Perpetual motion / heat / energy

[Matt123]

Following on from the 'attacking out of the sun' thread. I have gotta stop reading debates!

Much discusion has been made on 'waste heat', thermodynamic laws, etc in relation to IR detection in space. My schooling never went this high and there is an obvious assumption made that 'waste heat' must be radiated.

What is the principle behind this assumption? Layman logic tells me that you should be able to recycle the energy at greater and greater efficiencies as tech improves. The only energy I can see as having to be 'lost' is from drives swapping stored energy for momentum, comms & active sensors. Inefficiences will obviously be the main 'other' cause of waste heat and I would expect that inefficiences would reduce as tech increases.

& before anyone asks, no I'm not looking for 100% efficient TL15 'stealth ships'!

Cheers!

 

[robject]

Starships don't leak heat: there's no conductive medium to leak it out to. So it just accumulates until it bakes everything, unless you have some way to store it for a short while. That plus starship power plants are apparently sooo powerful that there's bound to be a lot of waste heat, even assuming high efficiency. More or less.

I tend to handwave it away, assuming there's a way to store it for a few weeks (or a year, or whatever). That probably opens up a new can of worms, though, since stored heat can theoretically be used for other purposes, right?

 

[Matt123]

I tend to handwave it away, assuming there's a way to store it for a few weeks (or a year, or whatever). That probably opens up a new can of worms, though, since stored heat can theoretically be used for other purposes, right?

I'm happy with the conventional handwave on the subject, its the apparent lack of recycling I'm interested in. In space surely you could dial down your reactor and use the latent captured energy in your ships cooling system.

I'm missing something obviously.

 

[Renaissance Man]

The second law of thermodynamics, if I understand it correctly, says that any "work" -- that is the harnessing of energy -- will produce waste heat. That includes recycling, co-generation, etc. etc. And a starship is generally drawing upon tremendous amounts of energy. Even with 99.9% efficiency, a ship will accumulate heat very fast.

"Heat", which is a property of matter, does not transmit into a vacuum because of course there is next to no matter in a vacuum. However, electromagnetic radiation does move through a vacuum, and anything with a temperature above 3 degrees kelvin will emit radiation in proportion to it's additional heat. The greater the differential the greater the emissions, and this is how heat energy is lost to the "coldness of space." This is also how the sun (which is very hot) transfers heat to the various bodies of the solar system.

It's also why a ship sticks out like a sore thumb in the void. To bring down the activity of a ship to the point where it is just north of absolute zero is tantamount to totally abandoning ship, and waiting the hours or days (weeks?) it would take to completely fade into the cold background of space.

 

[tjoneslo]

Or another way of putting it is, The second law of thermodynamics says that any energy you produce will turn to heat. So if your starship has a power plant produces 1 Megawatt of power, all of that power has to come off the starship at some point. Either as thrust from the Maneuver drive, weapons fire damage, or as heat.

If you have a 100% efficient heat generation engine, you should be able to prime it with a few seconds of fusion power plant, and only need additional power for the Maneuver drive and any beam weapons (lasers, plasma, fusions, PAWs, Meson guns).

 

[Matt123]

I think I've got it.

The second law of thermodynamics relates to entropy or waste heat. In an isolated system (eg: non-radiating space craft with internal working systems) waste heat is accumulated over time from operations/activities within the isolated system. The accumulation over time of the waste heat/entropy will approach a maximum value (temperature of your PP?). The consequence of approaching this maximum value is that your whole ship becomes a very hot heat reserviour.

Relating this to my question of why not harness the 'waste' energy and convert it to usable energy. If the vessel is getting hotter over time through entropy, cold sinks are getting used up. At some point all your cold sinks are used. Form here in order to 'use' the waste heat and convert it to energy a heat transfer is still required, but no cold sinks are available and handwaves are not allowed in thermodynamics. If you cannot release the energy in the heat, you cannot use it for other purposes.

My head hurts, I need a beer.

Thanks for the pointer RM.

Cheers!

 

[Matt123]

If you have a 100% efficient heat generation engine, you should be able to prime it with a few seconds of fusion power plant, and only need additional power for the Maneuver drive and any beam weapons (lasers, plasma, fusions, PAWs, Meson guns).

I assume you are referring to a engine capable of recycling waste heat. This would work assuming your system was no longer isolated [1] and radiated accumulated heat to keep your cold sinks cool.

So now, I guess you can run your non-isolated ship basically off waste heat energy [2]. I'd be interested to know how much IR radiation you produce under these circumstances (ie PP off, heat exchanger creating power & radiating purely to keep your cold sinks cool).

Cheers!
Matt
Budding Scientist

[1] it isn't anyway as obviously MD, weapons, comms & sensors all interact with the environment.
[2] Excluding the use of most interactions with the outside environment, MD, weapons, comms & sensors.

 

[ElHombre]

Heat management is one of the biggest MIA parts of most scifi spacecraft. Even 2001s USS Discovery had its heat radiators removed during preproduction becuse Kubrick worried that folks would think they're wings.

The only space game I've seen which takes heat seriously is Attack Vector: Tactical. The system basically works like so...

1) A spacecraft may choose to activate its reactors duting each turn.

2) Each active reactor generates 1 point of heat per turn and 1 point of power per segment.

3) Power goes to the batteries where it is used to power weapons.

4) Waste heat goes into a heat sink for the duration of the battle, but a ship can only store so much waste heat. Since the only way to rid the ship of heat is extending its radiators (which are big, juicy targets withdrawn into armored compartments before battle), the captain has to win the battle before his ship fries. The signal for surrender is extending the radiators.

 

[mike wightman]

[handwave]Waste heat is used to make the grav plates and acceleration compensators work - if it wasn't for the waste heat the grav plates and acceleration compensators would freeze all atomic motion inside the ship.[/handwave]

 

[far-trader]

[handwave]Waste heat is used to make the grav plates and acceleration compensators work - if it wasn't for the waste heat the grav plates and acceleration compensators would freeze all atomic motion inside the ship.[/handwave]

I like it

 

[Matt123]

Followed a link I found in my exploration of this to the Heat Death of the Universe, the ultimate conclusion of thermodynamics.
http://en.wikipedia.org/wiki/Heat_death

Seems we have a time limit on doing our interstellar thing. NASA & Branson better get thier buts into gear. Mind you if I conserve energy, switch my lights off & buy a smaller car, I'm helping to save the Universe. Pleasent thought.

 

[Renaissance Man]

Okay... to clear this up as best as I think I can...

There are NO exceptions to the second law of thermodynamics.

Thus you have your fusion generator. But it can't work at 100% efficiency because of said law, so it generates waste heat. No worries, you have your thermal co-generator to recycle the waste heat. But wait -- NO EXCEPTIONS -- your thermal co-generator also produces waste heat. You can keep on tacking on co generators and recycle ad infinitum, most likely with ever decreasing efficiency, and you will still end up with a pile of waste heat.

That's how I understand it. Note that I studied polisci and journalism in school so I'm sort of the peanut gallery when it comes to scientific issues, but I'm pretty sure that's how it works.

So... um... you can't hide in space. Not with any certainty.

 

[jfetters]

Or... You can't get something for nothing.

 

[Matt123]

There are NO exceptions to the second law of thermodynamics.

Thus you have your fusion generator. But it can't work at 100% efficiency because of said law, so it generates waste heat. No worries, you have your thermal co-generator to recycle the waste heat. But wait -- NO EXCEPTIONS -- your thermal co-generator also produces waste heat. You can keep on tacking on co generators and recycle ad infinitum, most likely with ever decreasing efficiency, and you will still end up with a pile of waste heat.

The issue doesn't appear to be the waste heat, the problem is running out of places to put it. This is only an issue for a 'closed system' (Ship attempting to be stealthy) otherwise you just radiate the waste energy into your environment (Ship not attempting to be stealthy).

It raises the question though, how long would cold sinks last before being filled up. This would obviously be tied in with the energy use of the ship, but with major systems switched off (excepting life support and Xbox...) to reduce the generation & use of energy.

Anyone got info on cold sinks suitable for stellar craft!

 

[mike wightman]

My earlier quip about grav plates and inertial compensators is actually a serious suggestion.
Once you go down the route of heat sinks and radiators as waste heat managers you will find that traveller ships are more akin to flying carpets than the space shuttle.

Use the magic components as a magic heat sink and you solve two problems for the price of one.

 

[Thunderbolt]

As Montgomery Scott is often quoted as saying, 'Yer canna change the laws of physics, Captain'.

Most has been said already, no amount of recycling is going to make this problem go away. Every process generates waste heat, and fusion reactors and drives capable of pushing a Tigress forward at six gravities are going to make a lot of waste heat.

The Space Shuttle has its own problem with waste heat which is why it opens it's bay doors to help dissipate it away. Likewise, the use of reflective surfaces on space craft to reflect away direct heating from the Sun. Any Traveller ship operating in the habitable zone is going to have to solve this significant heating problem by sending it back into space too.

As for storing it, containing the heat and expending work to do so would probably accelerate the problem rather than solve it, unless you have some Balonium handy of course...

 

[Renaissance Man]

The issue doesn't appear to be the waste heat, the problem is running out of places to put it. This is only an issue for a 'closed system' (Ship attempting to be stealthy) otherwise you just radiate the waste energy into your environment (Ship not attempting to be stealthy).

It raises the question though, how long would cold sinks last before being filled up. This would obviously be tied in with the energy use of the ship, but with major systems switched off (excepting life support and Xbox...) to reduce the generation & use of energy.

Anyone got info on cold sinks suitable for stellar craft!

Right. You've hit the nail on the head. Heat/cold sinks work by transferring heat from an object of higher temperature (the ship), to one of lower temperature (the cold sink.) The problem is: how does the cold sink get cold? The answer -- by radiating heat.

Now, perhaps you could find a medium for your cold sink that could efficiently absorb and store thermal energy for a significant period of time. Essentially, what your talking about is a co-generator linked to a battery. That process itself will generate some waste heat, even if it were able to absorb everything that a fusion reaction gives off.

Even if you ejected your thermal reactor, or shut it off, running off the battery alone would produce enough heat to stand out against the backdrop of space. And even if you ejected all sources of power, and waited on the ship as the coldness of space seeped into your staterooms, the very fact that you had life support systems on before would show up on sensors for hours, even days afterward.

Possibly a cold, dead ship with a small number of vacc-suited passengers could escape easy detection based on passive thermal signature alone. As I've said before, I'm not a real expert.

 

[Peter Schutze]

personal opinion only but I think you are greatly underestimating the needle in a haystack problem with detecting smaller ship's heat signatures

If it were so easy to find a ship that you could not hide at all .... why havent we properly mapped even the stars in our neighbourhood, most of which are far hotter than most parts of any ship should get and be livable ..... leaving the size difference out of the picture for the moment ?

I could understand having a general bearing pretty easily (assuming you were scanning the right area) but that's pretty useless for combat on its own except for terminal guidance (aka fire and forget) missiles at any great distance.

also the heplar maneovre drives in TNE seem to be perfect heat sumps .... you want to pump as much heat into it as possible.

 

[tjoneslo]

If it were so easy to find a ship that you could not hide at all .... why havent we properly mapped even the stars in our neighbourhood, most of which are far hotter than most parts of any ship should get and be livable ..... leaving the size difference out of the picture for the moment ?

Mostly because we haven't devoted the telescopes to the project. If we thought that national defense relied upon finding anomalous heat sources in the sky, it really isn't difficult.

 

[ElHombre]

If it were so easy to find a ship that you could not hide at all .... why havent we properly mapped even the stars in our neighbourhood, most of which are far hotter than most parts of any ship should get and be livable ..... leaving the size difference out of the picture for the moment ?

Short answer: There has never been any real interest (or need) for the information. Most of the technical parts of astronomy involves pointing the telescope in the right direction. Exact distance has never been a major factor, especially seeing as how no one was going to be travelling there. Yet.

Back on topic: Mike Wightman has the right idea, though. Most starship creation rules (or spacecraft fiction, for that matter) don't include heat management. Here's Bryn Monnery's page about 2300AD which makes an attempt to integrate heat management into the Star Cruiser rules. Even it gets problematic. A 150MW power plant needs at least three square kilometers of radiators. Eeek!!!