All the calculations that claim that there is no stealth in space are based on thruster plumes, not on emissions from a ship that isn’t accelerating. Yes, given a decent sized telescope on a stable platform you can spot a ship against the background, but spotting is not the problem - it’s getting a good enough track on it to predict the ship’s future location.
Spotting a ship doesn’t tell you its path, particularly if the way you spotted it is by noticing thruster emissions.
I’m not claiming interceptors will be stealthy, just that knowing where they are and being able to see them well enough to shoot at them are different problems, making it plausible that limiting emissions would be an effective defence strategy.
“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.”
IOW, by virtue of the fact that your ship’s systems produce heat to keep the crew alive, run the engines, etc, etc, it will be visible against the backdrop of space. And if they can see it, they can triangulate it’s range and direction over time.
The link I posted claims 4 hours to scan the entire sky. Probably much less in 50 years time. Even twice that time is no time at all for a target leaving Earth to assault Mars in a few months or year’s time.
That guy seems to be replying to the view of stealth that mistakes stealth with an invisibility spell. He’s right in that sense but that’s the common and erroneous view of stealth. Stealth is about reducing the probability (for a given range) or the range (for a given probability) that a target can be detected, IDed as a target rather than noise and tracked.
Emissions might travel long distances against little to no background but sensors do not have perfect sensitivity so they may fail to perceive a target even in space. Just like astronauts with their own eyes don’t see as many stars as Hubble. Sensors and processors may also have difficulty telling a target from a non-target like a distant star, comet or asteroid. Even if a target is IDed as such, there is the issue of tracking it which involves determining its vector, velocity and acceleration.
Passive detection methods may yield good angular data but fail to provide sufficient velocity information to engage. Active detection methods may be used and that most definitely is amenable to stealth because the signal echo can become weaker than receiver noise.
But it is quite true that stealth is more difficult in space than on earth and even on earth, stealth has never been an invisibility spell, despite what overenthusiastic movies/games/manufacturers/congressmen/officers would say.
The analogy I immediately thought of would be asking what a war would be like between the North Sentinelese, a Stone age tribe in the Indian Ocean, and an obscure tribe in the deepest Amazon. How would they fight each other?
Yes, the distance and related challenges would make it quite a bother, often too much of one. Which is why I amended to presuming any given of plausible technology.
Further presume that there are supplies of Moneyarium which make war worthwhile or that they must vanquish the other faction or be wiped out themselves.
So you can both see each other. No sneaking around. Both ships decide to engage the other. This is an interesting psychological exercise - neither party is going to engage if they think it’s hopeless.
While there might not be stealth, you could probably hide a ship’s weapon systems behind doors and foil screens so that the enemy doesn’t know what you are packing. Both free electron lasers and gauss guns use huge amounts of superconducting magnets, so the systems to drive them might look similar on IR. You could tell how heavy the enemy ship is by the intensity of the drive plume, the frequency of the resulting light, and the measured rate of acceleration of the vehicle. I wonder if you could tamper with this by purposefully making your engine look less efficient than it is or vice versa…
So you know they are packing something, but you also don’t know how much of their mass is propellant and how much is weaponry and armor.
Ships might be “glass cannons”, but this doesn’t matter - the fight is going to probably happen at the maximum possible range. Whoever has more effective firepower at that range probably wins. It’s entirely possible that at a range of a few thousand kilometers, armor would work - a better armored ship might be able to soak up diffuse laser fire at that range and not be damaged, while the ship with poorer armor gets holed and starts losing the ability to shoot back.
A victory doesn’t mean blowing the enemy ship up. If aneutronic fusion works for power (this is a good way to do it if it works), all it would take is a puncture the size of a quarter through one of the main superconducting magnets and no more power. No more power, no more rail/coilgun/laser fire from that ship.
Fission reactors, a hit that leaks out the working fluid for the heat engine would do something similar. The disabled warship would have to “core dump” just like they do in Star Trek, because without coolant, the reactor core would melt to radioactive vapor. So you might blow some explosive bolts and let the reactor float away.
You just send over the radio a demand to surrender, and if they refuse, launch a fission bomb at the disabled ship to kill it, or carefully snipe each point defense off the enemy ship’s hull with lasers and move in closer.
How would you reduce the probability?. Sure you can coat a spaceship with radar absorbing panels or use stealthy shapes and paint it black. But you can’t hide the ships heat signature. The Laws of Thermodynamics tell us that unless you want to cook your crew, all the heat produced by the space ship has to go somewhere. That’s how the ship will be detected. As a bright hot spot against a cold background.
You could in principle have the heat radiators behind the ship, and the front of the ship would be a big plate, cooled to the background temperature of space with liquid helium.
If you can keep the “stealthy” front aimed towards the enemy, and they don’t notice the stars you are occluding, it might work.
Except, if you have to maneuver, the thruster flare would give you away immediately. And if the enemy ship is not a lone vehicle but has a swarm of spy drones or observation satellites located across a large area of space, with the different platforms all scanning the sky in IR, they would spot the hot heat radiator from the angles where it is visible.
So it’s still basically a waste of time. Also, the defending ship is moving. It might be on a transfer orbit, it might even be on a continuous high ISP burn if we ever get the technology to do that. The “stealth” attacking ship has to make the maneuvers that will cause it to intercept the defending ship, and would emit a flare that could be detected anywhere in the solar system when it is doing this.
Maybe you could sneak up on “targets that can’t dodge” this way - planets, large space stations that don’t do any maneuvering except to maintain their position, etc.
1)The background isn’t completely cold. There are an awful lot of stars and other celestial bodies which emit radiation which can get to the sensor. That radiation (including infrared light) is noise.
More importantly though:
The intensity of the infrared radiation goes down at the square of the distance. At great distance, that’s an awful lot of reduction.To pick it up, you need to crank up the sensitivity of your sensor.
Thing is, the sensor itself emits radiation if it’s above 0 Kelvin. That’s sensor noise.* You could keep your sensor very close to 0 Kelvin but that will require a choice of A) getting rid of the coolant after use which will mean that you will get limited uses or B) cool it again which will require electricity and will heat up the ship just like a refrigerator is a net heat gain in a home.
Detecting with a noisy sensor is like trying to tell the color of a pen while wearing red-tinged glasses. You might but it’s far from obvious and the more noisy/red-tinged it is, the less likely you are to pull it off in a given amount of time.
Whether it’s background noise from other celestial bodies or sensor noise, it’s random. Being random, it is subject to variations since you may get a little more or less at particular times and in particular areas of the image you capture. Hence, probabilities of detection will vary.
I mentioned probability and distance but I also should have mentioned time as an element of detection which can be affected by stealth.
*You know those Facebook pictures which look like shit because they’re so grainy? That’s because they’re taken with phone cameras under insufficient light. The camera can only manage to get enough light (radiation visible to human eyes) by cranking up the sensitivity of its sensor. But the sensor also becomes more sensitive to its own emissions so you end up with those speckles which are sensor noise.
These two thread contains more info concerning detection of emissions in space which should show that the background isn’t so black and that signals can get so faint that they’re unlikely to be picked up even without an atmosphere getting in the way: How far in space can we detect our most powerful radio signals? - Factual Questions - Straight Dope Message Board http://boards.straightdope.com/sdmb/showthread.php?p=18518401#post18518401
This is incorrect. You actively cool the sensor to very close to 0 kelvin and you reject the heat from doing this with a heat radiator panel. The power to do this comes from a solar panel. You can build a complete system that does all this and only masses a few hundred kilograms.
You use multiple stages, as a side note - the pulse tube refrigerator cools just the sensor element which is a few square inches. There is a lot of shielding around it. The heat rejection side of the pulse tube refrigerator is cooled by a phase change cryocooler, and there are several stages of this. The hottest stage is pretty hot and, behind a shield, is on the other side of the satellite from the cryocooler, and is connected to a heat radiator. This is all 2015 technology.
Stealth is not impossible for space warfare purposes, though. One option is to reflect the heat away from your enemy.
Also, just because you can be seen doesn’t mean you can be identified as a space craft. Right now, we identify near-earth objects largely by taking multiple pictures of space and seeing what has moved against the fixed background of stars. It’s pretty hard to tell what is a star and what isn’t without this comparison. A sufficiently advanced system could spot other ships pretty easily using these comparisons, but our current technology is sadly lacking.
But I should really back up to the bigger question. I think space combat using the OP’s restrictions will look just like space exploration does today. We’ll launch “probes” that will carry warheads instead of cameras. They’ll take months or years to arrive. With low power requirements and a tiny size, they’ll be very hard to detect. Using the old-school MIRV delivery system, each probe can kill a dozen cities.
Once you’ve nuked your opponent back to the stone age, you win. Unless your opponent knew you were attacking them, in which case their probes nuke you back to the stone age a few days later.
This might actually work. With antimatter, you could make the warhead the size of a soda can, or not much bigger with a fission bomb. Not low power, no power - the electronics would wake up upon encountering the target (pressure sensor reconnects the battery) or you would send a high intensity coded laser pulse to the warheads to wake them up shortly before impact.
The only way to be safe in space is to always be adjusting your position.
If ISIS could make crude rockets capable of reaching orbit they could blow them to pieces and cause massive disruption of our satellite based civilisation