Aerospace & Defense Technology - October 2021 - 27

RF & Microwave Technology
Solar-Powered Satellite Hardware in Orbit
A
bout 18 months ago, U.S.
Naval Research Laboratory
(NRL) engineers launched the
Photovoltaic Radio-frequency
Antenna Module (PRAM) on an
Air Force X-37B Orbital Test
Vehicle as part of a comprehensive
investigation into pro -
spective terrestrial use of solar
energy captured in space.
" To our knowledge, this experiment
is the first test in orbit
of hardware designed specifically
for solar power satellites,
which could play a revolutionary
role in our energy future, "
said Paul Jaffe, PRAM principal
investigator. " Seeing some of
the effects of key differences
between testing in space and
on the ground has definitely
been eye-opening, " he said.
" The experiment is chugging along
and continues to operate and provide a
bounty of flight data. Sometimes we
scratch our heads but that's the beauty
of science: you keep researching to understand
the results. "
Added Jaffe, " It's been exhilarating
getting to this point. While we would
have liked the moment to arrive sooner,
it's great to feel that we're making forward
progress. "
The 12-inch-square tile module is
testing the ability to harvest power from
its solar panel and transform the energy
to a radio-frequency microwave. " PRAM
converts sunlight for microwave power
transmission. We could have also converted
for optical power transmission, "
said Chris Depuma, PRAM program
manager. " Converting to optical might
make more sense for lunar applications
because there's no atmosphere on the
Moon. The disadvantage of optical is
you could lose a lot of energy through
clouds and atmosphere. "
PRAM is testing functional components
of what would be part of a power
satellite network that could transmit
energy from space to anywhere on
Earth. Since the launch, the team has
been receiving data regularly. " The
analysis to this point has shown that it
has performed well in orbit and even in
temperature data, along with
PRAM's efficiency in energy production.
This information will
The Photovoltaic Radio-frequency Antenna Module (PRAM) with a 12 "
ruler for scale. The hardware is the first orbital experiment designed to
convert sunlight for microwave power transmission for solar power
satellites. (U.S. Navy photo by Jonathan Steffen)
some cases, exceeded our pre-launch
laboratory testing, " DePuma said. The
real " wow " moment for him was when
they received the very first data package
from the X-37B Orbital Test Vehicle. " It
confirmed all our hard work had paid
off and PRAM was working in orbit and
delivering valuable data to advance
space solar and power beaming research. "
The
flight experiment enables researchers
to test the hardware in actual
space conditions. Incoming sunlight
travels through the Earth's atmosphere,
both filtering the spectrum and reducing
its brightness. A space solar system
traveling above the atmosphere would
catch more energy from each of the
sunlight's color bands.
" There's more blue in the spectrum in
space, allowing you to add another
layer to solar cells to take advantage of
that, " Jaffe said. " This is one reason why
the power per unit area of a solar panel
in space is greater than on the ground. "
The use of solar energy to operate
satellites began at the start of the space
age with another NRL spacecraft: Vanguard
I, the first satellite to have solar
cells. The current experiment focuses
on the energy conversion process and
resulting thermal performance. The
hardware will provide researchers with
Aerospace & Defense Technology, October 2021 www.aerodefensetech.com
Intro
Cov
ToC
+
-
A
µ
drive the design of future space
solar prototypes.
" We are going into our extended
testing phase and working
with others in the community
to try out a range of oper -
ating conditions, " Jaffe said.
" PRAM is successfully laying the
foundation for the next iteration
of experiments and demonstrations
for space solar. "
Given PRAM results, a next
step would be fabricating a fully
functional system on a dedicated
spacecraft to test the transmission
of energy back to Earth that
could potentially help power remote
installations like forward
operating bases and disaster response
areas. Solar power satellites
would have the ability to provide clean,
constant electricity anywhere in the
world, capable of redirecting energy
anywhere it is needed.
" If a power grid has a designated receiving
site, a potential solar power
satellite could redirect energy during an
energy crisis, " said DePuma. " A solar
power satellite could potentially function
as a national disaster resource that
could deploy additional energy during a
time of crisis. Solar power satellites
could be used internationally to support
humanitarian missions as well as support
military operations, " said DePuma.
" These are designed to collect solar energy
in space where it is readily available
and then function as a power plant
in the sky that is capable of delivering
energy wherever it is most needed, " he
added.
There is still a lot of data to be analyzed
that will be used to iterate future
solar power satellite designs. " The work
done has been extremely accurate in
predicting exactly what the module
would do on orbit, so there haven't
been a lot of surprises in the perfor -
mance, " DePuma said.
For more information, contact NRL
Communications at nrlpao@nrl.navy.
mil; 202-480-3746.
27
È
http://www.aerodefensetech.com http://info.hotims.com/79418-967
Aerospace & Defense Technology - October 2021

Table of Contents for the Digital Edition of Aerospace & Defense Technology - October 2021
