Asteroid as heat shield?

[MachTurtle]

I'm working on redirecting a class E asteroid into LKO and have observed that my tug (pusher, actually) is subject to shock heating even though it's on the "shielded" side of the asteroid. I had assumed that the asteroid body would act as a heat shield during aerobraking, but that doesn't seem to be true in this instance.  Is this a result of using FAR or is it due to more fundamental KSP physics? Thanks in advance for any guidance you can offer!

[Mystique]

I tried using a bit smaller asteroids recently as shield for agressive aerobraking (to brake from solar orbit to Kerbin's orbit) and they vanished in seconds after hitting more or less thick layers of atmosphere. So I don't suggest using roids this way at all, maybe just to touch atmosphere a bit. Was using stock aero, btw.

[Snark]

Hm, interesting.

I know that "stack-mounted" parts provide shielding for heat (but not drag) to parts behind them-- e.g. if you have the 10m inflatable shield on the front of your craft, it shields everything in a 10m cylinder behind it (actually, I think it may actually be a very narrow cone).

However, with asteroids, the only way you can hold on to them is with the Klaw.  I wonder if there may be some limitation of the game for klaw connections?  i.e. does it not count the klawed part (an asteroid, in this case) when calculating heat obstruction for the parts on the klaw's side of the connection?

Might be an interesting experiment to have a small ship equipped with the 10m inflatable shield, and then klaw another ship onto the back of it such that the klaw ship is also "behind" the shield, and try reentering with that-- see what happens.  Does the whole shebang get shielded, or not?

Anyway, that's all just idle speculation on my part, I don't actually know the answer.  I tend not to tinker with asteroids much, since I'm allergic to klaws.  Perhaps someone with more experience in the area could weigh in?

[Geschosskopf]

6 hours ago, MachTurtle said:

I'm working on redirecting a class E asteroid into LKO and have observed that my tug (pusher, actually) is subject to shock heating even though it's on the "shielded" side of the asteroid. I had assumed that the asteroid body would act as a heat shield during aerobraking, but that doesn't seem to be true in this instance.  Is this a result of using FAR or is it due to more fundamental KSP physics? Thanks in advance for any guidance you can offer!

In stock anyway, asteroids make very lousy heatshields. Can't say about FAR.  But in stock, 3 things go wrong with this.  First, ships on the trailing end of the asteroid still get hot.  Second, asteroids explode almost instantly on air contact unless you've already captured them by thrust alone into fairly low orbits to begin with.  And finally, assuming the asteroid lives long enough, it always rotates so the ship attached to it is on the hot, front end, so there's no chance for the asteroid to shield it anyway.  This is because the asteroid is by far the bulk of the drag and the ship moves the overall CoM ever so slightly in the direction of the ship.

[MachTurtle]

On 7/27/2016 at 10:00 AM, Snark said:

Might be an interesting experiment to have a small ship equipped with the 10m inflatable shield, and then klaw another ship onto the back of it such that the klaw ship is also "behind" the shield, and try reentering with that-- see what happens.  Does the whole shebang get shielded, or not?

I liked your idea so I knocked together a quick test (pic below).  It looks like the Klaw isn't the culprit in spite of its tainted reputation. Ferram4 commented elsewhere that FAR isn't responsible either. It seems to me that asteroids just don't act as a heatshield at all.  I'm also posting a pic of my tug/asteroid making a pass down to 52 km at 3200m/s. I think I'll either have to add heat shielding to my tug/mining ships or undock them and maneuver to avoid atmospheric entry. Do you think asteroid heat shielding ought to be suggested for a future version of KSP?

[Snark]

6 hours ago, MachTurtle said:

Do you think asteroid heat shielding ought to be suggested for a future version of KSP?

Sure, why not?  For that matter... seems kinda like a bug to me, now.

• Idea #1:  post a suggestion over in the Suggestions subforum.
• Idea #2:  report it as a bug.

[DD_bwest]

On 27/07/2016 at 8:00 AM, Snark said:

 

However, with asteroids, the only way you can hold on to them is with the Klaw.  I wonder if there may be some limitation of the game for klaw connections?  i.e. does it not count the klawed part (an asteroid, in this case) when calculating heat obstruction for the parts on the klaw's side of the connection

while not stock, if you use kas you can bolt a docking port to it and dock lol

[MachTurtle]

On 7/31/2016 at 11:46 PM, DD_bwest said:

while not stock, if you use kas you can bolt a docking port to it and dock lol

It's hard to see from the images I posted, but in addition to the klaw-attached ship there's also a mini-refinery system I attached to the asteroid using a KAS pylon with a rigid link. This assemblage of parts seemed to be subject to the same shock heating as the ship.

On 7/28/2016 at 8:46 PM, Snark said:

Sure, why not?  For that matter... seems kinda like a bug to me, now.

• Idea #1:  post a suggestion over in the Suggestions subforum.
• Idea #2:  report it as a bug.

I've been intending to reproduce this effect in a stock game in order to make a proper bug report, but I haven't found the time to do so yet.  Would it be reasonable to Hyperedit a craft to the asteroid, restart the game without any mods, and then use that to document this behavior?

[Snark]

1 hour ago, MachTurtle said:

I've been intending to reproduce this effect in a stock game in order to make a proper bug report, but I haven't found the time to do so yet.  Would it be reasonable to Hyperedit a craft to the asteroid, restart the game without any mods, and then use that to document this behavior?

That sounds pretty reasonable to me-- just make sure to mention in the bug report that you used Hyperedit to set things up.  Probably doesn't matter, but is better to err on the side of caution.

[Adelaar]

I have a D-class asteroid in a polar orbit around Kerbin, which was put in place by a tug that didn't actually fulfill the job that well, but I did find that the heating only comes into play when parts are "out there into the wind". This conclusion comes from the observation that the heating bar (and heat display) only shows heating when parts turn beyond the lee of the asteroid, and because my tug was always moving around from side to side when in atmosphere, different parts got heated at different AoA. 

Edited August 15, 2016 by Adelaar

[Stoney3K]

It looks like asteroids just don't occlude atmospheric heating at all and have absolutely zero tolerance for re-entry heating.

The question is, *should* they. That's more of a gameplay decision than an implementation one.

[MachTurtle]

On 8/15/2016 at 5:28 PM, Adelaar said:

I have a D-class asteroid in a polar orbit around Kerbin, which was put in place by a tug that didn't actually fulfill the job that well, but I did find that the heating only comes into play when parts are "out there into the wind". This conclusion comes from the observation that the heating bar (and heat display) only shows heating when parts turn beyond the lee of the asteroid, and because my tug was always moving around from side to side when in atmosphere, different parts got heated at different AoA. 

From your observations, Adelaar, are you confident that changes in the heating of your spacecraft are due to varying degrees of asteroid shielding or might it be due to varying attitudes with respect to atmospheric entry? As I mentioned earlier, I'd like to set up a test to measure what, if any, protection an asteroid provides, but I just haven't found the time yet. Thanks for sharing your experience.

 

On 8/16/2016 at 1:41 AM, Stoney3K said:

It looks like asteroids just don't occlude atmospheric heating at all and have absolutely zero tolerance for re-entry heating.

The question is, *should* they. That's more of a gameplay decision than an implementation one.

I haven't had an asteroid self-destruct from aerobraking yet, but haven't maneuvered any deeper than a 50 km periapsis. Tolerance for aero-heating may be pretty low, but it seems to be non-zero in my experience. Regarding whether asteroids ought to be modeled to provide shielding, I think KSP should reflect real physics as much as possible. My amateur astrophysics instincts tell me that an object on the lee side of an aerobraking asteroid ought to experience less heating than it would on the other side or without any asteroid at all. If anyone can make an argument to the contrary, I'd like to hear it.  Thanks for contributing to the discussion, Stoney3K.

 

[Adelaar]

1 hour ago, MachTurtle said:

From your observations, Adelaar, are you confident that changes in the heating of your spacecraft are due to varying degrees of asteroid shielding or might it be due to varying attitudes with respect to atmospheric entry? As I mentioned earlier, I'd like to set up a test to measure what, if any, protection an asteroid provides, but I just haven't found the time yet. Thanks for sharing your experience.

Fairly confident, because only the parts that are clearly in the airstream get heated. I noticed that as the Pe gets lower, the craft became more and more unstable, eventually flipping over to a point where the asteroid was at the trailing end. Whenever that happened, things really started to heat up and explode... So I'm faily confident that the asteroid itself does indeed act as a heat shield.