[The following is an excerpt froma letter to Allen Meece]
[Updated 4 September 2002}
We have already determined that it is within our capabilities
(albeit barely) to send up a viable VBP platform without any reduction of cross
section during the ascent, so long as we can keep the starting cross section low
enough. If it is possible to create a platform that ascends with reduced
cross section then expands at altitude, and still make it sturdy, we could
increase the VBP's payload to take up the difference instead of actually
decreasing the starting volume. This could give allow us to lift as much
as three times the currently allotted payload.
If we can deploy and recover the platform more or less at will
instead of having to leave it up for months at a time, we can swap out most of
the platform with specialized payloads before every ascent. This could
open up all sorts of applications.
For instance, the smallest proposal for a manned Single Stage
To Orbit (SSTO) vehicle that I ever saw was about 40 tons GTOW, with only the
crew and supplies for payload. This would be within the capability of a
VBP designed for heavy lifting. In addition, the potential energy
difference between the ground and 20km is equivalent to the kinetic energy of
the same unit mass at 600m/s. Raising the platform to 20km also gets it
above enough atmosphere to shave another 600m/s off of the velocity lost to
atmospheric drag in the tropopause. That's a reduction of 1200m/s compared
to the delta-v required for a ground launch of the same vehicle. This
means that an SSTO specially designed to launch from the VBP could be
built with significantly less than 40T.
The "Short Ship"
The platform required to lift such a vehicle would be too
large to launch from the middle of, so the vehicle would have to be cut
loose during launch, along with most of the lift cells required to keep it
aloft. This means the SSTO would be subjected to three of the harshest
conditions of spaceflight -- temperature extremes, low pressure, and freefall --
before its crew even knew whether the engines would fire. The sudden shock
of dropping 40T of ballast would have to be countered by cutting loose that much
lift in the form of lift cells before or during the launch. But
it could be done.
We would have similar capabilities for unmanned
launches. With a bigger payload than the US Space Shuttle, the VBP could
conceivably carry paying passengers by the dozens on each trip rather than
four or five at a time. All manner of functions would be possible with
that much added payload. And with a functioning elevator we could have a
crew on the station in a few hours regardless of whether we sent up a manned
payload or not.
The "Short Ship"