A small team of researchers from the Johns Hopkins
Laboratory, in conjunction with NASA Goddard Space
Flight Center, have developed a novel radiator so small its
components are visible only under a microscope. The
temperature control device, formally known as the "Variable
Emittance (Vari-E) Coatings for Thermal Control," is based
on MicroElectroMechanical Systems technology employing
shutters so small that several abreast are smaller than the
width of a single human hair.
When NASA's Space Technology 5 satellites launch later
this month, 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
"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," said Ann Darrin, APL's
Vari-E program manager. "It's also the first demonstration
of MEMS technology used to actively control temperature."
Darrin said that the devices underwent the same rigorous
tests that all space products undergo prior to launch.
In a 4-inch-square section atop one of the
micro-satellites, tiny comb-shaped motors powered by
electrostatic charges will 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," Darrin said. "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 said. "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,"
Darrin said. "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, to be launched from Vandenberg Air
Force Base, Calif., no earlier than March 21 will provide a
platform for testing and validating new technologies. For
more information about the ST5 mission and its onboard
technologies being tested, go to
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.