How much easier is it, to explore space from a low orbit satellite, than from Earth?

Question

Note: in this question I'm considering cost in both money and fuel terms, and looking for answers that consider both.

So we know that using chemical rockets to reach the moon, or further into space, costs hugely more in fuel, weight, and money terms, than just aiming for low earth orbit.

That raises a question - how do the fuel budgets and economics work out, if we spent fuel and money to create a low earth orbit starting point for further exploration, and bring fuel and rocket components there from earth, as opposed to doing it direct from earths surface?

(Note that if our deeper space exploration started at earth orbit, it wouldn't need to be nearly as massive as we are used to - it wouldn't need the same fuel or rocket systems, nor streamlining, nor protection against atmosphere. It could also return to earth locality for reuse by any gravity-aided route, however slow and leisurely the route, taking months or years to do so if uncrewed, reducing return/deceleration fuel delta-v needs (on crewed ships, life support on average I guess adds less weight than extra fuel to shorten the trip, so a slow return would be viable?). Equally our earth-to-orbit delivery rocket wouldn't need the kinds of crew protection needed for longer travel in deeper space. So the ships involved are very different too, which makes a big difference as well, I suspect.)

By analogy, when we climb an Everest, usually we don't try to do it direct from our hotel in the nearby town. We create a base camp, lug our gear there, and set off on our more challenging and demanding expedition from that base camp, not from our hotel.

• What are the practical fuel, money/investment, and weight implications, when the two methods are compared for space exploration?

• If a LEO "base camp" is better, are two (LEO and further out) even better, or do they hit diminishing returns?

Answer 1

Whatever is used in space has to be sent up from Earth either way. Missions that can do it with a direct launch should. For missions with greater mass requirements than direct launch can do an orbital depot may be an answer but it adds the complexity and costs of making, supplying and using the depot to that of future missions. Sending up eg the full fuel tank modules that can be assembled into a larger orbit launched rocket may not require any permanent installation.

A big pre-investment would be needed for a dedicated space depot/launch station, that will be hard to justify without demonstrating a clear need.

Answer 2

In the 50's it was widely felt that the way to go to the moon would be to first establish a space station in earth orbit. Once that was a going concern, it would be much easier to go from there to the moon. But it turns out that the cost of maintaining a space station is almost entirely added cost. Equivalent spacecraft to the lunar module and command/service modules would still have to be launched into space, along with the fuel to get you to the moon.

Fundamentally, space is very hostile and resource poor. Because space is hostile, you want to do as much prep work as possible down here where you can breathe. This means not building your moon lander in orbit. And because space is resource poor, there is little to be gained by spending extra time up there on the way to somewhere else.

Finally, consider this: Skylab was a pretty minimal "base camp". It took one Saturn V launch to get it into orbit. But it also took one Saturn V launch to go to the moon. Even if Skylab were already in orbit, the easiest way to get everything else into orbit you needed for a moon landing would be to launch it all on another Saturn V. The separate base camp just does not buy you anything.