To get to the moon a Lunar Transfer Orbit is required. The Lunar transfer orbit is one half of an elliptic orbit that touches both the orbit that one
wishes to leave and the orbit that one wishes to reach; the moon.
(1 - LEO)
(2 - TRANSFER ORBIT)
(3 - Moons Orbit)
Problem is, the Moon is 363,104 km from Earth. In a similar Transfer Orbit, Geostationary transfer orbit (GTO), the Shuttle can only lift four
thousand kilograms of payload; and that's 'only' 35,786 km from Earth. However, it's not over, a transfer orbit only means it touches the
destination orbit, thus when you reach it, orbital energy must be added so your orbit matches the destination orbit.
I can't touch landing on the moon. But I can touch getting back to Earth. To get back to Earth we have to loose all the energy we just gained, so the
lowest point of our Orbit around Earth, is that of LEO, our desination orbit. Essentially it is Orbits 3, 2, 1, or the above transfer orbit in
reverse. Once we reach LEO height, we have to further loose even more energy to we don't wizz back up. And then we have to loose even more energy so
we can land at the runway.
Considering it doesn't have enough fuel to reach the moon, it certainly cannot do one trip there and one trip back, that would require double the
fuel. Of course, if you really wanted to, leaving Lunar orbit, you could loose enough energy so the orbit is extremely elliptical, where the lowest
point of the orbit is lower than the radius of the Earth - like the Apollo missions. But then, you still have enough energy to touch the moon again,
and that energy has to be absorbed through the heatsink. It would burn up.
My best bet is a modified Delta IV Heavy with an additional stage or two.
[edit on 15/1/2009 by C0bzz]