Planet cracking missiles

[Nyrath]

[1] Reactionless drives (http://en.wikipedia.org/wiki/Reactionless_drive) are spacecraft propulsion systems that do not use Newton's law of action and reaction, that is, they do not expend reaction mass. Just pump in electricity, and your ship accelerates. This would revolutionize spacecraft design, and open the entire solar system if not the stars.

[2] Reactionless drives are thought to be impossible by mainstream physicists because they violate the law of conservation of momentum (http://www.projectrho.com/rocket/rocket3am.html)

[3] Roger Shawyer's EmDrive (http://en.wikipedia.org/wiki/Emdrive) is a reactionless drive. All mainstream physicists are quite sure it is bunk.

[4] Chinese researchers are going to try and build it anyway (http://blog.wired.com/defense/2008/09/chinese-buildin.html).

[5] This could lead to serious consequences if they succeed. This would give China the ability to create planet cracking missiles (http://www.projectrho.com/rocket/rocket3a.html#advice).

[Cancer]

Actually, if the thing exhausts neutrinos (which you can't detect without extraordinary measures), it wouldn't, technically, be reactionless. I'm in no way suggesting that's what's going on here, but there is that loophole.

[Sundog]

Any time the scientific community gets totally up in arms about something like this, I usually take it as an indication that more research is appropriate.

[Nyrath]

Actually, if the thing exhausts neutrinos (which you can't detect without extraordinary measures), it wouldn't, technically, be reactionless. I'm in no way suggesting that's what's going on here, but there is that loophole.
True, but if you read the description of the EmDrive, it becomes clear that it is just a tired re-hash of the Dean Drive hoax.

[Nyrath]

Any time the scientific community gets totally up in arms about something like this, I usually take it as an indication that more research is appropriate.
Which the Chinese are doing...

[mirage]

[1] Reactionless drives (http://en.wikipedia.org/wiki/Reactionless_drive) are spacecraft propulsion systems that do not use Newton's law of action and reaction, that is, they do not expend reaction mass. Just pump in electricity, and your ship accelerates. This would revolutionize spacecraft design, and open the entire solar system if not the stars.

[2] Reactionless drives are thought to be impossible by mainstream physicists because they violate the law of conservation of momentum (http://www.projectrho.com/rocket/rocket3am.html)

[3] Roger Shawyer's EmDrive (http://en.wikipedia.org/wiki/Emdrive) is a reactionless drive. All mainstream physicists are quite sure it is bunk.

[4] Chinese researchers are going to try and build it anyway (http://blog.wired.com/defense/2008/09/chinese-buildin.html).

[5] This could lead to serious consequences if they succeed. This would give China the ability to create planet cracking missiles (http://www.projectrho.com/rocket/rocket3a.html#advice).

I would be more than happy to sell them plenty of write only memory, to help protect their data. :D

[pinecone]

It is likely bogus...but less shouting and more testing is the "scientific" way to settle such things....

[Outsider]

A planet busting missile isn't all that useful when you and your potential enemies live on the same planet, of course. Not that a working (& powerful) reactionless drive wouldnt have other uses...

[pinecone]

You could put a reationless drive bus in a looping patern and toss BB's at anyone who annoyed you (By say not joining your empire...) at near light speed glass beads are city killers at least....

[Cancer]

Just don't miss.

[Nyrath]

You could put a reationless drive bus in a looping patern and toss BB's at anyone who annoyed you (By say not joining your empire...) at near light speed glass beads are city killers at least....
Of course, by the same token, if the planet leisurely tosses a glass bead into the path of the drive bus, the bus will also experience the equivalent of a city killer nuke. It doesn't matter if you are a stationary city hit by a relativistic glass bead, or a relativistic bus that hits a stationary glass bead. The same energy will be released.

So the bus will have to jink around a little, to become a harder target.

Which is good, unstoppable weapons are boring.

Now, a city killer is about 25 megatons worth of "boom". Say 1.1 x 10^17 Joules of energy, refer to the boom chart (http://www.projectrho.com/rocket/rocket3x.html#boom).

For a glass bead to kill a city, it will have to be moving pretty freaking fast. About 0.9999999999 c according to my slide rule (http://www.projectrho.com/rocket/rocket3x.html#rbomb) (assuming a glass bead has a mass of about 0.02 grams).

If the projectile was one kilogram (about two pounds), it would only have to move at 0.95 c.

Note that once a projectile is moving faster than 0.866 c, it does more damage than a stationary lump of pure antimatter with the same mass.

The flip side is that you have to spend more than that amount of energy in the drive of your bus, in order to make the projectiles relativistic. Nothing is free.

[jaws]

Nyrath,

Don't know if i should hate or love you. You bring comprehension to us non-scientific bunch, but you really destroy the simplicity of fiction :p. As one reader complained on your site. I can never read sci-fi the same way again. Sure it forces authors to be more scientifically accurate. But doesn't that take away from their spell bound story weaving?

Ok well, innocence once lost can never be recovered. You need a major disclaimer at the beginning of your illusion destroying truth revealing website.

But oh well. Such is the price of knowledge and knowledge is power. SO I guess, thanks. :D

Yeah yeah yeah, spread spread... cant give it all to one genius it might go to his head.

[Nyrath]

Nyrath,

Don't know if i should hate or love you. You bring comprehension to us non-scientific bunch, but you really destroy the simplicity of fiction :p. As one reader complained on your site. I can never read sci-fi the same way again. Sure it forces authors to be more scientifically accurate. But doesn't that take away from their spell bound story weaving?
Thanks! {blush}

I did include Tom Clark's lament that you mentioned. But maybe I should put it closer to the top of the page.

However, even though I take away some innocence, in return I give you the Game Master a source of all sorts of diabolical ideas to spring on your hapless players.

[jaws]

Like I said.
Love... Hate... I can now take out my frustration on my players, for every sci-fi book I read from an author who though may be a great story teller, didn't do his physics homework :P

So i guess I'll just tell my players to hate you while I praise your great work.

:smoke:

[pinecone]

Of course, by the same token, if the planet leisurely tosses a glass bead into the path of the drive bus, the bus will also experience the equivalent of a city killer nuke. It doesn't matter if you are a stationary city hit by a relativistic glass bead, or a relativistic bus that hits a stationary glass bead. The same energy will be released.

So the bus will have to jink around a little, to become a harder target.

Which is good, unstoppable weapons are boring.

Now, a city killer is about 25 megatons worth of "boom". Say 1.1 x 10^17 Joules of energy, refer to the boom chart (http://www.projectrho.com/rocket/rocket3x.html#boom).

For a glass bead to kill a city, it will have to be moving pretty freaking fast. About 0.9999999999 c according to my slide rule (http://www.projectrho.com/rocket/rocket3x.html#rbomb) (assuming a glass bead has a mass of about 0.02 grams).

If the projectile was one kilogram (about two pounds), it would only have to move at 0.95 c.

Note that once a projectile is moving faster than 0.866 c, it does more damage than a stationary lump of pure antimatter with the same mass.

The flip side is that you have to spend more than that amount of energy in the drive of your bus, in order to make the projectiles relativistic. Nothing is free.

Well I figure it's easier to "stealth" a bus vs hiding a planet...:) Heck with a Emdrive I could use solar panels couldn't I?

As for "Lack of bang" just toss a handfull then, once you get up to speed, tossing junk gets easy...

[AmadanNaBriona]

Well I figure it's easier to "stealth" a bus vs hiding a planet...:) Heck with a Emdrive I could use solar panels couldn't I?

As for "Lack of bang" just toss a handfull then, once you get up to speed, tossing junk gets easy...

OK, everybody who's read Nyrath's site, all together now....

a one, and a two,
and a one, two, three, four...

"There's no stealth in space!"


Sorry man...
Had to do it.
One of those dearly held tropes I had to let go of after reading the site.


Now I know what it's like to read one of those Mythos tomes that you can't unread :help:

[pinecone]

OK, everybody who's read Nyrath's site, all together now....

a one, and a two,
and a one, two, three, four...

"There's no stealth in space!"


Sorry man...
Had to do it.
One of those dearly held tropes I had to let go of after reading the site.


Now I know what it's like to read one of those Mythos tomes that you can't unread :help:

OK, read the Blurb...an Emdrive is not a reactive motor.....and not all reactive engines are all that bright....(Say a laser...or a ion drive) so...nice shouting, but poor sciencing....

[AmadanNaBriona]

OK, read the Blurb...an Emdrive is not a reactive motor.....and not all reactive engines are all that bright....(Say a laser...or a ion drive) so...nice shouting, but poor sciencing....

:D
And how does one make the power for the the drive without heat?




(to be clear, I'm joshing with ya a teeny bit... I've literally spend days poring over his Atomic Rockets site.... call me one of Nyraths Disciples, spreading the word)

edit: linky (http://www.projectrho.com/rocket/rocket3w.html#nostealth)

[Nyrath]

OK, read the Blurb...an Emdrive is not a reactive motor.....and not all reactive engines are all that bright....(Say a laser...or a ion drive) so...nice shouting, but poor sciencing....
Ah, I suppose that in direct violation of the second law of Thermodynamics, the Emdrive is 100% efficient in converting electricity into thrust, without a single watt being lost as waste heat? ;)

And where, exactly, is the electricity for the Emdrive coming from?

Yes, not all reactive engines are all that bright. An ion drive can only be detected if it is closer than 93 million miles! This is approximately the distance between the Earth and the Sun.

The Space Shuttle's main engines can be detected as far away as Pluto's orbit. The Space Shuttle's manoeuvering thrusters could be seen as far as the asteroid belt.

There ain't no stealth in space (http://www.projectrho.com/rocket/rocket3w.html#nostealth).

[Cancer]

Yes, not all reactive engines are all that bright. An ion drive can only be detected if it is closer than 93 million miles! This is approximately the distance between the Earth and the Sun.

The Space Shuttle's main engines can be detected as far away as Pluto's orbit. The Space Shuttle's manoeuvering thrusters could be seen as far as the asteroid belt.

There ain't no stealth in space (http://www.projectrho.com/rocket/rocket3w.html#nostealth).

And "concrete" design concepts for antimatter rockets -- presumably on interstellar ships --- can be seen and identified hundreds of parsecs away (http://www.herogames.com/forums/showthread.php?t=46269).

[pinecone]

Yes all true...big energetic plumes are easy to see....but a infrared source Can be hidden with a heat sink (for while any way) and if that ion drive is facing away from you? 93 million miles?

Why are we all worried about detecting astoroids when everthing is so easy to see?

If someone is tossing photons out the back as a laser....how does anyone see it if they are not in the spread?

[L. Marcus]

It's the problem with heat pumps -- it takes energy to direct those exhaust photons, and that energy will produce even more waste heat that will have to be redirected . . .

It's a vicious circle. You'd just end up with a ship built around a giant cooling system.

[Nyrath]

Short answer: read the link
http://www.projectrho.com/rocket/rocket3w.html#nostealth


Yes all true...big energetic plumes are easy to see....but a infrared source Can be hidden with a heat sink (for while any way) and if that ion drive is facing away from you? 93 million miles?
An infrared source can be hidden with a heat sink, for about five minutes. Unless your heat sink is several miles in diameter.

Yes, an ion drive can be detected at a range of one astronomical unit, even if the drive is facing away from you. And this is only if the drive is throttled down to less than 1/1000 of a g of acceleration. If the acceleration is higher, the detection range grows.

The direction of the drive makes little difference. And even if it did, what use is it to only be able to accelerate directly at you? Unless you were trying to ram?

And the phrase "facing away from you" contains two assumptions:
[1] the ion drive owner knows where "you" are located
[2] "you" are the only observer in the solar system. If "you" deployed a few observational space probes around a few other planets, it will be impossible for the ion drive to face away from all of them.

And then there is the problem that an ion drive requires lots of electrical power to operate. Which requires a power plant of some kind, or a huge solar array. All of which will generate waste heat as it converts fuel or solar energy into electricity. Which will give away the ion drive's position.

You don't seem to understand that the background of space is at three degrees above absolute zero, so almost anything else stands out like a spotlight.


Why are we all worried about detecting astoroids when everthing is so easy to see?
We are not worrying that asteroids are hard to see. We are worrying that nobody is willing to fund a constant sky watch to detect dangerous asteroids.


If someone is tossing photons out the back as a laser....how does anyone see it if they are not in the spread?

[1] How can the laser user be sure they know where all the observational space probes are?
[2] A laser used as a photon drive requires about THREE HUNDRED MEGAWATTS to produce one measly Newton of thrust.

The three engines on the Space Shuttle produce a combined 5.37 million Newtons of thrust.

To produce this much thrust with a laser would require 1.6 petawatts (1,611,000,000,000,000 watts).

Lasers are notoriously inefficient. Most have efficiencies of about 25%. Say we have a free-electron laser which has a theoretical maximum efficiency of 65%. This means that 35% of the input energy becomes waste heat.

This means that if the laser energy is 1.6 petawatts, the waste heat will be 860 terawatts. This means that the laser will be creating waste heat at a power level of 300 times the yearly energy consumption of the United States each second.

And you are somehow going to hide all this waste heat?

Again, read the link. Chances are, whatever you try to come up with has been tried already.

Of course if in your role as a Game Master, you invent an exciting campaign for your players that depends upon magically creating stealth in space, then you can ignore scientific accuracy in the name of pleasing your players.

[Kristopher]

It strikes me as quite useful to the author if he simply supposes a system, built of handwavium, that performs an end-run around the 2nd law of thermodynamics. Such as, say, a system which converts heat above a certain threshold temperature into electical power, at a rate greater than it generates waste heat.

[Nyrath]

It strikes me as quite useful to the author if he simply supposes a system, built of handwavium, that performs an end-run around the 2nd law of thermodynamics. Such as, say, a system which converts heat above a certain threshold temperature into electical power, at a rate greater than it generates waste heat.

{shudder} :angst:

Ummmmmm, I have a suggestion. Wouldn't it be easier to just ignore the heat problems, pretend they don't exist?

Let me explain. As it turns out, your handwaving is more or less the same as a rather stubborn popular misconception (http://www.projectrho.com/rocket/rocket3au.html) that is the topic of many emails I get.

So if you take the easy route and ignore the heat problems, it's better for you, it's better for me, and it's better for any of your players that might decide to email me. :D

[pinecone]

Short answer: read the link
http://www.projectrho.com/rocket/rocket3w.html#nostealth


An infrared source can be hidden with a heat sink, for about five minutes. Unless your heat sink is several miles in diameter.

Yes, an ion drive can be detected at a range of one astronomical unit, even if the drive is facing away from you. And this is only if the drive is throttled down to less than 1/1000 of a g of acceleration. If the acceleration is higher, the detection range grows.

The direction of the drive makes little difference. And even if it did, what use is it to only be able to accelerate directly at you? Unless you were trying to ram?

And the phrase "facing away from you" contains two assumptions:
[1] the ion drive owner knows where "you" are located
[2] "you" are the only observer in the solar system. If "you" deployed a few observational space probes around a few other planets, it will be impossible for the ion drive to face away from all of them.

And then there is the problem that an ion drive requires lots of electrical power to operate. Which requires a power plant of some kind, or a huge solar array. All of which will generate waste heat as it converts fuel or solar energy into electricity. Which will give away the ion drive's position.

You don't seem to understand that the background of space is at three degrees above absolute zero, so almost anything else stands out like a spotlight.


We are not worrying that asteroids are hard to see. We are worrying that nobody is willing to fund a constant sky watch to detect dangerous asteroids.



[1] How can the laser user be sure they know where all the observational space probes are?
[2] A laser used as a photon drive requires about THREE HUNDRED MEGAWATTS to produce one measly Newton of thrust.

The three engines on the Space Shuttle produce a combined 5.37 million Newtons of thrust.

To produce this much thrust with a laser would require 1.6 petawatts (1,611,000,000,000,000 watts).

Lasers are notoriously inefficient. Most have efficiencies of about 25%. Say we have a free-electron laser which has a theoretical maximum efficiency of 65%. This means that 35% of the input energy becomes waste heat.

This means that if the laser energy is 1.6 petawatts, the waste heat will be 860 terawatts. This means that the laser will be creating waste heat at a power level of 300 times the yearly energy consumption of the United States each second.

And you are somehow going to hide all this waste heat?

Again, read the link. Chances are, whatever you try to come up with has been tried already.

Of course if in your role as a Game Master, you invent an exciting campaign for your players that depends upon magically creating stealth in space, then you can ignore scientific accuracy in the name of pleasing your players.

Certainly some fuel for thought...but you seem to use assumptions that counter your claims. "If they know where you are? You claim nothing can hide in space!

And the laser counter feels false somehow...if I have a drive so effiecient that it emits photons as it's reaction mass, finding a way to make them partially or completely coherant does not seem so hard. (in compareson, anyway)

How effective Is heat detection? Has someone shown that it is mathmaticly impossable to conceal heat emissions? If so why hasn't someone obtained Billions from the defence department to spot stealth aircraft? In comparison to a total skyscan in space spotting a big thermal plume in space, a smaller thermal plume in the atmospher should be childs play.

Why should anyone pay millions to build a asteroid watch? It seems as though it is a trivial task, using off the shelf componites.


I guess I'm saying you make a claim "You cannot hide in space" ...so where is the proof?

Shooting holes in proposals does Not constitute proof. Who detcted a ion drive at 1 AU? What was the methodology?

I'm thinking that detecting something that you know where is ...is not real hard....so was it tracked independantly? (Hard to test...only one has ever flown as far as I know...)
As I said so far I have heard claims...where is proof available? What tests have been performed?

And as always what is the "dogma" level? People used to claim "No aircraft could fly, undetected by Radar" ...even though they sometimes did...and then Stealth came along...

[Kristopher]

{shudder} :angst:

Ummmmmm, I have a suggestion. Wouldn't it be easier to just ignore the heat problems, pretend they don't exist?

Let me explain. As it turns out, your handwaving is more or less the same as a rather stubborn popular misconception (http://www.projectrho.com/rocket/rocket3au.html) that is the topic of many emails I get.

So if you take the easy route and ignore the heat problems, it's better for you, it's better for me, and it's better for any of your players that might decide to email me. :D

They wouldn't, because I wouldn't cite the Peltier-Seebek effect, exactly because, as your article points out, it does not convert heat into some other form of energy. :)

That's why I mentioned handwavium -- I wouldn't try to explain how it would work. If I had a way to convert heat to electricity directly, in violation of the 2nd law, I wouldn't be using it in a game, I'd be the richest man on earth. :D

[Nyrath]

Certainly some fuel for thought...but you seem to use assumptions that counter your claims. "If they know where you are? You claim nothing can hide in space!
It doesn't matter if the ship trying to be stealthy knows where the you and the observation platforms are. For a small investment in observation platforms, there will be no safe place to aim your heat emissions.



And the laser counter feels false somehow...if I have a drive so effiecient that it emits photons as it's reaction mass, finding a way to make them partially or completely coherant does not seem so hard. (in compareson, anyway)
Ummmm, I think you are mistaking "coherence" (http://en.wikipedia.org/wiki/Coherence_(physics)) with "efficiency" (http://en.wikipedia.org/wiki/Energy_conversion_efficiency).;) Have you had any course in physics?

Most laser generators produce beams that are pretty close to 100% coherent. This means the laser light is in lockstep.

But the generator efficiency is a measure of how much electricity input becomes laser energy output. The difference between the two becomes waste heat. Most laser generators have a theoretical maximum of around 25%, with the exception of the free electron laser at 65%. This is the maximum efficiency, in practice it will be lots worse.



How effective Is heat detection? Has someone shown that it is mathmaticly impossable to conceal heat emissions? If so why hasn't someone obtained Billions from the defence department to spot stealth aircraft?
I keep telling you: read the link (http://www.projectrho.com/rocket/rocket3w.html). All of this is covered there. You are not raising anything new.

[a] How effective is heat detection? Has someone shown that it is mathmaticly impossable to conceal heat emissions?


A full spherical sky search is 41,000 square degrees. A wide angle lens will cover about 100 square degrees (a typical SLR personal camera is about 1 square degree); you'll want overlap, so call it 480 exposures for a full sky search, with each exposure taking about 350 megapixels.

Estimated exposure time is about 30 seconds per 100 square degrees of sky looking for a magnitude 12 object (which is roughly what the drive I spec'd out earlier would be). So, 480 / 2 is 240 minutes, or about 4 HOURS for a complete sky survey. This will require signal processing of about 150 gigapizels per two hours, and take a terabyte of storage per sweep.

That sounds like a lot, but...

Assuming 1280x1024 resolution, playing an MMO at 60 frames per second...78,643,200 = 78 megapixels per second. Multiply by 14400 seconds for 4 hours, and you're in the realm of 1 terapixel per sky sweep Now, digital image comparison is in some ways harder, some ways easier than a 3-D gaming environment. We'll say it's about 8x as difficult - that means playing World of Warcraft on a gaming system for four hours is about comparable to 75 gigapixels of full sky search. So not quite current hardware, but probably a computer generation (2 years) away. Making it radiation hardened to work in space, and built to government procurement specs, maybe 8-10 years away.

I can buy terabyte hard drive arrays now.

I can reduce scan time by adding more sensors, but my choke point becomes data processing. On the other hand, it's not unreasonable to assume that the data processing equipment will get significantly better at about the same rate that gaming PCs get significantly better.

Now, this system has limits - it'll have trouble picking up a target within about 2 degrees of the sun without an occlusion filter, and even with one, it'll take extra time for those exposures.

It won't positively identify a target - it'll just give brightness and temperature and the fact that it's something radiating like a star that moves relative to the background.

On the other hand, at the thrusts given above, it'll take somewhere around 2 days of thrust to generate the delta v to move from Earth to Mars, and the ship will be in transit for about 1-4 months depending on planetary positions.


If so why hasn't someone obtained Billions from the defence department to spot stealth aircraft?

Stealth aircraft fly in the air. That's why they are called [B]aircraft. Air is found on Earth. Earth has something called the "horizon", which severely limits the range at which an aircraft can be spotted. The Earth's air is also quite hot compared to the space environment. The waste heat from a stealth aircraft is not as obvious since it is relatively much more close to the ambient temperature. The air is also a good heat sink, quickly erasing the thermal plume. Even so, a stealth aircraft can be spotted by thermal imaging, only you have to be quite close.

Spacecraft fly in space, That's why they are called spacecraft. Space is found in space. Space does not have any horizon, you can see out to the distant galaxies, so there is no range limit. Space is incredibly cold (three degrees Kelvin), so the waste heat from a trying-to-be-stealthy spacecraft stands out like it was lit up with powerful spotlights. Space also does not do much to erase thermal plumes. As mentioned before, you can see the thermal plume from the Space Shuttle main engines as far out as Pluto, or more or less the radius of the entire solar system.





Why should anyone pay millions to build a asteroid watch? It seems as though it is a trivial task, using off the shelf componites.
Ask NASA.

from http://usgovinfo.about.com/library/weekly/aa072702a.htm

What is the Government Doing About This?
In 1993 and again in 1998, Congressional hearings were held to study the impact hazard. As a result, both NASA and the Air Force are now supporting programs to discover Earth-threatening objects. Congress currently budgets only about $3 million per year for programs like the Near Earth Object (NEO) project. While other governments have expressed concern about the impact hazard, none have yet funded any extensive surveys or related defense research.




I guess I'm saying you make a claim "You cannot hide in space" ...so where is the proof?

Shooting holes in proposals does Not constitute proof. Who detcted a ion drive at 1 AU? What was the methodology?

I'm thinking that detecting something that you know where is ...is not real hard....so was it tracked independantly? (Hard to test...only one has ever flown as far as I know...)
As I said so far I have heard claims...where is proof available? What tests have been performed?
Go ask an astronomer. These figures are assuming total sky scans with off the shelf technology. You don't think I made up these figures, do you? I obtained them from real experts, not me.


And as always what is the "dogma" level? People used to claim "No aircraft could fly, undetected by Radar" ...even though they sometimes did...and then Stealth came along...
:confused: Do you have a quote for that? I never read anybody who claimed that? If I did know any better, it sounds like you are using the tired old "they said they couldn't break the sound barrier" (http://www.projectrho.com/rocket/rocket3al.html#breakthrough) argument.


90% of the email I get about my atomic rocket website is on only three topic: I don't want to admit there is no stealth in space, I don't want to admit that faster-than-light travel is impossible, and I don't want to admit that space fighters make no sense scientifically, economically, or militarily. You apparently fall into the first category.

But don't take my word for it. Go to the experts yourself and ask them, they can be found here:
http://games.groups.yahoo.com/group/sfconsim-l/

[SSgt Baloo]

I don't think undetectable means what you think it means. At the present level of technology, anything not in Earth orbit has an exceedingly good chance of remaining undetected. Space is big and unless you're looking in the right direction you won't see a thing.

[Nyrath]

I don't think undetectable means what you think it means. At the present level of technology, anything not in Earth orbit has an exceedingly good chance of remaining undetected. Space is big and unless you're looking in the right direction you won't see a thing.

I repeat:

A full spherical sky search is 41,000 square degrees. A wide angle lens will cover about 100 square degrees (a typical SLR personal camera is about 1 square degree); you'll want overlap, so call it 480 exposures for a full sky search, with each exposure taking about 350 megapixels.

Estimated exposure time is about 30 seconds per 100 square degrees of sky looking for a magnitude 12 object (which is roughly what the drive I spec'd out earlier would be). So, 480 / 2 is 240 minutes, or about 4 HOURS for a complete sky survey. This will require signal processing of about 150 gigapizels per two hours, and take a terabyte of storage per sweep.

That sounds like a lot, but...

Assuming 1280x1024 resolution, playing an MMO at 60 frames per second...78,643,200 = 78 megapixels per second. Multiply by 14400 seconds for 4 hours, and you're in the realm of 1 terapixel per sky sweep Now, digital image comparison is in some ways harder, some ways easier than a 3-D gaming environment. We'll say it's about 8x as difficult - that means playing World of Warcraft on a gaming system for four hours is about comparable to 75 gigapixels of full sky search. So not quite current hardware, but probably a computer generation (2 years) away. Making it radiation hardened to work in space, and built to government procurement specs, maybe 8-10 years away.

I can buy terabyte hard drive arrays now.

I can reduce scan time by adding more sensors, but my choke point becomes data processing. On the other hand, it's not unreasonable to assume that the data processing equipment will get significantly better at about the same rate that gaming PCs get significantly better.

Now, this system has limits - it'll have trouble picking up a target within about 2 degrees of the sun without an occlusion filter, and even with one, it'll take extra time for those exposures.

It won't positively identify a target - it'll just give brightness and temperature and the fact that it's something radiating like a star that moves relative to the background.

On the other hand, at the thrusts given above, it'll take somewhere around 2 days of thrust to generate the delta v to move from Earth to Mars, and the ship will be in transit for about 1-4 months depending on planetary positions.



The space background in the infrared wavelengths is near pitch black at a black-body temperature of three degrees Kelvin. A manned spacecraft with all engines and power plants turned off and with the habitat module set to the freezing point of water in a desperate attempt to hide is still going to be radiating at 273 degrees Kelvin, and will show up like a beacon. An unmanned drone will be cooler, but still warmer than space.

And if the drone or spacecraft actually tries to move, thus using some sort of propulsion system, well they might as well shoot off signal flares and set up ten foot neon signs saying "WE ARE HERE!!!"

[SSgt Baloo]

I repeat:

A full spherical sky search is 41,000 square degrees. A wide angle lens will cover about 100 square degrees (a typical SLR personal camera is about 1 square degree); you'll want overlap, so call it 480 exposures for a full sky search, with each exposure taking about 350 megapixels.

Estimated exposure time is about 30 seconds per 100 square degrees of sky looking for a magnitude 12 object (which is roughly what the drive I spec'd out earlier would be). So, 480 / 2 is 240 minutes, or about 4 HOURS for a complete sky survey. This will require signal processing of about 150 gigapizels per two hours, and take a terabyte of storage per sweep.

That sounds like a lot, but...

Assuming 1280x1024 resolution, playing an MMO at 60 frames per second...78,643,200 = 78 megapixels per second. Multiply by 14400 seconds for 4 hours, and you're in the realm of 1 terapixel per sky sweep Now, digital image comparison is in some ways harder, some ways easier than a 3-D gaming environment. We'll say it's about 8x as difficult - that means playing World of Warcraft on a gaming system for four hours is about comparable to 75 gigapixels of full sky search. So not quite current hardware, but probably a computer generation (2 years) away. Making it radiation hardened to work in space, and built to government procurement specs, maybe 8-10 years away.

I can buy terabyte hard drive arrays now.

I can reduce scan time by adding more sensors, but my choke point becomes data processing. On the other hand, it's not unreasonable to assume that the data processing equipment will get significantly better at about the same rate that gaming PCs get significantly better.

Now, this system has limits - it'll have trouble picking up a target within about 2 degrees of the sun without an occlusion filter, and even with one, it'll take extra time for those exposures.

It won't positively identify a target - it'll just give brightness and temperature and the fact that it's something radiating like a star that moves relative to the background.

On the other hand, at the thrusts given above, it'll take somewhere around 2 days of thrust to generate the delta v to move from Earth to Mars, and the ship will be in transit for about 1-4 months depending on planetary positions.



The space background in the infrared wavelengths is near pitch black at a black-body temperature of three degrees Kelvin. A manned spacecraft with all engines and power plants turned off and with the habitat module set to the freezing point of water in a desperate attempt to hide is still going to be radiating at 273 degrees Kelvin, and will show up like a beacon. An unmanned drone will be cooler, but still warmer than space.

And if the drone or spacecraft actually tries to move, thus using some sort of propulsion system, well they might as well shoot off signal flares and set up ten foot neon signs saying "WE ARE HERE!!!"

I'm not saying it's impossible, but does anybody have plans to set up a detection system like that anytime soon?

[Captain Obvious]

I'm not saying it's impossible, but does anybody have plans to set up a detection system like that anytime soon?

Probably not soon, but when attempts to build a stealthy spacecraft become likely, it will probably be a high priority for someone.

[Nyrath]

I'm not saying it's impossible, but does anybody have plans to set up a detection system like that anytime soon?
No. Seeing that is is all NASA can do to get funding for a detection system for rogue asteroids that could wipe out our civilization, there is no funding for a detection system for an alien invasion fleet.

However, in a universe where hostile armed spacecraft were common, such a detection system would also be common.

[steamteck]

Ok, Got it no stealth in space but I have two things I wonder about for my own campaign.
How far can radiated heat be detected and how fast does said heat travel.? That is how old is your observational data?

[L. Marcus]

Just take the example above -- the heat is, obviously, EM radiation so it travels at the speed of light. It takes light something like 5+ hours to reach Pluto from the Sun.

[Cancer]

Two separated observing stations separated by an AU or so ... this would be, for example, at the L4/L5 points of the Earth-Sun system, or one each in orbit around Earth and Mars ... would be adequate for locating something in 3 dimensions. This has actually been done for locating an X-ray source unambiguously in the sky, although serendipitously. The time lag between the stations nails down the spatial ambiguity, and for anything inside the solar system, assuming any kind of angular resolution, you'll be able to pin down the distance as well as direction by parallax.

Rapid-response all-sky observing networks are in place now, but not in the waveband or sensitivity required for this application. There hasn't been need for them. Most astronomical objects don't appear and disappear in a minute or less, so a more leisurely approach to looking for them is adequate.

[Nyrath]

How far can radiated heat be detected

Of course this depends upon how hot the object is.

I'll give you some examples then give you the dull boring equations.

If you have a spacecraft the size of a Russian Oscar-II submarine (about 154 meters long) that is keeping a frigid interior temperature of 273 Kelvin (32 Fahrenheit, where water freezes into ice) in a desperate attempt to be stealthy, with all the engines and power plants turned off, and you are using current day off-the-shelf infrared detection technology, the maximum distance the spacecraft can be detected is about 38,800,000 kilometers.

This is about one hundred times the distance between the Earth and the Moon, or about 129 light-seconds.

If the spacecraft raised the thermostat to room temperature, it could be seen at a range of about 43,800,000 kilometers.

Now, if the spacecraft turns on its rocket engine, you can see it from several solar system away. We will show some examples of two spacecraft. One is the same mass as an Oscar submarine (13,900 metric tons), the other is only 1000 metric tons. We will use a chemical rocket, an ion drive, a VASIMR plasma drive, and a Hydrogen-Boron Fusion drive. We will use accelerations of 1 gee, one tenth gee, and one one-hundredth gee.

We will show the maximum range the the ship can be detected by current off-the-shelf IR detectors, in kilometers, light-seconds, and astronomical units (the distance between the Earth and the Sun). The solar system is about 80 AU in diameter.
Detection range goes down as the ship mass, specific impulse and thrust go down.

Chemical 13.9 kton 1.00 gee = 3,500,000,000km/12,000ls/24au
Chemical 13.9 kton 0.10 gee = 1,100,000,000km/3800ls/7.5au
Chemical 13.9 kton 0.01 gee = 360,000,000km/1200ls/2.4au

Chemical 1 kton 1.00 gee = 960,000,000km/3200ls/6.4au
Chemical 1 kton 0.10 gee = 300,000,000km/1000ls/2.0au
Chemical 1 kton 0.01 gee = 95,000,000km/320ls/0.6au

Ion 13.9 kton 1.00 gee = 76,000,000,000km/260,000ls/515au
Ion 13.9 kton 0.10 gee = 24,000,000,000km/81,000ls/163au
Ion 13.9 kton 0.01 gee = 7,700,000,000km/26,000ls/51.4au

Ion 1 kton 1.00 gee = 21,000,000,000km/69,000ls/138au
Ion 1 kton 0.10 gee = 6,500,000,000km/22,000ls/43.6au
Ion 1 kton 0.01 gee = 2,100,000,000km/6900ls/13.8au

VASIMR 13.9 kton 1.00 gee = 76,000,000,000km/250,000ls/509au
VASIMR 13.9 kton 0.10 gee = 24,000,000,000km/80,000ls/161au
VASIMR 13.9 kton 0.01 gee = 7,600,000,000km/25,000ls/50.9au

VASIMR 1 kton 1.00 gee = 20,000,000,000km/68,000ls/137au
VASIMR 1 kton 0.10 gee = 6,500,000,000km/22,000ls/43.2au
VASIMR 1 kton 0.01 gee = 2,000,000,000km/6800ls/13.7au

H-B Fusion 13.9 kton 1.00 gee = 170,000,000,000km/550,000ls/1100au
H-B Fusion 13.9 kton 0.10 gee = 53,000,000,000km/170,000ls/352au
H-B Fusion 13.9 kton 0.01 gee = 17,000,000,000km/56,000ls/110au

H-B Fusion 1 kton 1.00 gee = 45,000,000,000km/150,000ls/298au
H-B Fusion 1 kton 0.10 gee = 14,000,000,000km/47,000ls/94.3au
H-B Fusion 1 kton 0.01 gee = 4,500,000,000km/15,000ls/19.8au

The dull equations

Ship with engines and power plant off
Rd = 13.4 * sqrt(A) * T^2
where:
Rd = detection range (km)
A = spacecraft projected area (square meters )
T = surface temperature (Kelvin, room temperature is about 285-290 K)
x^2 = square of x

If the ship is a convex shape, its projected area will be roughly one quarter of its surface area.

Ship with engines running
Rd = ( 1,780,0000 * sqrt( Ms*As*Isp*(1-Nd) ) ) * (sqrt(0.04 * π))
where:
Rd = maximum detection range (kilometers)
Ms = bogey spacecraft mass (metric tons)
As = bogey spacecraft acceleration (G)
Isp = bogey drive specific impulse (seconds) Chemical = 458, Ion = 21,400, VASIMR = 30,000, H-B Fusion = 100,000, other (http://www.projectrho.com/rocket/rocket3c2.html)
Nd = bogey drive efficiency (0.0 to 1.0) Chemical = 0.98, Ion = 0.5, VASIMR = 0.65, H-B Fusion = 0.5
π = Pi = 3.141593...
sqrt(x) = square root of x


and how fast does said heat travel.? That is how old is your observational data?
Infrared radiation travels at the speed of light. Divide distance in kilometers by 299792.458 to get how many seconds it takes the IR to travel the distance. Or use the figure for "light-seconds".

Divide time in seconds by 3600 for hours, 86400 for days, 2592000 for (30 day) months, or 31536000 for years

[steamteck]

Thanks. Co,plete brain glitch on IR's speed there. I knew that but didn't process. Your examples pretty much give me ehat I need for my game. Thanks again.

[Nyrath]

Your examples pretty much give me ehat I need for my game. Thanks again.
Glad to help

[pinecone]

Short answer: read the link
http://www.projectrho.com/rocket/rocket3w.html#nostealth


An infrared source can be hidden with a heat sink, for about five minutes. Unless your heat sink is several miles in diameter.

Yes, an ion drive can be detected at a range of one astronomical unit, even if the drive is facing away from you. And this is only if the drive is throttled down to less than 1/1000 of a g of acceleration. If the acceleration is higher, the detection range grows.

The direction of the drive makes little difference. And even if it did, what use is it to only be able to accelerate directly at you? Unless you were trying to ram?

And the phrase "facing away from you" contains two assumptions:
[1] the ion drive owner knows where "you" are located
[2] "you" are the only observer in the solar system. If "you" deployed a few observational space probes around a few other planets, it will be impossible for the ion drive to face away from all of them.

And then there is the problem that an ion drive requires lots of electrical power to operate. Which requires a power plant of some kind, or a huge solar array. All of which will generate waste heat as it converts fuel or solar energy into electricity. Which will give away the ion drive's position.

You don't seem to understand that the background of space is at three degrees above absolute zero, so almost anything else stands out like a spotlight.


We are not worrying that asteroids are hard to see. We are worrying that nobody is willing to fund a constant sky watch to detect dangerous asteroids.



[1] How can the laser user be sure they know where all the observational space probes are?
[2] A laser used as a photon drive requires about THREE HUNDRED MEGAWATTS to produce one measly Newton of thrust.

The three engines on the Space Shuttle produce a combined 5.37 million Newtons of thrust.

To produce this much thrust with a laser would require 1.6 petawatts (1,611,000,000,000,000 watts).

Lasers are notoriously inefficient. Most have efficiencies of about 25%. Say we have a free-electron laser which has a theoretical maximum efficiency of 65%. This means that 35% of the input energy becomes waste heat.

This means that if the laser energy is 1.6 petawatts, the waste heat will be 860 terawatts. This means that the laser will be creating waste heat at a power level of 300 times the yearly energy consumption of the United States each second.

And you are somehow going to hide all this waste heat?

Again, read the link. Chances are, whatever you try to come up with has been tried already.

Of course if in your role as a Game Master, you invent an exciting campaign for your players that depends upon magically creating stealth in space, then you can ignore scientific accuracy in the name of pleasing your players.

Well...I'l repeat myself, then drop it...I'm not interested in putting up ideas so they can be shot down. I'm trying to understand the basis for the claims.

Yes I do know that air is differant than space...but I also know that principles of physics aplly everywhere the same (as far as we know) So I wish to aply the claims to my own knowlage.

If the best you can do is suggest that I am too ignorant to understand that I should blindly accept your claims...well so be it.

I did not read the whole site because all I saw was claims, and a little math in the form of several terms that do not show how they were determined...leaving the result of little seeming proof. I remember a simular one from old sci-fi readings that "proved" that billions (or dozens...or none at all) of alien civs were out there.....it all depends on what value you assign to the variables. Leaving the equation a fancy way to convince people of a claim.

Best of luck to you.

[Nyrath]

If the best you can do is suggest that I am too ignorant to understand that I should blindly accept your claims...well so be it.
Look, don't take my word for it. Go find a physics professor or somebody who can give you the proof you want and ask them.

You can find some experts to ask your questions of at the usenet newsgroup rec.arts.sf.science
http://groups.google.com/group/rec.arts.sf.science/topics?hl=en
or in the Yahoo group SFConSim-l
http://games.groups.yahoo.com/group/sfconsim-l/

I did not say you were ignorant, I was asking if you had taken any course in physics.

[L. Marcus]

Well...I'l repeat myself, then drop it...I'm not interested in putting up ideas so they can be shot down. I'm trying to understand the basis for the claims.

Yes I do know that air is differant than space...but I also know that principles of physics aplly everywhere the same (as far as we know) So I wish to aply the claims to my own knowlage.

If the best you can do is suggest that I am too ignorant to understand that I should blindly accept your claims...well so be it.

I did not read the whole site because all I saw was claims, and a little math in the form of several terms that do not show how they were determined...leaving the result of little seeming proof. I remember a simular one from old sci-fi readings that "proved" that billions (or dozens...or none at all) of alien civs were out there.....it all depends on what value you assign to the variables. Leaving the equation a fancy way to convince people of a claim.

Best of luck to you.
. . . I must say, if you are in doubt, do the physics yourself. Or go the same experts Nyrath did.

[SSgt Baloo]

Of course, considering the forum we're in, the science might be a bit more rubbery in the campaign where such is going on than in our own. In a hard science campaign, I suspect someone wishing to remain undetected by such an early warning system would have to hack the system that does the detection and make an exception for their own particular "signature".


"What the... what just happened?

"Kelso Station just evaporated!"

"I don't understand!?! The detection grid didn't give a peep!"

"Run diagnostics! We've been hacked!

[Cancer]

You can estimate the infrared fluxes by yourself, though it gets tedious to convince yourself that you're doing it right. Here's a sloppy way to go about it.

For any kind of non-photon rocket, to figure out the amount of IR radiation generated, you need the temperature profile of the exhaust (that is, the temperature of the exhaust as a function of where you are in the rocket output) and the shape and size of the exhaust plume. I don't have an immediate suggestion for where to get such information, unfortunately.

Figure out how many square meters of exhaust plume are at what temperature, and what your view of those is. Any part of the plume that is blocked by the spacecraft you won't see, but in general the plume will be MUCH larger than the ship and all you'll have blocked is the very hottest core.

Pick the waveband your prospective lookout will be using. My suggestion is to pick three sample wavelengths, 1 micron, 10 microns, and 100 microns.

For each square meter of the plume, use Planck's Law and compute the total infrared emitted at each wavelength. Black-body radiation is isotropic (it goes equally in all directions). Add up all the square meters worth. You'll get a total power emitted per unit frequency (or wavelength) by the plume.

Next, assume that gets radiated isotropically -- spherical symmetry. Pick a number for how far away the rocket is ... say, 10 AU. Compute the area of the sphere of that size. Divide the total pwoer radiated by that area. You'll get a flux (power per unit area per unit wavelength or frequency).

You can compare that flux at each wavelength to the flux of a standard. Annoyingly, that turns out to be hard, because the absolute flux calibration in the far IR is arcane. (It's easy to compare your IR flux to that of Vega at 1 micron ... that calibration has long been done ... but at longer wavelengths than that, where you really expect the rocket to show up, it's much harder.)

[L. Marcus]

. . . Anyhoo, regarding tracking asteroids -- here's an interesting tidbit from New Scientist: Space rock collides with Earth right on time (http://space.newscientist.com/article/dn14897-space-rock-collides-with-earth-right-on-time.html?DCMP=ILC-hmts&nsref=news1_head_dn14897).

[Nyrath]

Yes, I wish they would go into some detail about how far the asteroid was from Earth when it was spotted.

[Cancer]

Trying to track that down now. According to the Mnor Planet Center page, it was discovered at Mt. Lemmon on UT date Oct 6.28, and hit the atmosphere on UT date Oct 7.115. Haven't found the data from the observation set yet.

EDIT: the text of IAU Circular 8990, with a set of images spliced into a movie, is here (http://www.astronomy.ru/forum/index.php/topic,45265.0.html); the main page is in Russian but the IAUC quotation is left in English. The circular doesn't mention the apparent magnitude, so I'm going to keep digging.

EDIT 2: I'll need to crunch numbers more carefully when I have more time, but I think it was roughly apparent magnitude 17 when discovered. The IAUC says Delta = 0.0033 AU at discovery, about 1.27 times the Earth-Moon distance.

EDIT 3: another pseudo-video (http://forum.slooh.com/viewtopic.php?p=22598#22598) towards the bottom of the page. You can see the streaks. The frames are taken in different colors, so the brightnesses of things aren't matched in the different frames.

[L. Marcus]

. . . UT date? Is that anything like stardate? :think:

[Cancer]

It just specifies the time in fractional days (rather than hours-minutes-seconds) in Universal Time.