[EternalRuin]

Eh, one point I've always disagreed with in that "no stealth in space" thing...

"Well FINE!!", you say, "I'll turn off the engines and run silent like a submarine in a World War II movie. I'll be invisible." Unfortunately that won't work either. The life support for your crew emits enough heat to be detected at an exceedingly long range. The 285 Kelvin habitat module will stand out like a search-light against the three Kelvin background of outer space.

I guess Nyrath never heard of insulation? 

The heat has to go SOMEWHERE eventually, though. Insulation will work for a while for stealth purposes, but at some point you're going to have to dump heat into space before you're roasted like a chicken.

[Alex Heartnet]

Not to mention that the enemy ships' crew will notice that you just disappeared off of sensors, and have your last known position and your last known trajectory.

...Wait, you can dump heat into space?  I thought heat could only be transferred through matter, which there is a distinct lack of in open space.

[Aardwolf]

Roasted like a chicken  The engines are off, and the crew is at a chilly 12 degrees Celsius. Or are you saying that if you had perfect insulation, the temperature inside the crew module would rise over time, just from the crew being warm-blooded?

[Dragon]

With good enough insulation, this can indeed hide you for a while. For how long, depends on the insulation and on whatever you're using to store heat. You can't stay hidden forever, but nobody says you need to. All you need is to get to a good hiding place where you can dump heat unnoticed (like behind an asteroid, or in atmosphere.

[headdie]

Not to mention that the enemy ships' crew will notice that you just disappeared off of sensors, and have your last known position and your last known trajectory.

...Wait, you can dump heat into space?  I thought heat could only be transferred through matter, which there is a distinct lack of in open space.

many materials emit EM radiation such as Infra Red and visible spectrum light when heated sufficiently while many need large amounts of heat to do this others dont.

Roasted like a chicken  The engines are off, and the crew is at a chilly 12 degrees Celsius. Or are you saying that if you had perfect insulation, the temperature inside the crew module would rise over time, just from the crew being warm-blooded?

Humans give off heat at fairly consistant rates, if this energy is not diverted somewhere it accumulates, also you cant shut down all power sources as air still needs to be circulated and refreshed along with lighting, sensors, computer systems etc so the ship will always be generating some heat on top of that created by the crew so yes they will fry if you dont get rid of the heat

[LordPomposity]

Not to mention that the enemy ships' crew will notice that you just disappeared off of sensors, and have your last known position and your last known trajectory.

...Wait, you can dump heat into space?  I thought heat could only be transferred through matter, which there is a distinct lack of in open space.

There are three types of heat transfer: convection, conduction, and radiation. Convection and conduction are both dependent on having matter to transfer the heat to. Radiation works in a vacuum, but transfers heat much more slowly than the other two.

To answer the initial question, missiles with bomb-pumped lasers. You can get a much more powerful laser by focusing the x-ray flux of a nuclear detonation than you can with any sort of weapon you can actually mount on a spaceship, and mounting it on a homing missile means that you can engage at ranges where the guys using lasers or railguns will be crippled by lightspeed lag. If you have the missile doing random zig-zags the last few light-seconds to the target and detonate at a couple tens of thousands of kilometers, it would require a statistical miracle for point defenses to shoot your missile down.

This is assuming a lightspeed cap on travel, sensors, and communications. If you're using FTL, pick whichever type of weapon looks coolest and continue to warp reality until it become most effective.

[Dragon]

Humans give off heat at fairly consistant rates, if this energy is not diverted somewhere it accumulates, also you cant shut down all power sources as air still needs to be circulated and refreshed along with lighting, sensors, computer systems etc so the ship will always be generating some heat on top of that created by the crew so yes they will fry if you dont get rid of the heat

Note, if you have a slab of metal specifically meant to store heat, and you can dump it there fairly efficiently, you can go quite long without the atmosphere getting hot enough to be a problem. Of course, the heat will build up, and will eventually become an issue, but if your slab is big enough, it can buy you enough time.

[headdie]

Humans give off heat at fairly consistant rates, if this energy is not diverted somewhere it accumulates, also you cant shut down all power sources as air still needs to be circulated and refreshed along with lighting, sensors, computer systems etc so the ship will always be generating some heat on top of that created by the crew so yes they will fry if you dont get rid of the heat

Note, if you have a slab of metal specifically meant to store heat, and you can dump it there fairly efficiently, you can go quite long without the atmosphere getting hot enough to be a problem. Of course, the heat will build up, and will eventually become an issue, but if your slab is big enough, it can buy you enough time.

true but brings about a couple of questions.

firstly, how do you deposit the heat in the metal slab once it is heated to the same temp as the rest of the ship?
secondly, how does it help if using non subspace magic inter system travel?  That's a lot of dead metal.

[Alex Heartnet]

Humans give off heat at fairly consistant rates, if this energy is not diverted somewhere it accumulates, also you cant shut down all power sources as air still needs to be circulated and refreshed along with lighting, sensors, computer systems etc so the ship will always be generating some heat on top of that created by the crew so yes they will fry if you dont get rid of the heat

Dumping any kind of heat when trying to be stealthy will make you easier to detect.

With good enough insulation, this can indeed hide you for a while. For how long, depends on the insulation and on whatever you're using to store heat. You can't stay hidden forever, but nobody says you need to. All you need is to get to a good hiding place where you can dump heat unnoticed (like behind an asteroid, or in atmosphere.

How do you plan on getting to that hiding place when your engines are offline, and the enemy vessel has your last known location and last known trajectory recorded?  All you are doing is stalling for time, and hoping that your enemy will think you are too stupid to actually try stealth in space.

If you have the missile doing random zig-zags the last few light-seconds to the target and detonate at a couple tens of thousands of kilometers, it would require a statistical miracle for point defenses to shoot your missile down.

This is assuming a lightspeed cap on travel, sensors, and communications...

There's a little something called inertia that can and will keep ships and missiles from doing zigzags in space.  A missile or ship that is moving at high speed will take some time to slow down or change trajectory.

Also, if the target ship is moving slowly relative to the missile, the target ship might be able to manage a major trajectory change, resulting in the missile not being able to correct its trajectory in time and overshooting its intended target.

Additionally, missile tracking systems just won't be as sophisticated as a starship sensor package (at least not without making the missile really expensive).  A missile could actually be spoofed by decoys and ECM.  Those same anti-missile systems won't spoof a sophisticated ship sensor package, but at least the missile didn't hit.

If I do have an FTL drive, I could always use that as a last-resort missile dodging technique.  All I need to do is jump a relatively short distance and all the missiles will be on a completely incorrect trajectory to hit me.

[headdie]

Humans give off heat at fairly consistant rates, if this energy is not diverted somewhere it accumulates, also you cant shut down all power sources as air still needs to be circulated and refreshed along with lighting, sensors, computer systems etc so the ship will always be generating some heat on top of that created by the crew so yes they will fry if you dont get rid of the heat

Dumping any kind of heat when trying to be stealthy will make you easier to detect.

thats the point i was making

[Aardwolf]

How do you plan on getting to that hiding place when your engines are offline, and the enemy vessel has your last known location and last known trajectory recorded?

The point of cutting the engines isn't to make yourself disappear once they've spotted you, it's to keep them from spotting you. Once you've been spotted, you stay spotted.

[Dragon]

How do you plan on getting to that hiding place when your engines are offline, and the enemy vessel has your last known location and last known trajectory recorded?  All you are doing is stalling for time, and hoping that your enemy will think you are too stupid to actually try stealth in space.

That's assuming they have your last known location and velocity. If you're already detected, why bother with stealth?

true but brings about a couple of questions.

firstly, how do you deposit the heat in the metal slab once it is heated to the same temp as the rest of the ship?
secondly, how does it help if using non subspace magic inter system travel?  That's a lot of dead metal.

For the first, it needs to be insulated so it doesn't transfer the heat to the rest of the ship. I don't remember the exact explanation now, but there's a clever abuse of thermodynamics laws that allow you to transfer any amount of heat from a colder place to a hotter one (and it works, surprisingly enough).
For the second, if you get the slab moving (and the rest of your ship along with it) and set the right course, and your only goal is stealthy travel, you can seem like a pretty convincing asteroid. You can drop the slab (or vent it if it's already vaporized, in case of a really long travel) before you start decelerating.

[Alex Heartnet]

The point of cutting the engines isn't to make yourself disappear once they've spotted you, it's to keep them from spotting you. Once you've been spotted, you stay spotted.

Then it becomes a question of how far can sensors see.  Granted, nebulas and asteroids are often portrayed as sensor-blocking despite anything that hard sci-fi might say, but in open space your sensors should be able to see quite a distance.

[Dragon]

It's less about how far (Mk.1 Eyeball can see as far as 2 billion LY, last time I checked), but about how precisely. Telling a ship from an iron-rich asteroid or a piece of space junk floating around isn't that easy from a distance.

[An4ximandros]

And if you are hoping to lose your tiny heat signature in the vastness of the sky, I've got some bad news for you. Current astronomical instruments can do a complete sky survey in about four hours, or less.

Ken Burnside said:

❝
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.

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.

[Scourge of Ages]

If I ever create a sci-fi world, I'm going to create a technology that converts heat energy directly back into electricity.

[An4ximandros]

First off, the answer is NO, you cannot solve the problem by using a thermocouple to convert the heat into electricity.

Ken Burnside said:

Most of the arguments on thermo and space detection run through a predictable course of responses:

"Space is dark. You're nuts!"
"OK, there's no horizon, but the signatures can't be that bright?"
"OK, the drive is that bright, but what if it's off?"
"But it's not possible to scan the entire sky quickly!"
"OK, so the reactors are that bright, what if you direct them somewhere else..."
"What if I build a sunshade?"
"OK, so if I can't avoid being detected by thermal output, I'll make decoys..."
"Arrgh. You guys suck all the fun out of life! It's a GAME, dammit!"

Seriously, the site actually has a long list of reasons why YOU CAN'T DO THAT STAR FOX.

[jr2]

How effective would ye olde chaff and flares be in space?  ECM/jamming equipment?

[An4ximandros]

And to forestall your next question, decoys do not work particularly well either. More specifically, a decoy capable of fooling the enemy would wind up costing almost as much as a full ship.

Just to make sure that we are both on the same page here, I am talking about time frames of weeks to months. Such as found when a task force weeks or months away from their target, attempting to fool the enemey observers into thinking that your are a force of twenty warships, when you are actually a force of one warship and nineteen decoys.

I am not talking about time frames of a few seconds. Such as found when a combat spacecraft, with a hostile heat-seaking missile attempting to fly up its rear, dumps off a couple of decoy thermal flares hoping the missile will be confused.

First off, a decoy needs to emit a similar amount of radiation and heat as the ship it is pretending to be. This means each decoy needs a power source comparable in size to a full ship, the same goes for radiator area.

If the decoy and the real ship thrusts, it becomes worse. The exhaust plume has to be the same, which means both the decoy and the real ship has to have the same thrust. This means the decoy has to have the same mass as a real ship, or it will accelerate faster, thus giving itself away. If you down-rate the decoy's thrust, the dimness of the exhaust plume will give it away.

So if each decoy needs a spaceship sized engine in a spaceship sized hull with a spaceship sized mass isn't much of a decoy. Why not add weapons an make it an actual spaceship?

And you'd better add defenses as well. Otherwise the decoy is nothing more than an unusually expensive, unusually easy to destroy missile.

Isaac Kuo points out that all of this assumes that the decoy and the warship are using rocket propulsion. It does not apply if they are using solar sails, laser light sails, magnsails, or other non-rocket propulsion.

But I repeat: while it is more or less impossible to use decoys to fool distant observers, it may be possible to use something like decoys in a dog-fight to protect your ship from enemy short-range antiship missiles. In the latter case, you are not trying to make a fake image of your ship so much as you are trying to break the target lock the hostile missiles have on your ship's vulnerable posterior.

So in resume:
Dog-fight flares? Possible.
Long range decoys? Nope.

[Alex Heartnet]

Regardless of any argument of sci-fi hardness, submarine warfare in space does kinda sound like it would make for a fun, tactical game.

Edit:

How effective would ye olde chaff and flares be in space?  ECM/jamming equipment?

A decoy capable of spoofing starship sensors would cost almost as much as an actual ship.  I suppose you could always sacrifice a spare ship if you were desperate to get away...

On the other hand, it's not really economical for missiles to have the same sensor package that starships have.  So missiles CAN be spoofed by ECM and countermeasures (unless someone REALLY wants you dead and has the cash for expensive missiles hardened against ECM)