Re: starship-design: Vapor Trail Fuel

["bugzapper" <bugzappr@bellsouth.net>]

Engine Details

Once hypersonic velocity is achieved, an air breathing vehicle can dispense
with scoop and combustion chamber. In their place, all you need is a solid
body which will hold its shape and orientation at such speeds. Scoops lose
their functionality at hypersonic speeds, and don't work any more. The
combustion chamber becomes superfluous, for the combustion is adequately
confined by the shock front, which is somewhat harder than a brick wall. If
the vehicle is externally fueled, flying up a path which has been preloaded
with fuel, there is no particular requirement put on the vehicle at all,
except that it hold together and stay cool. A rock at hypersonic speed would
do fine: its shock wave confines and ignites the fuel-air mix it encounters,
and it will accelerate. High-tech gadgetry does it better, though.

Agile Switching

For the sake of efficiency, an adaptable engine which can rapidly respond to
its ambient environment by feeding either fuel or oxidizer on demand would
be ideal. An externally-fueled vehicle will fly through alternating patches
of air and fuel vapor, so to keep the maximum burn rate it should always be
able to feed the other.

Improving the Jet Engine

To build a faster turbojet, make it centerless. Remove the turbine shaft and
all its fans, and all the other paraphanelia until you have only the tube of
the jet housing. Hang the turbine vanes off a spinning section of the wall
of this tube, so they point inwards and back. Leave the center airflow
unimpeded. Fix lightweight magnets behind the spinning section of wall
holding your vanes, and face them with electrical coils, making it a
rotating electrical machine. Make an identical machine of a wall section in
the hot back end of the tube. Connect their wires together. The hot vane in
back is your turbofan, and becomes your generator. The cold vane in front is
your compressor, driven by being the rotor of an electric motor. Then
iterate, repeat the construction of this pair a couple more times, because a
one-stage compressor has low efficiency. Centerless means you could poke a
stick through it from front to back, in the exact center, without hitting
anything. This engine should handle higher airspeeds than any contemporary
design. Its vanes are self-centering, for they run on magnetic bearings. It
weighs only a fraction of a conventional turbojet the same size. It should
preferably be built of nonmetallic material, again decreasing the weight
while allowing hotter combustion.

Stages

The principle of iteration is well adapted to the use of hydrogen shock
tubes, by using a string of them at sucessively higher altitudes. It may
seem hopelessly complex, to try to coordinate precise orientation and timing
of several such impulse devices in free air. However, we do have these
machines which can help us with the timing of mechanical tasks, and with
aiming as well. Since the vehicle may have an agile redox engine, as
mentioned above, allowance might be made for partial failure, such as one
shock tube out of six failing to fire correctly, to have the vehicle
sucessfully reach orbit anyway.

For the fuel distribution twirling aerostat which must turn a tether
weighted down with fuel, intermediate stages of aerostatic lift may be used.
Lifting bubbles are arranged on the tether, and they can turn too. An
extension of this principle to pumping water to a downwind location, by the
way, allows the aerial transport of water for quite long distances. This may
be handy for irrigation or fighting forest fires. I said "by the way", and
you don't have to stay exactly on topic when you say "by the way".

Johnny Thunderbird