Laser and Microwave Propulsion System Development

[Tad Blanchard <Tad.M.Blanchard.1@gsfc.nasa.gov>]

                          S P A C E V I E W S
                             Issue 2000.28
                             2000  July 10
                  http://www.spaceviews.com/2000/0710/
            

Laser and Microwave Sails Move Closer to Reality

	A piece of science fiction has moved closer to science fact
with the recent successful laboratory tests of sails propelled by
lasers and microwaves.

	In separate tests, scientists were able to move lightweight
sails using nothing more than a beam of microwaves or a laser, a
technology that could be used in coming decades for interplanetary or
even interstellar spacecraft.

	In one test, a laser beam pushed horizontally a thin piece of
carbon-carbon microtruss fabric, a specially-designed lightweight but
strong material capable of withstanding high temperatures.  In the
other test, a beam of microwaves accelerated a similar piece of fabric
off the ground a short distance.

	"Accelerations of several times the force of gravity were
observed during the microwave tests," said Dr. James Benford,
president of Microwave Sciences, Inc. in Lafayette, CA. "In one case,
the sail flew two feet in response to the high acceleration."

	The laser test, conducted at Wright-Patterson Air Force Base
in Ohio, and the microwave test, conducted at JPL, are believed to be
the first successful attempts to propel a sail in such a manner.

	"These are really two giant steps forward," said Henry Harris,
task manager for the microwave levitation and laser experiments at
JPL. "These results would not have been possible without newly
developed ultralight, high-temperature sail materials and beamed-
energy propulsion methods."

	"These experiments are the first known measurements of laser
photon thrust performance using lightweight sails that are candidates
for spaceflight," said Leik Myrabo, a professor at Rensselaer
Polytechnic Institute who led the laser-propulsion work.

	Laser- and microwave-propelled sails, like solar sails, don't
require any propellant, relying instead on the force imparted to the
sails by photons that collide with it.  While that force may be much
smaller than what a conventional rocket engine can provide, it is
continuous, allowing the spacecraft to slowly accelerate to speeds
that would either not be possible with conventional engines or would
require spacecraft that were much heavier and difficult to build.

	A disadvantage of a beamed-propulsion spacecraft is that they
require potentially huge amounts of energy to generate even small
amounts of thrust: baseline proposals for such spacecraft call for
hundreds of megawatts to gigawatts of laser of microwave power.  By
comparison, the recent laboratory tests used about 10 kilowatts of
laser or microwave power.

	However, that high power, focused on the spacecraft, would
permit acceleration of the spacecraft over far longer periods of time
than would be possible with a solar sail, whose thrust would drop off
as the sail traveled farther from the Sun.  This makes beamed-
propulsion spacecraft a leading candidate for eventual interstellar
missions, albeit decades in the future.

	Interestingly, while beamed propulsion could make interstellar
flight -- so common in science fiction -- a reality, several science
fiction authors are playing major role in developing beamed
propulsion.  The concept of laser- and microwave-propelled sails was
first proposed in papers by futurist and science fiction author Robert
Forward in the mid 1980s.  Another science fiction author, Gregory
Benford, worked on the theory of microwave propulsion with his brother
James, who led the microwave beam experiment at JPL.  And that
microwave-propulsion experiment grew out of a report on laser and
microwave propulsion by another science fiction writer, Geoffrey
Landis of the Ohio Aerospace Institute.


Tad Blanchard                   NASA-Goddard Space Flight Center
Sr Health Physics Tech           Code 205.9, Greenbelt, MD 20771
Parallax, Inc                                Phone: 301-286-9157
A Member of the OHI Team                     Fax:   301-286-1618
            mailto:tmblanch@pop200.gsfc.nasa.gov
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