Heat dissipation

[Azimech]

So we have these tremendously powerful cannons, a laser cooling booster, individual shields, a shield booster, fuel scoop with obviously a compressor, life support systems, hydraulic system or maybe electric motors for landing gear ... these all produce heat. Also there's the heating of the craft during re-entry or fast atmospheric flight, somehow, when the source is gone, the cooling is as quick as the heating up. Something that doesn't look very realistic to me.

The engines have a self-cooling effect, the evaporation of liquids has already been cooling rocket engines since the german V2, so we can forget about those. But let's assume all of the cooling capacity is being used by the engines. You'd want to be able to cool systems even if the engines aren't running, so these systems are seperate.

When you have atmospheric shielding, the goal is to prevent the underlying structure from heating up. And unless there's some very exotic material in the future, this prevents the dissipation of the internal heat as well.

So obviously there is some kind of dissipating technology, but these can only work when the ambient temperature is below that of the internal systems or structure. During fast re-entry or inside a solar corona or the atmosphere of Venus, the external circuits of the cooling systems are emptied and cooling is shut off.

At this moment ships are very well able to get rid the heat of individual systems but I propose a heat buffer that adds up and damages equipment if the maximum allowable temperature is reached for a certain amount of time, the higher the temperature, the sooner things break down or lose efficiency.

One interesting technology are the shields. Right now there is no penalty for having multiple shields, I can fill up the largest freighter with shields and the only drawback is the increased mass. When a shield is able to absorb all of the energy of a laser or cannon, shouldn't the shield generators dissipate that energy, which is heat, in the same amount as the weapon that fired heated up? This makes for some interesting gameplay. The larger ships have more of a heat buffer than the small ones.

The solution for overheating systems would be to dump and let evaporate a certain amount of hydrogen. Larger ships have more cooling capacity, so they need to dump more, obviously.

I love micromanagement and fiddling with systems but I know this is not for everyone. If I had my way, I'd be servicing big radial engines (gotta love the sound of 18 cylinders driving a three bladed prop) or be an engineer on a starship.

What's your opinion? Nice for a "hardcore" difficulty option?

[Luomu]

Systems require power. Reactor produces power but also heat. Increased power drain means increased heat.

The Mechwarrior (PC) games have a nice just reasonably complex heat system:

• One overall heat level
• Firing weapons increases heat
• Enemy fire can increase heat
• You can install extra heat sinks to reduce heat faster
• You can shut down to reduce heat faster
• Overheating results in an automatic shutdown, which you can override at the risk of going boom
• You can flush coolant to quickly reduce heat, but you have a limited amount
• Hot/cold environment is taken into account

[Brianetta]

Heat management is the biggest concern when it comes to real-world habitation of space.

I do think that each ship model should have a pair of attributes describing the rate at which they absorb heat, and the rate at which they lose it. This could even be scripted, to vary with the colour of the ship, if modellers were feeling up to it.

The cooling rate should definitely be lower than the heating rate, and it would be a simple task to have some sort of radiator available for sale in the shipyard which could dump heat into space as radiation.

[Azimech]

Yes a radiator is a good idea! But not a "one size fits all", it would be better to be able to buy multiple small modules and be able to see just how much heat will be dissipated per second. Otherwise the radiator should be proportionate to ship mass, in mass and price. But that's less interesting for the people who like to adjust everything to their own liking.

[Brianetta]

They could be cumulative, like shields.

[Azimech]

Exactly.

[robn]

I like the idea. I guess we then need to have equipment producing heat (which I think is what the OP is about but its a bit tl;dr).

Do you envisage a general cumulative "radiator" item replacing the laser cooling booster? Or is it that the cooling booster trades increased heat production for faster recharge? I guess that model makes some sense for the shield energy booster unit too - faster recharge at the expense of greater heat production.

It seems then that a "hotter" environment (eg atmosphere) your ship's ability lose heat is reduced, so you have to be careful about what equipment you run at that time. Do we need controls to let you selectively switch off certain equipment to reduce your heat output?

How does atmospheric shielding work in this model? The atmosphere that is increasing the ship's hull temperature via friction and presumably being heated by the heat removed from the ship via radiators/heatsinks. I'm confusing myself here but hopefully someone can see the point I'm trying to make and tell me the obvious answer :)

[Brianetta]

Re-entry heat is caused by compression. Just for the detail nuts amongst us... (-:

As I said before, heat management is the biggest concern for space flight. Energy and materials might be abundant, but getting rid of heat is the big one. Everything that happens generates heat, and the basic principle of entropy is that heat cannot be destroyed, only moved, and moving it... makes heat.

Since a space vehicle cannot conduct heat away through the vacuum, this leaves only two mechanisms for heat reduction. These are radiation and mass transfer. The former requires radiators, which radiate the heat away as electromagnetic radiation. The latter requires a medium, which is heated up and then ejected. The latter mechanism is really, really crappy. Nobody takes it seriously.

So, here are some of my own ideas for heat gain and loss.

Gain:

• Use thrusters. Minimal; much of heat is transferred away with the reaction mass.
• Use ECM or other specialist upgrades. Minimal; it's just electronics.
• Use an energy weapon. The rate would depend on the weapon. An expensive model might be much more efficient at the same power levels, directing more of its energy into the beam that might otherwise have stayed with the vehicle.
• Life support and passenger cabins. Fairly high; habitable areas must be kept at or near cabin temperature to begin with. Perhaps cooling can be sped up by selectively turning off life support, at grave risk to the occupants, if there are any.
• Certain cargo. Radioactives, for sure. They're continually heating up their environment.
• Proximity to radiation. Very high. If you're scooping from a star, expect high heat gains. Try a gas giant.
• Atmospheric speeds. Very high, although better than that star.
• Fuel scooping. Specifically, compressing the scooped matter is an exothermic process.

Lose:

• Radiators. The more, the bigger, the cooler. Trouble is, space-borne radiators look a lot like solar wings, and are as fragile. A good way to lose a fight is to have your radiators all shot up. A good way to break your ship is to enter an atmosphere with radiators deployed. A good way to cook your ship is to go close to a sun with radiators deployed; they'll absorb heat from stellar radiation as fast as they can radiate it.
• Docking. Presumably, once docked, your vehicle can be plugged into a convective cooling system and the heat will come right off.

Incidentally, heat is why stealth in space is impossible, at least for longer than very short periods of time. You need to get rid of it, and that means people can see your thermal output. So, if we ever have a stealth device, to be half-way realistic it should shut down all of your radiators, including those of your weapons. Presumably, that's why Star Trek ships have to de-cloak to fire (although I suspect its more to do with pretending to be submarines).

Atmospheric shielding is an interesting one. The black tiles used on the shuttle get very, very hot, and are designed to re-radiate that heat back into the atmosphere. The white ones aren't supposed to be directly exposed to bow pressure, and are designed to reflect away the radiant heat from the plasma generated by the pressure against the black tiles. This works because it doesn't happen for very long. It's sub-sonic before the tiles get close to breaking down, and any residual heat is then carried away by both radiation and convection. This is most likely what we'd want to model in Pioneer. http://en.wikipedia.org/wiki/LI-900

Older technology, such as Apollo, used an ablative heat shield. That didn't heat the capsule up because as the shield's molecules got hot, they jetted away; a form of direct mass transfer combined with a physical gaseous barrier to compressed plasma. Incidentally, they were made largely of plywood.

All current real-world technologies have real shortcomings; the Shuttles had to have tiles replaced fairly often due to damage and ablation. Precipitation during the landing flight could write off many of the re-usable tiles at once. Ablative shields used on Apollo had to be jettisoned after the capsule slowed down to the point where it was no longer undergoing pyrolysis, because then the heat could soak through to the capsule, effectively meaning that the capsule was sat upon a wood fire.

Atmospheric shielding should be pretty simple, I think. It drastically reduces the temperature rise caused by atmospheric flight. It's strong and able to withstand years of use and abuse, because it's had more than a millennium of development time beyond the Shuttle.

[Brianetta]

Deploying radiators in space could be analogous to deploying landing near the ground. Perhaps cooling down in an atmosphere should be a given (it's a fluid bath, after all) if you're not travelling so quickly as to incur compression (or re-entry) heat. Once in space, you need to deploy radiators. Before docking, retract them for safety. Perhaps it might be safe to deploy them after landing rough, just to take the edge off the heat.

It's fascinating to think about, although we might need modellers to come up with some cool looking radiators.

[robn]

Thank you for the lesson - I knew it'd be easier to ask here rather than go and research it myself :)

The list of heat gain/loss items is particularly interesting. That should be most useful if we ever get around to building this kind of thing.

[Azimech]

Instead of making a model of radiator(s) and modifying every model which is both impractical and a lot of work: Imagine the radiator(s) being enclosed and when dynamic pressure or temperature drops enough, a screen of atmospheric shielding will slide open, revealing the radiators. Changing a colour or maybe a small animation on a small tile would be enough.

But maybe a custom paintjob to come with a fuel scoop is a good idea. Using a black ship to scoop fuel from a star seems totally nuts.

[PinBlacniP]

So We are carrying x tons of H (H2) as non military fuel. Probably as a tetrahedral (H4) molecular isomer! To store H it must be very cold! or it will take up a lot of room!!! A temp of 0.0001 deg.K above Abs. Zero (ha ha) is suggested ... at this temp. it will be quite dense! (approaching a singularity!) We consider two (2) ways of reacting the H, do we not? !). The jump/hyper space reaction ... (Einsteinian E=mc2 reaction) with total conversion! (military - dirty matter/anti-matter later) and 2). In system (Fuel consumption ... not yet implemented) Chemical/reaction expel after heating for thrust ... mass ejection! or we need a catalyst for combustion! ... Discuss ! We want to channel any heat we have into the thrust reaction rather than expel it, as waste, don't we?

Military - dirty matter/anti-matter reaction ... for military fuel at the Centre of the tetrahedral (H4) molecular isomer is a single H (anathema) Possibly just an anti-proton! The jump reaction then leaves approximately 3T of radio active waste for 4T of Fuel burned! Scaled (improperly) for in system reaction use!

Tongue firmly in cheek! DISCUSS!

[Brianetta]

Chemical engines, no. We do not want to be burning our hydrogen. The only way to get more thrust from the same reaction mass is to eject it at a greater velocity, which is not something a chemical rocket is good at. Chemical rockets excel at ejecting lots of mass at once.

An electric engine is the most likely answer. Ionise the hydrogen, accelerate it magnetically, and return the electrons to the hydrogen on the way out. Current real-world ion motors use inert gases as propellant (xenon is popular) but any fluid could work in theory. In real life, we have really efficient ion thrusters, but they aren't powerful yet. Certainly no good for lift off. That will no doubt be sorted at some point in the next twelve centuries.

The important thing here is not to think of fuel as an energy source, but as propellant. Energy is abundant in space. Reaction mass is the tricky consumable.

Remember also, you don't need to cool a gas to compress it. Mechanical compression works just as well, and expels heat just as much. Unfortunately, this does mean that the very act of scooping fuel will increase the amount of heat on the ship, so I've added that to the list.

[Brianetta]

The idea of military fuel as a stable isomer that contains an anti-proton by electrical forces has some merit, although I doubt it's really practical. However we decide that military fuel works, we don't need to bend our civilian engines to fit. Their fuel systems might be utterly different technologies.

[Brianetta]

https://github.com/pioneerspacesim/pioneer/wiki/Idea.Power-use-in-ships

[tlhonmey]

A couple of things I notice, to keep the conversation interesting:

Since energy shields are available, there is no reason "atmospheric shielding" necessarily needs to be entirely physical. Energy-based or energy-reinforced shielding could eliminate the details of maintenance by converting it into fuel consumption. Potentially there could be multiple types of atmospheric shielding ranging from simple, ablative types (that wear out after a certain amount of use) through radiant types (that are longer lasting but more susceptible to physical shock) to entirely energy shields that simply hold the hot gases away from the hull and reflect the radiant heat and could, therefore, go "sun diving" until the ship gets cooked by its own power plant.

(Of course, atmospheric shielding isn't strictly necessary with these ships since it's perfectly possible to transition from orbital velocities to a sedate 100kph before the pressure gage even registers anything... So unless you're flying through something inherently hot, shielding just lets you burn less fuel.)

For the thrust levels generated and the amount of time they can be sustained, the most likely form of engine used would seem to be some type of fusion candle or orion drive where the hydrogen provides both the energy by being fused into helium and the reaction mass by flying out of the jets at an incredible speed. Fusion-powered ion drives could possibly have similar performance, but shuffling the energy around between generation and reaction mass leads to more heat buildup inside the ship, and seriously reduces the thrust/weight ratio of the engine. Of course, ion engines would also be more precise, so perhaps one type for the main engines and one for maneuvering jets. Interestingly, this would lead to greater heat generation from the lower-powered engines, along with higher fuel consumption per unit of thrust.

Also interestingly, such a drive setup would likely mean that "hydrogen fuel" consists (in a large portion at least) of some blend of deuterium and tritium.