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I think this article passed me by...
http://www.thespacereview.com/article/3343/1
Anyway, seems quite a thorough treatment of the subject and comes up with a figure of $240 per kg for BFR for Earth to Mars. The marginal cost of the return trip would presumably be less...but that's possibly open to debate. But certainly on these sorts of figures, all sorts of trade possibilities open up.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Return fuel is much more expensive than earth fuel, which comes out of a hole in the ground. Ditto oxidiser which can be separated from earth atmosphere quite easily. So every extra kilogram on the return journey will cost a great deal of money in extra propellant production and increased capacity, and therefore size and mass, in the fuel production plant, the power plant and the propellant and other flight costs for shipping these to Mars in the first place.
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There's no logic to that. Once you have a robot propellant plant up and running on Mars, you are into marginal cost theory. The plant is already there...are you going to charge yourself $1000 per kg just to make a point? Or you going to say - "Let's look at the marginal cost of usage." Of course if NASA want to use your propellant then maybe you would ask for a much higher figure, a retrospective capital contribution.
This is highly relevant because of course Space X is prepared to put that robotic plant up there on Mars out of its own pocket.
Return fuel is much more expensive than earth fuel, which comes out of a hole in the ground. Ditto oxidiser which can be separated from earth atmosphere quite easily. So every extra kilogram on the return journey will cost a great deal of money in extra propellant production and increased capacity, and therefore size and mass, in the fuel production plant, the power plant and the propellant and other flight costs for shipping these to Mars in the first place.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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If you leave a tanker ship behind to act as a storage unit and provide pumps and crogenic pipework and hoses sufficient to get the stored fuel to the returning ship over a distance exceeding the range of rocks and sand thrown up by the exhaust. It will be a while before we have a couple of well constructed pads suitable for launching a BFS and a huge supply of water for cooling.
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