T4 Only: Some people say no stealth in space, a discussion.

[kilemall]

Too bad, I was trying to visualize this laser working.

Something like channeling the heat into an exhaust chamber in the maneuver drive, feeding in a little hydrogen from the tanks, the laser cooling would then be applied on a macro level to the gas and at some point it would eject.

Have to decide if the half range doggo applies to minimal power/drives, the wording uses the term silence. That could mean no active sensors/comms/ weapons/drives, or require a power down. I’m inclined to go with zero accel drive and life support power on, as the m drive provides gravitic lensing confusing the output including mass.

For me it will be more about game options/feel either way I go.

 

[TheDS]

Hi! Long time, no see! Just barging in to interject some basic math that may or may not be of value. I read the first couple dozen posts, don't have time for the other 300. I apologize if someone beat me to this.

Regardless of the size of a craft, if it has something that consumes power, then it has a power source, which has waste heat. It's not unreasonable to assume ALL power produced will have to be radiated as waste heat. A 1 GW power source is fairly modest; most ships should have much greater power needs, especially if they're large, high-G, or armed, but we'll use it as our baseline.

Sensors measure things in dBm, or decibel milliwatts. This is a logarithmic system, where 0 dBm is defined as 1 milliwatt, so a power level of 1 GW would be 120 dBm. It's no secret that radars are capable of detecting things as faint as -120 dBm, or a femtowatt. (They're actually much more sensitive, but I don't know exactly how much so; it makes a reasonable baseline assumption for your DMs to start at.) That's a 240 dBm difference, or 24 ORDERS OF MAGNITUDE. A 1 with 24 zeroes following it. How far can you be to divide something by 1 septillion and still see it?

Since emissions fade by the square of the distance, it follows that if at a distance of 1 meter you see 1 GW, then at 1000 meters you see 1/1-millionth of that, or 1 kW. IOW, a distance increase of 3 orders of magnitude makes the signal 6 orders of magnitude fainter. In dBm terms, a 30 dBm increase in distance yields a 60 dBm decrease in signal strength. Step that out a few more times: to get our signal down 24 times, that's 4 such steps. Our 1 meter distance is now increased to 1 trillion meters, or 6,666 AU (comfortably larger than any solar system, though possibly discluding its Oort cloud).

As I said, this is just BASELINE; these are very modest numbers, and craft with significantly bigger power needs will be detectable from much further away, especially by much more sensative sensors. It's not implausible that you could detect ships in Alpha Centauri from here. Yes, they'll be 1 pixel, but that might be a very BRIGHT pixel, one bright enough that it bleeds over into several others.

This is just "detecting", not getting a firing solution or identification.

Whatever you might want to do to hide yourself, it's got to have the effect of orders of magnitude, and probably a lot of them. Hiding 99% of your signature is only 2 orders of magnitude. Powering down your reactor to a meager 1 MW is only 3 orders of magnitude. You also probably don't want your crew or recycling system to freeze to death, so you do have to have SOME power. Chances are, you're going to need to reduce your signature 12 or more orders of magnitude, which is probably impossible, outside of magictech. This can certainly be a combination of things.

Your main means of defeating sensors is hoping the sensor operator isn't looking for you (not terribly hard if they're not at combat stations), or to hide behind something that blocks line of sight, or hide in front of or near something really powerful, like maybe a star. You might also try to be close to some other ship or object to make it hard to discern you from it, and hope that ship doesn't give you away.

Usually the way to hide is to reduce your signal to that of the background noise, but this isn't really possible in space, unless you're near a star. But be aware, active sensors use coded beams that allow them to see BELOW background noise levels (like within atmospheres).

This is why the "there's no sneaking up on people in space" people say that. But these people don't generally consider that you CAN sneak, you just have to use INT instead of DEX.

 

[Rupert]

Hi! Long time, no see! Just barging in to interject some basic math that may or may not be of value. I read the first couple dozen posts, don't have time for the other 300. I apologize if someone beat me to this.

Regardless of the size of a craft, if it has something that consumes power, then it has a power source, which has waste heat. It's not unreasonable to assume ALL power produced will have to be radiated as waste heat. A 1 GW power source is fairly modest; most ships should have much greater power needs, especially if they're large, high-G, or armed, but we'll use it as our baseline.

Sensors measure things in dBm, or decibel milliwatts. This is a logarithmic system, where 0 dBm is defined as 1 milliwatt, so a power level of 1 GW would be 120 dBm. It's no secret that radars are capable of detecting things as faint as -120 dBm, or a femtowatt. (They're actually much more sensitive, but I don't know exactly how much so; it makes a reasonable baseline assumption for your DMs to start at.) That's a 240 dBm difference, or 24 ORDERS OF MAGNITUDE. A 1 with 24 zeroes following it. How far can you be to divide something by 1 septillion and still see it?

Since emissions fade by the square of the distance, it follows that if at a distance of 1 meter you see 1 GW, then at 1000 meters you see 1/1-millionth of that, or 1 kW. IOW, a distance increase of 3 orders of magnitude makes the signal 6 orders of magnitude fainter. In dBm terms, a 30 dBm increase in distance yields a 60 dBm decrease in signal strength. Step that out a few more times: to get our signal down 24 times, that's 4 such steps. Our 1 meter distance is now increased to 1 trillion meters, or 6,666 AU (comfortably larger than any solar system, though possibly discluding its Oort cloud).

1 x 10^12 metres is only 6.67 AU, which isn't enough to see something out by Saturn from the inner system. One of us is out by a factor of a thousand.

 

[Spinward Flow]

And the laser beam is easily detected.

If it's pointed AT you ... sure!
If a laser beam is pointed AWAY FROM your sensors ... in a vacuum ... how are you going to detect it?

Let me guess.
Your sensor system "sees" the laser light "reflecting" off the vacuum of space that the beam is passing through.

Which interacts with the dust in space and re-radiates in all direction, easily detected

Good news everyone!
The vacuum of space is filled with dust! Y'know ... like a 13.8 billion year old room that hasn't been swept in a while ...

Yes and it was refuted pages and pages ago, it won't work

ORLY?

https://forum.nasaspaceflight.com/index.php?topic=22649.0
Reply #10:

I sent David Brin a message pointing out to discussions on the net saying his refrigerator laser was implausible and asking him if he really thought the concept would work, if it would only work with the physics knowledge of the Galactics (in the books), etc

here is his answer
"Mr. Penna,

Thanks for your thoughtful and interesting message. It truly is gratifying when people write, and I always try to answer.

As a matter of fact, I ran the refrigerator laser past a couple of Nobel Prize winning physicists, back in the 1980s. Plasma physicist Hannes Alfven could find nothing wrong with my reasoning... and found it "plausible."

Remember the comparison to the refrigerator in your kitchen. With an effectively infinite energy source (wall current) your fridge pumps heat from one space (the freezer box) into another space (the surrounding kitchen)... along with the waste heat involved in the process. It simply works.

If the sun's Chromosphere is the 'kitchen' and the ship is the freezer"

So... two Nobel Prize winning physicists supported the concept, including a plasma physicist.

but here in the forum, we are saying its impossible...

And then there's this published towards the end of 2012 ...
https://www.sciencedaily.com/releases/2012/11/121113083534.htm

Fortunately, @mike wightman, who is so good at citing his sources (for independent verification of his assertions) has at least 2 Nobel Prize physicists and a plasma physicist who support his (repeated) assertions that the idea was "refuted pages and pages ago, it won't work" to back up his ... claims ...

But it is closed so your point is baseless

The only thing that is closed is your acceptance of what has been put in front of you (repeatedly).

because I am secure in my knowledge of the subject at hand

Reality points in the opposite direction though ...

Pure handwavium of the first order, anyone with a moderate understanding of thermodynamics can poke holes in it, not to mention handwavium superconductors

See previous citation in Reply #10 quoted above from David Brin himself on the research behind the idea of a refrigerator laser.

heat pumps are no different to fridges and air conditioners, they are not closed systems.
In an open system, not a close one
Nope, you still don't get closed versus open.

The failure to comprehend that a spacecraft is NOT A CLOSED SYSTEM with respect to rejection of waste heat is ... incredible.

And can easily be detected once the laser exits your craft, the photons can be detected (they difract and spread, they interact with atoms and molecules in space which then re-radiate in every direction)

What is the atomic density of a vacuum then?

In the Sol system, interplanetary space has an average density of 5 atoms/cm³ (according to a google search of the question).
That ought to make for a really nice reflector/refractor of high intensity radiation, right?
Right?

And this is your fundamental error.

Yeah, I'm going to have to agree with @Dragoner on this one.

Please, never post to me ever again.

Stealth aircraft are easily detected

Comprehension FAIL For The Win ...?
Obviously ridiculous assertions are obvious?

it a simple matter to shape the direction of the Heat/Size signature.

This is the key point which is hard to "get right" in simple game mechanics (particularly if space combat is completely abstracted with no "map" being used to track locations/course/acceleration in 3D) in a way that is "quick and dirty" enough for ease of play around the (virtual) table. Any kind of "-2 signature forward = +2 signature aft" type of game mechanic becomes quite meaningless if you aren't working with a "map" to visualize everything (see: LBB5.80 combat abstraction, for example).

However, if a Referee (and their Players) are willing to "go the extra klicks" to dig deeper into the granularity of "signature shaping" of their craft to try and sneak past locations of concern ... that's when things can start getting interesting ...

Mostly controlled by the experience of the crew in question.

Definitely agree.
ANY kind of signature "control" is going to be highly dependent upon the experience (and cohesion) of the crew.

A last note, engineering rather than the "Science" answer is the true limit.

VERY MUCH agreed!
Science tells you what CAN be done.
(Good) Engineering is what ALLOWS things to get done!

For me it will be more about game options/feel either way I go.

In the absence of a common set of RAW that we all agree upon (good luck with that one! ) this is honestly the best solution.

This is just "detecting", not getting a firing solution or identification.

Whatever you might want to do to hide yourself, it's got to have the effect of orders of magnitude, and probably a lot of them.

My Cr2 on the point you're making is that this is where computer model # (in CT), or whatever alternative paradigms get used in later editions comes to the fore. Your computer model is basically your ECM/ECCM capacity (to keep things simple). Low model # computers have a weak to negligible EW capacity, while high model # computers have a much more sophisticated/powerful EW capacity (generically speaking).

Thus, even if you're detected, a high(er) model # of computer is better at "protecting" yourself from firing solutions and/or identification. Helps to make the selection of a computer model for starship designs less a matter of "economizing" and more a matter of "security" investment.

 

[Condottiere]

1. Heat is created through the activities of the spacecraft.

2. The question might be how much, and through what activities.

3. Does this excess heat affect the performance of the spacecraft.

4. Does this heat affect the performance of the crew.

5. Can this be mitigated, either by (re)moving/transferring it, or by spacecraft design/architecture.

6. Most obvious form of removal would be through some existing conduit, like the manoeuvre drive, or rockets.

7. Or transformed into a different state, like plasma.

8. Some solutions might not be practical for all spacecraft.

9. You could dump it into the hydrogen fuel tanks.

A. Or, into the feed tubes as the hydrogen is dripped into the fusion reactor.

B. Preheated, so to speak.

C. Rockets being the least efficient way, since you lose fuel.

D. Skimming a gas giant would require an external connection, to pump the heat through the external hull.

E. Gravitic heat sinks seems to remind me of the black hole effect, though the question would be, does it go somewhere else, or just a super efficient way of storing it.

F. Which requires dumping somewhere, later on, like the garbage from a cruise ship.

G. If heat is energy, why not contain it in a magnetic bottle, and release it, like the Death Star's exhaust port.

H. Possibly, it might provide propulsion, by itself.

I. If not, accelerating away from that release would seem a form of separation, if not divorce from the issue.

 

[aramis]

Whomever mentioned the movement... position uncertainty at 2.1 sec (round trip+pointing time) is only ±22.5 meters per G. At lowest aspect, that puts a 50/50 shot at a type R to about 1 LS... (whether or not the beam actually is collimated sufficiently to do damage is another matter entirely.) At 1/2 LS with the same 0.1 sec pointing time, it's about ±5.5m per G. At 0.1LS (1 BL hex) it's ±0.45m per G. So that 6G fighter 15m long and 3m wide has a minimum cross-section of 3m diameter... it can be dodging at 1 BL hex... but the Type T has a MUCH harder time. (Needless to say, the ranges are insane for beam strength, but it's not hard at all to hit a cap ship with a laser at 1/2 LS...

No cooling systems ever work at all? (they do)

They work by transferring heat somewhere. There's an energy cost to doing so. That cost turns into additional heat.
Only certain exothermic reactions actually cool usefully. The ones I'm aware of don't really cool all that well. The only one that's notoriously useful is adding salt to ice and water. Bu -2°C isn't going to matter when the moons are –200°C

In space, you've almost nothing to conduct to, and so blackbody radiation of the radiators you moved the heat into, plus the cost of running the heat pump and/or coolant loops... it adds up.

A compressed liquid or gas, allowed to expand, can absorb heat, but then you have lukewarm gas to dump overboard... and while it will radiate a good bit quickly, not quickly enough to not be a magnification of your size.

Don't mix the processes (I can see you are not understanding how the laser is working, it isn't transfering heat with a material)

Sure, most don't get that it's essentially using light to limit the movement of atoms by light-pressure and wave interference.
But if the laser is aboard, it's dumping its working energy into two things: the beam, which is then transferred by reflection, and the lasing apparatus, which is dumping into the room it's in... so it's massive energy requirement is going to be a big heat source.

Plus, laser cooling isn't a large scale effective process.

 

[Dragoner]

They work by transferring heat somewhere. There's an energy cost to doing so. That cost turns into additional heat.

The most typical is a liquid cooled mechanical system such as in your car. It's not zero sum, it takes energy to run, and provides a net benefit. Saying that it doesn't work because it is not 100% efficient is intellectually dishonest, not a rational argument against.

A compressed liquid or gas, allowed to expand, can absorb heat, but then you have lukewarm gas to dump overboard... and while it will radiate a good bit quickly, not quickly enough to not be a magnification of your size.

Maybe siliconized salt or something, I have read of various different ways. Additionally there could be ways to excite it.

... so it's massive energy requirement is going to be a big heat source.

Plus, laser cooling isn't a large scale effective process.

The idea of technical advances, scaling, are small in comparison to the ideas of the spacecraft in general.

 

[Grav_Moped]

Just dropping in here to note that I finally "get" using the grav-drive as a heat sink: if the drive is so efficient that it breaks thermodynamics, dumping waste heat into it is merely a good-faith effort to balance the equation. You still one the universe some more energy to make it right, but you're at least trying.

 

[DentArthurDent]

1 x 10^12 metres is only 6.67 AU, which isn't enough to see something out by Saturn from the inner system. One of us is out by a factor of a thousand.

This matches calculations for power received, based solely on geometry of an expanding sphere:
Power received = Power emitted x (piR^2)/(4piD^2), where R is the antenna radius, D is the distance from the antenna
This is the theoretical maximum power received by an antenna. The actual reception is most likely closer to the number from TheDS and Rupert of 6.67 AU

There is a misconception on this thread about starships being 293 K.
A starship is a large flying thermos. The insides are thermally separate from the outsides, as much as possible. Once a temperature of 293 K is reached, there is no energy input or removed from the system.
Unless, the people inside are alive. In which case it would be necessary to remove the heat generated by the inhabitants. One person resting expends a little more than 100 W. One professional football(soccer) player expends a little more than 1000 W during a match. So, unless everyone on the ship is running around the starship, each person will emit about 150 W per person (about 0.003 K per person)

 

[TheDS]

1 x 10^12 metres is only 6.67 AU, which isn't enough to see something out by Saturn from the inner system. One of us is out by a factor of a thousand.

Ah crap. Yeah, I see where I did my boo boo. Misremembered an AU as 150 Mm, when it's 150 Mkm. Good catch.

Ok, so, 7 AUs is a little less difficult to hide than 7000. Three orders of magnitude down, 21 to go. It's still a lot farther than most engagements take place in. About 3333 lightseconds. Almost a lighthour. Whereas normal combat range (depending on your system of choice) tends to be about 1 lightsecond, and it takes ships something like 1 kS to travel each LS (if they're rocketing at 0.001 C), so still plenty of time to see them. Days. Weeks. Because jumping in would get them there a lot faster, but also serves as a blaring horn of announcement, what with that interdimensional light flash.

At any rate, the point stands: you can't hide by hiding, you have to use subterfuge to hide, and hope the enemy is on a coffee break.

 

[aramis]

The most typical is a liquid cooled mechanical system such as in your car. It's not zero sum, it takes energy to run, and provides a net benefit. Saying that it doesn't work because it is not 100% efficient is intellectually dishonest, not a rational argument against.

The issue is there's nowhere to push that heat too except by venting something or blackbody radiation. If you don't have adequate radiator, you're just going to be moving heat until it all equalizes anyway, or the radiator has a thermal induced material failure.

Either way, you're trading a medium signal omnidirectional for a much brighter but smaller semi-directional signal.

Further, if your ship's exterior is cooled to blackbody balance with background, it's going to suck heat up through the connections rapidly.

Basically, stealth cannot hide you. The best it can do is get you misidentified.

 

[Spinward Flow]

There is a misconception on this thread about starships being 293 K.
A starship is a large flying thermos. The insides are thermally separate from the outsides, as much as possible. Once a temperature of 293 K is reached, there is no energy input or removed from the system.

I agree.
Look at this (LBB S7) legacy deck plan for the Type-S Scout/Courier.

Every bulkhead line you see in that deck plan is a thermal insulator boundary.

Those fuel tanks?
Liquid Hydrogen needs to be stored at 14-20º Kelvin.

A show of hands from anyone here who thinks that liquid hydrogen (the "bog standard" starship fuel in Traveller) is going to be radiating heat through a starship's hull/bulkheads @ 293º K into space?
Anyone?
Anyone?
Bueller?
Anyone?

Remember, a LOT of deck plans for Traveller starships tend to put the fuel tanks "around" the inhabited volume inside the craft, allowing the fuel tankage to act as a "buffer" against weapons fire in combat and/or collision impacts with foreign objects.

The only way that can ... work ... is if the starship is functionally something of a thermos bottle of thermally isolated volumes.

Either way, you're trading a medium signal omnidirectional for a much brighter but smaller semi-directional signal.

Yes.
(polite clapping)

And if you can orient that "much brighter but smaller semi-directional signal" AWAY from any sensors you don't want to be observed by ... {expectant look}

Basically, stealth cannot hide you. The best it can do is get you misidentified.

Well, as I said earlier in this thread (in Post #8, actually) ...

Worse yet, people all too often associate "stealth" with what amounts to a Cloaking Device (or straight up "invisibility").
Stealth is NOT (only) ... this ...

Perhaps it would help to use different words to adequately describe what is going on.

The "goal of stealth" is to simply REDUCE SENSOR SIGNATURES ... meaning apply a -DM to signature, rather than a +DM.
Ideally speaking, you want your -DM to signature to be of sufficient magnitude that it renders sensor detection "hopeless at useful distances" yielding a functional invisibility rather than requiring actually perfect invisibility.

And yet, here we are ... over 300 posts later ... with people asserting that ANY reduction in sensor signatures (in space) is simply IMPOSSIBLE.

But if you reframe the point trying to be made into "signature modification" with the goal of either falling below the sensitivity threshold of any sensor systems, or otherwise being "easy to misidentify" as something innocuous/else (and thus, "safe" to ignore) ... that's all you really need in order to reduce the effectiveness of opposing sensor systems (and/or the crews manning them).

When you're outmanned, outgunned and out-equipped ... what else have you got?

 

[mike wightman]

Stealth in Space is Conditional. Just like real life.

Not really, there is no stealth in space
I kid, yes, there are conditions where you may have some temporary stealth.

Passive sensors range is limited by their inherent Margin of Error of the receiver and the amount of computer power available.

Couple that with Constant Thrust, it a simple matter to shape the direction of the Heat/Size signature.

I agree, but this can be countered by having a sensor network looking from different direction, you can't point your directional radiators away from a senor net with complete coverage.

Active Sensors will give more reliable results over the perceived combat ranges. Consider this your big passive array receives the know return signal from your active emitter. Further Related is the emitter is frequency agile such as there is not a single know frequency repeated over and over again.

Another note the Submarine model is very flawed for these discussions. The Aircraft model is probably best, followed by the Surface Warfare one.

No, all of these models are incorrect. Space is a totally different environment, the analogies become a hindrance after a while.

All of the preposed work around embedded in this topic would work, a variable number of times. Mostly controlled by the experience of the crew in question.

A last note, engineering rather than the "Science" answer is the true limit. Meaning Comparing a scientific instrument on a stable platform, is much different from the one on a moving/vibrating platform. Couple that to how much money the local system is willing/able to spend Early Spacebourne Detection.

Don't complicate a fictional science discussion with fictional engineering limitations...

Inertial compensation fixes it all.

 

[Condottiere]

Inertial compensation neutralizes an external force, even if co created in the same machinery.

Speaking of which, maybe what we should do is pass the heat through a nuclear damper.

 

[mike wightman]

There is a misconception on this thread about starships being 293 K.
A starship is a large flying thermos. The insides are thermally separate from the outsides, as much as possible. Once a temperature of 293 K is reached, there is no energy input or removed from the system.
Unless, the people inside are alive. In which case it would be necessary to remove the heat generated by the inhabitants. One person resting expends a little more than 100 W. One professional football(soccer) player expends a little more than 1000 W during a match. So, unless everyone on the ship is running around the starship, each person will emit about 150 W per person (about 0.003 K per person)

What about the heat generated by all the electrical systems - grav plates, acceleration compensatory, computers, pumps, sensors, etc - not to mention the waste heat from the fusion reactor?

 

[mike wightman]

Inertial compensation neutralizes an external force, even if co created in the same machinery.

Speaking of which, maybe what we should do is pass the heat through a nuclear damper.

Nuclear dampers affect the nuclear forces, heat is not a nuclear force.

 

[Condottiere]

We could try turning the heat radio active.

 

[mike wightman]

If it's pointed AT you ... sure!
If a laser beam is pointed AWAY FROM your sensors ... in a vacuum ... how are you going to detect it?
Let me guess.
Your sensor system "sees" the laser light "reflecting" off the vacuum of space that the beam is passing through.

Yes, that is exactly how it is done, and is done in the real world to study gases etc in so called empty space. You can go and look up the papers...

Fortunately, @mike wightman, who is so good at citing his sources (for independent verification of his assertions) has at least 2 Nobel Prize physicists and a plasma physicist who support his (repeated) assertions that the idea was "refuted pages and pages ago, it won't work" to back up his ... claims ...

Go do a search for using lasers to analyse space dust and read them for yourself.

The only thing that is closed is your acceptance of what has been put in front of you (repeatedly).

Reality points in the opposite direction though ...

See previous citation in Reply #10 quoted above from David Brin himself on the research behind the idea of a refrigerator laser.

Brin's solution is handwavium, it is not physically possible as he describes it.

The failure to comprehend that a spacecraft is NOT A CLOSED SYSTEM with respect to rejection of waste heat is ... incredible.

Emm, I'm the one who has repeatedly pointed out a spaceship is a closed system and that to remove waste heat you have to get it out, so at this pPlease try to keep up with the discussion.

What is the atomic density of a vacuum then?

In the Sol system, interplanetary space has an average density of 5 atoms/cm³ (according to a google search of the question).
That ought to make for a really nice reflector/refractor of high intensity radiation, right?
Right?

Yeah, I'm going to have to agree with @Dragoner on this one.

You may need to learn to refine your search terms, try looking up dust density in empty space...

Cosmic dust - Wikipedia

en.wikipedia.org

Comprehension FAIL For The Win ...?
Obviously ridiculous assertions are obvious?

Obviously not, as you are unaware of the failures on your part.