Abstract—
Schemes have been suggested for transferring energy
from Earth-to-space, space-to-Earth, and space-to-space using
high-power microwave (HPM) beams. All use power beaming.
Microwave beams have been studied for propelling spacecraft
for launch to orbit, orbit raising, launch from orbit into interplanetary
and interstellar space, and deployment of large space
structures. The microwave thermal rocket, called the “microwave
thermal thruster,” is a reusable single-stage vehicle that uses an
HPM beam to provide power to a heat-exchanger propulsion
system, with double the specific impulse of conventional rockets.
Orbital missions include orbit raising and space solar power.
Microwave-propelled sails are a new class of spacecraft that
promises to revolutionize future space probes. Experiments and
simulations have verified that sails riding beams can be stable on
the beam for conical sail shapes. Beam-driven sail flights have now
demonstrated the basic features of the beam-driven propulsion.
Beams can also carry angular momentum and communicate it to
a sail to help control it in flight. An early mission for microwave
space propulsion is dramatically shortening the time needed for
sails to escape Earth’s orbit. A number of missions for beamdriven
sails have been quantified for high-velocity mapping of the
outer solar system, Kuiper Belt, the Heliopause, and the penultimate
interstellar precursor mission. For large HPM systems at
fixed effective isotropic radiated power, minimum capital cost is
achieved when the cost is equally divided between antenna gain
and radiated power. This is a driver when considering design of
power-beaming systems such as interstellar Beacons, which the
Search for Extraterrestrial Intelligence is searching for. Much of
the technical means for these applications are already in hand.
Microwave and millimeter-wave array antennas are already in use
for astronomy; sources at high frequencies are being developed
for fusion and the military. Development of high-power arrays
is needed. A synergistic way to develop a space power-beaming
infrastructure is incremental buildup, addressing lower power
applications first, and then upgrading.
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