antimatter rockets

I had the great opportunity to meet Bob Forward back in the 1980s when
I attended the 25th anniversary of Project Ozma. I was a graduate
student working at OSU's radio observatory at that time. I had
developed a fast-fourier-transform analyzer to look for SETI signals.
Anyway, Bob was working on laser light sails and also a sci-fi novel
then. I had the opportunity to meet Barnie Oliver, of Hewlett
Packard, Carl Sagan from Cornell, and Paul Horowitz from Harvard.
Horowitz had completed his own FFT analyzer in suit-case SETI, and was
working on META at that time, and later upgraded it to BETA. Oliver
and others at NASA were working on SETI in the days before it recieved
the golden fleece awards from Senator Proximire.

One of the most interesting things Bob and I spoke about was anti-
matter. Or as he liked to call it, mirror matter. I was doing
research at the Sydney Public Library, and I came across a book
popularizing his ideas in 1988 and took the trouble to read it.
Mirror Matter: Pioneering Antimatter Physics.

Bob reported that through clever arrangement of counter-rotating beams
of protons, and clever placement of magnetic and electrostatic lenses,
efficiencies as high as 5% may be achieved. Which is rather amazing.
I was aware of compact systems that were 0.2% efficient, but was
unaware of this system. One difficulty was low luminosity of the
beams, but there are several fixes to that - particularly in space
based systems located in high vacuum.

I speak elswhere of highly efficient solar collectors that convert 60%
of the incident solar energy to electrical energy. This electrical
energy can harvest a portion of the solar wind impacting on the solar
collector surface and use that has proton source for anti-proton
production.

A 3 million kilometers above the solar surface 3.4 million watts per
square meter is incident on the device. Solar wind is tremendous and
provides a ready source of protons.

http://en.wikipedia.org/wiki/Bandgap

http://en.wikipedia.org/wiki/Dichroic_mirror

In effective light is reflected totally by the system. Effective
light is admitted. Specific range of colors for EACH bandgap is
caused to fall on a bandgap matched PV device. The electron stream is
efficiently loaded through an inverter tied to a specially built load
splitting transformer. The AC voltage and current make use of over
60% of the light - and 98% of the light admitted. 2 million watts per
square meter - 2 trillion watts per square kilometer.

Each kg of antimatter requires 1.8e17 Joules of energy. At 5%
conversion efficiency this is 3.6e18 joules of energy. A kg of anti-
matter therefor would take nearly 21 days to accumulate from a square
kilometer of solar collector located 3 million kilometers above the
solar surface.

With 2% of the total energy absorbed by the system, 38% rejected, and
60% efficiently used - 34 kW per sq km has to be radiated as absorbed
heat by the system (front and back) so according to Stefan Boltzman
the operating temp of the system at this altitude is 607C.

The sun facing window has the primary dichroic film. Behind it are
chevrons with two films set at 90 degrees to one another, angled 45
degrees to the incoming light. The result, bandgap matched light
falling on the walls, coated with the appropriate semiconductive
material. That semiconductor is loaded by an inverter and then a
transformer. The entire system, consists of 20 bands, squeezed into a
thin film only a few microns thick - held in tension by pneumatic
forces.

A disk, with high temperature superconducting coils around the rim,
form two counter propagating rings of proton beams. A 20 km diameter
system with a 62.8 km long ring pair create a system that covers 314.2
sq km - and create 1 metric ton of anti-matter every 62 days. The
ring's operation also serves to deflect the powerful solar wind AROUND
the sail, in a manner very similar to the operation of the magnetic
field around Earth. This limits damage to the thin film structure by
solar wind action. However, the magneto-pause created by the ring is
mined by the system as a ready proton source to replace protons lost
by the system due to collisions. Each ton of antiprotons produced by
the system requires the capture of 40 tons of protons over the same
period. This is easily achieved by this system.

A ton of anti-matter contains 1.8e20 joules of energy. An amount of
energy equivalent to the world's annual production of crude oil. A
single 20 km diameter system described above produces 6x this amount
in a year.

The energy to lift a ton of antimatter from 3 million kilometers to
150 million kilometers along a minimum energy orbit, is achieved by
use of antimatter.

The first impulse requires 75.2 km/sec increase in speed. 67 hours 16
minutes later another impulse of 23.2 km/sec is required to
circularize the orbit at Earth. The total delta vee required is 98.4
km/sec.

A vehicle with 200 km/sec exhaust speed would require 62.7% propellant
fraction. So, allowing for 1 metric ton of antimatter, and 5 metric
tons of structure means 16 metric tons of propellant are needed. To
eject 16 metric tons with 200 km/sec speed assuming 50% efficiency,
requires 3.5 grams of anti-matter. So, very little energy is wasted
in transporting 1 metric ton in this way. The 67 hour transit time
is not a problem either, since 1 ton vehicles are loaded every 62 days
over a 314.2 sq km area.

A single station as described would provide 6x the entire energy need
of Earth. 10 such stations would power armies of automated machine
systems to transform minor bodies of the solar system - like Ceres -
into usable products.