This picture shows the start of a servicing mission
with the launch of a space shuttle.
Hubble is designed for on-orbit servicing by
a team of astronauts. Servicing missions allow
for planned, periodic replacement and improvement
of Hubble's science instruments and other equipment.
During a servicing mission the crew maneuvers
the shuttle to rendezvous with Hubble, uses a
robot arm to place the telescope in the shuttle's
cargo bay, and then installs the new equipment.
After the work is complete, the crew sets Hubble
free and returns it to duty.
The Hubble Space Telescope's purpose is to spend
20 years probing the cosmos from the nearby planets
of our own solar system to the farthest and faintest
galaxies. Crucial to fulfilling this objective
is a series of on-orbit servicing missions. Hubble
was placed in orbit on April 25, 1990, and subsequent
servicing followed in December 1993 and February
1997. The third servicing mission has been separated
into two flights. The first of these flights,
Servicing Mission 3A, was in December 1999, and
the second, Servicing Mission 3B, is scheduled
During the December 1999 mission, astronauts
installed six fresh gyros, a powerful new computer,
an enhanced Fine Guidance Sensor, a new solid-state
data recorder, a new radio transmitter, and improvement
kits for batteries and electronics. On the next
service call, astronauts will install a powerful
new instrument called the Advanced Camera for
Surveys. This third generation science instrument
will greatly enhance Hubble's imaging capabilities.