[golem14]

Thanks for that comment, it made me think.

Couldn't you do something like a Hohmann transfer orbit ? As I understand it, adjusting the orbits far out there isn't as demanding as one might think (you don't have to spend the same energy you took to get out there to get into an orbit. Of course, this also means you will not be able to stay in one place and continuously map the same area, but you can map all the space within a disc?

It takes decades however to finish Hohmann transfers that far out apparently.

Rabbithole: Some calculations that may be entirely wrong would suggest that a <10000lbs spacecraft might be held "in place" for 100 yrs with a small fission reactor and an indium-based FEEP drive with about 15lbs propellant.

[myrmidon]

If you circularize the orbit at 550 AU (which is costly but possible, at ~1km/s of delta-v), then you end up with an orbital period of >10000 years (to complete your whole-sky survey in one plane).

But first-- the price to get that circular orbit is steep, you end up imaging empty space for a lot of the time (no real way to "skip ahead") and your orbital speed vector makes you leave the observation cone for any interesting target pretty quickly.

In conclusion: You probably really want to stick with "one telescope probe per target system", and to give them one-shot orbits because those are cheap, reasonably fast and inside the observation cone (for your single target) for longer.