A Radar Revolution: Space-based Radar Operating from Microsatellite Cluster Will Provide New Military Capabilities

With all its awesome capabilities, radar based on satellites
orbiting Earth does not yet detect moving targets on the
planet.

But researchers in the sensing community are working to
develop a space-based radar system with such capabilities,
though they face challenges in deploying antenna systems
large enough to detect moving targets.

A virtual antenna array, composed of multiple satellites
sharing information, is one solution, and engineers at
the Georgia Tech Research Institute (GTRI) have studied
this approach. For the past three years, they have
identified problems, developed solutions and ultimately
concluded — along with other research teams elsewhere —
that the concept has merit.

Now, the U.S. Air Force Research Laboratory (AFRL) is
planning a flight experiment, dubbed TechSat 21 and
scheduled for launch in 2006, to demonstrate a formation
of three lightweight, high-performance microsatellites.
The formation will operate together as a “virtual
satellite” with a single, large radar-antenna aperture.

Not only will the microsatellite formation find ground-
based, moving targets, it can be configured for a variety
of imaging, sensing and communications missions —
something not possible with a single, large satellite.
Missions include: precision geolocating; single-pass,
digital terrain elevation data collection; electronic
protection; single-pass, synthetic aperture radar imaging;
and high data-rate, secure communications. The benefits of
a microsatellite formation also include unlimited aperture
size, greater launch flexibility, higher system
reliability, easier system upgrade and low-cost mass
production.

“If this system works, it will be unique,” says lead
researcher Bill Melvin, a senior research engineer
in GTRI’s Sensors and Electromagnetic Applications
Laboratory. “There is no other concept like this.”

While the concept has merit, TechSat 21 is still facing
a number of hurdles, including properly timed wireless
linking between the microsatellites, methods for
calibrating system errors and reliable signal processing.
A team of four GTRI engineers, including Melvin and
senior research engineer Daniel Leatherwood, continues
to address these issues with algorithm development and
modeling and simulation studies funded by AFRL. They are
also helping with plans for experiments when the trio of
microsatellites is launched in 2006.

AFRL researchers will gather data, including measurements
to predict the system’s performance using simulation code
developed by GTRI engineers. Also, GTRI researchers are
developing algorithms for processing that data, either
in space or on the ground.

“The experiments will give us an opportunity to collect
data for an extended period of time, not just for one
day or one week,” Melvin says. TechSat 21 will provide
enough data to determine the data-sharing coherence
between satellites, the timing requirements for
communication and target detection capability, he predicts.

“Whether there is a residual military value from this
experimental system will be revealed during the
experiments,” he adds. “Pressing needs may affect its
missions.”

Experimental systems have been deployed in the past when
military needs arose. For example, during the Gulf War,
the U.S. Department of Defense deployed JointSTARS, an
airborne battle management system to conduct ground
surveillance and support attack operations. JointSTARS
detected the famous Iraqi retreat and guided the response
of military commanders in the field.

“We want to automate as many processes as possible because
the system will be gathering so much information,” Melvin
explains. “Certainly, the detection stage and switching
between modes will be automated. Of course, the user
could override the system.”

Various technological improvements are making these and
other TechSat21 capabilities possible. Advances in sensor
technology, antennas, satellites, electronics and digital
computing, as well as lighter-weight and more durable
components, are contributing.

“Because of these advances, we can implement advanced
algorithms and dream up new approaches that weren’t even
possible five or 10 years ago,” Melvin says. “Technology
is the driver of this project.”

Given that, technology has placed GTRI engineers in the
driver’s seat. Leveraging their extensive experience in
advanced signal processing and antenna modeling, they
generated results for the AFRL within a year of the
program’s onset, and AFRL responded by increasing GTRI’s
role.

“We have focused on understanding the problems and
developing suitable techniques to address them,” Melvin
explains. “Through modeling and simulation, we have
determined the best possible performance for the system
for ground moving target indication. So we know the
concept has merit.”

Only physics, not technology or research effort, will
limit what TechSat 21 can do, he adds.

“TechSat 21 is a very non-traditional approach in radar,”
Melvin says. “There are a lot of doubting Thomases in
the sensor community. So that makes it a challenge and
makes it fun. We want to prove we can do it. Our task
will be to convey to others that it can be done.”

IMAGE CAPTION:
[http://gtresearchnews.gatech.edu/images/microsat.gif (34KB)]
Rendering represents the U.S. Air Force Research
Laboratory’s proposed TechSat 21 microsatellite
configuration. A virtual antenna array, composed of
multiple satellites sharing information, could aid
military maneuvers worldwide. Georgia Tech engineers
have studied the concept, along with other research
teams. U.S. Air Force Research Laboratory Image