NASA studies novel space applications for GaN
Two teams of scientists and engineers at
NASA's Goddard Space Flight Center in Greenbelt, Maryland are examining the use
of GaN to enhance space exploration.
Engineer Jean-Marie Lauenstein and scientist Elizabeth MacDonald are investigating GaN HEMTs, for use in studying how Earth's magnetosphere couples to its ionosphere - a key question in the field of heliophysics, which among other things studies the forces that drive change in our space environment.
Stanley Hunter and Georgia de Nolfo,
meanwhile, are investigating the material's use on a solid-state neutron
detector that is relevant to both science and homeland security.
GaN transistors became
available commercially in 2010, but they have not yet found their way into
space scientists' instruments, despite their potential to reduce an
instrument's size, weight, and power consumption. There's a reason for that,
said Lauenstein. Even though GaN is predicted to be resistant to many types of
radiation damage encountered in space, neither NASA nor the US military has
established standards characterszing the performance of these
transistor-enabled devices when exposed to the extreme radiation in space.
When struck by galactic cosmic rays or
other energetic particles, electronic equipment can experience catastrophic or
transient single-event upsets. "We have standards for silicon,"
Lauenstein said. "We don't know if the methods for silicon transistors
would apply to GaN transistors. With silicon, we can assess the threshold for
failure."
With the funding, Lauenstein and MacDonald
are teaming with the Los Alamos National Laboratory in New Mexico, a parts
manufacturer, and the NASA Electronic Parts and Packaging to establish criteria
assuring a GaNs-type device could withstand the effects of potentially harmful
particles produced by galactic cosmic rays and other sources.
The material could be useful in
electron-beam accelerators - comprised of GaN transistors - built to map
specific magnetic lines in Earth's protective magnetosphere to their footprints
in Earth's ionosphere where aurora occur - helping to show how the two regions
of near-Earth space connect.
"The team's research on radiation
tolerance helps us understand how to fly these accelerators in the harsh space
environment over the mission's lifetime," MacDonald said.
According to Lauenstein, these standards
will also benefit other scientific disciplines. "We need a path forward
for this technology," she said "This opens the door for others to
incorporate this technology into their own missions."
Game Changing
For de Nolfo and Hunter, GaN offers a potential solution for building a detector for imaging neutrons, which are short-lived and typically expire after about 15 minutes. Neutrons can be generated by energetic events in the Sun as well as cosmic ray interactions with Earth's upper atmosphere. The neutrons generated by cosmic rays in the atmosphere can add to Earth's radiation belt - a swatch of radiation surrounding Earth that among other things can interfere with onboard satellite electronics - when they decay. Researchers have discovered GaN can form the basis of a highly sensitive neutron detector.
"The GaN crystal could be game-changing for us," de Nolfo said.
Under their concept, Hunter and de Nolfo would position a GaN crystal inside an instrument. As neutrons entered the crystal, they scatter off gallium and nitrogen atoms and, in the process, excite other atoms, which then produce a flash of light revealing the position of the neutron that initiated the reaction. Silicon photomultipliers attached to the crystal convert the flash of light into an electrical pulse to be analyzed by the sensor electronics.
"GaN is reasonably well understood in
the photo-electronics industry, but I think we're pushing the envelope a little
on this application," Hunter said, adding that the beauty of the concept
is that it would contain no moving parts, use little power, and operate in a
vacuum. If it works, the instrument would benefit different space science
disciplines and the military in detecting nuclear material, he added.
