RHESSI has two subsystems (SAS and RAS) of sensors, which acquire data for off-line reconstruction of the aspect solution. The SAS (Solar Aspect System) consists of three lens/sensor pairs measuring the Solar limb at about 670 nm. The off-line data analysis reconstructs the Sun center with respect to the imaging axis (the reference telescope axis). The RAS (Roll Angle System) is a star tracker pointing radially outwards. With respect to the rotating spacecraft, the images of stars are traveling over a linear CCD and are triggering star events to be included in the telemetry data. By comparing with a star catalog, the off-line analysis software calculates the momentary roll angle. The integration of both information provides the aspect solution to be used for image reconstruction.