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116 MEMS and Microstructures in Aerospace Applications

initially for microspacecraft applications in which the severe constraints on the size,
mass, and power consumption preclude non-MEMS solutions.

6.2.4 MEMS MICROSHUTTER ARRAYS FOR THE JAMES WEBB SPACE TELESCOPE
This space application represents an excellent example in which the only viable
solution is a MEMS device. Thus, without the 175 384 array of densely packed
microfabricated shutters 10,11 allowing the simultaneous selection of over 200 imaged
celestial objects, the near-infrared multiobject spectrometer (NIRMOS) instrument
would not be possible. The NIRMOS is an important part of the instrument suite for
the James Webb Space Telescope. It operates in the 0.6 to 5.0 mm wavelength range
with a 3.6 3.6 in. field of view (FOV) as shown in Figure 6.4. 11 Each individual
shutter is approximately 100 200 mm in size and subtends 0.2 0.4 in. within this
FOV. The microshutter approach has several advantages over micromirror arrays
namely, possibility of high contrast between open and closed states, interchangeabil-
ity of transmissive geometry with a fixed mechanical slit (backup solution) and
elimination of the need for flatness of the mirror surface. The MEMS microshutter
arrays are being developed for NASA/ESA by NASA’s Goddard Space Flight Center
(GSFC).

6.2.5 CARBON NANOTUBE-BASED THERMAL INTERFACE
The Hubble Space Telescope (HST) is soon expected to have its fourth servicing
mission. Installation of new and high-power instruments in the HST’s aft shroud
section is expected to generate excessive waste heat. A capillary-pump loop (CPL)

FIGURE 6.4 Scanning electron micrograph of 200 100 mm sized, hinged microshutters
forming part of a 175 384 array. The microshutter array is the enabling component for the
NIRMOS for the James Webb Space Telescope. Each SiN shutter is hinged about a torsion
bar and is rotated downwards using magnetic actuation. Once lowered, they can be electro-
statically clamped as required, to allow light from a selected celestial object to pass through
into the spectrometer. (Source: M. J. Li et al., Microshutter arrays for near IR applications,
SPIE Proceedings, SPIE Vol. 4981, 2003, pp. 113–121. With permission.)

© 2006 by Taylor & Francis Group, LLC