Satellite systems in
space keyed to detect nuclear events and environmental gasses currently face a
kind of data logjam because their increasingly powerful sensors produce more
information than their available bandwidth can easily transmit.
Experiments conducted
by Sandia National Laboratories at the International Space Station
preliminarily indicate that the problem could be remedied by orbiting more
complex computer chips to pre-reduce the large data stream.
While increased
satellite on-board computing capabilities ideally would mean that only the most
useful information would be transmitted to Earth, an unresolved question had
been how well the latest in computing electronics would fare in the harsh
environment of outer space.
The fear had been
that high-energy particles might collide with a transistor and, by changing a
zero to a one, alter the value of an individual calculation, producing
incorrect results in what could be matters of national security or critical
environmental calculations.
The Sandia experiments
are providing insights into the effects of high-energy radiation on these
computing electronics, enabling mitigation of these potentially crippling
effects in future processing-architecture designs.
“We’re getting true
on-orbit data from a space environment,” said Dave Bullington, Sandia’s lead
engineer on the experiment taking place in low Earth orbit. “Data messages are
being sent back every four minutes.”
How it works
NASA’s “Materials on the International Space Station Experiment” (MISSE) program,
under the direction of the Naval Research Laboratory, provides opportunities
for low-risk, quick and inexpensive flight tests of materials and equipment in
space aboard the ISS.
MISSE provides
suitcase-like containers called Passive Experiment Containers to hold multiple
experiments. These are mounted by astronauts on the exterior of the ISS, thus
exposing the experiments to the rigors of space.
The seventh in an
ongoing series of MISSE flights, MISSE 7 for the first time offered researchers
power and data connections provided by the ISS from which to run actively
powered experiments.
On Nov. 16, 2009, the
space shuttle launched carrying the MISSE 7 equipment and on Nov. 23,
astronauts manually deployed these containers on the exterior of the ISS. Sandia
has been receiving data from this research payload ever since.
At the heart of these
new computing architectures are powerful yet flexible computing chips,
configurable to support different missions. These chips are called
reconfigurable field-programmable gate arrays (FPGAs).
Since these FPGAs are
reconfigurable rather than limited to a predefined architecture, their circuits
can be overwritten, somewhat the way a read-write compact disk has more
possible uses than a read-only disk. This makes prototyping easier and also
permits changing missions on satellites previously designed for other purposes.
Because new
generations of FPGAs available from commercial suppliers may not have been
fully tested for reliable performance in space, Sandia engineers help validate
device performance in a spacelike environment before the devices are integrated
into high-consequence operational systems.
Sandia, in a
partnership with Xilinx,Inc., designed the SEU Xilinx-Sandia Experiment
(SEUXSE) for this opportunity to fly on MISSE 7. SEUs, or single event upsets,
refer to electronic changes caused by collisions with a single particle. The U.S. headquarters of Xilinx is in San Jose, Calif.
SEUXSE contains
space-qualified Virtex 4 FPGA and a nonspace qualified Virtex 5 FPGA from
Xilinx. Converting the ISS power to levels compatible with the Virtex devices
are Sandia-designed power converters known as point-of-load (POL) converters.
The POL design for
SEUXSE is the first time these efficient, high-quality power converters have been
used in space.
Special algorithms
were developed and programmed into both of these Virtex FPGAs to detect and
report particle-induced errors while the FPGAs were running typical satellite
data processing tasks.
With the data
collected from this platform, researchers in future Sandia programs will know
exactly how these FPGAs and POL converters perform in the space environment and
how to design mitigation approaches into these processing routines to account
for upsets encountered in space.
A second experiment
called SEUXSE II, featuring even more recent computing components, has already
been prepared to lift off on a future shuttle flight as part of MISSE 8.
For SEUXSE II, Sandia
researchers replaced the nonspace-qualified version of the Virtex 5 from Xilinx
with an early release version of the space-qualified Virtex 5.
“Fortunately,” said
Sandia SEUXSE researcher Jeff Kalb, “the new Virtex 5 from Xilinx had a
compatible footprint to the previous Virtex 5 and we could leverage the
hardware that was designed for MISSE 7.”
MISSE 8 is expected
to launch on the space shuttle in July 2010.
When it is deployed
on the ISS, it will replace the MISSE 7 Passive Experiment Containers, which
will be returned to earth on the shuttle, allowing Sandia researchers to analyze
SEUXSE hardware after being in orbit.
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