Low Kerbol orbit - how to cool the spacecraft?

[uncle_jew]

Hello,

I want to launch a mission into a low Kerbol orbit (5000km periapsis). Tried it twice, both times my spacecraft exploded due to overheating. On the 2nd attempt, I also had a medium-sized radiator attached, which didn't seem to help much.

How do you keep the spacecraft cool? Is it possible to calculate the needed number of radiators? Unlike solar panels, radiators are shown without any numbers that would indicate their heat dissipation.

Do radiators cool the whole spacecraft, or only the part they are directly attached to? I have KSP v1.0.4

Is it alternatively possible to construct an "umbrella" made of structure panels to shield the spacecraft from the solar heat? Does the KSP physics engine support it?

Thanks!

[Geschosskopf]

1 hour ago, uncle_jew said:

I want to launch a mission into a low Kerbol orbit (5000km periapsis). Tried it twice, both times my spacecraft exploded due to overheating. On the 2nd attempt, I also had a medium-sized radiator attached, which didn't seem to help much.

How do you keep the spacecraft cool? Is it possible to calculate the needed number of radiators? Unlike solar panels, radiators are shown without any numbers that would indicate their heat dissipation.

Do radiators cool the whole spacecraft, or only the part they are directly attached to? I have KSP v1.0.4

Is it alternatively possible to construct an "umbrella" made of structure panels to shield the spacecraft from the solar heat? Does the KSP physics engine support it?

Thanks!

A few months ago there was a challenge called "Solar Limbo".  It was about seeing how low you could go at the sun.  That was 1 or 2 updates ago but I don't think heat's changed since then (or at least not much) so the results and design information contained in that thread should still be pretty valid.  I recommend you check it out.  That should tell you how low it's possible to go, and how many radiators you need to do it.

As to radiators, there are 2 types, fixed and retractable.  The fixed kind only cool parts within 2 parts of the part they're attached to.  The retractable radiators cool every part on the ship.

[Spricigo]

Solar limbo

However this challenge was 

Quote

To build something that has both the delta-v to get a circular orbit around the sun, AND the thermal ability to survive it.

But there is some discussion about getting close

[Snark]

Put lots of radiators on the ship.  But, very very imporant, use the folding ones, not the static ones.

On 7/27/2016 at 0:57 PM, Geschosskopf said:

The fixed kind only cool parts within 2 parts of the part they're attached to.  The retractable radiators cool every part on the ship.

...That's not the real reason why you really, really want the folding (retractable) ones.

You want the retractables because they automatically rotate to keep themselves edge-on to the sun (basically, doing the exact opposite of what the folding solar panels do).  This allows them to radiate heat very effectively, without absorbing heat.

If you try to use just the static radiators, then unless you just happen to have them positioned so that they're edge-on to the sun, they'll actually hurt you by absorbing heat from the sun.

The key to keeping cool:

• Minimize the area of your ship that's exposed to sunlight, so you reduce heat you absorb.
• Maximize the area that's not exposed, so you increase how much heat you radiate.

The retractable radiators do both of those things, automatically, which is why you want them.  Other than that, orient your ship so that it presents the smallest possible "footprint" to the sun.  For example, if you have a long, skinny ship, point it so that it's pointing directly towards or away from the sun (i.e. with the long axis of the ship going through the sun's center, so it catches as little sunlight as possible.

[Geschosskopf]

40 minutes ago, Snark said:

Other than that, orient your ship so that it presents the smallest possible "footprint" to the sun.  For example, if you have a long, skinny ship, point it so that it's pointing directly towards or away from the sun (i.e. with the long axis of the ship going through the sun's center, so it catches as little sunlight as possible.

And it's usually better to point the nose at the sun than the tail.  Engine bells have a huge surface area-to-mass ratio.  While this makes them reasonably effective at radiating away the heat of running the engines, it also means they readily absorb ambient heat when not in use.

[Coga19000]

Retractable radiators should be what you need. Heat sinks will not help you here; they are basically batteries for your heat working on reverse (absorb heat when in use, stop working when full) and since there is not a night side to Kerbol (duh), they will simply extend your stay by a fixed amount.

If you see that radiators simply aren't enough, you can put a stack of heat shields on the front of the ship, connected by decouplers, and point them at Kerbol. They ALSO just extend your stay by a fixed amount, but they can really make a difference if in numbers, and combined with TONS radiators.

[Laie]

When I did some experiments for the solar limbo challenge, I found that a heatshield pointed towards the sun works great to keep your vessel out of harms' way. They seem to be insanely resistant.

It only took a pair of small (extendable) radiators to shed the heat that seeps through the panel.

However: by the time I came really low, I had to keep the heatshield pointed towards the sun at all times. Anything but the shield would blow up within moments when exposed to direct sunlight. Timewarp was out of the question, as was leaving the vessel for the tracking station and coming back later: it just wasn't possible to re-orient the vessel quickly enough.

The "Persistent Rotation" mod might help. Maybe.

[DDE]

On ‎29‎.‎07‎.‎2016 at 4:52 AM, Snark said:

Put lots of radiators on the ship.  But, very very imporant, use the folding ones, not the static ones.

...That's not the real reason why you really, really want the folding (retractable) ones.

You want the retractables because they automatically rotate to keep themselves edge-on to the sun (basically, doing the exact opposite of what the folding solar panels do).

Hey, sorry for piggybacking the thread, but are you sure they still work this way? They don't for me (while solar panels do), and I think I remember seeing a mention of such an issue.

[Snark]

1 hour ago, DDE said:

Hey, sorry for piggybacking the thread, but are you sure they still work this way? They don't for me (while solar panels do), and I think I remember seeing a mention of such an issue.

What version of KSP are you running?

There was once a bug that they didn't work right (they appeared to rotate edge-on to sunlight, but the actual heat flow acted as if they never rotated).  However, that was fixed quite some time ago, AFAIK it works correctly now (though I haven't done any sundiver missions lately).

If they're not working now, that would be a new bug, and ought to be reported so it can get fixed in 1.2.  Unfortunately I'm not in front of a KSP computer right now, so I can't check it myself at the moment, but it's an easy thing to verify.  Just have a ship with some radiator panels on it, send it reasonably close to the sun, and turn on debug thermal info via the Alt+F12 menu.  If the radiator's sun-tracking behavior is working properly, you should see the "radiated heat" at some high value, and the "absorbed heat" at a very low value, as soon as the panels have had a few seconds to rotate to be edge-on to the sunlight.

[DDE]

1 hour ago, Snark said:

What version of KSP are you running?

There was once a bug that they didn't work right (they appeared to rotate edge-on to sunlight, but the actual heat flow acted as if they never rotated).  However, that was fixed quite some time ago, AFAIK it works correctly now (though I haven't done any sundiver missions lately).

If they're not working now, that would be a new bug, and ought to be reported so it can get fixed in 1.2.  Unfortunately I'm not in front of a KSP computer right now, so I can't check it myself at the moment, but it's an easy thing to verify.  Just have a ship with some radiator panels on it, send it reasonably close to the sun, and turn on debug thermal info via the Alt+F12 menu.  If the radiator's sun-tracking behavior is working properly, you should see the "radiated heat" at some high value, and the "absorbed heat" at a very low value, as soon as the panels have had a few seconds to rotate to be edge-on to the sunlight.

I meant their rotation, similar to the solar panels. I have checked. And here's another clueless player: http://steamcommunity.com/app/220200/discussions/0/360670708795448585/

[Sharpy]

On 27.07.2016 at 8:52 PM, uncle_jew said:

Hello,

I want to launch a mission into a low Kerbol orbit (5000km periapsis).

 

Excuse me asking, but...

why?

That's generally a safe airbraking altitude as long as your apoapsis isn't too high. Instead of trying fancy heatsinks, give it a neat streamlined shape, following the occlusion rules (anything not node-attached in the stack under the heatshield is tucked in a cargo/service bay or a fairing) and a good heatshield on the front. And don't make the apoapsis too high.

 

 

Edited August 2, 2016 by Sharpy
fairing

[Diche Bach]

Is getting close to the sun pretty much the only real use of the "radiators" and stuff?

I've put them on some re-entry stuff that I figured would have issues with certain protruding parts getting hot, and it does seem to help there, but not sure what the various thermal stuff is really intended for.

[Hupf]

On 2.8.2016 at 8:51 PM, Sharpy said:

Excuse me asking, but...

why?

That's generally a safe airbraking altitude as long as your apoapsis isn't too high. Instead of trying fancy heatsinks, give it a neat streamlined shape, following the occlusion rules (anything not node-attached in the stack under the heatshield is tucked in a cargo/service bay or a fairing) and a good heatshield on the front. And don't make the apoapsis too high.

 

 

Kerbol. Not Kerbin

 

I did some testing with the various heatshields. It seems to me that Skin Temperature of the Heatshield seems to be the limiting factor as the radiators only seem to take away the Core Temperature. Also. With a deployed 10m HS I seem to be able to get lower than with a 1,25m one. I'm a little confused here: yes it does have 3500 vs 3300 max Skin Temp, but shouldn't the much larger surface cause a far greater buildup (i.e. actual Skin Temp) in the first place? With the 10m one I was able to reach 70Mm Ap stable orbit, with the 1,25m one I was stuck at 80Mm IIRC.

One other Idea, not tested yet, would be a highly excentric orbit (Ap around Eelo? :D) to minimize the time spent in the vincinity of Kerbol. Haven't done the math yet as to what the flyby time <70Mm would be then, though.

[Rath]

He wants to stop the billions of years old thermonuclear furnace we call Kerbol from melting his ship. 

[Plusck]

On 08/08/2016 at 9:02 PM, Diche Bach said:

Is getting close to the sun pretty much the only real use of the "radiators" and stuff?

I've put them on some re-entry stuff that I figured would have issues with certain protruding parts getting hot, and it does seem to help there, but not sure what the various thermal stuff is really intended for.

Radiators are mostly useful for drills and ISRU converters - they both produce a lot of heat and require cooling.

They are also vital if you have an LV-N running for any significant length of time.

Radiators don't generally have time to dissipate re-entry heat. For spaceplanes, however, I kow that people have needed radiators on top of the craft to protect the less heat-tolerant parts (I seem to remember problems with the Mk2 cockpit, for some reason) or at least slow down the heat spikes sufficiently to stop parts from exploding.

[Diche Bach]

Ah thanks Plusck!

I've got a few mods installed that add to the "thermal" element of the game, but as I'm only on year 3 of my career play, I have not yet got to the point of mining or the other things represented by the acronyms which I'll have to look up one of these days One mod in particular adds what I think are new types of parts: retracting and deploying thermal "regulation" systems it seems, though I have as yet found no use for them.

I think that some of the modded atomic stuff may produce lots of heat.

I've been figuring stuff out as I go. The quality of much of the scripting/programming/artwork/design is exceptional, it seems the prevailing norms for "documentation" in KSP modding leave a bit to be desired, and when I discovered this I decided against trying to "read up" on everything and follow a seat-of-the-pants approach even more than I typically do with heavily modded games.

I play with "Stage Recovery" which allows that debris objects which have a sufficient amount of heat mitigation ability, as well as drag production (I believe parachutes are the only thing which really counts), and which leave the active view area of the game in sub-orbital flight will be recovered at some percentage of their build cost, rather than simply burning up. I enjoy this mod (and the "Kerbal Construction Time" mod which I believe was made by the same person) a lot, and a little "trick" I've found:

destage my last sub-orbital stage (before periapsis extenstion burn) while pointed radially (or at least closely so), and with a sufficiently large decoupler charge AND immediately activate the boosters of the next stage at full throttle (to toss it back at Kerbal in a more steep entry which presumably will expose it to more intense, but briefer heating from re-entry) and I've managed to consistently recover stages, as long as they have a couple of the entry tier "small" radiators attached to them.

Having not yet got to the composite materials which I presume are integral to most space plane designs, I've toyed with building a "poor man's space plane" and seeing how it might handle re-entry with only radiators on it, but have yet to get one into orbit . . .