Page 94 - Modern Robotics Building Versatile Macines

74 Modern Robotics

according to what they are invested in emotionally. The research sci-
entist is often driven by the desire to learn as much as possible from an
experiment, even if this might have a negative impact on other aspects
of the mission. To the engineers who are responsible for particular
components, any risk that puts unnecessary stress on the component
is to be avoided.
Even choosing the launch date involved a balancing of risk.
If there is a four-week launch window, a launch date two weeks
into that period might allow for better final preparation of experi-
ments—but it brings the risk that if something goes wrong there will
not be enough time to fix it and still launch within the window.
On November 3, 1973, Mariner 10 launched successfully. Then,
as the craft approached its first rendezvous at Venus the following
January, one thing after another began to go wrong. The star tracker
that was supposed to keep the star Canopus lined up as a navigation
reference instead began to follow the little glowing flecks of paint
that were peeling off the spacecraft. The gyros that were supposed
to keep the craft stable also began to fail.
As Shirley offered suggestions and helped keep people communi-
cating, the guidance control team had to figure out how to maneuver
the spacecraft without turning it and possibly losing control. To
make things worse, the main power system went out. On top of all
that, the scientists had accidentally vented much of the gas that was
supposed to be used for controlling the craft’s attitude, or angle.
Finally, the Mariner team came up with a plan. The craft had
two big movable solar power panels. They decided to use these
panels like sails, using the pressure of the “wind” of photons from
the Sun to turn the craft in the required direction. This had to be
done very carefully because if the craft turned too fast the auto-
matic attitude control system would fire the jets, wasting the small
amount of gas that was left. To control the operation of the space-
craft, extremely precise commands had to be sent to the onboard
computer, which could hold fewer bytes of data than are needed to
store this paragraph.
Despite these difficulties, Mariner 10 was a spectacular success,
looping around Venus to take pictures and readings. About a month
later, the craft passed Mercury in the first of three flybys, getting
the first good pictures and data from that tiny sun-seared world.