News: Space Warfare II - Stealth Reconsidered [Archive]

Kraven Kor

Jun 22nd, '09, 02:11 PM

Couple thoughts I had on this for my campaign:

Large bodies can be used to hide behind if your prey doesn't have observation points behind as well - come into their system behind a large Gas Giant, keeping it between you and their world. Will at least change when you get detected from "years before you arrive" to "days to weeks before you arrive," depending on what methods of travel are available.

Some type of special material or shielding which limits how much particle or radio emissions your craft emits would help against some types of observation, but not all - your craft simply partially blocking background radiation can be enough to give away it's presence to a sensitive enough system (or an observant enough person.)

Sundog

Jun 22nd, '09, 02:44 PM

No way you could absorb enough of the EM radiation to make you invisible - especially not in the IR spectrum. Worse, that heat has to go somewhere - you'd eventually cook your crew.

Kraven Kor

Jun 23rd, '09, 08:13 AM

No way you could absorb enough of the EM radiation to make you invisible - especially not in the IR spectrum. Worse, that heat has to go somewhere - you'd eventually cook your crew.

Turn waste heat into power? Cool-running Cold Fusion Reactors? But yeah, I was saying that no matter how little emissions you put off, of any spectrum, that simply blocking the background "noise" of space can be enough to detect you (which is more or less how we were detecting planets until recently - essentially waiting for the telltale shadow or flicker against the backdrop.)

Clonus

Jun 23rd, '09, 08:57 AM

No way you could absorb enough of the EM radiation to make you invisible - especially not in the IR spectrum. Worse, that heat has to go somewhere - you'd eventually cook your crew.

I came up with a stealth scene where the intruders pop out of FTL in a blind spot and then go "cool running". Which is the opposite of what it sounds like since the interior of the ship, which has been cooled down to sub-zero temperatures, steadily heats up until everyone is on the verge of heat prostration by the time they are ready to launch their surprise attack.

The problem with realistic space combat of course is that space is boring and therefore space combat is boring. Oceans have currents, storms, shoals, fog banks, horizons, winds, mines. Space has...nada beyond the occasional rock and a bit of solar flare activity.

Nyrath

Jun 23rd, '09, 10:04 AM

Turn waste heat into power?
*sigh*
Again I must explain that it is impossible to convert waste heat into power.
Thermocouples and the like convert a heat gradient into power. But the original waste heat is still there.

http://www.projectrho.com/rocket/rocket3au.html

Nyrath

Jun 23rd, '09, 10:06 AM

The problem with realistic space combat of course is that space is boring and therefore space combat is boring. Oceans have currents, storms, shoals, fog banks, horizons, winds, mines. Space has...nada beyond the occasional rock and a bit of solar flare activity.
Which is why the better SF authors go to great lengths to invent an FTL system that is very un-boring. The system in the Honor Harrington novels has gravitational shoals and all sorts of peril.

Kraven Kor

Jun 23rd, '09, 10:07 AM

*sigh*
Again I must explain that it is impossible to convert waste heat into power.
Thermocouples and the like convert a heat gradient into power. But the original waste heat is still there.

http://www.projectrho.com/rocket/rocket3au.html

Sigh my arse. You enjoy correcting us fools and you know it ;)

Besides, until recently I've been absent from these boards for years, and apparently missed a whole lot of stuff :D

ajackson

Jun 23rd, '09, 10:48 AM

But the original waste heat is still there.
Well, sort of. If you were able to apply some device to it and generate useful power, it wasn't waste heat.

Nyrath

Jun 23rd, '09, 11:56 AM

Well, sort of. If you were able to apply some device to it and generate useful power, it wasn't waste heat.
But if the point of the exercise was to "consume" the waste heat so that your ship didn't show up like a supernova on the infrared detectors, the fact that the waste heat was not consumed will get you wasted by enemy warships. :D

Kristopher

Jun 24th, '09, 09:07 AM

*sigh*
Again I must explain that it is impossible to convert waste heat into power.
Thermocouples and the like convert a heat gradient into power. But the original waste heat is still there.

http://www.projectrho.com/rocket/rocket3au.html

There's certainly no known way to convert waste heat into anything else. I think declaring it impossible is a bit much.

Clonus

Jun 24th, '09, 10:09 AM

There's certainly no known way to convert waste heat into anything else. I think declaring it impossible is a bit much.

If it isn't, then the laws of thermodynamics are just suggestions.

Kraven Kor

Jun 24th, '09, 10:37 AM

If it isn't, then the laws of thermodynamics are just suggestions.

All Scientific Laws are Working Theories just waiting to be proven wrong. Not to say that laws like the Conservation of Energy and such *will* be proven wrong or inadequate, but to say they cannot be wrong or inadequate is folly.

ajackson

Jun 24th, '09, 12:17 PM

All Scientific Laws are Working Theories just waiting to be proven wrong. Not to say that laws like the Conservation of Energy and such *will* be proven wrong or inadequate, but to say they cannot be wrong or inadequate is folly.
The case for the second law is stronger than most (it comes from mathematics), but when you're talking about hard SF, you pretty much have to discard convenient mistakes, because, while there's a high chance of errors in current theory, there's a low chance of those errors producing any particular outcome, and the errors, such as they are, will almost always be in places that are currently inconvenient to impossible to observe.

Nyrath

Jun 24th, '09, 12:27 PM

All Scientific Laws are Working Theories just waiting to be proven wrong. Not to say that laws like the Conservation of Energy and such *will* be proven wrong or inadequate, but to say they cannot be wrong or inadequate is folly.
You are forcing me to sigh again. ;)

Scientific Laws are totally unrelated to Scientific Theories. A law is a description of observed phenomenon. A theory is a scientific explanation of an observed phenomenon.

So the laws of thermodynamics are "waiting to be proven wrong" in the same way that you can prove the law of gravity wrong by letting go of a 500 pound anvil over your foot and watching it float into the air. It's not the way to bet.

But you are using two of the tired old fallacies SF authors resort to when science denies them what they want: "It's Just A Theory" (http://www.projectrho.com/rocket/rocket3al.html#theory) and Maybe A Scientific Breakthrough Will Let Me Have My Way (http://www.projectrho.com/rocket/rocket3al.html#breakthrough)

Kraven Kor

Jun 24th, '09, 12:49 PM

I tried a quick google search (believe it or not I am working and thus have limited time to discuss this) but I know for a fact that there have been several instances of Scientific Laws that were held up as universal truths for some some time were then proven wrong or inadequate.

Any scientist who suggested any theory that went against such a law or "known truth" were mocked, ridiculed, called fakes and phonies and liars; or, worse, blasphemers. But then the new theory was proven true, the old law was retired or rewritten, and then generations later when someone challenged the new status quot, the new Law, the new known truth... they were treated the same way only to be vindicated when their new theory proved to hold water.

However, there have been many more claims that violated the Laws of Physics which were ultimately disproved.

The weight of evidence is in favor of the current Laws; but that does not mean that what we know now is 100% accurate and inclusive.

If we aren't brave enough to challenge conventional wisdom, we will never discover anything new again.

Nyrath

Jun 24th, '09, 01:21 PM

I would be interested to see examples of such refuted laws. If you can find them.

As for disproving theories, you are aware, are you not, that there is a 50% chance that the new theory could make things worse? There was an amusing SF story by George R. R. Martin called "FTA" where scientists discovered how to enter hyperspace. They were initially jubilant, with visions of FTL starships and Nobel prizes dancing in their heads. Their hopes were quickly dashed when they found out that the speed of light in hyperspace was slower than in our universe.

Theories are only rarely disproven, usually they are just modified. Newtonian theories of motion are still used, its just that they had to be modified by Einstein's relativity to apply to velocities above about 14% of light speed.

Kraven Kor

Jun 24th, '09, 01:29 PM

I'll look it up in my Einstein: 100 Years of Relativity book tonight, if I get a chance. But I know that both relativity and string theory and later quantum mechanics all faced a wall of "but that's impossible" arguments relating to Scientific Laws.

Again, I'm not trying to say "FTL is in fact possible without time travel" - I'm trying to say "It is possible that there is something we don't yet know" that could both be supported by current observations and known 'laws' while also opening up new possibilities by redefining what we know about the universe. Which, last I checked, was surprisingly little.

There will be another Einstein, some day, who will turn the world of science on its head once again.

Sundog

Jun 24th, '09, 04:03 PM

Without a doubt. However, just as Einstein did, he will change our way of looking at why the universe acts as it does - not what it does.

Yansuf

Jun 24th, '09, 04:17 PM

*sigh*
Again I must explain that it is impossible to convert waste heat into power.
Thermocouples and the like convert a heat gradient into power. But the original waste heat is still there. /url]

I admit it has been 48 years since I did any work with thermodynamics, and I haven't pulled any old texts out of storage, but what about using the heat to boil a working fluid and spin a turbine?

Nyrath

Jun 24th, '09, 05:28 PM

I admit it has been 48 years since I did any work with thermodynamics, and I haven't pulled any old texts out of storage, but what about using the heat to boil a working fluid and spin a turbine?
The original heat is still there, but the heat gradient is not. The temperature of the room has risen as the heat boils the water.

It's like a hydroelectric power plant.

It converts the gravity gradient of the falling water into electricity. But the water is not annihilated by the plant, it still pours out the sluices and flows downstream.

In technical terms, the second law of thermodynamics (http://en.wikipedia.org/wiki/Second_law_of_thermodynamics) says that entropy always increases. Turning heat into useful work would reduce entropy, which is forbidden. Turning a head gradient into useful work is allowed.

Kristopher

Jun 24th, '09, 09:34 PM

The original heat is still there, but the heat gradient is not. The temperature of the room has risen as the heat boils the water.

It's like a hydroelectric power plant.

It converts the gravity gradient of the falling water into electricity. But the water is not annihilated by the plant, it still pours out the sluices and flows downstream.

In technical terms, the second law of thermodynamics (http://en.wikipedia.org/wiki/Second_law_of_thermodynamics) says that entropy always increases. Turning heat into useful work would reduce entropy, which is forbidden. Turning a head gradient into useful work is allowed.

What bugs me, a lot actually, is when someone says "that would be impossible because it would violate the second law blah blah blah" about some novel effect that no one has actually tried to accomplish. Take for example a membrane that is permeable in one direction by gas molecules above a certain energy, and in the other direction by gas molecules below a certain energy (I think that's how it goes, bear with me). The assertion usually made is that it's not even worth looking for such a thing, because it "violates the second". How about we actually find out what's possible?

Clonus

Jun 24th, '09, 09:49 PM

ajackson

Jun 24th, '09, 10:59 PM

How about we actually find out what's possible?
People do work out the math on examples like that, actually. It's just time consuming and annoying, and so far hasn't produced any examples that differ from what we'd expect from the second law of thermodynamics, so unless you're specifically searching for second law violations it's generally legitimate to just assume the second law holds.

Nyrath

Jun 25th, '09, 02:33 AM

What bugs me, a lot actually, is when someone says "that would be impossible because it would violate the second law blah blah blah" about some novel effect that no one has actually tried to accomplish. Take for example a membrane that is permeable in one direction by gas molecules above a certain energy, and in the other direction by gas molecules below a certain energy (I think that's how it goes, bear with me). The assertion usually made is that it's not even worth looking for such a thing, because it "violates the second". How about we actually find out what's possible?
Well, by analogy:
The laws of mathematics state that 1 + 1 = 2. But you do not see lots of people trying to find a way to make 1 + 1 = 3, valiantly ignoring the fact that it is impossible because it would violate the law of addition.

In the same way, chemists calculate the results of chemical reactions using the laws of chemistry in order to tailor chemical products. They do not spend all day mixing random chemicals in the hope of violating any of the laws of chemistry. Even though it would be nifty to stumble over a way of turning lead into gold.

I take it that you are unfamiliar with the concept of a mathematical proof?
http://en.wikipedia.org/wiki/Mathematical_proof
Proofs are obtained from deductive reasoning, rather than from inductive or empirical arguments. That is, a proof must demonstrate that a statement is true in all cases, without a single exception.

Yansuf

Jun 25th, '09, 08:51 AM

The original heat is still there, but the heat gradient is not. The temperature of the room has risen as the heat boils the water.

It's like a hydroelectric power plant.

It converts the gravity gradient of the falling water into electricity. But the water is not annihilated by the plant, it still pours out the sluices and flows downstream.

In technical terms, the second law of thermodynamics (http://en.wikipedia.org/wiki/Second_law_of_thermodynamics) says that entropy always increases. Turning heat into useful work would reduce entropy, which is forbidden. Turning a head gradient into useful work is allowed.

As long as the increased entropy of the working fluid (via its state change from liquid to gas) is greater than the decrease in the entropy of the heat sink, second law is not violated.

Using your argument, it appears to me that all existing refrigeration cycles violate the second law. The temperature is lowered by allowing (great) expansion of the working fluid, not by dumping it into another system. The only input is the (electric) power needed to recompress the working fluid.

Nyrath

Jun 25th, '09, 01:05 PM

As long as the increased entropy of the working fluid (via its state change from liquid to gas) is greater than the decrease in the entropy of the heat sink, second law is not violated.

Using your argument, it appears to me that all existing refrigeration cycles violate the second law. The temperature is lowered by allowing (great) expansion of the working fluid, not by dumping it into another system. The only input is the (electric) power needed to recompress the working fluid.
Right, the input of electrical power prevents violation of the second law. If there was no power input, there would be a violation.

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw.html
(scroll down to Second Law: Refrigerator)
http://www.phy.duke.edu/~rgb/Class/phy51/phy51/node63.html

Without power input, it would violate the second law. There is a name for this: perpetual motion machine (of the second kind). (http://en.wikipedia.org/wiki/Perpetual_motion)

The earliest known example of somebody trying and failing to make a perpetual motions machine was in 1150 AD. In the almost 900 years since, people have been trying and trying to defeat the second law of thermodynamics, and they have failed every single time.

This is a good summary:
Use of the term "impossible" and perpetual motion (http://en.wikipedia.org/wiki/Perpetual_motion#Use_of_the_term_.22impossible.22_ and_perpetual_motion)

ajackson

Jun 25th, '09, 01:47 PM

Right, the input of electrical power prevents violation of the second law. If there was no power input, there would be a violation.
Actually, you're missing his point, though it's an artifact of clumsy wording. If you let a liquid move from a high pressure area to a low pressure area, and it transforms into a gas when doing so, its temperature goes down without external energy input, which looks like a second law violation. It's not -- modest pressure gas is higher entropy than a liquid, even if the gas is cooler than the liquid -- but using a careless definition of entropy it looks like one.

Yansuf

Jun 25th, '09, 02:01 PM

Right, the input of electrical power prevents violation of the second law. If there was no power input, there would be a violation.

True to my second comment.
Now please explain my first.

For that matter, referring to the first, refrigeration is possible inside the ship.
Now you say: "but what about the extra waste heat from generating the electric power needed for the refrigeration?" Good question.
It depends on how efficient the process is. If the efficiency is good enough, the refrigeration is more than the added waste heat, and no, that is not a perpetual motion machine.

BTW, remember in most of the "atomic rocket" designs, the main power plant (be it fission or fusion) is an open system, it generates thrust by expelling reaction mass. This removes a great deal of heat from the system, even if other "waste" heat is not used to pre-heat the remass.

Separately, another simple example; if the power for the refrigeration comes from a solar array, how much waste heat is there?

Yansuf

Jun 25th, '09, 02:23 PM

ajackson

Jun 25th, '09, 02:50 PM

On reflection, gas moving from high to low pressure will also drop in temperature -- you can in general produce energy from a pressure differential in much the same way you can produce energy from a temperature differential. There are also some categories of chemical reaction that are endothermic but have positive entropy.

Zeropoint

Jun 25th, '09, 04:35 PM

Separately, another simple example; if the power for the refrigeration comes from a solar array, how much waste heat is there?

NOT zero. There will still be a net positive amount of waste heat. You've got the resistance of the wires, and even assuming a peltier junction system with no moving parts, to move heat "uphill" requires an input of energy which is released as waste heat. It happens to be exactly the same as a heat engine running in reverse. Pump X joules of energy out of the fridge, put 1.5X joules into the ship's air. Heat that needs to be removed.

Kraven Kor

Jun 25th, '09, 05:03 PM

Could you build a system that recycled as much heat / emissions / waste as possible to bring the waste heat - and thus detectable emissions - "near zero?"

Say, you have some type of fusion reactors, which powered a variety of drive systems - ion and/or plasma drives or the like for in-system travel, the jump or whatever FTL drives (if they exist in the setting / our imaginary future reality for this conversation), and all the other stuff. Obviously, if your engines are actually providing thrust you can't mask that - but could your other systems be so efficient that you'd be significantly harder to detect? Or to where you might be mistaken for something other than what you are? Say a cruiser coasting along or parked in an orbit, observing or whatever it is your ship(s) is there to do?

Clonus

Jun 25th, '09, 08:22 PM

Say, you have some type of fusion reactors, which powered a variety of drive systems - ion and/or plasma drives or the like for in-system travel, the jump or whatever FTL drives (if they exist in the setting / our imaginary future reality for this conversation), and all the other stuff. Obviously, if your engines are actually providing thrust you can't mask that - but could your other systems be so efficient that you'd be significantly harder to detect?

Only if you lower your internal temperature to slightly above absolute zero.

Kristopher

Jun 25th, '09, 08:55 PM

Well, by analogy:
The laws of mathematics state that 1 + 1 = 2. But you do not see lots of people trying to find a way to make 1 + 1 = 3, valiantly ignoring the fact that it is impossible because it would violate the law of addition.

In the same way, chemists calculate the results of chemical reactions using the laws of chemistry in order to tailor chemical products. They do not spend all day mixing random chemicals in the hope of violating any of the laws of chemistry. Even though it would be nifty to stumble over a way of turning lead into gold.

I take it that you are unfamiliar with the concept of a mathematical proof?
http://en.wikipedia.org/wiki/Mathematical_proof
Proofs are obtained from deductive reasoning, rather than from inductive or empirical arguments. That is, a proof must demonstrate that a statement is true in all cases, without a single exception.

Yes, I'm familiar. But then you're claiming that the Second is a mathematical proof?

I'm not talking about wacko ideas like perpeutal motion machines. I'm just trying to leave the door open for things we might not have discovered yet, and constantly bashing even the most novel and unusual idea with "the second law says no!" before it's even tried strikes me as counterproductive and silly.

Clonus

Jun 26th, '09, 07:07 AM

Yes, I'm familiar. But then you're claiming that the Second is a mathematical proof?

I'm not talking about wacko ideas like perpeutal motion machines.

Yeah, you are. Any device that doesn't produce any waste heat is a perpetual motion machine.

Kraven Kor

Jun 26th, '09, 08:00 AM

Only if you lower your internal temperature to slightly above absolute zero.

So no amount of insulation / heat recycling could let you have heated interiors but still mask your heat signature?

Again, not talking zero waste heat, just talking maximum efficiency.

ajackson

Jun 26th, '09, 08:21 AM

Yes, I'm familiar. But then you're claiming that the Second is a mathematical proof?
Actually, it is. The second law is dependent on the information content of the system being finite, but it works for a wide variety of systems with little resemblance to our universe.

ajackson

Jun 26th, '09, 08:28 AM

So no amount of insulation / heat recycling could let you have heated interiors but still mask your heat signature?
Depends how much you want to mask it. There's no way you can over the long term reduce your heat signature below the biological heat output of your crew (on the order of 100W per person) but that's mostly irrelevant in real applications -- for non-accelerating vehicles, reflected signature generally exceeds heat signature anyway.

Clonus

Jun 26th, '09, 08:34 AM

So no amount of insulation / heat recycling could let you have heated interiors but still mask your heat signature?

Again, not talking zero waste heat, just talking maximum efficiency.

No amount would let you have heated interiors but still mask your heat signature for very long. Insulation just delays the time it takes for heat to get out and has the unpleasant side effect of causing heat to build up inside as long as it is being produced. "Heat recycling" runs up against the fundamental reality that energy is a conserved quantity, meaning that sooner or later all your heat will radiate out. All you can ever do is delay it. This of course means the logical method for launching a surprise attack would be using an entirely automated attack, or and better, pose as legitimate space traffic.

Nyrath

Jun 26th, '09, 08:43 AM

Actually, you're missing his point, though it's an artifact of clumsy wording. If you let a liquid move from a high pressure area to a low pressure area, and it transforms into a gas when doing so, its temperature goes down without external energy input, which looks like a second law violation. It's not -- modest pressure gas is higher entropy than a liquid, even if the gas is cooler than the liquid -- but using a careless definition of entropy it looks like one.

Well, perhaps, but not according to the original post.

Using your argument, it appears to me that all existing refrigeration cycles violate the second law. The temperature is lowered by allowing (great) expansion of the working fluid, not by dumping it into another system. The only input is the (electric) power needed to recompress the working fluid.
The confusion seems to be due to the original poster conflating "temperature" with "entropy." The second law of thermodynamics states that in a closed system entropy increases. Therefore all existing refrigeration cycles do not violate the second law.

Refrigerators can pump heat from one place to another, but they increase entropy while doing so. Thus the second law is maintained.

In any event, the heat is not destroyed, just moved. That's why on a chilly day you always find the cat curled up near the bottom vents on the refrigerator, where all the heat pumped from the interior is jettisoned.

CorpCommander

Jun 26th, '09, 08:46 AM

My first thought is you don't have to get rid of all your waste heat. Just enough to satisfy 1/r^2 such that your level of heat less than the level that can be detected at that range. The more efficient you are the closer you can get to your less stealthy opponent.

Stealth is simply a defense and a weak one at that. Once you are seen all of its value goes away. So perhaps a better use of time, energy and equipment space on your ship is to find a way to use that heat defensively. Turn a problem into an asset. Especially since it is pretty damn hard to mask anyway.

That said here is my Perpetual Motion Story. Totally True.

Back around 1960 or so my Dad was called out to his Uncle's house to help with something. When he got there his other Uncles were there too and so was a big truck which had a large iron wheel. They needed to get this down into the basement. Everyone was breaking their back trying to move this incredibly heavy wheel when my Dad asked Sal, "so are you going to use this as the foundation for a waterheater or something?"

Sal's eyes lit up and said "No." He became professor for a moment and explained, "this wheel will change history for I have figured out a way to make limitless energy." All work came to an instant stop. The sweaty men and the perplexed truck driver all looked on. "You see, we shall mount this wheel on a special bracket I have set up in the basement. We shall spin the wheel. It shall turn so fast that eventually it will be impossible to stop and we will draw energy from it."

"Oh for Christ's Sake!" said the 5 Italians and the truck driver. What the truck driver didn't know was the long standing rivalry between Sal and his brothers. You see they were all in the heating oil business. Sal was environmentally conscious long before it became fasionable. He wanted to create perpetual motion and put the Oil Industry out of business.

My father and his brother were both chemical engineers. Sal was the smartest of the old school Italians, having gone all the way through the 6th grade before getting a job (back in the old days school was looked down upon as a luxury and a waste of time.) He and my Uncle tried to explain to Sal a concept called friction and offered to take him to either Northeastern University or MIT to discuss his theory with engineers of repute.

Sal is still looking to put the Oil Industry out of business. He later won awards for improving the efficiency of heaters for homes. Ultimately we are all ignorant, but the difference between us is degrees of ignorance. I think for me the lesson is that enthusiasm for the subject matter and a willingness to accept the truth as you discover it will go a long way in helping build your understanding and perhaps lead you to find an application of knowlege no one else has developed.

Nyrath

Jun 26th, '09, 08:57 AM

True to my second comment.
Now please explain my first.
Explained in the post above this. Heat is moved by the refrigeration cycle, but entropy is increased in doing so. If I am not explaining this adequately, it is because I'm not a professional teacher. You might be better off finding a high school physics teacher and asking them to explain.

True For that matter, referring to the first, refrigeration is possible inside the ship.
Now you say: "but what about the extra waste heat from generating the electric power needed for the refrigeration?" Good question.
It depends on how efficient the process is. If the efficiency is good enough, the refrigeration is more than the added waste heat, and no, that is not a perpetual motion machine.
Again, the refrigeration pumps heat from whatever is being refrigerated to somewhere else. The heat is still there, just relocated. Add to that the heat from the power source attached to the refrigerator. The heat just gets larger and larger.

BTW, remember in most of the "atomic rocket" designs, the main power plant (be it fission or fusion) is an open system, it generates thrust by expelling reaction mass. This removes a great deal of heat from the system, even if other "waste" heat is not used to pre-heat the remass.
Yes, I know about open cycle cooling, you might have read about it on my website (http://www.projectrho.com/rocket/rocket3e.html).;) But the main thing that open cycle cooling is not is "stealthy". Which, if you recall, was the point of this entire thread.
Blasting out a sixty gigawatt plume of hot plasma is not the way to try and avoid being noticed.

Separately, another simple example; if the power for the refrigeration comes from a solar array, how much waste heat is there?
The current state-of-the-art solar cell arrays on the International Space Station are about 14.5% efficient. This means (in Earth orbit) every square meter of solar cell produces abotu 198 watts of electricity, and 1167 watts of waste heat.

CorpCommander

Jun 26th, '09, 09:08 AM

Blasting out a sixty gigawatt plume of hot plasma is not the way to try and avoid being noticed.

.sig worthy!

Nyrath

Jun 26th, '09, 09:14 AM

Could you build a system that recycled as much heat / emissions / waste as possible to bring the waste heat - and thus detectable emissions - "near zero?"
Forgive me but you are apparently not listening. It is impossible to recycle waste heat. The best you can do is pump the heat from one spot to another. If you use a radiator to throw the heat overboard, you are creating a huge thermal emission that will be visible for Astronomical Units away. If you do not throw the heat overboard, the temperature inside the spacecraft will grow until the crew dies and things start to melt.

Keep in mind that the background of deep space is at a chilly three degrees above absolute zero (-454.27 degrees Fahrenheit). Anything hotter than that will show up like a signal flare at midnight.

Say, you have some type of fusion reactors, which powered a variety of drive systems - ion and/or plasma drives or the like for in-system travel, the jump or whatever FTL drives (if they exist in the setting / our imaginary future reality for this conversation), and all the other stuff. Obviously, if your engines are actually providing thrust you can't mask that - but could your other systems be so efficient that you'd be significantly harder to detect?
Obviously if your engines providing thrust, you will be visible from Pluto's orbit.
Typical fusion reactor designs I've seen are hard pressed to have efficiencies of 50%. For a typical ion drive, you'd need about one gigawatt of electricity. With a 50% efficient fusion plant, it would put out 1 gigawatt of electricity and one gigawatt of waste heat.

Or to where you might be mistaken for something other than what you are? Say a cruiser coasting along or parked in an orbit, observing or whatever it is your ship(s) is there to do?
Again this is covered in my website (http://www.projectrho.com/rocket/rocket3w.html). Coasting along with the power plant off and the crew shivering in the dark, the detection radius will be reduced. Reduced from Pluto's orbit to a mere 150 times the distance from the Earth to the Moon (about 38,800,000 kilometers).

The trouble is, everybody will see you when you use your engines to insert yourself into your coasting trajectory. After that, your position can be calculated exactly according to the laws of orbital mechanics. If you light up your engine again to change your trajectory, again everybody will see it.

Nyrath

Jun 26th, '09, 09:18 AM

Yes, I'm familiar. But then you're claiming that the Second is a mathematical proof?

I'm not talking about wacko ideas like perpeutal motion machines. I'm just trying to leave the door open for things we might not have discovered yet, and constantly bashing even the most novel and unusual idea with "the second law says no!" before it's even tried strikes me as counterproductive and silly.
http://en.wikipedia.org/wiki/Perpetual_motion#Use_of_the_term_.22impossible.22_ and_perpetual_motion

The quote is in a page about perpetual motion, but it applies to any attempt to invest effort in something forbidden by the second law.

Yes, it is remotely possible that some flaw may be found. But after almost one thousand years of experiments failing to find a flaw with the second law, most scientists have better things to do with their time.

Nyrath

Jun 26th, '09, 09:25 AM

Kraven Kor

Jun 26th, '09, 09:35 AM

I just hate that your website is blocked at work, Nyrath.

Kraven Kor

Jun 26th, '09, 09:38 AM

And listening isn't my problem; comprehending is my problem. I apologize if we are constantly repeating tired old arguments. Believe it or not, I am learning something.

ajackson

Jun 26th, '09, 10:11 AM

The current state-of-the-art solar cell arrays on the International Space Station are about 14.5% efficient. This means (in Earth orbit) every square meter of solar cell produces abotu 198 watts of electricity, and 1167 watts of waste heat.
Somewhat less, actually; solar cells aren't black, so it might be producing something like 1000W of waste heat and 167W of reflected light.

Nyrath

Jun 26th, '09, 12:04 PM

Somewhat less, actually; solar cells aren't black, so it might be producing something like 1000W of waste heat and 167W of reflected light.
True.
Of course as far as stealth is concerned, reflected light is about equally bad to waste heat.

Nyrath

Jun 26th, '09, 12:06 PM

I just hate that your website is blocked at work, Nyrath.
Hrn. I wonder why? Does it give a reason?

At my work they use SonicWall, it blocks all sorts of sites under forbidden categories like "firearms". But it lets my Atomic Rocket site through.

Nyrath

Jun 26th, '09, 12:08 PM

And listening isn't my problem; comprehending is my problem. I apologize if we are constantly repeating tired old arguments. Believe it or not, I am learning something.
I apologize if I came across as a little bit testy.
But as you figured, yes these are the same tired old arguments.

Indeed, this entire thread is a shining example of Nicoll's Law: It is a truth universally acknowledged that any thread that begins by pointing out why stealth in space is impossible will rapidly turn into a thread focusing on schemes whereby stealth in space might be achieved.

Kraven Kor

Jun 26th, '09, 12:32 PM

Well, just keep in mind that some of our dreams are bigger than our brains.

Also; how the fark am I going to sneak up on my damned players if all my ideas get shot down? ;)

Nyrath

Jun 26th, '09, 01:16 PM

Also; how the fark am I going to sneak up on my damned players if all my ideas get shot down? ;)
You tell your players that the campaign is set in the SciFi universe of your choice where stealth exists but scientific accuracy does not. Problem solved. ;)

Kraven Kor

Jun 26th, '09, 01:26 PM

You tell your players that the campaign is set in the SciFi universe of your choice where stealth exists but scientific accuracy does not. Problem solved. ;)

Meh, too easy.

Clonus

Jun 26th, '09, 02:01 PM

Well, just keep in mind that some of our dreams are bigger than our brains.

Also; how the fark am I going to sneak up on my damned players if all my ideas get shot down? ;)

Just remember, FTL changes everything. Superscience in general does that. Once you can pop out of hyperspace, turn on your cloaking device and sneak around using your reactionless drives, the laws of the universe are whatever you say they are.

L. Marcus

Jun 26th, '09, 03:23 PM

You could always just dump your excess heat into subspace. :)

Blades

Jun 26th, '09, 05:08 PM

I assume your trying to approach an enemy without being detected.
I dont think there are any long term solutions without resorting to Sci-Fi solutions. But there can be short term solutions. But most of them require knowing where the enemy is located in advance.

Reflected light can be reduced by painting the ship with absorbant colors, ie black. That will reduce the visual reflection to about 1%, still detectable when you get close enough.

Visual light will be re-radiated as IR light, and the internal heat of the ship will also radiate as IR heat. Most forms of engines will both raise the heat of the ship and leave a trail of hot gas/plasma/ions behind that are also detectable, so most of the approach to the enemy needs to be coasting at a high speed.
1) mount a probe off the bow (in the direction of the enemy), and use it to spray a cold mist of H2. Some of the IR photons will go straight through, but some will hit the H2, and be re-radiated and a cooler frequency at random directions. The result could mask probably 95-98% of the IR signature, untill the H2 runs out.
2) since it is Sfi-Fi, use a force field in front of the ship that is opaque to photons, then no reflected light or IR signature.
3) arrive on the far side of the sun from the target. Dive past the sun and approach from the sun side of the target, perferably with the sun directly behind or slight offset. I dont think any IR detection system could pick out your appraoch aiming directely into the sun.

The ship will still pass in front of distant objects as it closes. For a small fast ship that is a little careful in its approach, this is not a very big problem. For a big ship or ship making slow approach, this will eventurally revield the ship, but not quickly. The enemy is also moving and that will occasionally cause stars to be occluded. So the enemy would have to keep a 360 watch and use powerful computers over time, to identify several times that the approaching ship occuded stars to prove it is there and estimate its course. So if the approaching ship can approach in days, it will probably not be found this way, but if it takes months, it will be found.

All the electrical motors on the ship radiate an EM signature. So every toaster, electric razor and electric watch all contribute some to the ships EM signature. But I presume the power source (and the electrical Generators off the power source) and drive engines cause most of the radiation EM. Unless a Sci-Fi force field can block it, at some point, it can be detected. So powering off most electronics will be required during approach

So my point is that an approaching ship is not invisable, but if it can make ita approach in a couple of days (instead of months), it should be able to get within several hours of a target or closer before detection. At some point it will be detected, but it may already be in long weapon range.

Note that this was assuming a coasting ship. It will probably still need to slow down unless it is only making one pass.

Zeropoint

Jun 26th, '09, 05:10 PM

It's a mistake to focus entirely on WASTE heat, too. Even if you're not using your engines, assuming that your ship is in steady state, every joule of energy produced on board--including the heat generated by the crew--is going to have to be radiated away.

If your power plant is 100% efficient, and putting out 1MW of useful electricity and NO waste heat . . . that megawatt has to be going somewhere. If it's charging a battery or capacitor bank, for example, then your ship isn't in steady state. Eventually that battery or capacitor will be full. Every piece of equipment that draws power is turning that power into heat, either directly or indirectly. A fan, for instance, turns some power into heat through resistance, some through friction in the motor, and (hopefully) turns most of the power it uses into kinetic energy of the air it blows. That moving air will turn the kinetic energy into heat through friction.

It comes down to conservation of energy. If your reactor turns some mass into 1 megajoule of energy every second, that energy MUST be entirely accounted for by one of three things: being turned back into mass, raising the energy content of the ship, or leaving the ship via easily detectable emissions.

Zeropoint

Jun 26th, '09, 05:24 PM

Reflected light can be reduced by painting the ship with absorbant colors, ie black. That will reduce the visual reflection to anout 1%, still detectable when you get close enough.

That's some pretty darn black paint! Also, it should be noted that 75% of known asteroids have an albedo of about .03 (that is, they reflect 3% of the light falling on them) and we, obviously, have seen them from here.

That's kind of a moot point, though . . . for anything with a power source on board, infrared radiation is going to dramatically exceed reflected visible light.

You CAN, of course, invoke various kinds of sci-fi handwavium, but once you step outside the rules of known science, all bets are off. From a scientific viewpoint--as opposed to a dramatic or game-balance viewpoint--a perfectly opaque non-reflective force field might as well be a magic spell of invisibility.

Nyrath

Jun 27th, '09, 04:31 AM

Just remember, FTL changes everything. Superscience in general does that. Once you can pop out of hyperspace, turn on your cloaking device and sneak around using your reactionless drives, the laws of the universe are whatever you say they are.
Yes, but then you have to be very careful not to go too far the other way.

Say that your FTL lets you go from any point A to any point B with no limit, and your ship is undetectable while in transit. The result is that most interstellar wars would last about five minutes.

The first warning that the Cyber-octopoids of Gamma Privia V have of a declaration of war from the Blortch of Delta Slimeball III is when a flight of Blortch space bombers pop out of hyperspace over Privia and carpet bomb the place with planet-cracking warheads.

The flight of space bombers then make the jump home to Slimeball. Only to discover that in the ten minutes they were away, a flight of Cyber-octopoid bombers had coincidentally given the same treatment to Slimeball. The End.

The reader takes the novel and hurls it across the room.

This is why powers in the Hero System have limitations.

Kraven Kor

Jun 27th, '09, 11:39 AM

It is also a darn good reason why I believe that if there is other life out there, they probably are no closer to cracking FTL than we are.

But I do like making sure any handwavium I use is at least rooted in some real science; that it be plausible.

--

Now, another thought, which isn't exactly true stealth, but could be used to gain an advantage...

It would take someone a bit to detect your ship. There are probably thousands of objects in our solar system we have yet to detect, simply due to the massiveness of space. With more advanced detection methods, this will probably be of less benefit, but I can imagine that a ship using as much of the feasible "stealth" we have mentioned here might be more likely to slip through the grid, but would be more luck than skill or tech - having nobody looking in your direction. Not reliable, but could be the hook for a story or adventure.

"Commander, we don't know how we missed this, but we have an unknown craft entering orbit..."

Kristopher

Jun 28th, '09, 06:17 PM

Kristopher

Jun 28th, '09, 06:20 PM

That's some pretty darn black paint! Also, it should be noted that 75% of known asteroids have an albedo of about .03 (that is, they reflect 3% of the light falling on them) and we, obviously, have seen them from here.

That's kind of a moot point, though . . . for anything with a power source on board, infrared radiation is going to dramatically exceed reflected visible light.

You CAN, of course, invoke various kinds of sci-fi handwavium, but once you step outside the rules of known science, all bets are off. From a scientific viewpoint--as opposed to a dramatic or game-balance viewpoint--a perfectly opaque non-reflective force field might as well be a magic spell of invisibility.

I'm of the opinion that you can have some conceits for the sake of story, without throwing the entire science book down the toilet, as long as you're fairly careful about consistency and limiting it to what's really necessary for the worldbuilding.

Zeropoint

Jun 28th, '09, 09:08 PM

An electric current flowing in a loop of superconducting wire is . . . a permanent magnet, basically. It might make a good energy storage device, but it's certainly not a power SOURCE. As soon as you use it--place a load on it--the current will start dropping off rapidly, until there's none left.

Nyrath

Jun 29th, '09, 05:23 AM

Yeah, you are. Any device that doesn't produce any waste heat is a perpetual motion machine.

Superconductors (http://en.wikipedia.org/wiki/Superconductivity)?

An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source. [1]

From http://www.kilty.com/pmotion.htm

Superconductivity also seems to be an example of a process that runs forever. Most physics textbooks explain that superconductivity is not perpetual motion because it is not a classical effect. It is a macroscopic quantum effect--sort of like a room sized atom, and we know that atoms are forever. They do not "run down." However, it seems to me that the unavoidable imperfections in the superconductor and its enviroment almost guarantee that this macroscopic atom will eventually stop.

Kristopher

Jun 29th, '09, 06:20 AM

Kraven Kor

Jun 29th, '09, 07:23 AM

Another way to look at Superconductors, I have been told, is to see them as merely a 100% efficient medium for energy transference.

Conservation still applies - they can't create energy, you can't get more energy out of them than you put it, and as soon as your energy is in a non-superconductive medium, you would see the same loss.

Something like that. High efficiency simply reduces the amount of waste, it does not eliminate it nor does it allow you to break the usual laws.

ajackson

Jun 29th, '09, 08:43 AM

Superconductors would have non-zero losses due to environmental effects, though the time scale would be very long. In any case, the real issue is that, if you put energy into a device, it has to come out somewhere. This is often in the form of waste heat, but might not be if the device has some other discernible output (for example, most of the energy put into a radar comes out as radio waves).

Nyrath

Jun 29th, '09, 12:05 PM

The original statement was that any device that doesn't produce waste heat is a "perpetual motion machine". I was only wondering if a superconducting loop would produce waste heat, and if not, would it be a "perpetual motion machine"?

Because at that point, either you have an actual "PMM" in existence, or you have something that doesn't produce waste heat and is not a "PMM" -- calling the "no waste heat = PPM" definition into question.
OK, you are going to get more information that you wanted.

There are three classes (http://en.wikipedia.org/wiki/Perpetual_motion#Classification) of perpetual motion machines:

Class 1: This produces energy from nowhere. It violates the law of conservation of energy.

Class 2: This converts waste heat into useful energy. It violates the second law of thermodynamics.

Class 3: This eliminates friction and other dissipative forces so an object moves forever. It does not violate any laws, but is not generally very useful.

A superconductor is a perpetual motion machine class 3. A machine that does not create any waste heat is a perpetual motion machine class 2. The latter is the one being discussed.

Cancer

Jun 29th, '09, 01:28 PM

I think the only way to go undetected in space is for parties from whom you are trying to conceal yourself not bother (or be not able) to look in the relevant way. (And to give them strong reasons to avoid coming to the correct conclusions.)

We're now back to social limitations, not physical effects. In this context, this (https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/csi-studies/studies/97unclass/ufo.html) makes for interesting reading.

frgough

Jun 30th, '09, 05:48 PM

Stealth in space is possible, but only under certain special conditions.

There are a couple of assumptions being made that result in the false idea that stealth in space is impossible. These same assumptions are made in the excellent Atomic Rocket web site.

The first assumption is that space is empty. It isn't. It's mostly empty. But mostly empty is infinitely more crowded than completely empty.

The second assumption is that the only hot object in an otherwise bitterly cold universe is your spaceship. This is also not true. Every object in a solar system is various shades of hot.

So the issue isn't one of "my ship shows up like a beacon because it's hotter than space in an infinitely empty universe therefore there is no stealth," but rather: my ship is a teeny-tiny speck that may or may not be hotter than other teeny tiny specks in the area.

First, dealing with the space is only mostly empty issue. Your detection system is going to have to have a complete, continually updated database with EVERY object in your solar system, and I mean every object. That means stuff in the oort cloud, too, so if a comet gets nudged, you can spot it instantly and send someone out to find out if it's a natural object or something more sinister. Remember those cometary fragments are hotter than background space, too, and their IR could be a ship rigged for silent running.

This is a major investment in time and resources, which means only highly strategic or important systems are going to have that kind of detection infrastructure. Border systems and less important worlds aren't going to have it. That allows us stealth using the other false assumption: that your ship is the only hot object in the universe.

The key, here, is to make your ship no hotter than any other object in thermal equilibrium at a similar distance from the sun. That's going to prevent you from firing up your main drive with its gigawatts or more of plume heat, but it will mask your normal ship operations, so, no, your crew doesn't have to shiver in the dark. The asteroid Eros has a dayside temperature of 373 Kelvins, way toastier than your ship crew needs to be comfortable and way, way, way above the bitter cold of space, and that's out in the asteroid belt. The night-side temperature is 250 degrees colder. Chilly for your crew but still pretty darned hot compared to space. That gives you nice, big window where you can radiate your waste heat. You simply radiate the heat cleverly as if you were a rotating body whose sunward side has now pointed starward and is radiating its stored heat. To the IR sensors throughout the system, you just look just like every other boring rock out there.

And just to forestall the potential argument, the fact that your ship may be on a highly eccentric or even hyperbolic orbit is not in the least suspicious. It happens all the time. That's why it's so important to have a continuous LIVE database of EVERY object in the solar system and its current trajectory along with its IFF.

So, basically, stealth in space isn't about hiding your ship from detection, but hiding it from identification.

Stealth attacks on important or strategic systems with a massive detection grid in place won't work, but in less important systems, it might be possible, and it certainly allows for pirate attacks on unsuspecting vessels traveling through poorly charted solar systems. Imagine your surprise when that 18th magnitude object your ship's scanners identified as the heat signature of a small asteroid with a 14-hour rotation period just opened fire on you.

Zeropoint

Jun 30th, '09, 06:51 PM

Two points: First, your ship would be picking up just as much energy from the sun as anything else at its distance from the sun. Second, your ship has a power source on board, and the asteroids don't.

It's not possible for your ship to be at equilibrium temperature, unless you're storing your heat output in an internal heat sink, and as Nyrath demonstrates, those won't last long enough to be useful unless they're HUUUUUGE.

frgough

Jun 30th, '09, 07:01 PM

Yes, my ship is picking up the same energy on the sunward side as everything else. On the darkside, it isn't picking up anything. It's radiating.

Second point: of course my vessel isn't in equilibrium. It's heating up on the day side and cooling off on the dark side. No rotating body in sunlight is in thermal equilibrium in the strictest sense, so that was a poor word choice on my part. What I meant by thermal equilibrium is a repeating cycle of heating and cooling. The engineering challenge is making my ship radiate in a way that mimics a naturally cooling rotating body. And I'm rigged for silent running which means I'm running on 100 KW worth of fuel cells and am not pumping out gigawatts of waste heat.

ajackson

Jul 1st, '09, 08:48 AM

So, basically, stealth in space isn't about hiding your ship from detection, but hiding it from identification.
Well, yes and no. It's not that hard to determine distances (you need parallax detection, probably requiring two ships at a separation of some kilometers, but that's not that hard to accomplish), at which point it's no longer good enough to get yourself lost in the volume of all the objects floating around out there, you have to get lost in the volume of objects out there that are in the area of interest. If you only care about objects within, say, a tenth of an AU of you, unless you're in a region of particularly cluttered space, something the size of a ship will stand out. Overall, it's pretty practical to hide as long as you don't go anywhere near anything of interest and you don't do anything, but, well, this fact doesn't have a lot of military application.

Imagine your surprise when that 18th magnitude object your ship's scanners identified as the heat signature of a small asteroid with a 14-hour rotation period just opened fire on you.
First of all, 18th magnitude is actually pretty bright and would likely be tracked. Second, well, an 18th magnitude object, unless incredibly small, is still probably upwards of a million kilometers away, making it rather unlikely to be able to 'open fire'.

Nyrath

Jul 1st, '09, 09:18 AM

First, dealing with the space is only mostly empty issue. Your detection system is going to have to have a complete, continually updated database with EVERY object in your solar system, and I mean every object. That means stuff in the oort cloud, too, so if a comet gets nudged, you can spot it instantly and send someone out to find out if it's a natural object or something more sinister. Remember those cometary fragments are hotter than background space, too, and their IR could be a ship rigged for silent running.

This is a major investment in time and resources, which means only highly strategic or important systems are going to have that kind of detection infrastructure. Border systems and less important worlds aren't going to have it. That allows us stealth using the other false assumption: that your ship is the only hot object in the universe.
Not quite.

Sitting on my desk right now is a one terabyte hard drive, which I use for my iTunes music and movie files. Not gigabye. Terabyte. It cost about a hundred bucks. By the time we have space warships, a hard drive with enough memory to contain such an astronomical object database will be the size of your thumb and cost the equivalent of about fifty cents, and be available at the check-out counters of your local office-supply store.

And all astro-militaries will maintain such databases. Why? Do you know how much damage a re-directed asteroid can do to Earth? Think "dinosaur killer." The astro-militaries of all nations will keep close tabs of the orbits of all small bodies (http://www.projectrho.com/rocket/rocket3t.html#orbit), just to be sure there are no unauthorized changes in their orbits.

frgough

Jul 1st, '09, 10:07 AM

Well, yes and no. It's not that hard to determine distances (you need parallax detection, probably requiring two ships at a separation of some kilometers, but that's not that hard to accomplish),

Once again, the need for a detection infrastructure present in space. I stated in the original post that stealth is ineffective against systems with such a structure in place, so you have no argument from me here.

at which point it's no longer good enough to get yourself lost in the volume of all the objects floating around out there, you have to get lost in the volume of objects out there that are in the area of interest.

It's not a question of getting "lost" in anything. I'm not hiding. I'm pretending to be something I'm actually not. Just another rock. Space is full of them.

If you only care about objects within, say, a tenth of an AU of you, unless you're in a region of particularly cluttered space, something the size of a ship will stand out. Overall, it's pretty practical to hide as long as you don't go anywhere near anything of interest and you don't do anything, but, well, this fact doesn't have a lot of military application.

Except for recon and ambushes in border systems with poor detection infrastructures.

First of all, 18th magnitude is actually pretty bright and would likely be tracked. Second, well, an 18th magnitude object, unless incredibly small, is still probably upwards of a million kilometers away, making it rather unlikely to be able to 'open fire'.

It was just an example pulled out of thin air to illustrate the point because I didn't want to figure out the absolute magnitude of a 50-meter long cylinder with an albedo of .03 at 3.5 AU. Besides, a million kilometers away is a nothing shot for a good laser. Laser range is primarily limited by lightspeed lag. And lightspeed lag is only an issue if you're doing evasive movement, and why would you be wasting propellant on evasive maneuvers if you don't know I'm there?

frgough

Jul 1st, '09, 10:24 AM

Not quite.

Sitting on my desk right now is a one terabyte hard drive, which I use for my iTunes music and movie files. Not gigabye. Terabyte. It cost about a hundred bucks. By the time we have space warships, a hard drive with enough memory to contain such an astronomical object database will be the size of your thumb and cost the equivalent of about fifty cents, and be available at the check-out counters of your local office-supply store.

Probably not. Physics limits the density of things like these. But regardless. Storing the data isn't the issue. Gathering the data and monitoring for changes is. That requires sensor platforms and monitoring stations and ships and logistics to back it up. It's a non-trivial investment of resources, even for a spacefaring society. I addressed this in my original post. This will not work in systems with good detection networks. Not all systems will have good detection networks because of the required investment of resources. We don't fly U-2 spy planes over every square inch of the planet and we don't re-task spy satellites just because. We only do it for areas of high strategic interest.

Identically, interstellar governments of the future won't be putting military-quality detection grids throughout every star system; only those with sufficient commercial or strategic value.

And all astro-militaries will maintain such databases. Why? Do you know how much damage a re-directed asteroid can do to Earth?

No they won't because they won't need to. Do you know how much energy it takes to nudge an asteroid? They don't need to track the rock, they'll spot the heat plume of the reaction drive needed to move it. Just like you can't move your ship without giving it away, no one can move an asteroid without giving themselves away. You don't need to spend a billion credits identifying and tracking every possible piece of dangerous rock. All you have to do is look for big mass moving heat blooms.

So, again, in poorly charted solar systems, stealth is completely possible by simply mimicking the radiative cooling of a naturally rotating object in sunlight. It won't work for major military assaults, but it will for recon and ambushes.

Nyrath

Jul 1st, '09, 10:59 AM

Probably not. Physics limits the density of things like these. But regardless. Storing the data isn't the issue. Gathering the data and monitoring for changes is. That requires sensor platforms and monitoring stations and ships and logistics to back it up. It's a non-trivial investment of resources, even for a spacefaring society
No, you can do most of the job with ground based telescopes, and a couple of orbital ones for the rest.

No they won't because they won't need to. Do you know how much energy it takes to nudge an asteroid? They don't need to track the rock, they'll spot the heat plume of the reaction drive needed to move it. Just like you can't move your ship without giving it away, no one can move an asteroid without giving themselves away.
The energy goes down by orders of magnitude with the distance between the asteroid and the primary star. For something in the Kuiper belt, it is quite modest.

And if you can spot the reaction gently nudging a rock that far out, you can certainly spot a hostile spacecraft attempting to insert itself into an asteroid imitating orbit. ;)

frgough

Jul 1st, '09, 12:22 PM

No, you can do most of the job with ground based telescopes, and a couple of orbital ones for the rest.

The fact that we haven't as of today is pretty compelling evidence that it's not going to be as trivial as you seem to maintain it will be. I think I'm safe in maintaining that the caliber of detection you're arguing for is going to require a non-trivial investment both on worlds and in space.

The energy goes down by orders of magnitude with the distance between the asteroid and the primary star. For something in the Kuiper belt, it is quite modest.

Well, yeah, if you don't mind it taking a couple of decades for your killer weapon to hit. You can do anything in space cheaply if you're willing to let it take a really long time.

And if you can spot the reaction gently nudging a rock that far out, you can certainly spot a hostile spacecraft attempting to insert itself into an asteroid imitating orbit. ;)

I wasn't aware there was a mandatory orbit required to be considered an asteroid. :)

For a recon mission, I come in on a hyperbolic orbit. All kinds of stuff in our solar system are on hyperbolic orbits. It's not suspicious in the least.

If I'm a pirate, I pick my spot in advance and set up my ambush and wait for unsuspecting ships to come by.

Like all stealth, you don't have undetectable carte blanche. But that's fine, because that's what drives plots. The point I'm making is that it is theoretically possible. Once you get the theory down, then you're into engineering details and tactics. And science fiction allows you to claim "they somehow figured it out," when it comes to engineering details, and your story plot gets to explore the tactics.

ajackson

Jul 1st, '09, 01:06 PM

Besides, a million kilometers away is a nothing shot for a good laser. Laser range is primarily limited by lightspeed lag.
Urr...not for hard science lasers. Laser range is mostly limited by the resolution of your optics, which is in turn limited by diffraction. If you have, say, a 10 nanometer hard UV laser, which is about the upper limit for physical mirrors, and your focal array is 10m across and diffraction-limited, beam divergence is 1e-9 radians, or one meter at a million kilometers, which is almost certainly substantially below the threshold of doing anything useful to the target at all. At the same time, any tech capable of building that laser is also capable of building sensors that vastly outperform anything currently available. If you limit yourself to what could plausibly be built without vast improvements in optics technology (resulting in improved detection technology), effective range is probably going to be a thousand kilometers or less.

Nyrath

Jul 1st, '09, 01:42 PM

The fact that we haven't as of today is pretty compelling evidence that it's not going to be as trivial as you seem to maintain it will be.
There is "civilian-trivial" and then there is "military-trivial."
Even though there is a real threat today from errant asteroids, all current governments are loath to spend the modest amounts required for an asteroid survey and sky watch.
This would instantly change if there was a demonstrable threat from attacking alien warships or Footfall-like asteroid strikes.

Be that as is may, new asteroids being discovered by astronomers are dimmer than prior discoveries. The lower the dimness of undiscovered bodies, the harder for a space pirate to hide.

I think I'm safe in maintaining that the caliber of detection you're arguing for is going to require a non-trivial investment both on worlds and in space.
I don't think so. Current technology can do a full sky scan of all objects down to magnitude 12 or so in four hours flat. Future technology will improve on that.

I wasn't aware there was a mandatory orbit required to be considered an asteroid. :)
Heh, no. Presumably your pirate ship cannot teleport from its home base to the point where you say it will hide in plain sight. I could find no concise way of expressing that, but that's what I meant by "asteroid orbit."

Which means you'll have to use your main engines at your base to inject yourself into a trans-plain-sight-hiding-spot trajectory, and use the engines again to slow down into a pseudo-asteroid orbit. Both of which will be quite noticeable by any observer based in the same solar system.

If I'm a pirate, I pick my spot in advance and set up my ambush and wait for unsuspecting ships to come by.
Oh, come now. You know orbital mechanics better than that.
Nothing is stationary in space unless it is under thrust. To wait at a spot for a ship to come by, you'd have to counteract the Sun's gravitational acceleration by burning your engines. This is a dead giveaway that you are not an asteroid. You can be a statite by unfurling a large mirrored solar sail but the same objection applies.

Nyrath

Jul 1st, '09, 01:44 PM

Laser range is primarily limited by lightspeed lag.
I was going to point out the diffraction limit but ajackson beat me to it.
You can find the equation here:
http://www.projectrho.com/rocket/rocket3x.html#laser

frgough

Jul 2nd, '09, 06:22 AM

There is "civilian-trivial" and then there is "military-trivial."
Even though there is a real threat today from errant asteroids, all current governments are loath to spend the modest amounts required for an asteroid survey and sky watch.

It's not modest, or they wouldn't be loathe to do it. You're contradicting yourself.

This would instantly change if there was a demonstrable threat from attacking alien warships or Footfall-like asteroid strikes.

Yes, if the world were strategically important enough to warrant it. Which point I made in my initial post. On strategically important worlds and systems, stealth is a no-go.

I don't think so. Current technology can do a full sky scan of all objects down to magnitude 12 or so in four hours flat. Future technology will improve on that.

Then why haven't we? Once again, your argument shows a disconnect from reality. I'm beginning to catch the whiff of agenda here.

Heh, no. Presumably your pirate ship cannot teleport from its home base to the point where you say it will hide in plain sight. I could find no concise way of expressing that, but that's what I meant by "asteroid orbit."

That's a question of tactics. And it's also why certain routes will be known as "pirate space" because they are areas where it's easy to set up the ambush. Ships will only go there when the potential reward outweighs the risk.

Which means you'll have to use your main engines at your base to inject yourself into a trans-plain-sight-hiding-spot trajectory, and use the engines again to slow down into a pseudo-asteroid orbit. Both of which will be quite noticeable by any observer based in the same solar system.

Yep. That's why it won't work for every system. If you have interstellar trade going on, this again devolves to tactics.

Oh, come now. You know orbital mechanics better than that.
Nothing is stationary in space unless it is under thrust. To wait at a spot for a ship to come by, you'd have to counteract the Sun's gravitational acceleration by burning your engines. This is a dead giveaway that you are not an asteroid. You can be a statite by unfurling a large mirrored solar sail but the same objection applies.

Yep. Again, this is tactics. You will basically have ambush windows of opportunity.

frgough

Jul 2nd, '09, 07:02 AM

I was going to point out the diffraction limit but ajackson beat me to it.
You can find the equation here:
http://www.projectrho.com/rocket/rocket3x.html#laser

Yep. But you forgot about this part:

http://www.projectrho.com/rocket/rocket3x.html#xray

You can make the configuration disposable and bomb-pumped to make the engineering problems much less challenging.

I personally liked your phrase "still a ravening death beam at one light minute."

Which, by the way, also gives me cover (due to lightspeed lag) to launch my weapon, get it to safe range and fire it off before my target sees what I'm doing.

Nyrath

Jul 2nd, '09, 10:16 AM

It's not modest, or they wouldn't be loathe to do it. You're contradicting yourself.
:lol: I guess you didn't read the part about "civilian-trivial" and "military-trivial."

Yes, if the world were strategically important enough to warrant it. Which point I made in my initial post. On strategically important worlds and systems, stealth is a no-go.
So you are saying that one can only have stealth where the target solar system is a Firefly-esque type populated with people riding horses? Can't argue with that. ;)

Current technology can do a full sky scan of all objects down to magnitude 12 or so in four hours flat. Future technology will improve on that.

Then why haven't we?
Ummm, maybe because we have? Have you spoken with any astronomers lately? I know I few I can link you up with.

Once again, your argument shows a disconnect from reality. I'm beginning to catch the whiff of agenda here.
:lol: Heh. Perceived atramentous tetsubin syndrome. In an ad hominem argument.

And it's also why certain routes will be known as "pirate space" because they are areas where it's easy to set up the ambush. Ships will only go there when the potential reward outweighs the risk.
:confused: Ummmm, have you had any orbital mechanics at all? I thought you did. There are no "routes" in space. Not ones that you can travel over a second time without a delay. Since both your starting point and destination are moving at different speeds, they generally will not repeat that configuration until a couple of years have passed. The technical term is "synodic period."

The only place that pirates can reliably ambush a merchant vessel is on the ground at the launching spaceport or the landing spaceport.

Nothing is stationary in space unless it is under thrust. To wait at a spot for a ship to come by, you'd have to counteract the Sun's gravitational acceleration by burning your engines. This is a dead giveaway that you are not an asteroid. You can be a statite by unfurling a large mirrored solar sail but the same objection applies.
Yep. Again, this is tactics. You will basically have ambush windows of opportunity.
ummmm, what window?
If the pirate is hovering in space with its engines burning for a few weeks waiting for the merchant ship to get close enough to attack, don't you think the merchant ship will notice and ask the Space Patrol for help?

Nyrath

Jul 2nd, '09, 10:24 AM

Yep. But you forgot about this part:

http://www.projectrho.com/rocket/rocket3x.html#xray

You can make the configuration disposable and bomb-pumped to make the engineering problems much less challenging.

I personally liked your phrase "still a ravening death beam at one light minute."

Which, by the way, also gives me cover (due to lightspeed lag) to launch my weapon, get it to safe range and fire it off before my target sees what I'm doing.
Heh, read it again.
"ravening death beam at one light minute" is in the section of Non-bomb x-ray lasers. This is the kind where you need an accelerator ring about one kilometer in diameter. Unless your ship is the Death Star, it isn't going to be carrying one of those.

If you do the math for the bomb-pumped x-ray laser, you'll find that the effective range is much shorter.

ajackson

Jul 2nd, '09, 12:37 PM

If you do the math for the bomb-pumped x-ray laser, you'll find that the effective range is much shorter.
Due to a lack of effective X-ray mirrors, beam spread is the sum of the aspect ratio of the lasing crystal and the diffraction limit. If we assume soft X-rays at 1 nanometer and lasing crystals 10 meters long, aspect ratio is 1e-1*width, diffraction is 1e-9/width, and we get the best value at width = 1e-4 (0.1mm) where both limits are 1e-5 so our beam divergence is 2e-5 radians, or 20cm per kilometer.

Kraven Kor

Jul 2nd, '09, 03:21 PM

LOL - even though I haven't rep'd anyone for months or years...

"You must spread some reputation around before giving it to Nyrath again."

frgough

Jul 2nd, '09, 05:25 PM

:lol: I guess you didn't read the part about "civilian-trivial" and "military-trivial."

I did. It's a distinction without a difference. You're discussing levels of degrees, not the fundamental issue.

So you are saying that one can only have stealth where the target solar system is a Firefly-esque type populated with people riding horses? Can't argue with that. ;)

Or one with early 21st century technology like Earth where it's not considered worth the effort. Or one where for political reasons one may not be deliberately put in place.

Ivory towers have little or no resemblance to the real world. There are many reasons why a solar system may not have a 100% stealth-proof detection system in place, but still have significant space travel.

Ummm, maybe because we have? Have you spoken with any astronomers lately? I know I few I can link you up with.

Um, yeah, we've done complete sky scans, but not in 4 hours. The Astrographic Catalog was divided among 20 observatories in order to reduce the burden of the task and took years to complete. The current US Naval Observatory catalog is the result of 50 years' work, yet it is only assumed to cover the entire sky, and only has an 85% accuracy in identifying stellar from non-stellar objects. The spaceguard report says that it will take six 2.5 meter telescopes 10 YEARS to plot 90% of near-earth large asteroids. 10 years, and it doesn't even get all of them. Real-world examples always trump theoretical postulations. This detection system you toss about so casually is not going to be as trivial, even militarily, as you maintain it is.

Ummmm, have you had any orbital mechanics at all? I thought you did. There are no "routes" in space. Not ones that you can travel over a second time without a delay. Since both your starting point and destination are moving at different speeds, they generally will not repeat that configuration until a couple of years have passed. The technical term is "synodic period."

Synodic periods are routes. By definition. You said so in your last sentence, in direct contradiction to your first sentence. Ships with limited deltaV are constrained to porkchop plot routes. Torchships run shortest-time routes. Routes exist in space.

ummmm, what window?
If the pirate is hovering in space with its engines burning for a few weeks waiting for the merchant ship to get close enough to attack, don't you think the merchant ship will notice and ask the Space Patrol for help?

The window where the pirate's orbit comes within range of the route ships moving between worlds must follow. No engine hovering required. A typical tactic would probably be something along the lines of setting up a hyperbolic orbit when nobody's around and then hoping someone shows up at the right time. If no one does, reset and try again.

There are many possible scenarios where setups like this can exist. A slight adaptation of the current Somali pirate practices is just one example.

frgough

Jul 2nd, '09, 05:40 PM

Heh, read it again.

I read it better than you, because I spotted that even though you corrected yourself on there being no such thing as x-ray mirrors, your bomb-pumped example happily goes on talking about how inefficient the laser is because there are no x-ray mirrors. In other words, your math is wrong. It's very possible for me to make a ravening beam of death from a one-shot bomb-pumped laser.

frgough

Jul 2nd, '09, 06:42 PM

A follow-up on the 4-hour sky scan and why it won't work.

The number comes from the Atomic rocket web site and is calculated by assuming a single wide-angle lens is taking 30 second exposures of 100 square degrees at one time to pick up 12th magnitude signals.

Except you won't get 12th magnitude signals. You'll get a whole bunch of overexposed lower magnitude images, washing out everything else on your plate.

The longer your exposure, the narrower your field of view has to be. It's physically impossible to look for 12th magnitude stars in 100 square degree chunks of sky at a time. Looking for twelfth magnitude stars restricts your field of view to arc-minutes or even arc-seconds. Suddenly, your 4-hour sky scan has turned into a 4 year sky scan.

And it gets even better. You have to take repeated pictures of the same portion of the sky, gradually narrowing down your field of view on the dark regions as you increase your exposure times. And if your 12th magnitude star is too close to a 4th magnitude star, you'll never spot it.

Which is another reason why you need sensor platforms scattered about your solar system. You need to take photos of the same portion of the sky from different angles to prevent a ship from hiding its 12th magnitude drive exhaust in the light of a 4th magnitude star. Yes, I know you can do a spectral analysis on the 4th magnitude star and find out that it has some unusual doppler characteristics. But that means you're going to be doing more than just taking pictures. Increase your sky scan yet again.

Moral: Stealth-proof detection systems are not trivial.

Because, to quote 2001 (the novel) "My God, it's full of stars!"

ajackson

Jul 2nd, '09, 11:03 PM

The longer your exposure, the narrower your field of view has to be.
Nope. The longer your exposure, the smaller your pixel size has to be. Now, I don't know of any system equivalent to said 12th magnitude scan, but I do know of the Large Synoptic Survey Telescope (http://en.wikipedia.org/wiki/Large_Synoptic_Survey_Telescope), which surveys 10 square degrees at a chunk (about 4,200 frames to cover the sky, if it had sufficient coverage) down to magnitude 24.5. Build a few of those and you're scanning most of the sky (you'll have a bit of a dead spot near the sun) nightly.

It's physically impossible to look for 12th magnitude stars in 100 square degree chunks of sky at a time. Looking for twelfth magnitude stars restricts your field of view to arc-minutes or even arc-seconds.
See the above.

CorpCommander

Jul 3rd, '09, 05:35 AM

I was under the impression Governments were much more active in things like Sky Guard after the Shoemaker-Levy 9 comet strike on Jupiter. Perhaps that interest was short lived.

How long does it take to do a whole sky survey? My question here is aimed at determining how "instant" detection would be for various energy outputs. The earlier post about there being a lot of junk in space was something I had been thinking about. How do we know some of the asteroids AREN'T alien space stations watching over us? How often are we looking? Apparently not very often at all. At what point does a world suddenly decide to start looking and watching? Maybe not until after it's first pearl harbor in space! At which point it is too late, their planet is enslaved. So maybe you only need to be stealthy once per system, early enough.

How much energy would it take to move an asteroid into Earth orbit? Once it makes it's run how much energy would it take to prevent a collision (would that even be possible?)

CorpCommander

Jul 3rd, '09, 05:45 AM

What other civilizations are detecting about us: http://abstrusegoose.com/strips/electromagnetic_leak.PNG

frgough

Jul 3rd, '09, 06:16 AM

Nope. The longer your exposure, the smaller your pixel size has to be.

Nope. CCDs suffer from blooming when the pixel well is overloaded (the equivalent of photographic overexposure). It doesn't matter how many pixels you have. You get too much light coming in (long exposure time) and you'll get blooming all over your image.

If you want to pick up faint objects, you have to mask out the brighter ones. That means tighter fields of view.

Now, I don't know of any system equivalent to said 12th magnitude scan, but I do know of the Large Synoptic Survey Telescope (http://en.wikipedia.org/wiki/Large_Synoptic_Survey_Telescope), which surveys 10 square degrees at a chunk (about 4,200 frames to cover the sky, if it had sufficient coverage) down to magnitude 24.5.

It can do 10 square degree shots or go down to 25th magnitude. Not both. See the above about blooming.

Nyrath

Jul 3rd, '09, 06:16 AM

Due to a lack of effective X-ray mirrors, beam spread is the sum of the aspect ratio of the lasing crystal and the diffraction limit. If we assume soft X-rays at 1 nanometer and lasing crystals 10 meters long, aspect ratio is 1e-1*width, diffraction is 1e-9/width, and we get the best value at width = 1e-4 (0.1mm) where both limits are 1e-5 so our beam divergence is 2e-5 radians, or 20cm per kilometer.
So with about 1.8e7 kilometers per light minute, that would make the spot size grow to about 3600 kilometers, and become about as dangerous as a flashlight.

Kristopher

Jul 3rd, '09, 09:22 AM

Kristopher

Jul 3rd, '09, 09:43 AM

MOD: as a general note, I'd ask that people keep their arguments to the science and speculation and gaming uses, and not what they suspect other people's motives to be.

ajackson

Jul 3rd, '09, 10:42 AM

Nope. CCDs suffer from blooming when the pixel well is overloaded (the equivalent of photographic overexposure). It doesn't matter how many pixels you have.
The amount of noise a pixel captures is equal to (time) * (background brightness) * (angular area covered by pixel) * (collector area). Reduce the angular area of each pixel, and you reduce noise -- but you also reduce coverage, unless you add more pixels.

It can do 10 square degree shots or go down to 25th magnitude. Not both.
No, it does both. That's what it's for -- it's a survey telescope.

Nyrath

Jul 3rd, '09, 05:34 PM

I was under the impression Governments were much more active in things like Sky Guard after the Shoemaker-Levy 9 comet strike on Jupiter. Perhaps that interest was short lived.
Alas, the voting public has the attention span of a five-year-old.
The closest thing we have to Sky Guard is the NASA Near-Earth Object program (http://neo.jpl.nasa.gov/index.html). Like all things NASA, it is chronically underfunded. They track asteroid only to the point where they can determine that it has no chance of striking Earth, then it is put on the "ignore" list.

How long does it take to do a whole sky survey? My question here is aimed at determining how "instant" detection would be for various energy outputs.
Well, as a data point, one of my experts estimated it would take about four hours to do a full sky scan down to the 12th magnitude (a little longer than that since it takes more time to scan for objects within two degrees of the Sun's glare, using an occlusion filter).

The earlier post about there being a lot of junk in space was something I had been thinking about. How do we know some of the asteroids AREN'T alien space stations watching over us? How often are we looking? Apparently not very often at all. At what point does a world suddenly decide to start looking and watching? Maybe not until after it's first pearl harbor in space! At which point it is too late, their planet is enslaved. So maybe you only need to be stealthy once per system, early enough.
Currently nobody is really looking for an alien base disguising itself as an asteroid for the same reason that the military has no plans for defending themselves from an attack from Atlantis: they calculate it to be an exceedingly low probability event.
The technical term for mis-calculating the probability is "being blindsided." Yes, "Pearl Harbor" is a synonym.

Now, if the aliens do something stupid like using an antimatter power plant, they'll be spotted right away. Electron-positron annihilation has a characteristic signature of 511 keV. The astronomical satellites used to detect gamma ray bursters would pick it up right away. This would be quite suspicious since there are no non-artificial sources of antimatter annihilation in the asteroid belt.

How much energy would it take to move an asteroid into Earth orbit? Once it makes it's run how much energy would it take to prevent a collision (would that even be possible?)
Lots and lots.

To nudge an asteroid into a collision course with Earth takes an amount of energy determined by [1] the mass of the asteroid (higher=more), and [2] how far from the Sun the asteroid currently is (closer=more).
The energy is proportional to the asteroid's momentum, which is mass times velocity. The mass comes from [1] and the velocity change required comes from [2].

To prevent a collision, the energy required depends upon [1] the momentum of the asteroid, and [2] how far in advance of collision that counter-measures are taken. The farther in advance, the less the angular change in the asteroid's course will result in missing the Earth.

There are some techniques here:
http://www.cosmicdiary.org/blogs/nasa/franck_marchis/?p=245

How much to nudge the asteroid?
An example I was given:
100 megaton asteroid, assume a delta-V of 1 kps is required (the asteroid is a bit big, but the delta-V is a bit low). It is large enough to be close to a mass-extinction event.

So you start with a 200 megaton asteroid, and use a mass driver to use half the mass as propellant to give it 1 kps.

The energy requirements would be on the order of 1 x 10^17 joules. This is roughly the total output of a one-gigawatt nuclear reactor run for a bit over three years.

ajackson

Jul 3rd, '09, 05:54 PM

The energy is proportional to the asteroid's momentum, which is mass times velocity.
Actually, that's not true. The lowest-energy solution involves basically splitting the asteroid in half and sending one half towards the planet while the other half becomes reaction mass, and requires energy proportional to the mass times the square of the delta-V.

Nyrath

Jul 3rd, '09, 07:38 PM

Actually, that's not true. The lowest-energy solution involves basically splitting the asteroid in half and sending one half towards the planet while the other half becomes reaction mass, and requires energy proportional to the mass times the square of the delta-V.
I stand corrected.

frgough

Jul 11th, '09, 03:19 PM

The amount of noise a pixel captures is equal to (time) * (background brightness) * (angular area covered by pixel) * (collector area). Reduce the angular area of each pixel, and you reduce noise -- but you also reduce coverage, unless you add more pixels.

No, it does both. That's what it's for -- it's a survey telescope.

Yes, it will find 25th magnitude stars and 1st magnitude stars at the same time. What it won't find is 25th magnitude stars sitting next to 1st magnitude stars at the same time.

frgough

Jul 11th, '09, 03:23 PM

Well, as a data point, one of my experts estimated it would take about four hours to do a full sky scan down to the 12th magnitude [I](a little longer than that since it takes more time to scan for objects within two degrees of the Sun's glare, using an occlusion filter).

Your expert is wrong.

http://upload.wikimedia.org/wikipedia/commons/1/11/Galactic_Cntr_full_cropped.jpg

There's a ship in there somewhere. Find it for me. It could be hiding in the glare of one of the overexposed stars.

This also illustrates the incorrect assumption that there is no terrain in space. That picture is full of terrain.

Kristopher

Jul 12th, '09, 05:25 AM

Your expert is wrong.

http://upload.wikimedia.org/wikipedia/commons/1/11/Galactic_Cntr_full_cropped.jpg

There's a ship in there somewhere. Find it for me. It could be hiding in the glare of one of the overexposed stars.

This also illustrates the incorrect assumption that there is no terrain in space. That picture is full of terrain.

If it's on a course that keeps it, as seen from Earth, directly in front of one of the brighter stars, does that make picking it out much harder? At first thought, it seems that at the very least you'd need to be able to pick its light out from the light of the star, and be able to do fast parallax work (ie, have two stations far enough apart and synched together) on all your sky scanning.

ajackson

Jul 12th, '09, 03:08 PM

There's a ship in there somewhere. Find it for me. It could be hiding in the glare of one of the overexposed stars.
Given images separated by an hour, probably trivial. Given two sensors with enough separation to produce a parallax exceeding the sensor resolution, almost certainly trivial.

Cancer

Jul 14th, '09, 08:14 AM

The thing is, to find asteroids (or other objects), you don't simply take pictures, you use differences between pictures. Most of the "terrain" changes slowly enough that differencing takes care of it more or less completely, though as has been noted, scaling exposure times near bright objects may be needed.

But more to the point, things move, and in general they don't move together. A hostile object cannot hide indefinitely in the glare of a 1st-magnitude star, except by using an engine, which is almost certainly detectable.

After attending an unclassified talk a year or two ago about detecting objects comparable to laptops in LEO, I think "stealth" is going to be, "pick a mode of detection, and you'll be hidden to that, but you can't be invsible to everything all the time".