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Microsystems in Spacecraft Thermal Control 199
densities for future science instruments and engineering equipment on board a
2
spacecraft are expected to exceed 25 W/cm . Some applications, such as higher
2
power lasers, may involve fluxes in excess of 100 W/cm . Advanced thermal
control concepts and technologies are essential to keep future payloads within
allowable temperature limits and to provide accurate temperature control.
JPL’s MEMS-based pumped liquid cooling is a mechanically pumped cooling
system which consists of a working fluid circulated through microchannels by a
micropump. Microchannel heat exchangers have been designed and fabricated in
silicon. The microchannels are 50 mm deep, with widths ranging from 50 to 100
mm. In the development stage, the heat exchangers are subjected to hydraulic and
thermal performance testing in simulated microspacecraft heat loads using deion-
ized water as the working fluid. The test data will be evaluated and used for
numerical thermal model validation. Optimization studies will be conducted using
these numerical models on various microchannel configurations, working fluids,
and micropump technologies.
The MEMS-based pumped liquid cooling is an attractive thermal control device
for future missions. It may be particularly beneficial for chip level applications as
The working fluid in the cooling loop provides efficient coupling to the hot surface
of the electronics, and the cooling loop provides flexibility in locating the heat sink
inside the spacecraft. The cooling loop provides a simple mating to semiconductor
surfaces through bonding techniques. MEMS cooling system can be easily inte-
grated with the overall spacecraft thermal control system.
Future spacecraft used for deep space science exploration are expected to
reduce in size by orders of magnitude. MEMS-based pumped liquid cooling will
be useful in resolving many thermally induced problems.
9.4.6 MEMS STIRLING COOLER
Stirling cooling, an active thermal control method, is theoretically able to achieve
the maximum efficiency in cooling. With a minimum of moving parts, a Stirling
cooler consists of a hermetically sealed capsule and a small amount of gas as its
working medium. A free piston Stirling cooler has a piston to compress the internal
gas and a displacer to move the gas from the cold side to the hot side, where the heat
is dissipated.
Stirling coolers have been applied in several space missions. The long-life
Stirling coolers, either single-stage or two-stage, are available for cooling instrument
detectors. The advancement of wavelength infrared and submillimeter imaging
instruments for space applications demand further improvement in areas of vibration,
electromagnetic interference, and temperature stability. A two-stage linear Stirling
cycle cooler has been developed for use by instruments on several Earth Observing
System (EOS) spacecraft. Stirling coolers will clearly be of use to many other NASA
programs in Earth science, astronomy, microgravity sciences, interplanetary sci-
ences, and the Human Exploration Initiative. These conventional coolers are
designed to have long mission life, high reliability, and low vibration, as well as
being small, light weight, and efficient. A typical cooler has a weight of about 15 kg.
© 2006 by Taylor & Francis Group, LLC