Solving the IR problem in Traveller

[AnotherDilbert]

And yet, despite that, the bumblebee still flies.

Despite silly statements from the early days of aerodynamics, the bumblebee have never violated any basic physical laws.

http://www.todayifoundout.com/index...-flight-does-not-violate-the-laws-of-physics/

Basic physical laws are of course only very strong theories that might be proved wrong, but they are rather well tested for centuries. They're highly unlikely to be proved completely wrong.

 

[AnotherDilbert]

Hide behind some planetoid, and occasionally launch the heatsink onto the surface.

Which means it would need to be disposable.

For long term stealth you might sink a shaft into an asteroid and transfer heat into the interior of the asteroid. It would take awhile for the surface of the asteroid to heat up enough to radiate noticeably more brightly.

A small asteroid, say 1 km radius, with a specific heat of about 1 kJ/kgK would take E = ⁴/₃π1000³ × 2000 × 1 ≈ 8 × 10⁹ kJ = 8 TJ to heat 1 K (= 1°C). That would be 1 Power for 100000 s or 27 h.

A small ship on minimal power would need to depose of 10 - 20 Power. It would heat a small asteroid in a few hours, oops... We would need quite a large asteroid to hide even a small ship behind.

 

[locarno24]

Once you're in a complex environment - with asteroids, atmosphere, a moon/ring system, or anything else involving solid bodies to hide behind or amongst 'clutter', stealth becomes a lot easier. After all, you're talking about an environment where the background temperature is now uneven and potentially significantly higher than the default 'background temperature' of deep space.

The only time there's a problem is trying to be 'invisible' in deep space with no real surrounding cover.

 

[atpollard]

As an Architect in Florida, I deal with AC all of the time. We routinely cool the cool inner space (where the people are) and heat the hot outside using heat pumps that manage to violate no laws of either thermodynamics or entropy.

Traveller posits a FTL Starship (that already violates more laws of physics than I can shake a stick at) propelled by a reactonless drive (that violates still more laws of physics) powered by a fusion power plant (a technology that has been 10 years away for half a century). I propose a far simpler approach of actively cooling the outer hull and pumping the heat to the fusion reactor. As the temperature difference becomes greater, efficiency will drop and the system will become an energy hog, this STEALTH is not for those on a budget, however, this requires no new violations of any laws of physics and just takes advantage of those already in place and the hand-wave that the people that can violate 'causality' by traveling faster than light and 'conservation of momentum' by creating reactionless drives can solve the technical issues of a heat pump that can operate at the temperatures required. You already have a sun in a bottle.

As an ironic aside, like the ramjet engine increasing efficiency with speed, Stealth might actually increase the efficiency of the Power Plant as the temperature rises from its use as a heat sink.

 

[Reynard]

As discussed in other threads, I always assume what looks like exhaust nozzles on Traveller ships are actually very efficient excess energy dumps to direct waste away from the vessel in a particular direction in a manner as stealth planes vent exhaust to reduce the thermo signature of their engines. You'll have decreasing thermo bleed the further from the parallel of the heat dump mostly to get waste energy away from the ship but the ship would still have an ambient hull EM. As a part of a stealth system and higher cost it could be refined more including an integral system to cool the hull and divert energy to the waste dumps.

 

[Galadrion]

As an ironic aside, like the ramjet engine increasing efficiency with speed, Stealth might actually increase the efficiency of the Power Plant as the temperature rises from its use as a heat sink.

The biggest problem I can see with this is that you run the risk of having too much energy to dump into the fusion plant/heat sink. Increasing efficiency is all well and good, until you pass a certain threshold. You do know what a too-efficient fission or fusion power plant is called, don't you?

That's right. A thermonuclear explosive device. Not the kind of thing you really want to be sharing the inside of a hull with, y'know? But up until that point... yeah, you've got a point. I'd probably place a cap on the effectiveness of the stealth based on the tech level - a higher-tech power plant likely has better energy-handling systems and more robust materials - but this could be a possibility. Almost certainly not a cheap one, though.

 

[AnotherDilbert]

As an Architect in Florida, I deal with AC all of the time. We routinely cool the cool inner space (where the people are) and heat the hot outside using heat pumps that manage to violate no laws of either thermodynamics or entropy.

Quite, heat-exchangers work well but they require an external heat sink (aka the outside) to work. Spacecraft generally lack a surrounding atmosphere.


The active, hot, fusing part of the power plant is probably a quite small amount of plasma (we need vary little hydrogen to maintain energy production). A small mass will not work as a heat sink.


A tonne of steel machinery with a specific heat of say 1 kJ/kgK will take about 1500 × 1000 × 1 = 1 500 000 kJ = 1,5 GJ to melt. That would be 1 Power for 1 500 000 000 [J] / 5 000 000 [J/s] = 300 s = 5 minutes.

A Scout produces 60 Power. That amount of Power will melt 60 × 60 / 5 = 720 tonnes of machinery per hour. A Scout will melt itself in about an hour if it does not radiate heat. The entire ship will not work as a heat sink, much less a small part of it.

 

[Condottiere]

Sounds like it's time to eject that magnetic bottle.

 

[atpollard]

As an Architect in Florida, I deal with AC all of the time. We routinely cool the cool inner space (where the people are) and heat the hot outside using heat pumps that manage to violate no laws of either thermodynamics or entropy.

Quite, heat-exchangers work well but they require an external heat sink (aka the outside) to work. Spacecraft generally lack a surrounding atmosphere.


The active, hot, fusing part of the power plant is probably a quite small amount of plasma (we need vary little hydrogen to maintain energy production). A small mass will not work as a heat sink.


A tonne of steel machinery with a specific heat of say 1 kJ/kgK will take about 1500 × 1000 × 1 = 1 500 000 kJ = 1,5 GJ to melt. That would be 1 Power for 1 500 000 000 [J] / 5 000 000 [J/s] = 300 s = 5 minutes.

A Scout produces 60 Power. That amount of Power will melt 60 × 60 / 5 = 720 tonnes of machinery per hour. A Scout will melt itself in about an hour if it does not radiate heat. The entire ship will not work as a heat sink, much less a small part of it.

Go ahead, calculate the size of those radiators.
Then tell me while you are flapping your arms why one physics violating handwave is better than another?

What keeps that PP from melting itself even without my using it as a heat sink?
The handwave was already there.
Thermodynamics and material sciences were already broken.
Where are these magic radiators on every known ship design? Conspicuously missing. That's the nature of Space Opera. [shrug]

I prefer to use the handwaves already there rather than add new ones. YMMV.

 

[AnotherDilbert]

Go ahead, calculate the size of those radiators.
Then tell me while you are flapping your arms why one physics violating handwave is better than another?

Tastes may vary, of course. I feel no particular need to flap my arms.

Basic physics hints that we need to disperse heat. How we disperse heat is engineering detail.

If we can make the radiators hot enough they do not need to be very large. The hotter they are the more heat they can radiate away.

We might be able to move heat in desired directions, e.g. into radiators:

Some new news: http://phys.org/news/2016-10-posit-locally-circumvent-law-thermodynamics.html

We might even have convenient radiators on many designs:

As discussed in other threads, I always assume what looks like exhaust nozzles on Traveller ships are actually very efficient excess energy dumps to direct waste away from the vessel in a particular direction in a manner as stealth planes vent exhaust to reduce the thermo signature of their engines.

What keeps that PP from melting itself even without my using it as a heat sink?

The cooling system built into all power plants for this very purpose?

But all this is speculation and you play your game as you wish, of course.

 

[phavoc]

One thing is that we don't even have a specific way of HOW fusion plants work in Traveller. I think it's pretty safe to say that they don't work like our power plants today (i.e. heating water to drive machinery). I would assume that the fusion plants of the 52nd century would directly convert the fusion power into electricity. Could the fusion bottle somehow keep the heat of reaction contained is a question.

There's a certain amount of handwavium already here (not that it's a stretch, but it's still not technically possible for us to do this today).

The original posting on this thread talked about converting heat directly into electricity, though not at this scale. IF that is possible, then potentially much of the reactor heat would be converted and thus it needs not need to be radiated away.

At this point it's all just gaming technology, and that allows for pretty much anything to occur. Sometimes it's just easier to accept the hand wave and move on. There's better, more interesting things to kibbitz about.

 

[Condottiere]

You could install a vacuum intake in front, or repurpose the fuel scoops, and allow coldspace to flow through the heatsinks and out the back.

 

[phavoc]

You could install a vacuum intake in front, or repurpose the fuel scoops, and allow coldspace to flow through the heatsinks and out the back.

It's a vacuum, not an atmosphere so there's no need for intakes anywhere. Heat radiates in the form of photons from the radiator. All you need to do is have the radiators sticking away from the ship so that the ships outer hull doesn't abosorb the heat you just got rid of.

Back/front doesn't mean much when you can rotate your hull - you would just want to keep the radiators away from direct observation of whomever you are trying to hide from (though you will still show up on IR since the heat still has to dissipate from the radiator).

 

[AnotherDilbert]

One thing is that we don't even have a specific way of HOW fusion plants work in Traveller. I think it's pretty safe to say that they don't work like our power plants today (i.e. heating water to drive machinery). I would assume that the fusion plants of the 52nd century would directly convert the fusion power into electricity.

Converting the high entropy energy from the fusion reaction into low entropy electrical energy runs into thermodynamics again...

If we assume it is better than today, but not breaking thermodynamics, it will perhaps produce twice the thermal energy than the resulting electrical energy. So a 100 MW (electrical) power plant would produce 200 MW thermal energy and convert half into electrical energy and radiate away 100 MW heat.

The 100 MW electrical energy would then be used, i.e. converted to heat that would have to be radiated away from the ship.

So a ship with a 100 MW (electrical) power plant would have to radiate away perhaps 200 MW heat.

 

[AnotherDilbert]

You could install a vacuum intake in front, or repurpose the fuel scoops, and allow coldspace to flow through the heatsinks and out the back.

It's a vacuum, not an atmosphere so there's no need for intakes anywhere.

I suspect he left out the sarcasm-tag...

 

[atpollard]

Basic physics hints that we need to disperse heat. How we disperse heat is engineering detail.
If we can make the radiators hot enough they do not need to be very large. The hotter they are the more heat they can radiate away.

When I suggested a direction (into the fusion plasma), you presented calculations for melting 720 tons of steel machinery per hour for a scout ship. I was just pointing out that you will have no more luck with your steel radiators and your same energy calculation.

When you make them 'hot enough', they might as well conduct the heat into the fusion plasma as try to radiate it into the vacuum of space (some hyperbole, but not much).

 

[AnotherDilbert]

When I suggested a direction (into the fusion plasma), you presented calculations for melting 720 tons of steel machinery per hour for a scout ship. I was just pointing out that you will have no more luck with your steel radiators and your same energy calculation.

When you make them 'hot enough', they might as well conduct the heat into the fusion plasma as try to radiate it into the vacuum of space (some hyperbole, but not much).

Yes, certainly, a radiator hot enough to radiate away hundreds of MW would be beyond the melting point of any known metal. We would have to use some extremely heat resistant material. Perhaps something will be invented in the next few thousand years?

Carbon (such as graphite or diamond) has a melting point of about 4000 °C. A 1 m² surface at 4000 K would radiate away about σT⁴ = 5,67 × 10⁻⁸ × 4000⁴ ≈ 14,5 MW. Not hot enough but we are getting closer.
A Scout would need to dispose of ~100 Power = roughly 1 GW. Using 1 m² that is σT⁴ = 1 GW leads to T = ( 1 000 000 000 / σ )^1/4 ≈ 11500 K. Using 2 m² that is σT⁴ = 1 GW / 2 leads to T = ( 1 000 000 000 / 2σ )^1/4 ≈ 9700 K.
Lets say we need a few square metres at 10 000 K with some margin of safety.
Can we do that today? No.
Could it be possible 3000 years from now? Perhaps.


If you dump massive amounts of heat energy into the power plants plasma it will quickly become hotter. As it gets hotter it will radiate more heat into its environment, probably the power plants cooling system. The cooling system will have to dump the heat somewhere, in this scenario back into the plasma, creating a recursion. What you are suggesting is basically an AC that cools a house and dumps the heat into the house using energy from a power plant inside the house (that produces even more heat). In short, no, you cannot use the power plant as a heat sink for the heat produced by the power plant...


If we could (magically) dump heat from something cool (the ship) into something extremely hot (plasma) without extremely high energy costs, we could create an enclosed plasma outside the ship and we would have our "hot enough" radiator.

 

[steve98052]

. . . Carbon (such as graphite or diamond) has a melting point of about 4000 °C. A 1 m² surface at 4000 K would radiate away about σT⁴ = 5,67 × 10⁻⁸ × 4000⁴ ≈ 14,5 MW. Not hot enough but we are getting closer.
A Scout would need to dispose of ~100 Power = roughly 1 GW. Using 1 m² that is σT⁴ = 1 GW leads to T = ( 1 000 000 000 / σ )^1/4 ≈ 11500 K. Using 2 m² that is σT⁴ = 1 GW / 2 leads to T = ( 1 000 000 000 / 2σ )^1/4 ≈ 9700 K.
Lets say we need a few square metres at 10 000 K with some margin of safety.
Can we do that today? No.
Could it be possible 3000 years from now? Perhaps.

This is one good solution, but probably not a good low-stealth solution, because it would need to radiate that heat through a fairly large angle, even with a reflective baffle surrounding the radiating plates. (A 10 000 K radiating plate is similar in color to the hottest "A" and coolest "B" stars, by the way.)

. . . If we could (magically) dump heat from something cool (the ship) into something extremely hot (plasma) without extremely high energy costs, we could create an enclosed plasma outside the ship and we would have our "hot enough" radiator.

Because on the Traveller technology scale, grav vehicles and fusion turn up around the same time, I jumped to the hand-wave that Traveller fusion counts on grav technology in some way. Maybe it's possible to enclose a plasma radiator with grav technology, as long as the radiating opening isn't too large for the grav bottle technology.

 

[Condottiere]

You could allow it to leak to the reaction drives, maybe even supercharge them.