posted on Mar, 9 2005 @ 02:39 PM
feyd rautha says:
"hehe and what if i would fire a gun from the moon directed to earth, would it hit earth one day considering it does not collide with the iss
If you fired it at the earth, it would probably miss; you'd have to fire at at a place where the Earth was going to be, which involves
orbital mechanics and a humongous gun to get the bullet into lunar escape velocity in the first place.
"how close to earth would i have to fire the bullet to bring it into earths gravityfield, and would it dissolve(because of the heat) entering the
(1) it depends on the trajectory of the Earth, but if you're still talking about firing from the moon, the bullet would have to have at least some
earthwoard vector and be closer than one of the Lagrange points. (2) Whether it burns up or not depends on its composition and the angle and velocity
it has when it enters the Earth's atmosphere.
"btw. am i right that the biggest problem with going to mars is reaching escapevelocity to go back again, from a technical point of view?"
From a plain old planetary physics point of view, getting the ship into Earth orbit would cost you the most as far as expended energy is concerned,
since Earth's orbital (and thus escape) velocity is higher than that of Mars.
The logistics of such a program would be very big, because you have to determine if you can mine fuel on Mars to get you back to Earth. This is a
toughie, because without mining either your fuel or oxidizer on Mars, you might have to have a hugely expensive set of fuel 'caches' along the way,
but if you planned on mining and couldn't get your apparatus to work, you'd die; simple as that.
But the biggest problem -- the one which dwarfs all the rest -- is building and sustaining the national or international will to do this thing.
"asuming there were minerals worthy to transport from moon to earth the transport itself would not be the biggest problem, again from a technical
point of view?"
Technically, that wouldn't be a big deal; all you'd have to do is to put your minerals into a steel can which would be launched by rail-gun into
lunar escape orbit, captured by the Earth's gravity well, and parachutes into the ocean somewhere. No costs for life support; no minimizing 'g'
forces to keep the passengers from being squashed, because there wouldn't be any; and you can pick the most energy-efficient ballistics, even if it
took six months and nineteen loops to get to the Earth, because, again, you don't have any passengers to starve to death in the can.
But even so, the energy costs for the rail gun would be pretty high, and you'd want to make sure that whatever exports you sent back to Earth were
valuable; otherwise, it just wouldn't be cost-effective.