Tech Briefs Magazine - May 2021 - 36

Propulsion
High-Power Microwaves for Launching Space-Bound Rockets
Using microwaves reduces the cost of launching rockets.
University of Tsukuba, Japan

U

sing rockets to launch satellites and
people into orbit currently requires
a lot of high-energy fuel, which is 95% of
total rocket mass. Launching a pound of
payload can cost $10,000 or more, so
minimizing the total cost of launching
rockets would maximize the scientific
payloads and increase the feasibility of
space exploration.
Researchers have solved important
wireless power transmission and other
efficiency issues that must be overcome
to use high-powered microwaves to
supplement - or nearly replace -
chemical fuel for rocket launches. It is
commonly believed that a rocket re-

quires a megawatt of beam-powered
propulsion - approximately the power output of 10 automobiles - per
kilogram of payload to reach a minimal
orbit. Whether microwave transmission
is efficient for real-world applications is
an open question.
Microwave beams have been transmitted using a ground antenna that is
the same size as a rocket antenna. Practical applications will require a large
ground-based transmitter and a small
receiver on the rocket and thus, variable-focus transmission.
The researchers calculated the efficiencies, at short distances, of a ground-

based microwave generator wireless
power supply that sends the microwaves
to the rocket propulsion system, receiving antenna on the rocket, and propulsion device that uses the microwave
energy to heat the rocket propellant.
Researchers can now put numbers on
how efficient variable-focus transmission
is at present.
Future research will study and improve efficiencies at long distances. This
is an important next step in advancing
microwave technology to practical use in
rocket launches.
For more information, contact Kohei Shimamura at shimamura@kz.tsukuba.ac.jp.

Hybrid-Electric Plane Concept Could Reduce Air Pollution
The proposed design could reduce nitrogen oxide emissions by 95 percent.
Massachusetts Institute of Technology, Cambridge

A

t cruising altitude, airplanes emit a
steady stream of nitrogen oxides
(NOx) into the atmosphere, where the
chemicals can linger to produce ozone
and fine particulates. Nitrogen oxides
are a major source of air pollution and
have been associated with asthma, respiratory disease, and cardiovascular disorders. Engineers have come up with a
concept for airplane propulsion that
could eliminate 95 percent of aviation's
NOx emissions.
The concept is inspired by emissions
control systems used in ground transportation vehicles. Many heavy-duty diesel
trucks today house post-combustion emissions control systems to reduce the NOx
generated by engines. The researchers
now propose a similar design for aviation
with an electric twist.
Today's planes are propelled by jet
engines anchored beneath each wing.
Each engine houses a gas turbine that
powers a propeller to move the plane
through the air as exhaust from the turbine flows out the back. Due to this configuration, it has not been possible to use
emissions control devices, as they would

Distributed
propulsion

Catalyst wall
Flow-through catalyst
N2 + H2O
Electric motor

Ducted fan

Gas turbine
exhaust

NOX + NH3
Treated exhaust

Electric transmission

Power turbine

Electric generator
Small-core
gas turbine
Boundary layer
ingestion

The new design could reduce global nitrogen oxide (NOx) emissions by 95 percent. (Image courtesy
of the researchers)

36

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Tech Briefs Magazine - May 2021

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