Paul Gilster at Centauri Dreams has been thinking about solar sails for space travel. Specifically, pointing a solar-sail vessel inwards, towards the sun, to get a massive solar thrust effect:
…the numbers on a sail one mile in diameter moving to within nine million miles of the Sun. They find that a sail of this class could achieve a Solar System exit velocity of 250 miles per second. Johnson talks about all this in miles per second but let’s switch to kilometers, which is my normal practice here. 250 miles per second works out to about 400 kilometers per second, which we can usefully compare to Voyager 1’s 17 km/sec, as Johnson does:
And here he quotes:
A craft traveling this fast would pass the Earth in four days, Jupiter in twenty-one days and reach the Alpha Centauri system in just over three thousand years. By comparison, the fastest rocket we’ve ever sent into space won’t cover the distance to the Alpha Centauri system for another seventy-four thousand years! By increasing the sail size and keeping the payload mass the same, we can see an engineering path to building a sail that could cover this immense distance in about a thousand years.
Mr Gilster gets very excited about these numbers. But I got left behind, a bit. I stopped at “Jupiter in twenty-one days.” Wait. You send a probe screaming around the sun to develop a speed that’d probably have it pass Pluto in a month… and you point it out into interstellar space? Explain to me now how you’ve just put the outer solar system into commuting distance and don’t do anything with that first? Jettison the goddamn sail and coast in. Point a laser at a deceleration sail. Unload probes as you pass. Or, the hell with it, just fire a sensor-loaded penetrator at Europa. Even if it takes a year to perform the sundive manoeuvre, even if it takes three, it’d still get there before a conventional probe launch.
Chucking sun-powered smart missiles all over the solar system sounds like fun to me.