Page 350 - MEMS and Microstructures in Aerospace Applications

Osiander / MEMS and microstructures in Aerospace applications DK3181_c015 Final Proof page 343 1.9.2005 12:53pm

Design and Application of Space-Based MEMS 343

such effects be considered in determining the environmental strength for electronic
equipment that must achieve a specified reliability goal.
Electromagnetic radiation often produces interference and noise effects within
electronic circuitry, which can impair system performance. Sources of these effects
include corona or lightning discharges, sparking, and arcing phenomena. These may
be associated with high-voltage transmission lines, ignition systems, brush type
motors, and even the equipment itself. Generally, the reduction of interference
effects requires incorporating filtering and shielding features or specifying less
susceptible components and circuitry.
Nuclear radiation can cause permanent damage by alteration of the atomic or
molecular structure of dielectric and semiconductor materials. High-energy radi-
ation also can cause ionization effects that degrade the insulation levels of dielectric
materials. The migration of nuclear radiation effects typically involves materials
and parts possessing a higher degree of radiation resistance, and the incorporation of
shielding and hardening techniques.
Each environmental factor experienced by an item during its life cycle requires
consideration in the design process. This ensures that adequate environmental
strength is incorporated into the design for reliability.
In conclusion, failure to perform a detailed life cycle environment profile can
leadtooverlookingenvironmentalfactorswhoseeffectiscriticaltoMEMSreliability.
If these factors are not included in the environmental design criteria and test program,
environment-induced failures may occur during space flight operations. Therefore, it
is recommended that at the onset of the design process, researchers identify the
operating conditions that will be encountered during the life of the equipment.

15.5.6 ELECTRICAL STRESSES
Civilian and military space missions are susceptible to corona and high break-
down voltage. Understanding the role and the potential degradation caused by these
events is important for the MEMS designer. Historically, spacecrafts are vulnerable
to corona when exposed to regimes of critical pressure during ground test and
flight. NASA has encountered this problem many times. These coronal discharge
problems have occurred many times in NASA history and can cause serious damage
among craft components. Hardware susceptibility to corona-induced damage should
be addressed in subsystem design and in test and operational procedures.
Ionizing portion of the atmosphere may subject a spacecraft to unequal flux of
ions and electrons that can induce a charge. In low-earth orbit (LEO) a
spacecraft travels through dense but low energy plasmas and the spacecrafts are
negatively charged and may charge to thousands of volts. In geostationary orbit
(GEO) there is a greater concern where biased surfaces, such as solar arrays, can
affect the floating potential. 29 Particular attention must be paid to prevent arcing to
MEMS devices if placed on the surface or skin of the satellite. Traditional ap-
proaches to assure that the surface of the satellite is conductive to bleed off charges
can be used with MEMS devices on the surfaces with a conductive plating or
coating depending on design and application.

© 2006 by Taylor & Francis Group, LLC