Henry Spencer wrote:
In article .com,
wrote:
Another idea, that I don't know enough about to speak to, is to drop
down into the atmosphere and then pitch up so that you fly out of the
atmosphere like a rock skipping on a pond. You're still on a sub
orbital trajectory though, you don't fly off into space, you come back
down into the atmosphere and repeat the process.

Skipping doesn't really help with the fundamental problem, that there
isn't *enough* aerodynamic lift available to stay up in the thin air where

To elaborate - aerodynamic lift doesn't work nearly as well at orbital
speeds. Gliders can get lift/drag of 40. A reentry L/D of 5 is astoundingly
good.

And as lift on average has to be the same as the weight of the vehicle,
then drag (which creates heat) has to be 1/5 of this value on average.
This doesn't change the total heating if you go deep enough to accellerate
upwards at 2G, so you can skip.
deceleration is gradual. Sure, the heating is concentrated in brief
periods, but so is the lift -- there is no net gain.

There may be gain though.
Some proposals have been to skip, and dissipate the heat over the whole
vehicle while it's back in space.
However, nobody has come up with numbers saying that this is astoundingly
good.

It turns out that shedding heat from a heatshield that's glowing white-hot
is really efficient, and other schemes tend to get a bit messy as they
have to absorb and store or radiate at low temperatures the heat.