A
small team of researchers from the Johns Hopkins
University Applied Physics Laboratory (APL) in Laurel,
Md., in conjunction with NASA Goddard Space Flight
Center (GSFC), have developed a novel radiator so
small its components are only visible under a microscope.
The temperature control device, formally known as
the "Variable Emittance (Vari-E) Coatings for Thermal
Control," is based on MicroElectroMechanical Systems
(MEMS) technology employing shutters so small that
several abreast are smaller than the width of a single
human hair.
When
NASA's Space Technology 5 (ST5) satellites launch
tomorrow, one of the three overhead projector-sized
micro-satellites will be "wearing" this device on
its "skin" to demonstrate that MEMS-based technology
can be used to regulate the temperature of a satellite
or one of its instruments.
"This is the first time a fully space-qualified
device of this type has ever been flown, and the
first to be flown on the outside of a satellite," says
Ann Darrin, APL's Vari-E program manager, who explained
that the devices underwent the same rigorous tests
that all space products undergo prior to launch. "It's
also the first demonstration of MEMS technology used
to actively control temperature."
In
a 4-inch square section atop one of the micro-satellites,
tiny comb-shaped motors powered by electrostatic
charges open and close microscopic shutters to regulate
the temperature of that area of the satellite. "When
a satellite's in space, you need to keep its temperature
constant," says Darrin. "As we shrink the size of
satellites and their onboard systems, it becomes
harder to regulate and maintain a constant temperature.
By putting these devices on the outside or ‘skin'
of a satellite you can change its emissivity.
"When the satellite is facing the sun, for example,
you could cool it by closing our shutter doors and
reflecting the heat," Darrin says. "Or if you need
to absorb more heat, the shutters would open."
The 4-inch square radiator contains 36 chips, each
about the size of a single key on a computer keyboard.
Looking at a chip under a microscope, one could see
72 shutter segments, each driven back and forth by
six tiny motors controlled from the electrostatic
charge-based power source located inside the satellite.
To
protect the tiny devices from dust and condensation,
which could hinder their operation, the team developed
a unique packaging solution. They encased the devices
in a "window" using a clear material known as CP-1,
a polymer rugged enough to sit on the outside of
a satellite during space-based operations, and more
cost-effective than materials like single crystal
(clear, not blue jewelry quality) sapphire.
"Often people associate small with being frail," says
Darrin. "But our tiny shutters, which don't touch
when they close, are exceptionally strong, especially
when operating in space where there's no gravity,
weight or resistance forces to wear or degrade moving
parts."
According to Darrin, the very small, lightweight
devices could shave off numerous pounds from a micro-sat,
resulting in smaller radiators, for example, and
making the overall micro-sat more efficient and cost-effective.
APL is the principal investigator of the Variable
Emittance devices, which were fabricated by Sandia
National Laboratories in Albuquerque, N.M.
The ST5 satellites, currently scheduled for launch
from Vandenberg Air Force Base, Calif., on March
14, will provide a platform for testing and validating
new technologies. For more information about the
ST5 mission and its onboard technologies being tested,
visit http://www.nasa.gov/mission_pages/st-5/main/index.html .
The ST5 project, managed by NASA GSFC, is part of
NASA's New Millennium Program created to identify,
develop, build and test innovative technologies and
concepts for infusion into future missions.
The Applied Physics Laboratory (APL)
is a not for profit laboratory and division of The
Johns Hopkins University. APL conducts research and
development primarily for national security and for
nondefense projects of national and global significance.
APL is located midway between Baltimore and Washington,
D.C., in Laurel, Md. For information, visit www.jhuapl.edu.
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