I suspect that the Prop is only to get to the 140Kft Dark sky Station.
The big gas bag uses solar powered Ion thrustors to get to orbit.
Much better specific impulse than traditional rockets.

The Space nuts at sci.space.tech seem to think that if the air is
dense enough for lift/ boyancy then it is too dense to go fast enough
to get to orbital velocity. The general consensus is that it takes
"impossibly" efficent aerodynamics at an unbelieveibly huge scale.

Very Very cool idea if it works.



On Mon, 24 May 2004 20:15:34 -0700, "C J Campbell"
wrote:

Nice idea, but:

1) They want to build a 6,000 foot long airship using a construction
facility permanently parked at 140,000 feet up. Might be a little tough.
They are probably right in their calculations that it would take an airship
of this size to reach 200,000 feet.

2) They want to use a solar powered electric motor with a propeller over a
period of five days to accelerate the big airship to orbital velocity at
200,000 feet. Aside from the problems of using a big paddle bladed propeller
to reach supersonic speeds, one might ponder the problem of how much drag a
6,000 foot long airship is going to produce. I suspect that the electric
motor will not be able to accelerate the airship to anything near orbital
velocity.

3) But then they want to cruise about the solar system using this same
electric motor for propulsion. For this, the airship must achieve not only
orbital velocity, but escape velocity. It would be especially interesting to
see how they get a propeller to work in the vacuum of space.