Long cables to power plasma rockets to orbit.

On Feb 8, 11:53 am, Robert Clark wrote:
...
Theplasma thrusters I discuss and the Vasimr engine are designed to
work in vacuum. If the lightweight inflatable vacuum chamber does
indeed work we might use it to allow these advanced forms of
propulsion to be used on the sled rather than the multistage chemical
rockets now used. The advantage would be they have such high exhaust
velocities the fuel is only a small proportion of the rockets mass,
about the same fraction as is the ratio of the rocket's ending
velocity to the exhaust velocity. This means you would need a much
smaller vehicle for reaching orbital velocity.
The Vasimr engine has been called unsuitable for Earth launch because
it works in vacuum and because of the large size of the (nuclear)
power plant needed to run it. However, it may be by using the
inflatable vacuum chamber idea and eliminating the power plant and
supplying the power from the rails or cables would make it feasible
for Earth launch.

Bob Clark

Both plasma thrusters and the Vasimr engine work in vacuum. To allow
them to work in the atmosphere we might be able to use the recently
invented "plasma window". This uses a constrained high temperature
plasma to separate a high vacuum from standard pressure air. It allows
high velocity electron beams to pass through it while keeping out the
outside air. Then this might also work to allow the high velocity
plasma ions to pass through while keeping out the outside air.
Andrew Nowicki suggested this as a means to keep out the air while
maintaining the vacuum with, for example, gun launch systems which
would still allow the rocket to pass through:

PLASMA WINDOWS.
http://www.islandone.org/LEOBiblio/SPBI1PW.HTM

Another possibility might be instead to use plasma thrusters that
operate on atmospheric air rather rather than on board fuel. There are
plasma torches that are used for cutting thick steel plates that
operate on atmospheric air or sometimes nitrogen gas. These plasmas in
the torch can be formed by electric arcs or by microwave heating. They
can reach temperatures of 20,000 °K:

DEVELOPMENT OF AN INDUCTIVELY HEATED PLASMA WIND TUNNEL (THE
"PLASMATRON").
http://www.vki.ac.be/research/themes/aeros/plasma.html

Plasma Pyrolysis.
http://www.plasmaindia.com/medicalpyro.html

D.C. plasma torches.
http://www.mi.infn.it/DIP/SEZIONI/btorcia.html

This report discusses a simple microwave heated plasma torch able to
reach 5000 °C:

Simple Microwave Plasma Source at Atmospheric Pressure.
"We have developed a thermal plasma source operating without
electrodes. One electrodeless torch is the microwave plasma-torch,
which can produce plasmas in large quantities. We can generate
plasma at an atmospheric pressure by making use of the same magnetrons
used as commercial microwave ovens. Most of the magnetrons are
operated at the frequency of 2.45 GHz; the magnetron
power microwave is about 1 kW. Electromagnetic waves from the
magnetrons propagate through a shorted waveguide. Plasma was generated
under a resonant condition, by an auxiliary ignition system. The
plasma is stabilized by vortex stabilization. Also, a high-power and
high-efficiency microwave plasma-torch has been operated in air by
combining two microwave plasma sources with 1 kW, 2.45 GHz. They are
arranged in series to generate a high-power plasma flame. The second
torch adds all its power to the plasma flame of the first torch.
Basically, electromagnetic waves in the waveguide were studied by a
High Frequency Structure Simulator (HFSS) code and preliminary
experiments were conducted."
http://icpr.snu.ac.kr/resource/wop.p...042S030876.pdf

These plasma torches are not used for propulsion so do not generate
high exit speeds. However, simple application of de Laval nozzles
would allow them to be used as thrusters from the high temperatures
produced if high pressures also were produced:

De Laval nozzle.
http://en.wikipedia.org/wiki/De_Laval_nozzle

To insure the high pressures required would be generated we could use
the principle used in ramjets and scramjets. Here the air stream being
greatly slowed down generates high pressures in front of the engine
that stops the heated fuel, or air plasma in this case, from leaving
in the front. The problems with getting the combustion to operate at
hypersonic speeds in scramjets wouldn't apply in this case since the
air would be heated by electric or EM fields. Note also the limited
energy available from chemical reactions would also not apply in this
case.
Instead of ram/scramjets we could also used pulse jets. These
generate high pressure by closing and opening the intakes and applying
the heating in rapid pulses.
We would also need means of cooling the chamber walls from the high
temperature plasma. We might be able to use methods such as
regenerative cooling or transpiration cooling commonly used with
liquid fueled rockets. Here, some of the fuel is made to flow over the
inside or outside of the chamber walls to draw off some of the applied
heat. Since the amount of fuel used for the cooling in liquid fuel
rockets is such a small proportion of the fuel carried, the cooling
liquid required probably in this case as well would be low.
Another possible choice for cooling might be the swirled air
technique used in the "Simple Microwave Plasma Source at Atmospheric
Pressure" report.

Bob Clark