Best way to detect ships in space: Heat. Even just living on a spaceship produces a lot of heat, there being nowhere for it to go except out into space. Air-cooling is not an option, so everything must be radiated out.
Radars were introduced in late WWII, the previuos inexistence of this useful invention didn't stop airforces from both sides to shoot down the other side's planes. Both sides had similar tech levels. In Transcendence you can acquire (most of the time) the tech to match your opponent's tech level.
Before radar, the "targeting system" was the Mk I Eyeball. By "targeting system" I mean the system which finds your opponent. Perhaps "sensors" is a better term.
Cameras and Painting it Black:
Combat in transcendence takes place at extreme range. I would say ALL combat ships would be painted black.
Visual (actual real visual, with your eyes or cameras) detection in space is poor at best and pointless at worst. First of all, you'd have to actually watch the cameras, or have a computer do it (let's face it, even in the future asteroids look like Sandstorm gunships) Long before a ship (unless it is huge, miles and miles huge) would be in visual range it would be in either radar range or infrared range or be detectable by it's radio emmisions.
Once on UTF I brought up the question of shields and radar. If shields absord radar energy like they do lasers, then radar in space is effectively useless. If they
reflect it, however, then there is another interesting question. Are they form-fitting or round? A round object is extremely detecable on radar. But a form fiting shield could take advantage of radar deflecting angles. The existence of Stealth plate and it's description about angles leads one to belive they're form fitting.
I for one would like to not be able to see ships on the other side of planets, even if it was only on the LRS.
It would be an excellent strategic extension. Asteroid belts would then be twice as dangerous, with both ejecta and hidden enemies to worry about, and ambushes would be possible.