Refueling depots

At first blush, it would seem that lifting fuel out of the Earth's deep gravity well wouldn't offer any advantages.

However, if you had a reusable spacecraft, like a Falcon 9 Reusable, it could start to make sense.  That would imply, however, that costs could be brought down sufficiently.

According to the Wikipedia article, the cost target for a Skylon is somewhere between 400 to 500 bucks per pound.  As for Spacex, Elon Musk once said that he believed he could get costs down to 500 bucks a pound.

Now, if you were to use one or the other, for a relatively small price, you could get a substantial amount of fuel positioned in LEO for less than 100 million bucks.  Perhaps with some intelligent planning, you could do a lunar landing mission and return with that much fuel.

Take the Apollo missions.  The S4B rocket wet massed at about 250k pounds.  This rocket could deliver 100k pounds to a lunar trajectory that had all the mass needed for the landing and return.  Thus, to deliver 230k pounds at 500 bucks per pound, the cost of fuel for the similar mission would be $115,000,000.  Make everything reusable, and the numbers get lower ( because of lower mass requirements).

If everything were to be made reusable, the fuel costs would become the primary costs of the mission.  That would mean regular visits to the moon for a little over 100 million per pop.  Not bad.  Especially since every Shuttle launch was said to be about a billion bucks.

Not only that, but a trip to Deimos wouldn't require much more in fuel than a lunar landing trip.  Maybe even less.  Since Deimos may have a lot of water and carbon, there is the possibility of making a fuel depot there for subsequent Mars landings.

Reusable launching craft could enable fuel depots.  It would seem to make a lot of sense to do this, so you have to wonder what the delay is all about.