Originally posted by Pragmatist:
dehammer,
You forget its still got to be 'boosted` onto
the orbit for the trip.
Actually, you could use water, (also usefull
as reaction mass for decelleration with some
drive systems, or drinking, or needed when you
finally arrive), but you've still got to push a heluva lot more mass on a manned trip and that either costs energy or slows you down a lot.
We're probably stuck with robot probes for the
near term.
Pragmatist
why do you have to boost an object into space that is already there.
nasa has plans they hope to realise, that involve using an electomagnetic rail on the moon to "boost" a rail cart carrying a payload to a specific speed, then release it. the cart would then decelerate along the same rail, while the payload would continue to move along the same trajectory. once it was high enough it could use several methods to alter its course (including solar sails) to take it to the desired destinations.
the same sails could be used to alter the course of near earth objects, enabling them to become captured by the earth's gravite with no or little risk of hitting the earth. with gravity in the micro range, most of these would enable ppl to mined them, meaning little or no matterial would have to be boosted from the earth. only the energy to change orbits would be required. some of that could come from the asteroid or the sun.
once the ship was ready to go, it would be possible to alter its course with solar energy.
i forget where i saw it, but there was one suggestion that it we should not actually build a star ship before we launch it. the reason, if we use solar sails or something like it, plus gravity slings (simular to the way the saturn probe that recently arrived there was sent) it would take close to a decade to get the ship fast enough to leave the solar system. during this time, it would pass near the earth several times.
this proposal involved sending a small probe to a moderate size near earth asteroid, with a solar sail. a ship would be built near the earth at the same time, a bit larger than a 747 with a solar sail propulsion system. when the object was closeing on the earth, the shuttle would begin making several trips between the earth and moon, using their gravity to boost the speed up to where the shuttle could catch the asteroid. once they had caught it, they would stablize it into a spin, then they would begin to mine a living area. once it was capable of surviveing on its own, they would send the much lighter ship back to the earth. this would continue for sometime as they made the ship more liveable. just before it became fast enough to leave the system, the shuttles would make a last trip with the last of the ship crew.
ive not been able to find this on the net, and even then questioned his math, but according to this theory, it would be possible to send a ship to another star that would reach about half light speed this way. he also claimed that in 1970's dollars it would be cheaper to build and send this ship than the space program cost to send a man to the moon.
unfortuantely, your right about the near term.