Heat shields when coming in hot

[Snark]

9 hours ago, Streetwind said:

New?

People have been lithobraking landers on modular girders since the dawn of time...

Well, yes.

But the irony of using landing gear as the "super-powerful almost invulnerable exploity way to land unharmed in an unreasonable situation", when the entire community is up in arms about how "the damn landing gear is unusably fragile" just tickles my funny bone. 

[Loren Pechtel]

On 6/16/2016 at 6:42 PM, Snark said:

[Before testing]  No, of course not, don't be silly.  When it says "impact tolerance 70 m/s" that doesn't mean it can take impact straight down into terrain at that speed, it's just some way of expressing the fact that it can land while the aircraft is traveling quickly.

[After testing]  Huh.  I'll be damned, you're right.  Just made a small, lightweight test craft that came down on four of the big landing gear, vertically at over 50 m/s.  Landed without a problem, no damage.

So of course this raises the "but I thought they were breakable now?" question.  I think the key, here, is that I had a very lightweight craft, so it had extremely low mass that the very heavy-duty shock absorbers in the landing gear could handle.  If I had had a few dozen tons of rocket riding on them, I expect it would have been a very different story.

But yeah, looks like we've discovered a new exploit.  Oh joy.

I wouldn't say that I'm right, I was just being curious.

[fourfa]

On 6/16/2016 at 9:42 AM, bewing said:

Don't you think, though, that squashing may be a potential future feature for KSP?

As usual, there's a mod for that

[xendelaar]

On 17-6-2016 at 4:17 AM, StrandedonEarth said:

Have you tried "rotiserrie mode?" Spin it really fast, that may help spread the heat around. Or not. But it's fun to try!

How far out is your last quicksave? I seem to recall that 1.1.2 added backups of autosaves. I haven't looked for those, but perhaps that can get you farther back emough to get a more favorable encounter.

I did the rotiserrie thing but that didn't help. I eventually reverted to an older savegame, where I just left Kerbin's SOI. Here, I fiddled with the manoeuvre node until I had a proper encounter where my orbital velocity was only 3200 m/s... At this speed, re-entry was a cake walk! Thanks for all the help.

 

 

 

 

Edited June 19, 2016 by xendelaar

[the_Demongod]

If anybody is curious as to why heat shields  become useless after a certain point, it has to do with how ablative cooling works.

Ablative cooling works by allowing the heat to vaporize the ablative surface of the shield (or engine nozzle in the case of an ablative nozzle), and this vaporization absorbs a lot of heat energy and allows it to be transferred away from the surface by the vaporized ablative. While this helps cool a little, the primary mechanism involves the vaporizing ablative creating a thin barrier of gas over the ablative surface to protect the surface from being directly exposed to the shock heated air, effectively shielding it to a certain extent. If you are moving too fast through the medium, however, the pressure of the incoming air is so great that the barrier of vaporized ablative is unable to hold the atmosphere away from the surface due to the extreme onslaught, effectively rendering it useless as the shock heating transfers its energy directly to the surface of the vessel.

[StarStryder]

Am I being dumb here?  Is the hole in the middle of the 4 heat shields simply letting the heat through to the central ship core?

[Streetwind]

7 hours ago, StarStryder said:

Am I being dumb here?  Is the hole in the middle of the 4 heat shields simply letting the heat through to the central ship core?

xendelaar stated before that there is a 1.25m heatshield behind that hole.

[xendelaar]

47 minutes ago, Streetwind said:

xendelaar stated before that there is a 1.25m heatshield behind that hole.

yup, there is a shield back there. I removed it during some re-entry tests and without it, I was also able to land as well. apparently, the other oversized shields are covering the central stack. However, the large shields (and the 1,25m one) don't protect bob's capsule and that's the only part that gets really hot as you can see here.

 

11 hours ago, the_Demongod said:

If anybody is curious as to why heat shields  become useless after a certain point, it has to do with how ablative cooling works.

Ablative cooling works by allowing the heat to vaporize the ablative surface of the shield (or engine nozzle in the case of an ablative nozzle), and this vaporization absorbs a lot of heat energy and allows it to be transferred away from the surface by the vaporized ablative. While this helps cool a little, the primary mechanism involves the vaporizing ablative creating a thin barrier of gas over the ablative surface to protect the surface from being directly exposed to the shock heated air, effectively shielding it to a certain extent. If you are moving too fast through the medium, however, the pressure of the incoming air is so great that the barrier of vaporized ablative is unable to hold the atmosphere away from the surface due to the extreme onslaught, effectively rendering it useless as the shock heating transfers its energy directly to the surface of the vessel.

Thanks for the information.That really is interesting! I doubt that these complicated physics apply to the kerbin universe though

Edited June 20, 2016 by xendelaar

[the_Demongod]

13 hours ago, xendelaar said:

Thanks for the information.That really is interesting! I doubt that these complicated physics apply to the kerbin universe though

You might be surprised. While they wouldn't actually simulate it directly, it would be very easy to use a simple function of speed to calculate the effectiveness of the ablative cooling, with would eventually cross the point at which it becomes useless. I can't say for sure but I would be surprised if a similar system wasn't implemented.