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I've never been satisfied with how this has been handled in any sci-fi story I've read, watched, etc. It always seems to get handwaved away with "we have sensor packages of various powers" and "they have stealth capabilities of various effectivenesses". I want to get much more specific than that.

Try to keep this within the realm of basic plausibility and Clarke's Third Law. I want technology in this future warfare to be advanced, but still basically within the realm of what we currently know to be plausible.

This is what I've been able to come up with:

  • Visual sensing; video collection and analysis comparable to modern day techniques, like what guides the FGM-148 Javelin. In space there's no ambient light, which already presents difficulties with shadows cast by planets, moons, and even other large ships, which would effectively create blind spots unless searchlights were used (which would immediately reveal the craft carrying the light). Add to this that warships will almost certainly be painted matte black, and I don't think visual sensing will be a reliable means at all.

  • Thermal sensing; works like visual sensing, but with the benefit that spacecraft will emit this naturally (blackbody radiation), so there's no worry about shadows and such. Ships could theoretically defeat this with cooling systems built into their hull plating, but my concern would be that supercooling the hull enough to appear invisible against the black background of space would severely compromise its structural integrity, especially if it includes complex elements like reactive armor. Protruding sensory packages and weapons, and also engines also wouldn't be able to be cooled in this manner without losing all functionality. The best countermeasure I can come up with for thermal sensing would be dispersing a wide cloud of superheated gas around your craft to disguise it (like an IR smoke screen), but I can't imagine this would last long; the cloud would either disperse or cool rapidly, and would need constant renewal to remain effective.

  • Radar; similar to the current technology. Although we currently have the means to almost completely defeat it (our only current barrier is cost, and this will likely vanish in the future), I'm not certain how the detection could also evolve in the future. In any case, sending out radar signals would probably also allow the detected craft to see the source of the incoming signals, and would compromise the position of the broadcasting craft.

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Gravity

Your ships spew out mini nanodrones that just float around in space, broadcasting its' location on an encrypted frequency.

Since everything distorts spacetime and has gravitational attraction, your nanodrones will naturally be attracted to larger masses. You might get "outlines" of larger ships this way.

When these masses move through your drones, your drones will also be displaced, and as such you can detect the "holes" in the droned areas.

The added bonus for using these nanodrones is that you can program them to identify parts of what it's sticking to, or composition, or w/e. For example, if some happened to be on the Engine, it could broadcast that it detects heat - if some were near missles, it could broadcast that it's detecting radiation from nuclear weapons or whatnot. Perhaps it's actually on a space rock - then it'd just be a slow moving mass of cold rock and report it's speed so that the mothership can confirm if the rock is really a rock (Is it accelerating with no apparent cause? If so, it's probably not a rock...).

Countermeasures:

  • periodically throw emp waves out to disable the drones in a large area while you travel through that particular sector
  • antiminidrone drones

Option 2: Use the stars. There are millions of them in the sky. I expect a future civilization capable of space warfare to have some decent star maps. Literally, just look outside the bridge and see which stars are blocked by something. It's probably a ship if it's not supposed to be blocked.

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    $\begingroup$ This is by far the most creative answer I've seen anywhere I've asked this question, and the crazy thing is I can't think of a reason why it wouldn't work. You're a genius. $\endgroup$ – AmoebaMan Jun 20 '15 at 4:02
  • $\begingroup$ The primary reason this wouldn't work is that space is big. But it does sound really interesting. $\endgroup$ – Erik Jul 30 '15 at 10:10
  • $\begingroup$ In addition to space being really, really, really big, nanodrones are essentially space dust which will be destroyed by impact at any sort of velocity which will allow the detected vehicle to traverse a solar system in useful time. Can you say "micometeorites"? Oh yes, and gravitation is really weak. A ship simply doesn't have a useful attraction. $\endgroup$ – WhatRoughBeast Jul 30 '15 at 14:36
  • $\begingroup$ @WhatRoughBeast But in the future, perhaps the drones have shielding to protect it? If that's the case, then the drones can detect when something hits it, which still allows for the same outlines and displacement holes described. I'm also assuming that the speeds aren't too fast, since this is a war situation and the fighters probably aren't going to be flying at hyperspeed while fighting. Furthermore, I fail to see how space being big is an issue. Just spit out more drones - they're meant to be disposable anyways. $\endgroup$ – Aify Jul 30 '15 at 15:38
  • $\begingroup$ Star occlusion has a limited range: for similar reasons to why laser beams end up diverging, at long range light will appear to skirt the object. So even if it should result in dimming the star, a small enough, far enough object won't have a detectable imp. Very small compared to the Solar System, but potentially useful for short-range orbital detection. $\endgroup$ – Eth May 9 '18 at 16:17
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The best two sources on the internet for discussions on Space warfare are the "Atomic Rockets" blog http://www.projectrho.com/public_html/rocket/index.php and "Rocketpunk Manifesto" http://www.rocketpunk-manifesto.com. I might also throw in the Unwanted Blog http://up-ship.com/blog/ for a bit of out of the box thinking.

While you can spend hours parsing the details of various systems and ideas, there are a few fundamentals about space warfare that Hard SF will have to take into account:

  1. There is no stealth in space. Since the background is so cold, any energy emission from the ship will stand out like a bright beacon. Even refrigeration will not help; the refrigeration unit must eject the waste heat. Ships will not only emit thermal radiation, but most practical spacecraft capable of operating in deep space will need nuclear energy (fission or fusion) to power their systems, which means they will also be emitting neutrinos. Even hiding behind a planet won't block neutrino emissions from the spacecrafts power source.

  2. Space is really, really big. So you can see the enemy Stardestroyer from the edge of the solar system? What practical steps can you take? Firing a missile, torpedo or even a Ravening Beam of Death isn't going to help; it will tai anywhere from hours to years for a weapon to cross the Solar System. By that time the target will have moved, the political situation may have changed and any number of systems failures may have disabled the weapon. In a practical universe, most engagements will probably be limited to one light second (just under the distance from the Earth to the Moon) so the targeting systems can acquire the target, take a shot and adjust based on the results.

  3. Practical space combat is going to be very energy intensive. Being able to "jink" your spacecraft will take a massive amount of energy, and the rocket equation will mean carrying fuel for combat manoeuvres requires even more fuel to carry the fuel...space warships will be the size of supertankers. Generating a Ravening Beam of Death (RBOD) might require a linear accelerator a kilometre long to generate an x ray frequency laser that can hit a target a light second away and deposit enough energy to do serious damage at that range. Space warships will be huge, like ballistic missile submarines or aircraft carrier size rather than X-wing fighter sized. Even missiles will become huge ICBM sized devices to accelerate their busses and warheads to as high a speed as possible (the ultimate weapon would be a missile travelling at relativistic speed, which would be essentially impossible to spot, coming right behind it's own light cone, and delivering tens of thousands of Gigatons of energy on impact).

  4. Successful space combat means filling the sky. Filling the sky with sensor drones in a one light second diameter array to get fine grained 3D targeting information. Filling the sky with tens of thousands of coke can sized "Soda Cans of Death" (SCoD) kinetic weapons. Filling the sky with laser energy (the higher frequency the better) to take out the carrier ships with all the kinetic warheads and sensor drones, and the various drones, missile busses and SCoDs as well.

Space warfare will not resemble air or sea combat at all. On the Rocketpunk site, one description of space warfare was a majestic unfolding of a "constellation" of ships and systems, much like a mobile Vauban style fortress. If you use different starting assumptions, you may end up with a different outcome.

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  • $\begingroup$ 1. Refrigeration can work; heat can be removed from the hull material by conventional means, then exhausted by means of a refrigeration laser. Such a technique would require energy from the ship's reactor, but is definitely feasible. Regarding neutrinos, those are already basically everywhere, and we have a terribly difficult time catching them anyhow; I don't see those being a viable sensing tool. $\endgroup$ – AmoebaMan Jun 20 '15 at 3:46
  • $\begingroup$ 2. We're talking about sensing in a military context, which means within ranges of efficacy. And in all likelihood, standoff distances would be much smaller anyway; relativistic-speed projectiles seem nice on paper, but I don't see them being practical for a number of reasons. $\endgroup$ – AmoebaMan Jun 20 '15 at 3:49
  • $\begingroup$ 3. Do not make the mistake of discounting the utility of small craft. A single motorboat can destroy an entire armada if it's not prepared to defend against such a threat. Yes, incredibly powerful brute-force weaponry would be massive, but lighter tools applied intelligently can be just as effective and much more efficient. $\endgroup$ – AmoebaMan Jun 20 '15 at 3:53
  • $\begingroup$ All of your speculation is just that; speculation, and it is so because you failed to address the very first point properly. I chose this topic because it's probably the most important; how you see dictates how you fight. You also need to consider countermeasures; I may not be able to hide from thermal scanners, but I can easily and instantly defeat any sort of thermal tracking by releasing IR smoke and turning my own backdrop hot. $\endgroup$ – AmoebaMan Jun 20 '15 at 3:57
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    $\begingroup$ A refrigeration laser is essentially a very powerful point heat source. Unless you have 100% certainty of where every enemy sensor is, you won't be able to keep the beam out of view. Small "motorboats" or even SCoD's" are still highly visible; if a weapon can target you at 1 light second, you will never get close enough unless you overwhelm the target with 10's of thousands of weapons, The speed of light is absolute; crossing the solar system at "c" takes 8 hours. And a constellation of sensors 1 light second across will see "around" a smoke cloud. Inside the cloud you are blind. $\endgroup$ – Thucydides Jun 20 '15 at 12:22
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Cosmic Rays

Or rather, the absence of cosmic rays.

A target of any considerable size is likely to be shielded from cosmic radiation. If your targeting system can sense the field of cosmic radiation, and then see a "hole" in that radiation, then you have a potential target. Naturally, you'd probably want some other targeting system in addition to this, to help distinguish friend from foe from asteroid.

Countermeasure

Periodically drop your shielding, or rotate your shielding through different parts of your ship. Or perhaps drop your ship's shielding altogether when battle becomes imminent, and put your crew up in shielded suits, to reduce their footprint.


Note that I am not an astrophysicist and this may all be junk science. I have not done deep research to see if this is plausible, nor do I have the time right now. Please feel free to correct me if this isn't a practical answer.

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  • $\begingroup$ A good solution, but incomplete. Silhouetting is good for getting a location, but it's imprecise and not good for precision targeting. If you need to hit a particular weapon emplacement on a flagship, a silhouette won't much help you. $\endgroup$ – AmoebaMan Jun 20 '15 at 4:00
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Might be considered necro-posting, and there has been an answer accepted, but this is my favourite subject, so here goes.

Sensing(finding the location of the enemy) and target acquisition(getting the information needed to shoot) can and should be regarded as different matters. As others have remarked there is no stealth in space. And that is true, in general terms. But as any military theorist knowns there are levels of stealth, and all can grant a significant advantage.

So while there are no effective countermeasures against long range observation - aside from pretending to be someone you're not - there are a number of methods for both detection and stealth. I'm talking about while the spacecraft is actually in combat. You will have incoming projectiles that are trying to hide, and active homing ones will be countered by incorporating stealth and countermeasures into the ship.

Radar is pretty simple. Make missiles and KE projectiles have a minimal RCS to make them hard to shoot, and cover them with radar absorbing material. The ship will want to disrupt radar used for ranging, as without that information an accurate intercept is difficult. Also, if the ship can hide its orientation the incoming missiles cannot predict the direction it is about to accelerate. The missiles could also use radar decoys like those used by ICBM warheads.

Thermal is much the same. KE rounds could be supercooled before firing, and are small enough to make them almost invisible in practical terms. Missiles could be cooled by compressed gas, use cold gas RCS thrusters, and have a large 'skirt' of cooled material blocking the target's view of the missile's incandescent drive plume. For hot projectiles thermite charges could be deployed at the larst second as a destruction.

Then there is the option to blind sensors with lasers or particle beams - even at ranges where they cannot cause structural damage they can burn out receptors. A nuclear detonation could dazzle sensors, as could reflected sunlight. A spacecraft close to the sun(between the sun and its target) is harder to spot with visual and optical equipment, as would its projectiles be. I think it even disrupts radar to some extent, but I'm not sure. Just remember that space is big and spacecraft are small. At multiple tens of kilometres per second closing velocities even a small inaccuracy will result in a miss. So while there is no 'stealth' as we think of it, there is a lot to incorporate into any SF story.

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Another take on the Gravity answer - If we're talking about the far future "anything is possible" sort of scenario.

Since everything emits gravity, a wide-ish array of ridiculously sensitive gravity sensors may be able detect all mass-having objects within a particular range. If they are sensitive enough they'd be able to make out movement, shapes and mass-distribution of individual objects to tell the difference between warships and rocks.

And if you think that it would be impossible to invent sensors that sensitive given gravity is such a weak force, think of things like blu-ray discs and microchips, examples of things capable of manipulating unfathomably tiny scales.

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one of the issues is we're attempting to describe something that doesn't exist so the only thing we have to fall back on is what we know.

Stealth technology as we know it at our now cutting edge relies on either building vehicles with specific shapes to trick radar, reducing heat emissions to fool thermal imaging or using camouflage systems that mimic how digital information is captured and displayed, or a combination of all 3.

Slightly less cutting edge technology is reflective chaff and flares to confuse local radar and heatseeking weapons.

What we can do from looking at these real world examples is see that depending on the sensors being used, knowledge of how they work helps you understand how to counter them. Like hunters standing down wind of prey for example.

So you want to find a spaceship where do you start looking on the visible (to us) spectrum, infra red, ultra violet? Does it use chemical propulsion? Does it emit radioactive isotopes and so on. You'd build up a profile of how that ship would be expected to appear across a range of tests that would make it stand out from its background. What if you made a projector that could emit random elements that didn't fit that pattern? Or could emit patterns typical of neardby asteroids or other space entities, the technological equivalent of rubbing yourself with dirt so you don't stand out from the background - would that be describing a cloaking system?

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