A new space-qualified, high-power, high-efficiency, K-band traveling-wave tube amplifier (TWTA) will provide high-rate, high-capacity, direct-to-Earth communications for science data and video gathered by the Lunar Reconnaissance Orbiter (LRO) during its mission. Several technological advances were responsible for the successful demonstration of the K-band TWTA

Force, Dale A.

Peterson, Todd T.

Simons, Rainee N.

Spitsen, Paul C.

NASA Technical Reports Server

NASA Tech Briefs, April 2010 9
A new space-qualified, high-power,
high-efficiency, K-band traveling-wave
tube amplifier (TWTA), shown in the fig-
ure, will provide high-rate, high-capacity,
direct-to-Earth communications for sci-
ence data and video gathered by the
Lunar Reconnaissance Or biter (LRO)
during its mission. The TWTA is de-
signed for 20 years of operational life,
well in excess of the expected 7 years of
mission life. It is a vacuum electronics de-
vice that is used to amplify microwave
communications signals. TWTs are
needed for high-frequency and high-
power applications, such as communica-
tions from the Moon, because they have
significantly higher power capability and
efficiency than solid-state devices. Ampli-
fication in a TWT is by a factor of about
100,000. The RF power and data rate val-
ues for the LRO TWTA, when compared
with other space based K-band transmit-
ters, are an order of magnitude higher
and represent a new state of the art. 
Several technological advances were
responsible for the successful demonstra-
tion of the K-band TWTA. A numerical
model enabled manufacturing a wide-
band TWT with high power output and
efficiency leading to a first-pass design
success. A dual-anode isolated-focus elec-
trode electron gun enabled excellent fo-
cusing, which kept the power loss due to
beam interception minimal over a wide
range of voltage and current values. A
WR-34 waveguide was used for the
input/output couplers and larger,
thicker RF quartz windows, allowing op-
eration not only at LRO frequencies but
also at future near-Earth mission fre-
quencies. Furthermore, it is more robust
against mechanical shock and vibrations,
and lowers the total attenuation of the
signal in the waveguide run between the
TWT output and the antenna. An exter-
nal filter was developed to suppress the
unwanted conducted emissions from the
EPC (electronic power conditioner) to
the spacecraft bus by greater than 20 dB. 
The TWTA has successfully completed
a vigorous spaceflight qualification effort,
including random vibration testing and
cycling between temperature extremes
that the hardware is expected to experi-
ence during mission operation. Other
possible applications in clude high-data-
rate transmission from geosynchronous
communications sat ellites to Earth. 
This work was done by Dale A. Force, Rainee
N. Simons, and Todd T. Peterson of Glenn Re-
search Center, and Paul C. Spitsen of L-3 Com-
munications Electron Technologies, Inc. Further
information is contained in a TSP (see page 1).
Inquiries concerning rights for the commer-
cial use of this invention should be addressed
to NASA Glenn Research Center, Innovative
Partnerships Office, Attn: Steve Fedor, Mail
Stop 4–8, 21000 Brookpark Road, Cleve-
land, Ohio 44135. Refer to LEW-18443-1.
Electronics/Computers
K-Band Traveling-Wave Tube Amplifier 
This amplifier can be used for high-data-rate transmission from communications satellites. 
John H. Glenn Research Center, Cleveland, Ohio
A K-Band 40-W TWTA is shown here for the Lunar Reconnaissance Orbiter Mission.
Simplified Load-Following Control for a Fuel Cell System
A load-dependent voltage would be used to control a parasitic device.
Lyndon B. Johnson Space Center, Houston, Texas
A simplified load-following control
scheme has been proposed for a fuel cell
power system. The scheme could be
used to control devices that are impor-
tant parts of a fuel cell system but are
sometimes characterized as parasitic be-
cause they consume some of the power
generated by the fuel cells.
The parasitic devices can include
the following: a pump for circulating
coolant to remove waste heat, pumps
for circulating reactant gases and hu-
midifying inlet gases, an electric
heater for keeping the fuel cell stack
above a minimum operating tempera-
ture when the production of waste
heat is insufficient for this purpose,
and a centrifugal water separator. Op-
erating these parasitic devices steadily
at their full power levels would waste
power, reducing the overall efficiency
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K-Band Traveling-Wave Tube Amplifier

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