My setting is more Space Opera than science based, but I am attempting to keep a consistent set of rules for space travel. I'll try to narrow down my question to a "lowest denominator" for the benefit of Worldbuilding–SE.
In an otherwise unpopulated solar system, can I detect the arrival of another spaceship? I'll have a variety of engine types in my story, but I'll omit their specifics for this question and ask that you imagine "common" sci-fi tropes.
My constraints are:
- Detection within the solar system only (in Star Trek they inconsistently "scan" ships that are light years away in other star systems. That seems ridiculous even for space opera)
- All engines are "noisy". There is no special stealth technology. This one is braking from FTL and probably the noisiest it will get. Decelerating from interstellar speed to in-system speed takes days from the point of view of the traveling ship, longer from the point of view of an outside observer. (Traveling star-to-star takes weeks, if not months).
- Ships range in size from cargo freighters to battleships. Compare roughly to modern ocean ships plus space engines. (The ship I need to detect is a military destroyer, not enormous like a colony ship, but large engines and heavy armor)
- The "listening" ship is in the inner solar system orbiting the star. I have made no decisions about the composition of the solar system other than it is uninhabited.
- The scenario is a one-on-one showdown between two ships. The "listener" has arrived early and is actively attempting to detect the other ship.
As you see, I am aiming for making it easy but I leave the method of detection open. I realize that asking if something is "possible" in Space Opera isn't a valid question, but what method(s) can I use to detect the ship?