Space and Sensor information
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Icosahedron
SOC-14 1K
The natural forces at work in water are water molecules, which absorb and dissipate heat. Space is empty, there is nothing to stop the IR signature.
The heat is largely contained within the reactor chamber, but by the chamber walls and coolant, not the magnetic field. The heat transfer to the coolant is what provides the useable energy from the reactor, and it is only the heat that cannot be recovered from the coolant that is emitted as an IR signature. (on a TL8/9 reactor anyway) As you say, there is little emission from the chamber walls.
Again, whatever the source of the reaction, it is the efficiency in converting the output to useful electrical energy that determines the waste heat that is detectable outside the ship.
A 100MW power plant with a 40% efficiency is going to have a 60MW IR signature, whether the power source is hot fusion, cold fusion, or a hundred billion people pedalling bicycles.
What you do with that heat, store it, use it, direct it, or whatever, is the basis for your stealth technology. The laws of thermodynamics do not prevent you from emitting heat in a single chosen direction, using it in a long term process, or storing it for a week and dumping it in dock, IIRC.
PS. Has inertial containment fusion fallen out of favour? Nobody has mentioned it so far.
Well, sort of. You can only eliminate heat by dumping it into some form of heat sink; on board a spaceship that's generally a radiator, but if you have some means of storing it, you could offload it at a planet and they could maybe drag a bit more energy out of it by using a lower temperature sink than is normally available on board a ship.
For directional emissions, your basic problem is that the heat elimination of a radiator is proportional to T^4 * area * coverage, so assuming constant radiator temperature, if you emit to only 10% of the sky your radiators can only handle 1/10 as much power. Increasing radiator temperature reduces power plant efficiency and radiators are generally limited to a temperature that won't destroy the power plant or radiator.
The other problem is that the power plant is not the only heat source on board the ship -- every shipboard component that uses power also produces some amount of heat.
As far as heat goes, it's pretty much the same as magnetic confinement fusion.
I guess I don't understand. Heat is radiation, as deadly in huge amounts as any alph, beta or gamma radiation. Why should a magnetic bottle that could withstand the fury of the actual fusion reaction, ie a mini-sun, somehow be transparent to infra-red radiation (heat) but not alpha or gamma radiation?
Without the heat being fully contained by the fusion bottle, a fusion reaction in any sort of mobile installation is impossible. Anything less than 100% containment would mean that the reactor vessel and it's surroundings would melt, sooner than later from the accumulating heat load. So if your ship was radiating gigawatts of power as infra-red and radiators are not 100% efficient, tell me how much the heat load in the ship is and why it hasn't melted down and charbroiled the crew, especially in a 100dton scout ship?
As far as water vs deep space goes in diffusion, if 200' of water will hide the IR signature of a nuclear sub and space is only .001% as efficient, a million kilometers should be able to hide the heat source just as easily, diffusing it beyond being noticed.
As my candle analogy goes, a solar system is not empty, much less a black background within you get to search for the candle. Add in heat sources, i.e. planets, moons, ships that you know of, etc., as well as the natural background heat of the universe and you no longer have that perfect blank background you seem to think space provides.
If IR was such a great way to detect bodies in space, ships or planets, why are there basically only 2 types of telescopes in operation, optical and radio? How many IR satellites are there, in comparison with optical satellites? Also, how efficient would an outward looking IR satellite be, with a major heat body right behind it, i.e. a planet? Now you might have them just sitting out in space but then you start running into the problem of communications lag.
Without the heat being fully contained by the fusion bottle, a fusion reaction in any sort of mobile installation is impossible. Anything less than 100% containment would mean that the reactor vessel and it's surroundings would melt, sooner than later from the accumulating heat load. So if your ship was radiating gigawatts of power as infra-red and radiators are not 100% efficient, tell me how much the heat load in the ship is and why it hasn't melted down and charbroiled the crew, especially in a 100dton scout ship?
As far as water vs deep space goes in diffusion, if 200' of water will hide the IR signature of a nuclear sub and space is only .001% as efficient, a million kilometers should be able to hide the heat source just as easily, diffusing it beyond being noticed.
As my candle analogy goes, a solar system is not empty, much less a black background within you get to search for the candle. Add in heat sources, i.e. planets, moons, ships that you know of, etc., as well as the natural background heat of the universe and you no longer have that perfect blank background you seem to think space provides.
If IR was such a great way to detect bodies in space, ships or planets, why are there basically only 2 types of telescopes in operation, optical and radio? How many IR satellites are there, in comparison with optical satellites? Also, how efficient would an outward looking IR satellite be, with a major heat body right behind it, i.e. a planet? Now you might have them just sitting out in space but then you start running into the problem of communications lag.
TheEngineer
SOC-14 1K
Hi !
Hu, many questions.
Generally I guess we`re hitting the border between real world physics and Traveller technology here again
Assuming limited abilities of handwave technogy and mixing that with harder science problems causes more problems.
So I would suggest to look at Travellers power plants as based on fusion plants we know today, but with a totally different energy conversion technology (direct conversion of kinetic energy and radiation into electricity), resulting in a device, where hydrogen goes in and electrical energy/hydrogen/helium with a minimized "waste heat" ammount comes out.
This assumption would support starships and other craft as they are presented in Traveller.
Otherwise things start to become awfully technical, complicate and still would appear unrealistic.
...
Regards,
TE
Hu, many questions.
Generally I guess we`re hitting the border between real world physics and Traveller technology here again
Assuming limited abilities of handwave technogy and mixing that with harder science problems causes more problems.
So I would suggest to look at Travellers power plants as based on fusion plants we know today, but with a totally different energy conversion technology (direct conversion of kinetic energy and radiation into electricity), resulting in a device, where hydrogen goes in and electrical energy/hydrogen/helium with a minimized "waste heat" ammount comes out.
This assumption would support starships and other craft as they are presented in Traveller.
Otherwise things start to become awfully technical, complicate and still would appear unrealistic.
...
Regards,
TE
P
Pickles
Guest
Good point by The Engineer, as usual. It just doesn't pay to make a wild guess and then calculate it to the Nth degree. Traveller spaceship drives are not going to work with any physics we* know, so trying to splice the two is only going to cause headaches ...
*Ok, by 'we', I mean people other than I.
*Ok, by 'we', I mean people other than I.
TheEngineer
SOC-14 1K
A magnetic bottle is good for keeping charged particles inside (e.g. the plasma).
Non-particle radiation (like IR or gamma) cannot be shielded by a magnetic field.
And while IR could be shielded by some material layers high energy radiation is even more difficult to weaken...
Well, if not using the magic non thermodynamic radiation/kinetic energy converter, you could use some other sophisticated radiator material (e.g. W-carbides), which could help to get rid of the power plant exess heat at around 3500 K.
So the plant temperature level would be quite high
In order to get rid of the low level heat, you would need some heat pumps to reach higher emission levels on the low temp radiators.
Space is perhaps 10E-25 times as diffusive as water. Good for long distance views
I guess IR detection of space objects from the dirtside is tricky due to the high amount of reflected IR in the upper atmo and the strong dispersion.
Regarding detectors in space, radiation from behind should not disturb a detector as those are usually designed shielded in order to grep directed "light".
COBE and WMAP satellites are pretty examples for IR detection capability. Hubble contains a near IR camera, too. So does lost Mars Observer.
Guess IR detectors are located on most satellites.
But as I said, accepting a simplifying handwaves help out.
Regards,
TE
Magnetic bottles are transparent to radiation. The physical containment vessel can (and likely is) opaque. However, in order to prevent the physical containment vessel from overheating and being destroyed, you need to cool it -- which you do by transferring heat out to some sort of heat sink, which on a space ship is a radiator.
Nowhere near enough zeroes there. A meter of water is about as opaque as several billion lightyears of space.
Infrared astronomy is a major field. It's mostly space-based, however, because IR sensors work relatively poorly in atmosphere.
Not sure of the ratio, but there's plenty of IR satellites. In terms of astronomy satellites, NASA has four major astronomy satellites:
Hubble: optical/near IR
Compton: gamma rays, hard X-rays
Chandra: soft X-rays
Spitzer: infrared
Note astronomers are not, by and large, terribly interested in finding yet more little rocks.
It means you need slightly more coolant than you otherwise would. Other than that, it has no effect.
I just skimmed through this topic quickly so if I'm duplicate someone else's comments I aplogize in advance...
Back in the 80's and 90's I worked for the Navy in wargaming advanced and conceptual systems where sensors were consistently a major player. One of the things that one noticed immediately is that operational capabilities significantly fell below what engineering models said they should be. This was typically because components degrade and fail over time, operational wear-and-tear moves elements out of adjustment/aligment, and engineering models often fail to take into account all the system, environmental, and operational factors in the real world. This resulted in long discussions when trying to simulate the impact of conceptual systems in scenarios that included current systems whose operational performances had been measured. This is one of the reasons why detection ranges are typically modelled as cumulative probability curves rather than a target with signature "x" will be detected at a range of "y." Depending on a variety of factors its operationally possible for a small signature target to be seen further out than it should be while a larger signature target at the same altitude flies overhead without being seen by the same sensor until its too late.
"Realistically," I would expect this lack of certainty to hold true generally for Traveller technology with probablity curves being moved further out but countered to some degree by having to maintain more complex technology. This does provide an opportunity to add a little more more tension in a game--although not as much as experienced by current day aircrews and air defense units.
Back in the 80's and 90's I worked for the Navy in wargaming advanced and conceptual systems where sensors were consistently a major player. One of the things that one noticed immediately is that operational capabilities significantly fell below what engineering models said they should be. This was typically because components degrade and fail over time, operational wear-and-tear moves elements out of adjustment/aligment, and engineering models often fail to take into account all the system, environmental, and operational factors in the real world. This resulted in long discussions when trying to simulate the impact of conceptual systems in scenarios that included current systems whose operational performances had been measured. This is one of the reasons why detection ranges are typically modelled as cumulative probability curves rather than a target with signature "x" will be detected at a range of "y." Depending on a variety of factors its operationally possible for a small signature target to be seen further out than it should be while a larger signature target at the same altitude flies overhead without being seen by the same sensor until its too late.
"Realistically," I would expect this lack of certainty to hold true generally for Traveller technology with probablity curves being moved further out but countered to some degree by having to maintain more complex technology. This does provide an opportunity to add a little more more tension in a game--although not as much as experienced by current day aircrews and air defense units.
Kaale: You are confusing opacity and the inverse-square law of projection.
Totally different functions.
The reduction in signal strength over distance in space is caused almost exclusively by the ISL... and almost none to opacity. In water, however, the opacity becomes a much larger factor than distance.
Totally different functions.
The reduction in signal strength over distance in space is caused almost exclusively by the ISL... and almost none to opacity. In water, however, the opacity becomes a much larger factor than distance.
The problem with the magnetic bottle being transparent to radiation, heat, alpha, & gamma, as seems to be claimed, is that fusion becomes impossible to work with and we know we can, we just can't control and maintain the bottle.
But if the magnetic bottle does not contain the heat of the fusion reaction, where did we come up with the refractory metals that can handle heat that is close, if not hotter than the surface of the sun? Even if we had such materials able to handle the heat, the radiation leakage from even a few seconds of fusion, would have the entire complex, scientists, etc., radiating themselves in a very short time.
As far as easily hiding a planetary heat signature from an orbital satellite, that is harder than radar, which is directional, vs IR which is omni-directional. There is not a IR shadow You might be able to fudge the software around but then that leaves the ability of others to use that fudging.
Anyway, as the Engineer says, we are trying to figure out present science to the hand wavium of our traveller universe, which is no worse than that by many authors. As long as they stay consistent in their handwavium, I am not going to complain, too much at least.
But if the magnetic bottle does not contain the heat of the fusion reaction, where did we come up with the refractory metals that can handle heat that is close, if not hotter than the surface of the sun? Even if we had such materials able to handle the heat, the radiation leakage from even a few seconds of fusion, would have the entire complex, scientists, etc., radiating themselves in a very short time.
As far as easily hiding a planetary heat signature from an orbital satellite, that is harder than radar, which is directional, vs IR which is omni-directional. There is not a IR shadow You might be able to fudge the software around but then that leaves the ability of others to use that fudging.
Anyway, as the Engineer says, we are trying to figure out present science to the hand wavium of our traveller universe, which is no worse than that by many authors. As long as they stay consistent in their handwavium, I am not going to complain, too much at least.
I'll just address theis first part and I'm sure others can chime in. As mentioned above, current fusion or fusion power generation schemes use this heat to generate power. The radiation you are worried about,e.g., gamma rays etc can be stopped by other materials. Finally the surface, i.e. photosphere, of the sun is really not that hot in the cosmic scheme of things (I'll try to find a number) and the materials we use to contain nuclear reactions are cooled. We are always ciculating some heat excahnge material to keep things from melting. The thing is the power used in Traveller is so far beyond the pale that nothing we can think of with current physics could possibly do the trick.
As said by thengineer and others, to me it is not so much bending of hard science but choosing what rules to bend, postulating the new physics, then tracking the logical consequences.
On IR signatures one can certainly assume a power output into space, then calculate the signature. If spread across a large eough sphere the signature is tiny. Calculations early in the thread seemed to indicate at 1 AU a standard fusion power plant is hard to discern. Ignoring the melting of your ship part, this sets an upper limit on your signature.
Then you need to postulate sensor advances based on unknown physics. The first hard science point shows you can hide, now you postulate advances where you can't hide; moving further from the realm of hard sci-fi but on the sensor side.
Bottom line, for hard sci-fi the feasible operating temperatures you can achieve with your power plant (without melting your ship) are easy to hide at 1 AU assuming hard sci-fi sensors.
Maybe one conceptual problem is the idea of temperature, which can be an ill defined concept believe it or not. A better concept, which relates directly to detection, is energy flux. That is Joules per meter squared. I can have a power plant hotter than the sun, but that doesn't mean by any stretch of the imagination that it is putting out more detectable energy than the sun.
I think Aramis has the point here. It is the ISL that makes waht appear to be hot objects hidable (if that's a word). On Earth a signature is spread over at most a sphere of what 8000 miles
(8 x 10^3). That's important but opacity due to air, water, etc. is much more important. In space there is mcuh less stuff, but the distances are immense. 1 AU is 93 million miles, (9.3 x 10^7) small distance on solar system scales.
That's 4 orders of maginitude in distance so the effect is 8 orders of magnitude with respect to the signature. It's really hard to imagine as most images we see of the solar system on a piece of paper, if properly to scale, would have to render the planets as indiscernable dots.
TheEngineer
SOC-14 1K
Hi folks !
Actually I'm working myself thru the book "Understanding Space - Introduction to astronautics" by Jerry Jon Sellers a.o.
It's a really good read, dealing with many astronautical topics in a very practical way, but also with a very digestable form of physical/mathematical content.
If somebody is able to borrow it perhaps from a university library (the book itself is quite expensive) and really is interested to get an insight into real world space tech I would highly recommend it.
Yesterday evening I looked again at the heat problem in fictional spaceships and sadly again came to the conclusion, that without the usage of some handwaved or, well extremely sophisticated heat/electricity conversion technique scout vessels with a 850 MW powerplant (or others with even higher power output) are simply not possible.
My suggestion with the high temp radiators wouldn't work, too, as the rising heat "sink" temperature would lift any regular carnot process for the main power production into regions of decreasing efficiency, making things just worse
So, if we want hard science spaceships with respect to heat management we would have to build really low energy things, maybe in the 150 kW range for a scout ship sized one...no fun with m-drives, lasers and stuff.
regards,
TE
Actually I'm working myself thru the book "Understanding Space - Introduction to astronautics" by Jerry Jon Sellers a.o.
It's a really good read, dealing with many astronautical topics in a very practical way, but also with a very digestable form of physical/mathematical content.
If somebody is able to borrow it perhaps from a university library (the book itself is quite expensive) and really is interested to get an insight into real world space tech I would highly recommend it.
Yesterday evening I looked again at the heat problem in fictional spaceships and sadly again came to the conclusion, that without the usage of some handwaved or, well extremely sophisticated heat/electricity conversion technique scout vessels with a 850 MW powerplant (or others with even higher power output) are simply not possible.
My suggestion with the high temp radiators wouldn't work, too, as the rising heat "sink" temperature would lift any regular carnot process for the main power production into regions of decreasing efficiency, making things just worse
So, if we want hard science spaceships with respect to heat management we would have to build really low energy things, maybe in the 150 kW range for a scout ship sized one...no fun with m-drives, lasers and stuff.
regards,
TE
Icosahedron
SOC-14 1K
The plasma itself contains most of the heat, and that heat is what is drawn off to provide power for the ship. The plasma (with its contained heat) is contained by the magnetic field. It is only the heat that escapes from the plasma that needs to be contained by the chamber walls.
There IS IR shadow. In space all radiation travels in straight lines. IR is no different than light, and without the diffusion aspect of atmosphere, shadows are very sharp.
The key thing to understand about power plant heat output is that it's not really about heat leaking through the walls of the fusion chamber -- while some of that happens, there's no specific reason it has to. Instead, power plant heat is caused by the process of generating power: the second law of thermodynamics places a lower limit on how much heat you can generate while producing a given amount of power (this lower limit is based on temperature; fusion can theoretically be very efficient). In addition, the same law says that any component that uses power will also produce heat. For most components, the heat output is very close to equal to the power input.
far-trader
SOC-14 10K
I've long felt that the power requirements needed to come down a lot for most of the ship elements. Though it's hard to argue that thruster plates and other magic tech is depicted as too energy hungry. I mean, who knows how many MW it might take to open a hole into jumpspace?
Even so I've long advocated a general slash of power needs by 10, but someone pointed out that even that wouldn't be enough to keep ships from melting let alone make them hard to spot.
Even so I've long advocated a general slash of power needs by 10, but someone pointed out that even that wouldn't be enough to keep ships from melting let alone make them hard to spot.
