The orientation or attitude of the spacecraft is critical at all stages of the mission. After the Trans Lunar Injection stage is complete the spacecraft stack begins its three day long journey to the moon. The difference in temperature between the side exposed to the sun and the side in the shade can be as high as 135 degrees. This temperature gradient can cause structural damage to the spacecraft and effect the performance of the Breaking Stage solid motor. To ensure that the temperature is distributed evenly a monopropellant Reaction Control System (RCS) is used to slowly spin the spacecraft about the flight axis.
The RCS is also used to perform any Mid-Course Manoeuvres (MCMs) needed during the lunar transit and to optimise the spacecraft's attitude for the breaking burn on approach to the lunar surface.