On the radiation of heat in space

[Ford Prefect]

Doing some thinking in the quiet moments between exams, I have decided to vaguely explore in my head some science-fiction story ideas. While the content is not particularly important itself, one of my thoughts was: 'I wonder, what are some of the best materials for the purpose of radiating waste heat? And I wonder, what are some different methods for dealing with such heat, beyond the usual arrays of radiators'.

I didn't actually think that, but the general idea is the same. My knowledge in the ares of waste heat, heat sinks and the like are imaginary at best, and I was looking for interesting ideas. I'm not particularly fussed by how feasible the concept actually is, however.

[Ariphaos]

Certain forms of carbon will get you into the ~10 MW / square meter range. Really, without doing some form of venting, you can't beat it. Hell, it would be hard to make use of it.

Two plates, forming a plane around a craft (giving it 'wings'), are the most materially efficient at radiating heat, at least with any obvious solution. If you add in a third, or fourth, etc. such that they would be at 120 degree angles and 90 degree angles respectively, the net effect is going to be as if you had 2.5 plates and 3 plates respectively.

Basically, each time you add another solid plate in line with the first two, one 'side' of it is basically lost in that 'it' is re-absorbing the heat you are trying to shunt off. You can of course mitigate this by using the extremities to radiate the majority of the heat, etc., and perhaps grills along the inner portion of the heat wings, but it's still a design concern.

To get any more efficient than that with currently understood technology, you pretty much need to vent something. Pick a gas with a high heat retention, vent it for emergencies. It would probably need to be elemental or otherwise very simple as you are likely getting it exceedingly hot.

There are other things that come to mind as 'maybies' but anything beyond the above is speculation at best, at least from me.

[metavac]

Doing some thinking in the quiet moments between exams, I have decided to vaguely explore in my head some science-fiction story ideas. While the content is not particularly important itself, one of my thoughts was: 'I wonder, what are some of the best materials for the purpose of radiating waste heat? And I wonder, what are some different methods for dealing with such heat, beyond the usual arrays of radiators'.

I didn't actually think that, but the general idea is the same. My knowledge in the ares of waste heat, heat sinks and the like are imaginary at best, and I was looking for interesting ideas. I'm not particularly fussed by how feasible the concept actually is, however.

You're looking for a set of materials that combine high heat conductivity, high radiative efficiency, high reflectivity, and high emissivity. Spacecraft today generally fly with radiators coated in silver-teflon to form a 'second surface mirror.' But you're probably looking for something more far out than that. Take a look into magnetized liquid drop radiators. I also recall a discussion about using plasma circulating in huge magnetic fields to reject heat, but I haven't seen much reading in that direction.

[Connor MacLeod]

Certain forms of carbon will get you into the ~10 MW / square meter range. Really, without doing some form of venting, you can't beat it. Hell, it would be hard to make use of it.

Two plates, forming a plane around a craft (giving it 'wings'), are the most materially efficient at radiating heat, at least with any obvious solution. If you add in a third, or fourth, etc. such that they would be at 120 degree angles and 90 degree angles respectively, the net effect is going to be as if you had 2.5 plates and 3 plates respectively.

Basically, each time you add another solid plate in line with the first two, one 'side' of it is basically lost in that 'it' is re-absorbing the heat you are trying to shunt off. You can of course mitigate this by using the extremities to radiate the majority of the heat, etc., and perhaps grills along the inner portion of the heat wings, but it's still a design concern.

To get any more efficient than that with currently understood technology, you pretty much need to vent something. Pick a gas with a high heat retention, vent it for emergencies. It would probably need to be elemental or otherwise very simple as you are likely getting it exceedingly hot.

There are other things that come to mind as 'maybies' but anything beyond the above is speculation at best, at least from me.

I've noticed Carbon seems to have very good thermal properties but I haven't been able to find any specific numbers (specific heat, melting point, the latent heats, etc.)

[metavac]

To get any more efficient than that with currently understood technology, you pretty much need to vent something. Pick a gas with a high heat retention, vent it for emergencies. It would probably need to be elemental or otherwise very simple as you are likely getting it exceedingly hot.

Additionally, dimpling or honeycombing will increase the surface area, but at varying costs to efficiency. But yes, you'll need some form of active rejection for the high heat loads generated by rockets with powered interplanetary ranges. Venting might not be the best solution, especially if ablating or bleeding a surface will do.

[Connor MacLeod]

Venting also has the problem that you a.) have to carry the materials to carry off your heat, which can pose problems the way fuel/propellant can. b.) Its not a very good long-term solution, unless you have some easy method of replenishing the lost material (under most cases I could think of, not very likely.)

[metavac]

Venting also has the problem that you a.) have to carry the materials to carry off your heat, which can pose problems the way fuel/propellant can. b.) Its not a very good long-term solution, unless you have some easy method of replenishing the lost material (under most cases I could think of, not very likely.)

Recapturing some of the vented material after it's rejected the heat would mitigate that cost.

[Starglider]

Recapturing some of the vented material after it's rejected the heat would mitigate that cost.

That sounds like a droplet radiator:

Liquid-droplet radiators are also a possibility. There do exist liquids which have extremely low vapor pressure at high temperatures - certain organics up to ~600K, liquid metals (esp. lithium) to ~1500K. Using a carefully-designed nozzle to create a fan-shaped spray of fine droplets towards a linear collector results in a very efficient radiator, with minimal weight per unit radiating surface, high temperature, and high throughput.

The radiator would be essentially triangular when "deployed", with the spray nozzle at one vertex and the collector along the opposite side. If the nozzle-vertes is adjacent to the ship body, the collector "arm" will have to extend outwards. Alternately, the collector can be run along the side of the ship, and the spray nozzle extended on a boom and aimed inwards. A series of closely-spaced, narrow-angle nozzles would approximate a rectangular array.

There is always some loss of coolant due to evaporation in vacuum, hence use of liquids with extremely low vapor pressure. You also lose coolant if such a radiator is run under acceleration, unless the collector is over-long and aligned parallel to the thrust axis, which imposes a constraint on system geometry. You also lose coolant if the radiator "panel" is hit by enemy weapons fire; on the other hand there is no mechanical damage unless the much smaller nozzle or collector arms are hit. Bottom line - you'll need a small surplus of coolant, unless you are running a warship, in which case you'll need a large surplus.

If liquid metal is used as the coolant, MHD pumping can be used at the collector arms, resulting in a simplified design with no moving parts. Indeed, in such a case the coolant could also be used as the working fluid in an MHD generator, resulting in a single-fluid, single-cycle power system from primary energy generation to waste heat radiation. Again, a simple, efficient design with no moving parts.

(from Atomic Rocket, radiator capacipty online calculator here)

[metavac]

Oh that's just all kinds of awesome. Thanks, Starglider.

[Ford Prefect]

Interesting, though I wonder if there are any other concept for heat radiation - the droplet radiator was most intruiging.

As this story (naturally) has space battles, and because you can't really armour radiators, you must likely run with them closed during combat. For the moment, the primary propulsion will be fusion drives, and I think you can use such a things exhaust plume as its radiator (I think. I know you can do it with certain types of nuclear rockets). However, there are point-defense lasers to think about, which get one hell of a workout. During combat then, one must rely on heatsinks, and less effective methods of radiation; unless there are potential methods of heat radiation which aren't enormous targets* - which is an iffy proposition at best.

*By enormous target I don't mean in a thermal sort of way, I mean in actual size. Ships wouldn't have anything approaching traditional shielding as such, so it's basically one close range missile detonation and you're gone. Radiators tend to get very large, which means that explosions can be further away and still do damage, which is potentially ... problematic.

[Surlethe]

For heat sinks, you could simply find an element or compound with a high specific heat. That way, you can direct all of your battle-generated heat into this compound, and it will heat up only a little bit for lots of energy directed into it. Then, after the battle, you can take your time dumping the heat from the sink and cooling it down without having a problem with detection.

[Starglider]

For soft sci-fi there is always the Star Wars option; neutrino radiators. Can be embedded in the hull and from the geometry apparently emit large amounts of neutrinos without absorbing them (at least, not any more than normal matter does). Unfortunately the 'carry around a micro black hole and expose internal radiators to that' option does not work since the discovery of Hawking radiation, as any singularity small enough to haul around with you is going to evaporate explosively.

[Wyrm]

Unfortunately the 'carry around a micro black hole and expose internal radiators to that' option does not work since the discovery of Hawking radiation, as any singularity small enough to haul around with you is going to evaporate explosively.

Worse than that. Any black hole that's small enough to carry around is going to be fucking hot. Second law still applies.

[Beowulf]

If you utilize a droplet radiator, you can effectively armor it by making the panel out of armor plate.

[Darth Wong]

It would be interesting to see a sci-fi story where the ship is not armoured at all. The whole idea of armour plate on starships implies that mass is not an issue at all, and that's really one of the most absurd (albeit common) conventions in sci-fi. Hell, the lunar lander had fucking foil between the astronauts and the vacuum.

[Darth Servo]

It would be interesting to see a sci-fi story where the ship is not armoured at all. The whole idea of armour plate on starships implies that mass is not an issue at all, and that's really one of the most absurd (albeit common) conventions in sci-fi. Hell, the lunar lander had fucking foil between the astronauts and the vacuum.

Probably due in large part to the confusion between mass and weight in the US measurement system. Damn, WHEN CAN WE GO METRIC ALREADY?!?

Yes, I know, its a rhetorical question, the answer to which is, "When it becomes profitable for the corporations to do so"

[Beowulf]

It would be interesting to see a sci-fi story where the ship is not armoured at all. The whole idea of armour plate on starships implies that mass is not an issue at all, and that's really one of the most absurd (albeit common) conventions in sci-fi. Hell, the lunar lander had fucking foil between the astronauts and the vacuum.

Well, some armoring is necessary, if only to protect against micrometeorite damage. That doesn't require very much though. You quickly end up with an eggshells with sledgehammers situation, if there isn't an armor. The fact that any interesting drive system is also a weapon is much more a factor without armor (interesting being defined as not requiring long amount of time for travel).

[Darth Wong]

It would be interesting to see a sci-fi story where the ship is not armoured at all. The whole idea of armour plate on starships implies that mass is not an issue at all, and that's really one of the most absurd (albeit common) conventions in sci-fi. Hell, the lunar lander had fucking foil between the astronauts and the vacuum.

Well, some armoring is necessary, if only to protect against micrometeorite damage. That doesn't require very much though. You quickly end up with an eggshells with sledgehammers situation, if there isn't an armor.

We already have that with fighter planes in real-life, assuming you're talking about sci-fi space combat. There's really no reason you have to show ships being able to absorb punishment rather than trying to evade or intercept it.

The fact that any interesting drive system is also a weapon is much more a factor without armor (interesting being defined as not requiring long amount of time for travel).

That assumes you're fighting at close range. The bane of sci-fi space combat depictions in TV or the movies is the desire to make everything look comprehensible to viewers who want to see a WW2-style dogfight.

[andrewgpaul]

Ford and Darth Wong, have either of you seen Attack Vector by Ad Astra Games? There's apparently some hand waving in terms of weapon and drive efficiencies, but apart from that, it's fairly rigorous.

[metavac]

Alternatively, you could reduce your scale a bit; say everything happens between Earth and the Moon, so it is just a few days away by real-life rockets, while still having plenty of sci fi potential.

Good point. A lot of science fiction is driven by the idea that anything interesting out in space is going to be found on some rocky world like ours. This sort of planet bound bias can blind author and reader a like to an equally rich if not richer inhabited ecology possible in outer space itself.

[Ford Prefect]

You quickly end up with an eggshells with sledgehammers situation, if there isn't an armor.

I'm not particularly fussed because I already had that in mind. There is a massive gap between the effective firepower a ship can put out and the amount of firepower it can take. Even with inflated materials science, it can effectively come down to a single missile or a single shot from a large particle cannon.

For soft sci-fi there is always the Star Wars option; neutrino radiators.

I'm not quite sure this story would be that soft. I like the idea of heat having to go place and stuff, so I don't want to just handwave it away totally.

[Beowulf]

It would be interesting to see a sci-fi story where the ship is not armoured at all. The whole idea of armour plate on starships implies that mass is not an issue at all, and that's really one of the most absurd (albeit common) conventions in sci-fi. Hell, the lunar lander had fucking foil between the astronauts and the vacuum.

Well, some armoring is necessary, if only to protect against micrometeorite damage. That doesn't require very much though. You quickly end up with an eggshells with sledgehammers situation, if there isn't an armor.

We already have that with fighter planes in real-life, assuming you're talking about sci-fi space combat.

Somewhat. A plane like a B-52 can take certain smaller missiles that a F-16 couldn't. But the F-16 can out manuever a missile designed to take down a B-52. Of course, you could stick a nuke on a missile, and nothing's going to dodge that. At which point you're at the eggshells with sledgehammers stage.

[Ariphaos]

As this story (naturally) has space battles, and because you can't really armour radiators, you must likely run with them closed during combat. For the moment, the primary propulsion will be fusion drives, and I think you can use such a things exhaust plume as its radiator (I think. I know you can do it with certain types of nuclear rockets). However, there are point-defense lasers to think about, which get one hell of a workout. During combat then, one must rely on heatsinks, and less effective methods of radiation; unless there are potential methods of heat radiation which aren't enormous targets* - which is an iffy proposition at best. :)

In the earlier part of my stories (before it goes into the magitech arena), an exotic allotrope of carbon is used to double as heat sink and 'armor', as much as that counts for in space. It's light, you aren't going to find anything that will radiate more heat per square meter, and has a higher tensile strength than you will find in any other material as well.

The design of the warship isn't intended to stop a blow, but rather, to retain integrity after it's been compromised (at least for awhile). An attacker then needs to use some form of explosive ammunition that can ultimately only so so fast, while the ship has random thrusters that use light delay to give it an 'optimal attack range' - Ie, a light-minute or light-hour.

...there really is quite a bit of design strategy to space combat - it's just at ranges you hardly ever see in scifi.

[Ford Prefect]

In the earlier part of my stories (before it goes into the magitech arena), an exotic allotrope of carbon is used to double as heat sink and 'armor', as much as that counts for in space. It's light, you aren't going to find anything that will radiate more heat per square meter, and has a higher tensile strength than you will find in any other material as well.

So essentially the outer hull itself is used as the radiator? I considered something like this briefly, but didn't know how feasible it was. Admittedly, feasible shouldn't be a problem when the primary medium for anti-ship exploding is antimatter, but I'm funny like that.

while the ship has random thrusters that use light delay to give it an 'optimal attack range' - Ie, a light-minute or light-hour.

...there really is quite a bit of design strategy to space combat - it's just at ranges you hardly ever see in scifi.

Actually, the range thing was something that I was woondering about. In my mind, I imagine a major problem is with the response time to detection. Even with arbitraily enhanced reaction speeds for the crew using 'virtual reality', and faster reaction times for the AI 'Expert' at the heart of the ship, the lightspeed limit makes it problematic to target and hit an enemy beyond a few lightseconds. When it takes minutes for radar and lasers to cross the distance, and when your opponent is pulling a few gees, as you can imagine, hits become far less likely than misses. I suppose you coudl try predicting the position of your foe ...

[Ariphaos]

I've noticed Carbon seems to have very good thermal properties but I haven't been able to find any specific numbers (specific heat, melting point, the latent heats, etc.)

...can't believed I missed this

Its specific properties vary based on allotrope. More properly, it sublimates around 4,000 Kelvin in a vacuum, so you won't see it melting unless you bring it to insane pressures (triple point at ~4300 K and 10 MPa). Specific heat is fairly low, but emissivity of some allotropes is quite high (around .9), so the radiative cooling equation maxes out close to 10 MW/M^2 in space. Since radiative cooling increases with the fourth power of temperature, only Tungsten is going to come close - and weigh a whole lot more.

So essentially the outer hull itself is used as the radiator? I considered something like this briefly, but didn't know how feasible it was. Admittedly, feasible shouldn't be a problem when the primary medium for anti-ship exploding is antimatter, but I'm funny like that.

Yes. The warship is basically a giant spinning saucer (not for gravity, but to reduce predictable exposed face), usually with one main cannon (sometimes two or mounted on a sort of turret) and is designed to engage at vast distances.

Assaults are actually rather difficult in this scenario, as the planetoid is basically a giant heat sink. This gets worse and worse for the energy expended up until you point your Dyson Swarm at the offending world, and if your enemy has reached that point it will likely just piss them off. R-bombs have a speed limit and the energy required to make them work can also be used to move planets defensively.

Actually, the range thing was something that I was woondering about. In my mind, I imagine a major problem is with the response time to detection. Even with arbitraily enhanced reaction speeds for the crew using 'virtual reality', and faster reaction times for the AI 'Expert' at the heart of the ship, the lightspeed limit makes it problematic to target and hit an enemy beyond a few lightseconds. When it takes minutes for radar and lasers to cross the distance, and when your opponent is pulling a few gees, as you can imagine, hits become far less likely than misses. I suppose you coudl try predicting the position of your foe ...

This begins to happen with realistic ship accelerations at about a light-minute. At accelerations of around 10% of c per second you can have relativistic dogfights in space.