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Handling and Contamination Control for Critical Space Applications 303

or changes in absorptivity of a thermal control surface, which will eventually reduce
its effectiveness and cause loss of performance. It is necessary to minimize contri-
bution to spacecraft contamination through outgassing product in modern MEMS
packaging materials. All nonmetallic materials should be selected for low
outgassing characteristics and baked out in meeting their outgassing requirements.
The thermal vacuum bake is an effective method to assure that outgassed
materials have been removed. Generally, the hotter and longer the item can be
baked, the better the chance that the item will not contaminate the chamber or test
article. Space flight hardware are typically baked at 508C or higher, under 5 10 6
torr vacuum environment for at least 48 h unless otherwise noted. Visible degradation
of the material during bakeout will obviously result in the rejection of the material.
Some materials must be qualified for use by monitoring the outgassing levels during
the bakeout. The use of MSFC-SPEC-1238 14 is recommended for critical optical
applications. Bakeouts of MEMS devices are required unless it can be satisfactorily
demonstrated that the contamination allowance can be met without bakeouts.
MEMS devices operated on-orbit require proper protection from various
contamination sources. Plume impingement poses a great threat to MEMS devices
with both thermal heating and contamination degradation effects. Propulsion sys-
tems and attitude control systems are major contributors to plume contamination.
Plumes contain particulates that may be impinged on the exposed surfaces. For
example, solid rocket motors emit Al 2 O 3 and gaseous HCl, H 2 O, CO, CO 2 ,N 2 , and
H 2 . The shuttle Orbiter and International Space Station may also release water
vapor and ice particles along with gases leaking from the pressurized cabins. 15 To
warrant proper on-orbit operations, it is necessary to protect MEMS devices from
plume impingement. The protection is attained by a combination of mitigation
methods including placing plume shields, optimizing thruster operations, or install-
ing active decontamination devices.

13.6.6 CONTAMINATION CONTROL ON SPACE TECHNOLOGY 5
The Space Technology 5 (ST5) mission, as part of NASA’s New Millennium
Program (NMP), is a technology demonstration mission designed and managed
by NASA Goddard Space Flight Center (GSFC) that consists of three nanosatellites
flying in Earth’s magnetosphere. A thermal management method developed by
NASA and JHU/APL as one of the demonstration techniques of variable emittance
surfaces is a MEMS-based device that regulates the heat rejection of the small
satellite. 16 This system consists of MEMS arrays of gold-coated sliding shutters,
fabricated with the Sandia ultraplanar, multilevel MEMS technology fabrication
process, which utilizes multilayer polycrystalline silicon surface micromachining.
The shutters can be operated independently to allow digital control of the effective
emissivity.
For variable emissivity radiators the concerns of contamination and
handling drove the packaging design. The shutters open only 6 mm by 105 mm
with a concern that a small particle can lodge in the devices within the hinges of
the MEMS shutters and prohibit movement. Placing a protective window over the

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