Flying a spacecraft to a far planet, millions of miles away,
takes many talented people working with very special equipment.
In planning the mission, engineers and scientists decide what
kinds of instruments ride on board the spacecraft and what kind
of information is gathered. They plan the spacecraft's journey
by making precise calculations of its path through space. The
spacecraft itself is a complex machine that must operate
perfectly in alien environments -- under conditions of intense
radiation, and extreme cold and heat. The spacecraft receives
commands from mission controllers and sends scientific data back
to Earth. A computer on board the spacecraft manages the two-way
communications equipment and controls the scientific instruments
and the other activities of the spacecraft. NASA tracks missions
using a world-wide communications system called the Deep Space
Network. Huge antennas --- some nearly as big across as a
football field --- capture the faint signals from spacecraft.
The signals carry the s