Tuesday, September 30, 2014

Stepping stones redux

Joseph makes an astute observation...
Well... It depends on what you're lacking. If delta-V is limited then stepping stones don't make much sense but if mass is limited, they do.
So which is it?

We can assume he's talking about limited fuel mass because you want the ship mass to be low. The premise is you build fuel stations along your route like an interstate. Eventually that must happen but would actually slow progress to a halt if attempted today.

A refuelable ship in orbit is it's own depot. The place you want a depot is at the destination so you can get back. Anywhere else is a very costly detour. A settlement trip is one way. Tourists come back. A business person could certainly build one in LEO or a Lagrange point but that's a business decision, not required infrastructure. You don't run out of fuel in space, you coast forever which is where the interstate analogy breaks down. You don't need more delta V than you need until you have a new destination... so put one in mars orbit to fill a need.

A refuelable ship has unlimited delta V from the point of departure because tankage in space doesn't require much structure. You don't need islands or stepping stones to get anywhere. Building them before a market develops is how ghost towns happen.

Will depots bring down costs? Of course, but leaving from a Lagrange point requires ship and crew to get there first. That's exactly what business people are for... to see a market and fill it.

Look at it another way... is island hopping going to be THE PLAN or will companies do what they always do... focus on their own specialty? One company will provide transportation. Another company will sell them fuel. Or rather many companies will compete to provide transportation and many companies will compete to sell them fuel. That's the real world. But no company is going to start up without customers. Fuel companies require transportation companies first. Transportation companies need customers and cargo to transport. Build it and they will come is a risky business venture.

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