Mikko wrote:
kirjoitti:

Mitch wrote:

Should this not allow for much greater payloads to be
carried since less fuel is needed to get up to 30,000 ft?



Not *much* greater payloads.

There is an improvement. The spacecraft can be smaller, or deliver a
slightly larger payload, or get into orbit in a single bound.

But 30,000ft and, say, 600mph isn't much of a boost. It's a long, long,
long way from orbit. The difficulty of getting to orbit is better
described by "17500 miles per hour" than any figure of altitude.


Why is that speed needed?

To stay up there. If you're going into orbit, you need lots of
horizonta; speed (the 17,000 mph, in fact) to get the centrifugal force
that holds you up. Otherwise, you just come falling back down again.

Only thing I can think is, that since earths gravity effects the craft
whole time, the longer it takes, the more gravity will "drag back" the
craft?

Yup, that's right.


But also gravity gets smaller when you get more away from the earth?
How high does one have to go to have only half of gravity?

It doesn't change that much. The distance from the center of the earth
must change by the square root of two -- 1.414 to reduce gravity by
half. That's 41 % of 4000 mi, or 1600 miles. Low earth orbits are only
a few hundred. Anyhow, even if you cut the gravity by half, you'd still
need speed to stay up there. Even the moon, as far away as it is, moves
at some 2000 mph.

Jack