[gurps] Flow of passengers, cargo, fuel: TL10 hard science space background

[Onno Meyer]

Say you have a system with one earthlike world, a moon around that
world, a marslike world and a couple of asteroids. An specialized 
transport system might include:

* Winged shuttles from the earthlike world to orbit and back.
* A big orbital station.
* Short-range transfer vehicles for the flight to the moon and 
  long-range transfer vehicles for the other world or asteroids.
* Non-winged landers for the moon and the marslike world, either
  optimized or one general-purpose model.

I'm assuming that passenger flows even out - whoever goes up must
come down again, long-term migration is too low to distort that.

The same can't be said for cargo, which depends on development 
patterns. If people arrive from interstellar space, they could 
start with the orbital station and asteroid miners before the 
colonists with locally made gear go down to the worlds and moons.
If the world is a homeworld, everything has to be lifted out of 
the gravity well.

And where is the most convenient water source? If water comes 
from the world, the shuttle would lauch a payload and enough 
fuel for an OTV and a lander, the OTV would take the payload,
fuel for itself and the lander, and the lander would take the
payload and its fuel. 

If water comes from the moon, it goes the other way around. In 
a neat world, cargo and fuel flows might balance. If the moon 
exports more than it consumes, moonward flights can carry fuel. 

Or there could be multiple fuel sources. Shuttles refuel on 
the world, landers refuel on the moon, ice miners bring ice 
from the belt to the station for redistribution to the OTVs.