The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) images solar hard X-ray and gamma-rays from 3 keV to 15 MeV with spatial resolution as high as 23 arcseconds Instead of conventional optics  nine rotating modulation collimators are used to time-modulate the incident flux as the spacecraft rotates in a manner which depends on the location and morphology of the source