I suspect it might be less easy to detect really stealthy stuff than what you are saying. While TODAY modern RAM and geometry cannot, for example, shield against S-band radars too well, the B-2, because it is entirely tailless actually doesn't show up on S-band much at all (the F-22 and F-35 do, quite well actually). So, I'd expect that by 2300 AD or whatever that we'd have pretty good stealth! Of course things like 'quantum radar' are likely to mean it will be a contest between sensors and stealth, much like it is today in the naval and aerospace regime. I guess positing that the sensors won that contest decisively is a defensible extrapolation. Still, I think it is likely to be quite possible to have small, stealthy, 'things' that can come at an opponent and get pretty close before detection. A lot of this will likely be due to the fact that active sensors basically broadcast your location, so their use will be pretty limited. Even today in an actual all-out battle ships and aircraft try to rely on passive detection until they make contact with, or are pretty sure about, the existence of an opponent within firing range that they want to attack or must defend against. Only large units that presumably cannot really hide, like carrier battle groups, would be constantly running search and fire control radars, as their general location is probably well-known already.
In space, I'm curious how you go about masking your heat?
Well, look at JWST, it has a 'cold side' and a 'hot side'. So, a hot radiator located in a parabolic dish on the 'hot side' of your spacecraft can dump heat in a direction that HOPEFULLY doesn't contain any hostile sensors (guess what the other side wants to do). A maser or something might work, obviously what you can do is going to rely on tech speculation. Traveller already assumes some rather fanciful advances, so how you deal with that seems open to speculation. This is also ANOTHER reason you would probably like to put your 'hot stuff', like powerful active sensors, somewhere else besides stuck to the hull of your spacecraft.
Even empty space is filled with radiation at 2.7K... There's really no such thing as a situation where there isn't a 'noise floor', and if you can, even temporarily, be down right near that noise floor, then you WILL be hard to detect! Obviously coming out of the Sun might be one tactic, and maybe other celestial bodies would be similarly useful.
So basically the opposite of Classic Traveller Book 2!
Yeah, well, that's what I have been saying. While Traveller's space combat system is somewhat of a 'hard science' kind of thing, compared with most other similar genre material, Marc is not IMHO knowledgeable about these sorts of things. The system is intended to 'feel' hard, but also present a simple game where the action is explained in terms familiar to likely actual players, and centers on the PCs.
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Bluntly, CT Bk 2 is a minis game first, and a physics sim only in the movement phase, and that even being very low fidelity, as there's almost infinite delta-v...
Well, Traveller's ships were never very realistic in the larger sense. There's no realistic simulation of the elements of mass/energy/momentum which go into the rocket equation that dominates all else in the real world. On day one Marc simplified non-jump space travel to an extremely simplistic rule of thumb that doesn't even come close to working. It serves the RP purpose of describing what people think space travel in the far future might be like, and that's all. So when it came to space combat, what could they do? Realism already didn't fundamentally exist in the description of the ships and their function! Anyway, realistic would mean a lot of number-crunching and trying to visualize everything in not only 3D but Hamiltonian phase space! Good luck with that, not even NASA rocket scientists would like to play that game.
