It'd be a lot easier and cheaper to ship from the Moon down to Earth. (That's basically the plot of The Moon is a Harsh Mistress.)
I was thinking about Mercury. If you're shipping from Mercury to Earth (or parts in the outer solar system), if it's a one way trip, you could just use a solar sail, right? Its essentially a free ride.
But if you're shipping from the Earth to Mercury, it'd be more expensive, you wouldn't have the free ride. Right?
Is there an aspect I'm missing here?
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Answer by Steven Potter
You could get some free-ness out of a trip to Mercury. As I recall, NASA used the gravity of Venus and Mercury to help get the MESSENGER probe into the orbit of Mercury so it wasn't only using fuel to get from point A to point B like we think of in Sci-Fi space travel.
http://www.youtube.com/watch?v=otF2FjpCyZk (the animation becomes a bit crowded, but you get the idea).
I would think that type of trajectory wouldn't be useful for shipping as it takes a lot longer and would probably be worth expending fuel to shorten the trip. If we were shipping materials from Mercury we probably have the technology for more efficient space-travel between planets. Perhaps having a fleet of cargo ships, departing years in advance at regular intervals before the first shipment needed to return would offset the cost of the long-haul gravity-propelled route.
My apologies to any aerospace engineer or astrophysicist that is reading this.
Answer by Rick Bateman
It depends on planetary alignment at the time of the trip. A probe leaving Mercury could slingshot around the sun a couple of times to build speed much greater than a solar sail. You would just need the fuel for that first part, and the rest is smooth sailing.
Earth to Mercury could do something similar with Venus, but the gravitational pull to sling the ship would be much less than what an Earth-bound probe would use. There is also the fuel expended to leave Earth's atmosphere and gravitational pull, both much greater than that of Mercury.
So yes, Mercury to Earth would be faster and more efficient.
Answer by Tom Lindholtz
You'd have to buy rope to tie yourself to the mast as you solar sail past the Venusian sirens. And of course, high temperature wax to make the ear plugs of the galley crew.
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