reply another question: Can I configure vehicle that radiator panel was oriented on edge to the sun on warp mode? Maybe some mods?

 
 
3 hours ago, Snark said:

Another thing to consider... could you just design the ship to get by without ablator?  You mention that you're going 5000 m/s when you hit Kerbin.  If you can build a bit more dV into your ship, so you can cushion the blow a bit-- i.e. reduce it down to 3500 m/s or so before you hit atmosphere-- then the inflatable heat shield (which has no ablator to start with) can handle it just fine.  So if you can just build another 1000-1500 m/s or so of dV into your ship (for slowing down prior to hitting atmosphere), then you can stop worrying about ablator completely.

No, no) I like when relatively small ships make a great affairs)

Edited by Bleach

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2 hours ago, Bleach said:

Can I configure vehicle that radiator panel was oriented on edge to the sun on warp mode? Maybe some mods?

No need for mods or special configuration; that's the stock behavior.  They do that automatically when in warp-- same as the rotating solar panels.  :)

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Thermal control system don't work in this case. With extended thermal panels ablator degradate much faster than if is retracted. Any ideas?

Ship:screenshot7.png

@Starwaster. So only way out is not use ablator near Sun and use fuel engine to break before reentry to Kerbin athmosfear?

Edited by Bleach

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6 minutes ago, Palaceviking said:

A pile of heatshields?

Tried, not working. Its evaporate at one time.

Edited by Bleach

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1 hour ago, Palaceviking said:

A Really Big pile of heatshields? 

No. Now I will check. 5 items will be enough?

PS. And it don't have sens, because weight of pile of heatshields is much than fuel to brake before reentry Kerbin atmosphere.

Edited by Bleach

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