Stealth in Space: There ain’t no stealth in space.
This applies especially to lighthuggers, inasmuch as an antimatter torch at high burn can be detected for light years even if you’re not the star system that it’s pointed at. If you are, all the more so. Much the same goes, at least for the destination system, for even the best-collimated of the launch lasers starwisps use. Any way you look at it, there’s no way to be subtle when engaging in near-luminal travel.
But it applies to everyone else, too. Even small reaction-drive burns – and vector-control drives of similar energy consumption – are bright enough to be seen most of the way across the system, and more to the point, the heat of operating life-support systems for biosapiences – or even the waste heat for the minimum technology needed to support digisapiences – stands out like a searchlight against the 3K sky background.
It’s not impossible to manage a degree of sneakiness. It involves making use of thermal superconductors to capture your emissions in most or even all directions, and heat pumps (which, let us not forget, generate even more heat which you have to then capture) to capture them in heat sinks – which will fill up and roast you if you keep it up for very long, so be careful about how long you need to use them. It involves making maximum use of cover – cold objects in space to hide behind, and hot objects to hide in front of, while being careful not to visibly occult anything, and always pointing the right bits of your ship in the right direction (observer-dependent, so best hope the system’s not busy). It involves limiting your propulsion to careful use of (hideously slow and inefficient) cold-gas thrusters and leveraging vector-control to get a tow from other ships or celestial bodies (in which case, being careful to ensure that you keep your effect on their apparent mass below the threshold that will trigger alerts in their engineering department or your target’s paranoid skywatching AIs.). And, of course, essentially none of this will help if someone happens to look out the wrong window or point a telescope in the wrong direction and spot you visually.
But it’s difficult and constrained enough – especially since you have to enter systems via the choke-points of their stargates – or suffer the above lighthugger problems – that it’s usually much easier to pretend to be something other than what you are, or bury yourself inside an asteroid big enough to act as a decent thermal sink, or get an insider agent to plant a You Can’t See Me data worm in their traffic-control systems, or otherwise engage in some kind of tactics that are more masquerade and less outright stealth.
(The ontotechnological engineers are working on – well, technically, working on the possible theory that might just possibly begin to underlie the engineering principles of – an actual bona-fide cloaking device that bypasses at least some of these difficulties. Still some awkward implications from physics, though: firstly, it’s inescapably double-blind, so while no-one can see you, you can’t see out either. The possibilities for things to go horribly wrong for you while you can’t see them are… large. Secondly, it involves basically hiding behind the domain wall of your own personal baby universe, possibly the only thing that does retain heat with 100% efficiency, which is to say, it actually makes the heat dissipation problem worse. Better have really good heat sinks, or you’ll cook yourself to death in really short order… and then release all that heat in a nice position-illuminating flare anyway.)