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Noclevername
2018-Sep-24, 09:26 AM
What would be the best way to armor or otherwise protect the radiators on a combat spaceship?

The vessel in question is capable of (Earth) atmospheric landings, with dual purpose radiator/wings. So droplet or dust designs are out. I'd want a mechanism that can withstand a few punctures and still function. If they can be retracted, great (but I'm not married to the idea). Uses a near term tech level (20-30 years?).

Nuclear powered, probably an NTR. 70 meters long, main body is arrowhead shaped.

swampyankee
2018-Sep-24, 08:24 PM
Store up a few thousand tons of ice to use as a heat sink, and fold the radiators up.

Noclevername
2018-Sep-24, 09:10 PM
Store up a few thousand tons of ice to use as a heat sink, and fold the radiators up.

On a 70 meter long craft?

Swift
2018-Sep-24, 09:27 PM
I don't know what you wish to armor it from. Yes, I understand "attack", but what are they shooting: bullets, nuclear warheads? If it is bullets or something like that, can't you just make the radiator out of heavier gauge metal? Make it out of titanium sheets.

Noclevername
2018-Sep-24, 09:55 PM
I don't know what you wish to armor it from. Yes, I understand "attack", but what are they shooting: bullets, nuclear warheads? If it is bullets or something like that, can't you just make the radiator out of heavier gauge metal? Make it out of titanium sheets.

Assorted threats, mainly projectiles or fragments.

Noclevername
2018-Sep-24, 10:07 PM
What would be appropriate defenses for things like radiation or lasers? (Yes, there are multiple kinds of lasers, so maybe let's just go with the best general case)

Solfe
2018-Sep-25, 02:15 AM
If the threat is slugs and such, then a blade like edge and a very hard metal along that edge would be good. You'd need the radiators to move a good bit to protect them like that because you want that edge facing the threat. More like butterfly wings than the swing wings of a fighter jet.

If you had a railgun, the magazine could be in the radiator so that when the gun fires, you lose a bit of heat with each shot from the magazine. Obviously not even close to 1 for 1, but still better than nothing.

Noclevername
2018-Sep-25, 03:24 AM
OK, I'll take these suggestions into account. Titanium butterfly.

What about when they do get punctured? Any design elements that will make them more leak resistant or otherwise still useable even with gaping holes?

Swift
2018-Sep-25, 12:47 PM
OK, I'll take these suggestions into account. Titanium butterfly.

What about when they do get punctured? Any design elements that will make them more leak resistant or otherwise still useable even with gaping holes?
Small leaks could probably be dealt with the way they are on car radiators - a substance in the radiator fluid that solidifies when exposed, in this case, to vacuum. For big holes, valve off that section.

Swift
2018-Sep-25, 12:51 PM
What would be appropriate defenses for things like radiation or lasers? (Yes, there are multiple kinds of lasers, so maybe let's just go with the best general case)
I'm not sure radiation would be much of a threat to the radiator. For lasers, making them reflective would help, but that might make them poorer radiators, would make the ship more visible by reflected light.

Maybe the radiators could be covered by an electrochromic (https://en.wikipedia.org/wiki/Electrochromic_devices) material, that would be one color (probably black) when you want to optimize it as a radiator, but change color when under attack to protect from lasers.

Noclevername
2018-Sep-25, 01:27 PM
Cool! I didn't know such materials existed... outside of the movie MegaForce (https://en.wikipedia.org/wiki/Megaforce)!

Roger E. Moore
2018-Sep-25, 02:15 PM
Clouds of gas, smoke, or dust to decrease effectiveness of energy weapons. Small decoys that duplicate ship signature in every way. Rotate ship to prevent energy weapon from heating one area excessively. Use shield (second spacecraft controlled to move between you and energy weapons). Use energy-cloaking device that makes ship undetectable for heat or radiation signatures. Design ship to reflect away radar and other bouncing-signal detectors. Narrow the firing profile of the ship to make it harder to hit, more likely shrapnel from shotgun bombs will bounce off instead of penetrating. Hide behind real space debris or rocks. Disguise ship as space debris or rock. Spoof electronic signals from enemy vehicles to disarm/turn aside missiles, disarm mines.

Darrell
2018-Sep-25, 06:41 PM
Not sure if this is something you'd wish to consider, might be too speculative, but perhaps you could forego radiators altogether and have your ship use a laser refrigeration system for dumping heat. The idea of using lasers to dump heat has been speculated about by a few people. Physicist turned novelist David Brin used the concept in his novel Sundiver.

This Science Daily story, Powering lasers through heat (https://www.sciencedaily.com/releases/2012/11/121113083534.htm), from 2012 relates an idea a couple of physicists at the University of Innsbruck had for a quantum cascade laser driven by a temperature gradient. From the article . . .


"In such a temperature gradient driven laser, electrons are thermally excited in the warm area and then tunnel into the cooler area where photons are emitted."

This produces a circuit where light particles are emitted and heat is absorbed from the system simultaneously. "Between the consecutive emissions of light particles a phonon is absorbed and the laser is cooled. When we develop this idea further, we see that the presence of phonons may be sufficient to provide the energy for laser amplification," says Kathrin Sandner. Such a laser could be powered without using electric current.

I don't know if any further work has been done since with this concept.

Perhaps you can invent a cooling system for your ship that has no conventional radiators but instead dumps heat by firing quantum cascade lasers. Turn a weakness into a strength. Dump your waste heat into your opponent, or deep space.

Roger E. Moore
2018-Sep-25, 06:49 PM
Heat radiation is a liability, per Sidewinder missiles.

selden
2018-Sep-25, 08:14 PM
One technique is to dump it into an heat reservoir which you can eject later, either as a discrete body or as a cloud of liquid, gas, etc. In the short term you're limited by how well you can insulate extreme temperatures from the rest of the spacecraft or from external visibility. In the long term you're limited by the amount of excess mass you have.

Noclevername
2018-Sep-25, 08:41 PM
Heat radiation is a liability, per Sidewinder missiles.

But it's an unavoidable liability for a spacecraft, especially one with a large power plant. Vacuum is the perfect insulator.

Solfe
2018-Sep-25, 08:41 PM
I had a silly thought about the radiators after watching a video about a self-solving Rubik's cube (https://www.youtube.com/watch?v=xCoH2AORcEQ). If the radiator is modular, you could have replacement parts sitting within easy reach to account for damage. Eject the damaged part, the wing pops into a configuration where it can connect to a new part and then the whole structure rearranges itself to get the new part into place.

Radiators are aluminium on the ISS, which isn't especially heavy and the new parts wouldn't be full of liquid while waiting. Damage will cause a leak and the leak will drop the pressure cooling the structure. Dropping the damaged section will remove more heat, as will adding a cool part. Then you have the process of pumping new liquid in from a tank, which also gets a temperature drop. It almost sounds like cheating entropy, but your limit is physical parts instead of heat. Too much damage will make everything worse, but a little damage could be beneficial. You don't need to have the part in the correct place to work, only connected to the modular system. Running too many motors to replace parts will make your ship hotter.

Noclevername
2018-Sep-25, 09:07 PM
I had a silly thought about the radiators after watching a video about a self-solving Rubik's cube (https://www.youtube.com/watch?v=xCoH2AORcEQ). If the radiator is modular, you could have replacement parts sitting within easy reach to account for damage. Eject the damaged part, the wing pops into a configuration where it can connect to a new part and then the whole structure rearranges itself to get the new part into place.

Radiators are aluminium on the ISS, which isn't especially heavy and the new parts wouldn't be full of liquid while waiting. Damage will cause a leak and the leak will drop the pressure cooling the structure. Dropping the damaged section will remove more heat, as will adding a cool part. Then you have the process of pumping new liquid in from a tank, which also gets a temperature drop. It almost sounds like cheating entropy, but your limit is physical parts instead of heat. Too much damage will make everything worse, but a little damage could be beneficial. You don't need to have the part in the correct place to work, only connected to the modular system. Running too many motors to replace parts will make your ship hotter.

Sounds like a lot of added complication and mass.

Noclevername
2018-Sep-25, 09:13 PM
Not sure if this is something you'd wish to consider, might be too speculative, but perhaps you could forego radiators altogether and have your ship use a laser refrigeration system for dumping heat. The idea of using lasers to dump heat has been speculated about by a few people. Physicist turned novelist David Brin used the concept in his novel Sundiver.

This Science Daily story, Powering lasers through heat (https://www.sciencedaily.com/releases/2012/11/121113083534.htm), from 2012 relates an idea a couple of physicists at the University of Innsbruck had for a quantum cascade laser driven by a temperature gradient. From the article . . .



I don't know if any further work has been done since with this concept.

Perhaps you can invent a cooling system for your ship that has no conventional radiators but instead dumps heat by firing quantum cascade lasers. Turn a weakness into a strength. Dump your waste heat into your opponent, or deep space.

Lasers would have to be thermodynamically almost 100% efficient to act as heat dumping, wouldn't they?

Solfe
2018-Sep-25, 10:01 PM
Sounds like a lot of added complication and mass.

It is complicated.

VQkr
2018-Sep-25, 11:33 PM
Armor is very heavy, particularly for something as large-surface area as a radiator. Retractable panels that pull into a small, protected section would work. Backup cooling when under fire could be provided by a single-pass evaporative (or sublimator?) cooling system, as long as the water (or whatever the fluid was) reserves held out.

For suitability after punctures, I would suggested pulling from animal circulation systems. Nanobots would be circulated (or injected upon damage) that would take the place of platelets - clotting up around the puncture to limit coolant loss. For larger damage, valves would isolate sections of the radiator panels.

Noclevername
2018-Sep-26, 12:23 AM
If the threat is slugs and such, then a blade like edge and a very hard metal along that edge would be good. You'd need the radiators to move a good bit to protect them like that because you want that edge facing the threat. More like butterfly wings than the swing wings of a fighter jet.

Would it be easier to just turn the spacecraft's nose to face the threat? The main hull armor would be more effective that way anyway, since it's a pointy angle.

Roger E. Moore
2018-Sep-26, 12:43 AM
I might have found a solution to your problem.

https://arxiv.org/pdf/1809.09196.pdf

Noclevername
2018-Sep-26, 12:53 AM
I might have found a solution to your problem.

https://arxiv.org/pdf/1809.09196.pdf

Before I click on it, what is it?

DaCaptain
2018-Sep-26, 01:30 AM
Sheesh, everyone is wrong. You turn on your Ion Shields. Ion shields deflect any and all inbound "missiles" and absorb all radiant energy weapons.

But if that doesn't work simply retract the radiators into the hull.

Solfe
2018-Sep-26, 04:53 AM
Would it be easier to just turn the spacecraft's nose to face the threat? The main hull armor would be more effective that way anyway, since it's a pointy angle.

That does work, but if you can put your nose on the enemy while reducing the visibility of the radiators, that's best. Can't hit what you can't reach.

There has to be some sort of economy to a fight. You have missiles and beams. They are very different weapons, so they have to have very different purposes. Defending everything equally well can't really be an option. As I am picturing the scenario, I would think that missiles would be awesome for smashing soft targets like radiators with little energy cost. Beam weapons are killers but have a high energy cost, forcing the use of supplemental missiles. Since you have both, it is easy to envision an attacker launching missiles first, then a barrage of beam weapons as the missiles arrive at the target. No kill like overkill.

Of course, a captain won't willing step into the kill zone, so he has to now consider avoiding absolutely deadly fire while also preventing a cheap hit to the radiator and other soft bits. That is a game of cat and mouse, where the danger is sliding up and down the scale.

Noclevername
2018-Sep-26, 05:07 AM
But if that doesn't work simply retract the radiators into the hull.

Right. I suggested as much in the OP.

But retraction is only viable until it isn't. If your heat sinks are at capacity, you have no options but extend the radiators or vent coolant, and coolant runs out real fast.

VQkr
2018-Sep-26, 05:45 AM
...and coolant runs out real fast.

What kind of power level are we talkin' here?

Noclevername
2018-Sep-26, 11:25 AM
What kind of power level are we talkin' here?

Well, the ship is a 70x40x30 meter arrowhead/wedge with room for crew & some cargo, assume power output equivalent to 3x the best closed cycle nuclear achievable in that volume with today's tech.

(Tech level is efficient small fusion reactor, so the 3x factor is kind of arbitrary. No hard numbers available. Hard rad/neutron emissions are handwaved away.)

selden
2018-Sep-26, 11:32 AM
Before I click on it, what is it?

Directed Energy Interception of Satellites

Harrison Shea,b,∗, Will Hettelb, Phillip Lubinb

DaCaptain
2018-Sep-26, 11:37 AM
Right. I suggested as much in the OP.

But retraction is only viable until it isn't. If your heat sinks are at capacity, you have no options but extend the radiators or vent coolant, and coolant runs out real fast.

Shutdown to a bare minimum. Wait for the danger to pass. Then redeploy.

Convert the extra heat into something useful like electricity using a thermoelectric generator. You could then store the electricity in spare batteries and discharge them when all is safe. Or use the extra electricity as a weapon and zap the incoming missile.

Noclevername
2018-Sep-26, 11:40 AM
Shutdown to a bare minimum. Wait for the danger to pass. Then redeploy.

In combat?


Convert the extra heat into something useful like electricity using a thermoelectric generator.

Yes, but thermodynamically, that's ultimately a dead end. Generates more waste heat than it consumes, I'm told.

DaCaptain
2018-Sep-26, 11:56 AM
In combat?

You can't always be throwing punches.

Roger E. Moore
2018-Sep-26, 12:23 PM
Before I click on it, what is it?

Directed Energy Interception of Satellites
Harrison Shea, Will Hettel, Phillip Lubin (just released, 2018)

Noclevername
2018-Sep-26, 12:31 PM
You can't always be throwing punches.

You can't always be shooting in a firefight, should you unload your gun in the middle of one?

kzb
2018-Sep-26, 01:06 PM
Lasers would have to be thermodynamically almost 100% efficient to act as heat dumping, wouldn't they?

Not in this instance. It uses a temperature gradient to generate photons which can then be radiated off ship. So thermodynamically it is allowed I think.

The problem is, it needs a temperature gradient. In other words you will need a radiator of some sort :)

Darrell
2018-Sep-26, 02:13 PM
Not in this instance. It uses a temperature gradient to generate photons which can then be radiated off ship. So thermodynamically it is allowed I think.

The problem is, it needs a temperature gradient. In other words you will need a radiator of some sort :)

I certainly don't have the knowledge or experience to offer a valid opinion, but judging by some discussions I've read between people who do it doesn't sound like you need a radiator in order to create a temperature gradient. Or rather the laser is the radiator. The emission of photons from the laser supposedly cools the device. The temperature gradient you need to run the radiator, as I understand it, could be achieved by collecting and storing the waste heat internally, inside the ship. It's pretty straightforward to create two heat sources of different temperature.

Waste heat is stored in an on-board heat sink of some sort. The gradient between that heat sink and another at ambient ship temperature powers the quantum cascade refrigeration laser assembly, which is cooled by the process of lasing. Could a laser refrigeration system like this actually work? I'd say unknown but possible. Some experts say the thermodynamics look like it could work. Some experts say the thermodynamics don't work out. Its firmly in the realm of speculative right now.

VQkr
2018-Sep-26, 03:42 PM
Well, the ship is a 70x40x30 meter arrowhead/wedge with room for crew & some cargo, assume power output equivalent to 3x the best closed cycle nuclear achievable in that volume with today's tech.

(Tech level is efficient small fusion reactor, so the 3x factor is kind of arbitrary. No hard numbers available. Hard rad/neutron emissions are handwaved away.)

Sublimating water into vapor in the vacuum of space gives you 2.8 MW of cooling for each kg/s of water expended.

Your craft has a volume of ~~0.333*70*40*30=28000 m^3. An American 688 class submarine has a volume of ~~10000 m^3 and 165 MWt reactor. Assuming 3x the power density, we get 165*28000*3/10000=1400 MW of heat, requiring 500 kg/s of emergency open-circuit cooling water to maintain at full power if the normal closed-circuit radiator is shut down or disabled, so each 1 m^3 of water would provide 2 seconds of backup. 10 minutes of emergency cooling would take about 1% of the ship's volume in water storage.


I certainly don't have the knowledge or experience to offer a valid opinion, but judging by some discussions I've read between people who do it doesn't sound like you need a radiator in order to create a temperature gradient. Or rather the laser is the radiator. The emission of photons from the laser supposedly cools the device. The temperature gradient you need to run the radiator, as I understand it, could be achieved by collecting and storing the waste heat internally, inside the ship. It's pretty straightforward to create two heat sources of different temperature.

Waste heat is stored in an on-board heat sink of some sort. The gradient between that heat sink and another at ambient ship temperature powers the quantum cascade refrigeration laser assembly, which is cooled by the process of lasing. Could a laser refrigeration system like this actually work? I'd say unknown but possible. Some experts say the thermodynamics look like it could work. Some experts say the thermodynamics don't work out. Its firmly in the realm of speculative right now.

No, that pesky 2nd law of thermodynamics gets in the way. Two heat sources of different temperatures would rapidly equalize (ie, you'd warm up the colder source) if you tried to use them as a heat sink. Ultimately, what your radiator is offloading is entropy, and a laser is not going to do that for you.

Noclevername
2018-Sep-26, 04:25 PM
Sublimating water into vapor in the vacuum of space gives you 2.8 MW of cooling for each kg/s of water expended.

Your craft has a volume of ~~0.333*70*40*30=28000 m^3. An American 688 class submarine has a volume of ~~10000 m^3 and 165 MWt reactor. Assuming 3x the power density, we get 165*28000*3/10000=1400 MW of heat, requiring 500 kg/s of emergency open-circuit cooling water to maintain at full power if the normal closed-circuit radiator is shut down or disabled, so each 1 m^3 of water would provide 2 seconds of backup. 10 minutes of emergency cooling would take about 1% of the ship's volume in water storage.



Thanks!

kzb
2018-Sep-26, 04:49 PM
I certainly don't have the knowledge or experience to offer a valid opinion, but judging by some discussions I've read between people who do it doesn't sound like you need a radiator in order to create a temperature gradient. Or rather the laser is the radiator. The emission of photons from the laser supposedly cools the device. The temperature gradient you need to run the radiator, as I understand it, could be achieved by collecting and storing the waste heat internally, inside the ship. It's pretty straightforward to create two heat sources of different temperature.

Waste heat is stored in an on-board heat sink of some sort. The gradient between that heat sink and another at ambient ship temperature powers the quantum cascade refrigeration laser assembly, which is cooled by the process of lasing. Could a laser refrigeration system like this actually work? I'd say unknown but possible. Some experts say the thermodynamics look like it could work. Some experts say the thermodynamics don't work out. Its firmly in the realm of speculative right now.

You still need a hot end and a cold end to make it work.

Don't get me wrong I am not discounting it entirely.

Collecting and storing waste heat at two different temperatures in itself uses energy and therefore creates even more waste heat. On the other hand if you had a higher temperature heat source in the ship, such as a nuclear reactor, it is possible this heat powered laser could carry away some of the reactor waste heat and reduce the heat load on the radiators.

I think the best you could hope for is the radiators could be reduced in size. In a combat situation this would be worthwhile because it reduces the target area.

Noclevername
2018-Sep-26, 04:57 PM
So using an online calc and assuming light water as the coolant, I get a size of... way too big! Square miles. Even cutting power level to regular nuclear-sub output isn't helping enough.

Reducing the area needed would require a hotter coolant. Any suggestions for the coolant??

VQkr
2018-Sep-26, 06:08 PM
So using an online calc and assuming light water as the coolant, I get a size of... way too big! Square miles. Even cutting power level to regular nuclear-sub output isn't helping enough.

Reducing the area needed would require a hotter coolant. Any suggestions for the coolant??

Hydrogen gas. Your panels are going to need to be hot to radiate this kind of power from panels similar in area to the surface of the craft (as opposed to massive fold-out arrays like on the ISS). Energy dissipated from a radiator increases with the fourth power of absolute temperature, so increasing radiator temperature is the most efficient way to increase the thermal power (though a warmer cold sink decreases the amount of useful work you can get from a heat source).

BTW, you mentioned a NTR (nuclear thermal rocket) in your OP. All this radiator talk presumes a closed system (ie, a reactor driving a turbine to produce electrical power for weapons or ion engines). If most of your power is going toward thermal propulsion such as an NTR, your waste heat leaves with the exhaust - you don't need a large radiator for that.

Noclevername
2018-Sep-27, 10:30 AM
I've got an idea for a dramatic scene involving repairing a coolant leak in a running battle. A hot hydrogen leak inside the ship will lead to big bonfire and probable total loss, I'd like to avoid quite that much drama. Would helium work instead?

kzb
2018-Sep-27, 11:22 AM
I've got an idea for a dramatic scene involving repairing a coolant leak in a running battle. A hot hydrogen leak inside the ship will lead to big bonfire and probable total loss, I'd like to avoid quite that much drama. Would helium work instead?

NaK. This was used in fast breeder reactors as coolant and has already been used in space.

A leak onboard would give a spectacular fire but without blowing up the whole thing.

https://en.wikipedia.org/wiki/Sodium-potassium_alloy

kzb
2018-Sep-27, 11:28 AM
<EDIT>



No, that pesky 2nd law of thermodynamics gets in the way. Two heat sources of different temperatures would rapidly equalize (ie, you'd warm up the colder source) if you tried to use them as a heat sink. Ultimately, what your radiator is offloading is entropy, and a laser is not going to do that for you.

I was thinking last night, from a thermodynamics point of view is there any difference between this laser idea and a thermocouple?

A thermocouple could generate electricity from a temperature difference. That electricity then powers a resistor which radiates energy to space at a high temperature.

The high temperature means it can be much smaller than a radiator at room temperature.

But there is still this problem of needing a hot end and a cold end to make it work.

Darrell
2018-Sep-27, 04:53 PM
If I understood the article correctly the configuration of quantum cascade laser that the researchers where speculating about cools down by the process of lasing. I've no idea of the efficiency or the basic principles of how it is supposed to work. But, again if I understand it correctly, this laser is powered directly by heat and as a result of producing photons it is cooled. The researches were specifically speculating about using this type of laser for cooling, initial applications considered were cooling of electronics.

swampyankee
2018-Sep-27, 06:59 PM
So using an online calc and assuming light water as the coolant, I get a size of... way too big! Square miles. Even cutting power level to regular nuclear-sub output isn't helping enough.

Reducing the area needed would require a hotter coolant. Any suggestions for the coolant??

Liquid metals -- lead-bismuth eutectic, sodium, sodium-potassium eutectic, and mercury have all been used as high-temperature heat transfer fluids -- molten salts, such as thorium fluoride, or gases.

All have been used in ground and some in space-based systems.