In space, there’s nothing to anchor objects in place, so a spacecraft will tend to spin unless it can maintain its orientation with some kind of engineered system. Juno rotates like a giant gyroscope or spinning top because once it is set in motion at the beginning of its mission, it will continue rotating in a very stable and predictable way for the rest of its lifetime.

With very little to perturb its spinning motion in space, Juno’s controllers on Earth can be confident that the spacecraft’s antennas, solar arrays and science instruments are pointing in the direction they are supposed to. Mission controllers can adjust Juno’s orientation when needed by commanding the spacecraft to fire any of its 12 thrusters. The three solar arrays can also change their tilt by a small amount to help balance Juno’s spin, much like a person uses outstretched arms to remain steady on a balance beam.

The thrusters also can be used to adjust the rate at which Juno spins. The faster the spacecraft spins, the more stable it becomes. This is especially important during the engine burn that will place Juno into orbit around Jupiter.