Moving Roman - Reaction Wheels

There are two systems that are responsible for moving the Nancy Grace Roman Space Telescope: thrusters and reaction wheels. They use very different methods and have different purposes. This two-part video series explores the two and the roles they play in moving Roman. See the second half here.

Reaction wheels are an essential part of moving most space telescopes. They are basically flywheels driven by electric motors, which makes them more precise than thrusters and capable of running indefinitely on solar power.  They spin to store angular momentum.  By slowing or speeding the rotation of a given wheel, changing the amount of momentum, a computer can precisely adjust how the spacecraft points around its center of mass in one plane.  With three wheels set at specific angles, a satellite can control its pitch, roll and yaw to point in any direction and then hold that position without any change.

NASA’s Nancy Grace Roman Space Telescope has added its set of reaction wheels to the main spacecraft body, or bus. Roman 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 – about the size of an extra-large pizza – weighs roughly 45 pounds and spins up to 4,000 rpm.