Hubble doesn't "visit" celestial objects it never leaves
its orbit it does need to point itself to different directions
to see different objects. But there are no rockets on Hubble, because
rockets would fill the space near the telescope with contaminating jet
Therefore, Hubble uses some very basic physics to turn itself around
and look at different parts of the sky. Located on the telescope are
six gyroscopes (which, like a compass, always point in the same direction)
and four free-spinning steering devices called reaction wheels.
The gyroscopes sense when the telescope needs to be repointed. When
they "tell" Hubble that it needs to turn itself, a computer
gives a command to give the reaction wheels a "push" or "spin."
According to Newton's Third Law of Motion, every action has an equal
and opposite reaction. Therefore, as Hubble accelerates its reaction
wheels in one direction, Hubble's reaction is to rotate in the opposite
Since the rotation axes of the four reaction wheels point in different
directions, Hubble is able to use combinations of them to point itself
toward any location in the sky.
through the underside of the telescope's midsection.
Hubble can make an observation, it must find a pair of "guide stars"
located alongside the observational target. To find these directional
beacons, mission planners refer to an immense catalog containing the
sky "addresses" for 15 million stars.
Hubble's Fine Guidance Sensors its "targeting" devices
help aim the telescope by locking onto those guide stars and
measuring the telescope's position relative to the target.