Tiny heat shield pointless?

[Spyderborg]

Just tried using the smallest heatshield for the first time, and it pretty much did nothing it seemed like. It couldn't even protect a probe core from re-entry from Minmus. What is it for then if it fails at its obvious purpose?

[maj.solo]

it can protect vessels as wide as itself, just as the other heat shields. But if you are doing 3000m/s I guess you are screwed if you go below 40K.

Me myself did a silly thing today. I sent away a ship called "Educational" to train kerbals. And it got refuled at Minmus. Then I got the sick idea of buying more scientists etc so I thought I do NOT want to land this thing as originally intended. But if I am not going to land and will go on ANOTHER trip I need to save all fuel. How do I do that.... by not retroburning when I get to Kerbin but aero breaking instead.
Aerobreaking a ship full of fuel ..... takes many passes.
First pass you do about 3000m/s and you taste the atmosphere and go no deeper then 47K just to check. Many laps , last lap I whent down to 36K doing 2400m/s. And it was without heatshields.
I think heatshields should withstand 2000 2200 if you decide to aim for the surface. If you go deep into the atmosphere faster then that I suspect even a heat shield will not save you.

So ............... what was your speed????

Also were you able to aim the heat shield properly all the way down or did the craft wobble??

[Spyderborg]

I was going about 3000m/s and straight as an arrow. The probe core I was using was the OCTO one; could it be that the stupid little corners of the octagon caused it? Since those corners hang over the heatshield very slightly.

[maj.solo]

Well you are brave. 3000m/s is a dangerous speed Well that is what KSP is for ... to blow up things as long as no kerbal is aboard.

[Rhedd]

3000m/s is pretty normal if you're aerobreaking directly from a Munar transfer, let alone from Minmus. I'm not sure a small heatshield CAN handle a direct descent from Minmus! Never tried it.

Did the shield run out of ablator, or did it fail before that? If if failed before it was spent, I can't really say why. Did you see fire or yellow light on anything other than the heatshield?

Pretend it was a manufacturing defect in the heatshield, make excuses to the public, and try again.

[Sergeant-Hawk]

I haven't tried the smallest heatshield but I have used the two bigger ones for my manned missions. I usually have no problem aerobraking at 30-33 km return from minmus, when I want to land on the first pass. I'll have to test the small heatshield though.

[Operation40]

I bet heat is just radiating to the OKTO core; its only got max temp 1200K
put a battery (2000K) or almost any other part between it and the sheild and you'll be fine

[Spyderborg]

Originally posted by Rhedd:

3000m/s is pretty normal if you're aerobreaking directly from a Munar transfer, let alone from Minmus. I'm not sure a small heatshield CAN handle a direct descent from Minmus! Never tried it.

Did the shield run out of ablator, or did it fail before that? If if failed before it was spent, I can't really say why. Did you see fire or yellow light on anything other than the heatshield?

Pretend it was a manufacturing defect in the heatshield, make excuses to the public, and try again. :KOh:

I didn't know they could "run out"? The little temperature bar was well below the maximum if that's what you mean. But nothing else was really heating up at all; just all of the sudden a solid red bar appeared on the probe core and exploded seconds later.

Originally posted by Operation40:

I bet heat is just radiating to the OKTO core; its only got max temp 1200K
put a battery (2000K) or almost any other part between it and the sheild and you'll be fine

I also tried it with an experiment storage container in between and the same thing happened.

[Sergeant-Hawk]

Well, I just tested this using hyperedit to simulate a return from minmus ( Apo 47M, Peri 30K ). The vessel i tested had the 0.625 m heat shield, octo core, a few Z-200 Batteries, a small reaction wheel, and an experiment storage unit, in that order. Used SAS to point retro. Peak speed was 3250 m/s and it survived and used about 9 out of 50 units on the heat shield ablator.

The core got a little hot but didn't explode.

I even tested different periapsis for the return all the way down to a 0 km periapsis. and the result was the same. It only failed when i set my orbital speed to 0 at apoapsis which would give a periapsis at the center of the planet).

If your ship is managing to point retrograde the whole way then it is probably your periapsis is way too low, make sure it is above zero and give that a try. You don't want to be coming straight down onto the planet, you want to skim thru the atmosphere. If your ship is struggling to point retrograde then it is another problem, like not enough electricity, or reaction wheels, or another design flaw. Let us know how it goes. Good Luck!

[Rhedd]

Yes, heat shields can "run out". They have a resource (that you can see) called ablator. An ablative shield works by intentionally falling apart, or "ablating". As layers get hot, they burn off and are shed from the shield, taking their heat with them. So in KSP, a shield has the "ablator" resource that gets used up during heating. When that runs out, the shield is basically useless.

Doesn't sound like that was your problem though, thanks to Sergeant-Hawk's comprehensive testing. Thanks for the info, Hawk!