From: Forrest Bishop (forrestb@ix.netcom.com)
Date: Thu Jul 20 2000 - 07:32:20 MDT
Research in the 1960's-1990's on particle beams for space weaponry (Strategic
Defense Initiative) was not able to solve the problems of beam dispersion and
beam deflection (due to magnetic fields, photon pressure, solar wind). Lasers
and kinetic-kill vehicles are currently considered more feasible.
=======
Ultracold Matter Beam Generators
Abstract
The advent of laser cooling and manipulation of diffuse, ultracold matter
will find many kinds of applications in space exploration and development. Near
and mid-term possibilities include the shipment of streams of ultracold gas or
its condensate
[Condensation into microclusters would occur in free space downrange of the
launcher, in effect increasing the ballistic coefficient.]
over distances of hundreds or perhaps millions of kilometers, the formation of
artificial aerobraking corridors and beam propulsion for micro and
nanospacecraft.
Several designs for "Ultracold Matter Beam Generators" are proposed
specifically for, though not limited to, use on the Lunar surface for launching
material into space, for providing an "Artificial Reentry Corridor", and for
matter beam propulsion. Designs variants include a laser-cooled thermal jet
based on recent experiments, a laser-accelerated and cooled beam, and a
laser-cooled, neutralized ion beam based on current ion thrusters. The equipment
for a commercially viable device might be quite compact, with characteristic
barrel lengths on the order of one meter. The generated atomic or molecular beam
may have an initial launch temperature in the millikelvin range or lower. A
launch velocity of 1-10 km/sec would then give a matter beam dispersion on the
order of a milliradian or less- the central issue of propagating a particle beam
in free space. A higher launch velocity would of course reduce this dispersion.
Since its introduction in the late 1970's, laser cooling and trapping has
made some very impressive advances in fields as diverse as high-resolution
spectroscopy, atomic-transition timekeeping, atom interferometry atom
lithography reflecting and imaging atomic beams, the formation and
characterization of optical lattices, and the creation of a heretofore
theoretical state of matter- the Bose-Einstein Condensate and its associated
"atom laser". Materials used to date for ultracold atom beams and traps include
isotopes of Na, Cs, Rb, Cr, He, Ne, Ar, Xe, atomic H, and Al. There do not
appear to be any serious proposals to date to develop this class of technology
for space applications.
A reference design of one gram per second launched at a nominal 2 km/sec is
used for comparison between different systems and for feasibility studies. Two
solutions are explored in more depth, the laser cooled thermal beam and the
laser-cooled, neutralized ion beam.
=======
Example application:
=======
A ion beam source such as the 30 cm NASA NSTAR xenon ion thruster might serve
as the first stage of a neutral atom beam for small spacecraft. The cooling and
velocity leveling would require at least three separate laser systems and
associated sidebands to operate on transitions of singly and doubly charged ions
as well as neutral atoms. It may be more cost effective to magnetically divert
and discard the doubly charges species. The use of a noble element is
particularly appealing as it won't plate out onto the accelerated spacecraft.
A nominal thrust of 93 mN at 2.3 kW input power might produce a collimated
beam force of 50 mN after cooling and jet losses. A beam-propelled
nanospacecraft would consist of a pusher plate or solar sail [65], attitude
control system and payload, with or without its own rocket engine and
propellant. A single 30 cm thruster for example, producing a nominal 50 mN beam
of variable Isp (to provide a constant relative beam velocity), operating over a
100 km distance, could add a DV of about 3 km/sec to a one gram spacecraft in
about one minute. This is also dependent on the intercepted fraction of the beam
as well as the fraction of momentum transferred to the spacecraft [67], which
can be larger or smaller than unity.
========
-- Forrest Bishop Manager, Interworld Productions, LLC Chairman, Institute of Atomic-Scale Engineering http://www.speakeasy.org/~forrestb
This archive was generated by hypermail 2.1.5 : Fri Nov 01 2002 - 15:30:04 MST