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 Post subject: Re: Stealth
PostPosted: Fri Jan 04, 2008 7:38 pm 
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Ken Burnside wrote:
Premise 1) You may not know where ALL the observing platforms are. Therefore, directional stealth is dubious at best.


But if stealth is impossible (or at least dubious), then you *do* know where all the observing platforms are. Therefore directional stealth is possible.

But if directional stealth is possible, then stealth is possible, and therefore you *don't* know where all the observing platforms are. Therefore directional stealth is impossible (or at least dubious).

But if...

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 Post subject: Re: Stealth
PostPosted: Fri Jan 04, 2008 7:41 pm 
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Ken Burnside wrote:
Premise 4) You don't get to keep the crew and ship running at liquid helium temperatures for two months. People have to work on these ships, live on these ships and otherwise be comfortable enough to do the job you want them to do.


This premise is invalid if we violate Burnsides zeroth law. Which isn't one that I particularly care to violate in a sci-fi novel, OTOH.

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PostPosted: Fri Jan 04, 2008 9:15 pm 
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Jon Brase wrote:
Ken Burnside wrote:
Premise 1) You may not know where ALL the observing platforms are. Therefore, directional stealth is dubious at best.


But if stealth is impossible (or at least dubious), then you *do* know where all the observing platforms are. Therefore directional stealth is possible.

But if directional stealth is possible, then stealth is possible, and therefore you *don't* know where all the observing platforms are. Therefore directional stealth is impossible (or at least dubious).


Not sure why you need any sort of circular reasoning... why do the observation platforms need to manned and mobile (i.e., the type of platform that can't be stealthed)?

I'd imagine a passive sensor platform in planetary orbit would do quite nicely, and the heat/radar/power signature of something like Hubble or Chandra (or the ISS, if we insist on a manned platform) should be a few orders of magnitude smaller than that of a manned vessel... enough to blend in with the background noise of the planet they orbit.

Worst case scenario, there's always the option to use planet-side installations, no?


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 Post subject: Re: Stealth
PostPosted: Fri Jan 04, 2008 10:01 pm 
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In how may directions can you achieve "directional" stealth? In how many directions are the sensor platforms? It's pretty easy, and pretty cheap, to place a few sensor platforms so as to always get a "good" angle on an intruder.

Of course, you can't stealth a fusion drive, directionally or otherwise.

Jon Brase wrote:
But if stealth is impossible (or at least dubious), then you *do* know where all the observing platforms are. Therefore directional stealth is possible.

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PostPosted: Fri Jan 04, 2008 11:32 pm 
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Ken Watanabe wrote:
Not sure why you need any sort of circular reasoning... why do the observation platforms need to manned and mobile (i.e., the type of platform that can't be stealthed)? I'd imagine a passive sensor platform in planetary orbit would do quite nicely, and the heat/radar/power signature of something like Hubble or Chandra (or the ISS, if we insist on a manned platform) should be a few orders of magnitude smaller than that of a manned vessel... enough to blend in with the background noise of the planet they orbit.

Worst case scenario, there's always the option to use planet-side installations, no?


The circular reasoning was mostly just for humor.

But I still was making a bit of a point.

You're going to see the launch of any observation platform, manned or not. You can use the tracking data from that to figure out the platform's orbit. Unless it thrusts, you're going to know where it is, and thus be able to direct your emissions away from it. Of course, it will detect your launch, and whenever you thrust, it will see you, and in between the opponent will be able to extrapolate your course as well.

My point: "Drive heat gives you away" is a far more valid reason that stealth doesn't work in space than "Directional stealth doesn't work."

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 Post subject:
PostPosted: Sat Jan 05, 2008 4:39 am 
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Jon Brase wrote:
My point: "Drive heat gives you away" is a far more valid reason that stealth doesn't work in space than "Directional stealth doesn't work."


The thing about directional sensors is this:

It's too easy to put out a series of platforms over decades (and makes too much sense, financially) to just put unmanned platforms out and run them.

Now, those platforms are going to have hot spots of about 300-400K from their power supplies or solar arrays, but they're low power objects. Much less power needed to run a computer, CCD, and periodic transmitter that runs a mesh network than it takes to run a real warship.

It's also really hard to tell if a dim 300-400K signature is a sensor platform or something else...and you really can't stealth against everything, even coasting on your vector.

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 Post subject: Re: Stealth
PostPosted: Sun Jan 06, 2008 10:59 pm 
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John Dearmore wrote:
My question in this instance is whether or not it is physically possible to create a stealthy ship at all... not using TW tech; just theoretically.


What, and remove the biggest reason for painting ships in patterns of color that would make a Liberace blush with embarassment? :lol:

On a side note, my computer is finally up and running again!


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 Post subject:
PostPosted: Mon Jan 07, 2008 6:51 am 
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Todd Kes wrote:
Easy answer - there is no stealth in space.

Long answer - you have your people sitting in a vehicle that is roughly 273 Kelvin, against a background temperature of 3 Kelvin. So figure your ship is ninety times hotter than the background. This is assuming that the ship is the temperature of frozen water/ice, not if they had a 800+Kelvin reactor running.




The 273 Kelvin figure assumes two things that are not necessarily true-- The ship is roughly sperical and it is absolutely black. A Wasp that manages to remain end-on to the system primary will be noticeably cooler and kept broadside will become warmer. Give your ship a copper coating burnished to a mirror shine and it will only absorb five to ten percent of the radiation of an absolutely black one for an equilibrium temperature between about 70 and 100 K

However, that copper coating sure is shiny. Stealth works for aircraft and submarines for the simple reason that there are only a few good ways to detect them. A stealthy spacecraft has to be stealthy across the entire electromagnetic spectrum and there are conflicting requirements to what makes something stealthy between different parts of the spectrum. A very cold spacecraft is a bright, shiny object (high albedo) and an absolutely non-reflective spacecraft gets quite warm. No spacecraft can be both at the same time.

Stealth in space requires you to shed your excess heat into hyperspace, not build your gravity planar with magnetic monopoles (which the Kzin learned eventually), and run your gravitics in dipole mode (alot more power, but the field emissions fall off at the inverse cube, instead of the inverse square [the only plausible explanation for why stealth requires power in Honorverse]). It also helps if your power source directly converts mass to electrical power, without an intermediate and lossy stage of generating heat.

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 Post subject:
PostPosted: Mon Jan 07, 2008 1:56 pm 
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Within certain types of technical assumptions, stealth does become possible in space. All it requires is a low power drive and extremely long ranges. The typical apparent magnitude of an energy source, over all wavelengths, is about 39.5 - 2.5 * log (Power) + 5 * log (distance in AU), so a 1 megawatt source at 1 AU averages out at about 24.5. That is detectable with a modern telescope if you know where you're looking, but a telescope array that can scan the entire sky and detect objects that dim is unlikely to be found on a spaceship, and doesn't exist today, though LSST may be that sensitive, and would scan the sky every three nights.

The real problem is with stealth at tactical ranges. Directional radiators, even if they can be made practical, won't help against visual spotting, and a 10m object with an albedo of 0.001 (which is incredibly low), at a range of 15,000 km, which is likely beyond weapons range, would have an apparent magnitude of 13, which is pretty straightforward to detect.[/url]


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 Post subject:
PostPosted: Mon Jan 07, 2008 8:27 pm 
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Richard Bell wrote:
Todd Kes wrote:
Easy answer - there is no stealth in space.

Long answer - you have your people sitting in a vehicle that is roughly 273 Kelvin, against a background temperature of 3 Kelvin. So figure your ship is ninety times hotter than the background. This is assuming that the ship is the temperature of frozen water/ice, not if they had a 800+Kelvin reactor running.


The 273 Kelvin figure assumes two things that are not necessarily true-- The ship is roughly sperical and it is absolutely black. A Wasp that manages to remain end-on to the system primary will be noticeably cooler and kept broadside will become warmer. Give your ship a copper coating burnished to a mirror shine and it will only absorb five to ten percent of the radiation of an absolutely black one for an equilibrium temperature between about 70 and 100 K


The 273 Kelvin is for the crew on board, not from solar heating. You know, keeping the ship habitable for an onboard crew? Try this math problem: how many square meters of surface are needed to dissipate the waste heat produced by an average human being (assume 1000 calorie diet), so the surface never gets hotter than 273 Kelvin? Ignore stellar radiation to make it easy. Remember that you don't want to turn on the 800 Kelvin reactor, so the only way to cool the ship is passive systems.

Now if we get into intelligent automated warships that can run much colder, with only solar power to run basic maintenance, then things get interesting. Especially if the automated fleets decide not to fight any more.

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 Post subject:
PostPosted: Tue Jan 08, 2008 11:01 am 
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Todd Kes wrote:
The 273 Kelvin is for the crew on board, not from solar heating.

There's no guarantee the hull is at the temperature of the living area. You can have arbitrarily good insulation in space.
Todd Kes wrote:
Try this math problem: how many square meters of surface are needed to dissipate the waste heat produced by an average human being (assume 1000 calorie diet), so the surface never gets hotter than 273 Kelvin?

A 1,000 calorie diet? Ouch. Anyway, a resting human produces 70-100 watts of thermal energy, and a 273K blackbody emits 315W/m^2, so about 0.3 square meters. With life support requirements, a more realistic figure is about 1 kW per person on board. Unless you're parked well beyond the snow line, this will usually be swamped by solar heating, and a 1 kW source isn't detectable at much range anyway.


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 Post subject:
PostPosted: Wed Jan 09, 2008 7:39 pm 
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Todd Kes wrote:
Richard Bell wrote:
Todd Kes wrote:
Easy answer - there is no stealth in space.

Long answer - you have your people sitting in a vehicle that is roughly 273 Kelvin, against a background temperature of 3 Kelvin. So figure your ship is ninety times hotter than the background. This is assuming that the ship is the temperature of frozen water/ice, not if they had a 800+Kelvin reactor running.


The 273 Kelvin figure assumes two things that are not necessarily true-- The ship is roughly sperical and it is absolutely black. A Wasp that manages to remain end-on to the system primary will be noticeably cooler and kept broadside will become warmer. Give your ship a copper coating burnished to a mirror shine and it will only absorb five to ten percent of the radiation of an absolutely black one for an equilibrium temperature between about 70 and 100 K


The 273 Kelvin is for the crew on board, not from solar heating. You know, keeping the ship habitable for an onboard crew? Try this math problem: how many square meters of surface are needed to dissipate the waste heat produced by an average human being (assume 1000 calorie diet), so the surface never gets hotter than 273 Kelvin? Ignore stellar radiation to make it easy. Remember that you don't want to turn on the 800 Kelvin reactor, so the only way to cool the ship is passive systems.



I thought so,too, at first. Then I saw the worked example in my thermodynamics textbook that made the clear assertion that all spherical, black objects will reach thermal balance at 273 K, due to insolation at the Earth's radius from the sun. The temperature on the inside of a habitation section of a spacecraft is usually understood to be 293 K (about 70 fahrenhiet or 20 degrees celsius). A third assumption that I did not realize, at first, is that the object is not large enough to support much of a temperature gradient.

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 Post subject:
PostPosted: Wed Jan 09, 2008 11:59 pm 
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This is just a little side track, but the only way to make such problems of thermodynamics with stealth go away in a hard science fiction setting is to take stances like Greg Bear did in [u]Anvil of Stars [/u] or Alaistar Reynolds in [u]Absolution Gap[/u]. That would require playing tricks with quantum mechanics and quantum chromodynamics at levels that might as well be magic with abilities of changing matter to antimatter at the flip of a switch or funneling heat back into the fabric of space-time.


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 Post subject:
PostPosted: Fri Jan 11, 2008 12:24 pm 
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Anthony Jackson wrote:
There's no guarantee the hull is at the temperature of the living area. You can have arbitrarily good insulation in space.


True, which means that the interior of the ship just gets hotter and hotter, until either you start radiating that heat, or you bake the crew alive, melt down the reactor, and then start radiating heat.

Anthony Jackson wrote:
A 1,000 calorie diet? Ouch. Anyway, a resting human produces 70-100 watts of thermal energy, and a 273K blackbody emits 315W/m^2, so about 0.3 square meters. With life support requirements, a more realistic figure is about 1 kW per person on board. Unless you're parked well beyond the snow line, this will usually be swamped by solar heating, and a 1 kW source isn't detectable at much range anyway.


Now figure how easy it is to spot 273 Kelvin against a 3 Kelvin background. The ship is literally ninety times hotter than the background. Current technology could detect that .3 square meter surface at 273 Kelvin at roughly half a million kilometers, or a third of a million miles.

Now if you want to drop the temperature, and raise the surface area, that would be possible. If you halve the surface temperature, the detection range is only 1/4 the value above. However, if you quadruple the surface area, you double the detection range. Feel free to mix and match as wanted to get an optimum solution.

From Atomic Rockets
Detection range in kilometers = 13.4 * SQRT(surface area in square meters) * (Temperature in Kelvin)^2

Now if you start lighting up a reactor, your hull temperature will be rising to ~700-800 Kelvin, or about three times the prior temperature, for nine times the detection range.

If you light off an engine to accelerate that person, assuming 100 kilos, 10,000 Specific Impulse, and accelerating at 1 m/s (about .1G), then you are looking at about twenty million kilometers detection range.

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 Post subject:
PostPosted: Fri Jan 11, 2008 3:14 pm 
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Todd Kes wrote:

True, which means that the interior of the ship just gets hotter and hotter, until either you start radiating that heat, or you bake the crew alive, melt down the reactor, and then start radiating heat.

Yes, but you only need to radiate heat equal to internal power production plus external power.
Todd Kes wrote:
Now figure how easy it is to spot 273 Kelvin against a 3 Kelvin background.

First of all, it's not a 3K background; the majority of the background noise for a thermograph will probably be either internal sensor noise or zodiacal dust, both of which will tend to be at or near the local blackbody temperature of space (273K). Secondly, background brightness affects noise, but it doesn't affect signal. It doesn't matter what the background noise is, if you don't pick up a certain minimum number of photons, you're not going to spot whatever the object is.


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