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ROBOT EXPLORERS 69

ibly harsh: Temperatures can change rapidly from hundreds of
degrees (in direct sun) to nearly absolute zero in shadow. A constant
sleet of charged particles and radiation strikes the spacecraft, and
it can be suddenly augmented by solar flares. Here on Earth, the
atmosphere protects living things and machines from most of these
effects, but materials used in spacecraft and space robots must be
specially selected and “hardened” in order to survive in the hostile
environment of space.
Space probes must also endure the shock of liftoff from Earth and
survive a journey of tens or hundreds of millions of miles. Probes
intended to visit the surface of a planet will undergo what will at
best be a bumpy landing. Although some redundancy (development
of duplicate or backup systems) can be built into the spacecraft
design, this can only go so far. Weight is the main constraint: Every
additional pound or kilogram means the launching rocket has to be
bigger. A related constraint is cost—particularly in the modern era,
in which NASA’s budget has greatly declined from the triumphant
Apollo days of the 1960s.
The engineers on Shirley’s team thus had to make hard choices.
For example, could they afford the weight and cost of a backup
radio transmitter? If the main transmitter failed, having a second
one might ensure that the space probe could send back at least a
portion of the planned pictures and instrument readings. Or should
the money and weight allowance be used instead to improve the
landing system (increasing the chances of a safe touchdown) or per-
haps to allow a rover to carry an additional scientific instrument?
As an engineer and designer of space probes, Shirley became
familiar with the need to make such trade-offs. But as her manage-
rial responsibilities increased, so did the challenge in getting highly
opinionated scientists and engineers to work together effectively.
Each instrument on a space probe, lander, or rover represents a
capability that someone has probably spent years working and
planning for. Theoretical scientists generally want the biggest and
best instruments possible, seeking always to see or sense farther.
Engineers, on the other hand, want the system to be as reliable as
possible. They know that unlike laboratory experimenters, they will
have no opportunity to try plugging in a different part once the mis-
sion is underway.