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Most space telescopes,
from NASA's Hubble to Webb,
use components called reaction wheels
to change where they are pointing.
The reaction wheels are basically flywheels driven by electric motors.
They spin to store angular momentum.
By slowing or speeding the rotation of a given wheel
a computer can precisely adjust how the spacecraft points
in one plane.
With three wheels set at specific angles,
a satellite can control its pitch,
roll,
and yaw,
and then hold that position without any change.
NASA's Nancy Grace Roman Space Telescope
has six reaction wheels,
rather than the necessary three,
to give it more angular momentum for faster pointing,
as well as complete redundancy
should any one wheel fail.
Each of Roman's wheels is 18 inches across,
weighs roughly 45 pounds,
and spins up to 4000 rpm.
As long as the solar cells provide them with electricity,
the reaction wheels can keep Roman perfectly pointed at the stars.