re: The �Fantasy� of Propellant Depots?
It would be worthwhile for low-thrust spacecraft that require fuel to stationkeep in LEO. The depletion time of the fuel supply would have to be alot less than the operating lifetime or the mission duration of the spacecraft. The cost of the spacecraft would have to be huge as well, such that a refuelling mission is less expensive than launching an entirely new spacecraft.
Candidates include:
- space telescopes
- multiple module space laboratories
- landers for other planets & moons