Zero-propellant maneuver

A zero-propellant maneuver (ZPM) is an optimal attitude trajectory used to perform spacecraft rotational control without the need to use thrusters.

Spacecraft rotational operations, such as turning to point in a new direction, are usually performed by angular momentum storage devices such as reaction wheels or control moment gyroscopes.

However, momentum storage devices have a limited capacity, and that capacity soon becomes saturated when they are required to absorb spacecraft disturbance torques caused by (gravity gradient, solar wind, and aerodynamic drag); when in other words they reach their momentum storage limit.

Once saturation is reached, momentum storage devices cannot apply torque to control the spacecraft's orientation.

Therefore, if momentum desaturations can be reduced or eliminated, a larger fraction of propellant can be used to maintain the spacecraft in its desired orbit, and it will have a longer operational lifetime.

ZPM trajectories can also be used to reduce propellant consumption even when the spacecraft uses thrusters instead of momentum storage devices.

A ZPM is a non-eigenaxis attitude trajectory that exploits the spacecraft environmental dynamics (e.g. gravity gradient, solar pressure, aerodynamics etc.)

[1][2] ZPMs are developed by solving a specific nonlinear two-point-boundary-value optimal control problem for a fixed maneuver end time.

The ZPM optimal control problems for both ISS maneuvers were solved using DIDO software.