Are radiators effective inside of closed cargo bays?

[Pecan]

So we all know that many things about rocket science are counter-intuitive (to catch-up with something in orbit, go slower, etc.)
Is it really the considered opinion of the space engineers here that radiators cool-down a ship by transferring heat to an atmosphere that is at plasma temperatures?

[Kerbart]

[quote name='Gooru']Why the hack such a stupid gameplay mechanics is introduced long after beta.... thats just ridiculous.[/QUOTE]

The question why the game went from alpha to beta to gold in a short time before these kind of mechanics were settled on has indeed been discussed multiple times on this forum. So... yeah.

Still, I'd rather seem them improve the game mechanics even (or sometimes [I]because[/I]) if it makes the game harder. In the pre 1.0 days you could return from Mun or Minmus, hit the atmosphere at a 70° angle at 4000m/s, deploy the parachutes at 60km altitude and be ensured you'd land just fine. In fact it was a lot harder in said scenario to get yourself killed.

Re-entry, in my book, should be a white-knuckle ride and never be easy. And maybe we need heatshields that can attach to wings. With a severe weight penalty. Why not?

[numerobis]

[quote name='Pecan']So we all know that many things about rocket science are counter-intuitive (to catch-up with something in orbit, go slower, etc.)
Is it really the considered opinion of the space engineers here that radiators cool-down a ship by transferring heat to an atmosphere that is at plasma temperatures?[/QUOTE]

I'm not a real engineer, but that seems ridiculous. However, having radiators pull heat from the exposed skin and radiate it out on the top side of the re-entry vehicle makes plenty of sense.

[NathanKell]

The plasma shockwave is only towards the bow, and even there it's at [I]very low density[/I]. Recall that radiative flux depends on the solid angle of the object radiating (from your POV), and despite the air at that altitude being very hot, there just isn't very much of it so the solid angle is, err, sparse.

Many, many RV designs rely on radiative cooling.

Now, as to radiators in bays: that won't work too well, because they'll just radiate into the bay, so there will be no net gain or loss of heat.

[Pecan]

[quote name='numerobis']I'm not a real engineer, but that seems ridiculous. However, having radiators pull heat from the exposed skin and radiate it out on the top side of the re-entry vehicle makes plenty of sense.[/QUOTE]

[quote name='NathanKell']The plasma shockwave is only towards the bow, and even there it's at [I]very low density[/I][/QUOTE]

I refer to [URL="http://forum.kerbalspaceprogram.com/threads/139564-Are-radiators-effective-inside-of-closed-cargo-bays?p=2297749&viewfull=1#post2297749"]Kuzzter's post above[/URL], amongst others. In that pic you can see two radiators beneath the cockpit which I would have thought would be the worst possible place. Since they're in the hottest air there they'd be heating up most, unless by conducting heat straight into the cockpit itself. Presumably this is the exact opposite of what was intended.

[Srpadget]

[quote name='sal_vager']Radiators don't contribute to drag inside a bay or fairing, they still work though, but then [URL="http://www.nss.org/settlement/nasa/spaceresvol2/thermalmanagement.html"][U]so did the radiators[/U][/URL] on the [U][URL="http://www.nss.org/settlement/nasa/spaceresvol2/images/fig37.GIF"]NASA space shuttle.[/URL][/U][/QUOTE]

Hrm... Need to be careful with that example. The Shuttle's radiators were mounted on the inside of the cargo bay doors, yes. But the doors had to be open and exposed to space before they'd function. So: if you have radiators inside a cargo bay, positioned so they're properly exposed to space (i.e., NOT facing some other part of the vehicle, such as the other side of the payload bay), then they will work WHEN THE PAYLOAD BAY IS OPEN. (That's the real-life constraint. KSP, of course, may operate differently. Its heat transfer mechanics are still pretty new and a little wonky.)

But mostly I had to hit reply because OMG YOU REFERENCED AN ABE HERTZBERG PAPER! I worked for him in grad school! Among other things, oddly enough, doing some work on advanced heat-rejection concepts for space-based applications. Good times... (Heh. I see he managed to work a sales pitch for his beloved Liquid-Droplet Radiator into that paper. :D I wonder if he ever solved the problem of the working fluid coating the OUTSIDE of the receiver in zero-g...?)

[NathanKell]

Pecan: Again, it depends on the air density. If the air density in the bow shock, when combined with the air temperature, leads to a lower radiation temperature than your own vessel, you will be a net loser of heat via radiation. If not, you will gain heat.

Note that in real life it's only on lunar-level reentry speeds that you gain significant quantities of heat through radiative flux; for LEO reentries you'll keep a negative (i.e. outflux > influx) radiative balance due to your thermal control system quickly heating up to 1800+ K.

Srpadget: Yep, same deal in KSP. If the bay's closed, all that will happen is you radiate heat...into the bay part itself. :]

[Gooru]

I just put down an old spacestation for LKO.
I did a quick retrogradburn to PE 45km and let it drop.
It survived without loosing parts and had no radiators, heatshields or care for AoA or anything on it.
It wasn´t streamlined at all.

Please take this as constructive criticism. I really think the reentry heat system need some rework on it.

All the talk why this radiator works that way, and why this is correct and so on is fine.
But if an old station can drop throught the atmosphere without damage while a streamlined spaceplane expoldes all the time due to overheating there simply is something wrong.

[Pecan]

[quote name='Gooru']...It survived without loosing parts and had no radiators, heatshields or care for AoA or anything on it...[/QUOTE]

Brilliant!
Did it actually land safely, or just survive re-entry?

[Gaarst]

[quote name='Gooru']I just put down an old spacestation for LKO.
I did a quick retrogradburn to PE 45km and let it drop.
It survived without loosing parts and had no radiators, heatshields or care for AoA or anything on it.
It wasn´t streamlined at all.

Please take this as constructive criticism. I really think the reentry heat system need some rework on it.

All the talk why this radiator works that way, and why this is correct and so on is fine.
But if an old station can drop throught the atmosphere without damage while a streamlined spaceplane expoldes all the time due to overheating there simply is something wrong.[/QUOTE]

This may seem counter-intuitive but the more drag you have during reentry, the better off you are.
Shock heating doesn't depend on drag because it is not the same as friction. Higher drag means losing more speed, and you'll heat less.
This might be the reason why your station survived reentry.

Also, spaceplanes and shuttle have very shallow reentries compared to other crafts/objects, mainly because of lift generated during the reentry. They then stay longer exposed to shock heating in high atmosphere, lose less speed, and in the end heat more.
Even in RSS with orbital speeds >7km/s, an unshielded craft, as long as it is a little "bulky", will not lose more than solar panels and antennas.

[Workable Goblin]

[quote name='Gaarst']This may seem counter-intuitive but the more drag you have during reentry, the better off you are.
Shock heating doesn't depend on drag because it is not the same as friction. Higher drag means losing more speed, and you'll heat less.
This might be the reason why your station survived reentry.

Also, spaceplanes and shuttle have very shallow reentries compared to other crafts/objects, mainly because of lift generated during the reentry. They then stay longer exposed to shock heating in high atmosphere, lose less speed, and in the end heat more.
Even in RSS with orbital speeds >7km/s, an unshielded craft, as long as it is a little "bulky", will not lose more than solar panels and antennas.[/QUOTE]
If it seems counter-intuitive, it's because it [i]is[/i] counter-intuitive that something not designed for reentry is better able to survive reentry than something that is so designed. If you look at actual space stations like Skylab or Mir, a surprising amount of material [i]did[/i] make it down to the ground, but it was all in the form of fragments, or to put it in game terms they overheated and were destroyed (or experienced excessive aerodynamic forces and broke up, either one works). By contrast, the Space Shuttle (and other spaceplanes, e.g. the X-37) fairly routinely reentered, with the only reentry failure occurring because one critical part was, thanks to launch damage, less heat-resistant than required.

If the overheating system is functioning to make it hard to land spaceplanes and easy to land space stations, then something is not right here, because the latter should be (almost) [i]impossible[/i] to land, and the former should be easy if you use the right technique and have a decent enough design.

[Gaarst]

[quote name='Workable Goblin']If it seems counter-intuitive, it's because it [I]is[/I] counter-intuitive that something not designed for reentry is better able to survive reentry than something that is so designed. If you look at actual space stations like Skylab or Mir, a surprising amount of material [I]did[/I] make it down to the ground, but it was all in the form of fragments, or to put it in game terms they overheated and were destroyed (or experienced excessive aerodynamic forces and broke up, either one works). By contrast, the Space Shuttle (and other spaceplanes, e.g. the X-37) fairly routinely reentered, with the only reentry failure occurring because one critical part was, thanks to launch damage, less heat-resistant than required.

If the overheating system is functioning to make it hard to land spaceplanes and easy to land space stations, then something is not right here, because the latter should be (almost) [I]impossible[/I] to land, and the former should be easy if you use the right technique and have a decent enough design.[/QUOTE]

That's because in real life, space agencies do not bother making their space station parts resistant to 2000K.
In KSP all parts are thermally protected so that they can withstand a reentry, except a few which are down to 1200K or less. But overall, most KSP parts designed for space have a max temp of 2000K.
But guess what ? If you exposed the ISS to 2000K it wouldn't have a gauge magically appear, become red and come back down after a while, as your KSS would.

KSP's overheating system if not perfect, but it is not responsible for the issue you described. Thermally insulated parts are responsible for your space station making it to the ground.

And for equivalent thermal protection, spaceplanes and shuttle will always be harder to reenter than capsules or bulky assemblies.

[Workable Goblin]

[quote name='Gaarst']That's because in real life, space agencies do not bother making their space station parts resistant to 2000K.
In KSP all parts are thermally protected so that they can withstand a reentry, except a few which are down to 1200K or less. But overall, most KSP parts designed for space have a max temp of 2000K.
But guess what ? If you exposed the ISS to 2000K it wouldn't have a gauge magically appear, become red and come back down after a while, as your KSS would.[/QUOTE]
Hm, no, it's just that the components would begin to heat up and eventually reach a temperature where (combined with whatever forces happened to be getting applied to the ISS) they would drop below the structural strength needed to hold together and the station would break up. Or, if the temperature was not applied long enough for that to happen, they would gradually cool off by radiating heat back out.

Which, come to think of it, is actually rather similar, no?

[quote name='Gaarst']And for equivalent thermal protection, spaceplanes and shuttle will always be harder to reenter than capsules or bulky assemblies.[/QUOTE]
Capsules, maybe, bulky assemblies, no. "Bulky assemblies," as you put it, will tend to be torn apart by aerodynamic forces on entry, regardless of any heating issues. Substantial fragments may reach the ground, but in KSP terms they would merely be debris at best.

[Gaarst]

[quote name='Workable Goblin']Hm, no, it's just that the components would begin to heat up and eventually reach a temperature where (combined with whatever forces happened to be getting applied to the ISS) they would drop below the structural strength needed to hold together and the station would break up. Or, if the temperature was not applied long enough for that to happen, they would gradually cool off by radiating heat back out.

Which, come to think of it, is actually rather similar, no?[/quote]

So you're saying if you exposed the ISS to excessive heating (2000K is excessive) it would break up ?
That is exactly what I said, except with a bit of sarcasm.

Similar to what ? KSP ?
Even if an unprotected part was exposed to such a heat for a short time, there would consequences. I mean 2000K is pretty hot, hot enough to make a nice hole in any module not designed for it.
KSP doesn't care about damages to a part: under 2000K: everything is fine; 2001K: BOOM! (or whatever max temp your part has), regardless of exposure time.
Whether a part would actually break up because of heating or forces does not matter: heat damages things, if it does not break up this time, it will cool down but be severely damaged, and will definitely break up next time.

[quote]Capsules, maybe, bulky assemblies, no. "Bulky assemblies," as you put it, will tend to be torn apart by aerodynamic forces on entry, regardless of any heating issues. Substantial fragments may reach the ground, but in KSP terms they would merely be debris at best.[/QUOTE]

What I mean by "bulky assembly" is anything less aerodynamic than a shuttle. For example a station module.
Of course an entire station would break up and burn during reentry in realistic conditions, but I was only talking about heating.

[fireblade274]

[quote name='NathanKell']Now, as to radiators in bays: that won't work too well, because they'll just radiate into the bay, so there will be no net gain or loss of heat.[/QUOTE]

I have been wondering about this; Good to know