Photo of Grid 1, the finest-pitch grid. The darker diagonal bars going from bottom left to top right are the supports (the photo is back-lit). The 34 micron slit/slat structure runs perpendicular to the supports.


The key components of the RHESSI imager are two identical sets of nine grids mounted on front and rear grid trays.  A corresponding set of nine cooled germanium detectors is mounted behind the rear grids.  As the spacecraft rotates at ~15 rpm, the nine rotating modulation collimators time-modulate the incident flux.  From the time and energy of counts recorded in the detectors, as well as precise aspect information, images can be reconstructed using software algorithms.

Each grid is a planar array of equally-spaced, X-ray opaque slats separated by transparent slits.  The nine subcollimators each consist of a pair of grids with identical pitch and parallel slits separated by 1.55m in front of a detector.  The grids have pitches from 34 microns to 2.75 mm and provide a spatial resolution as high as 2.3 arcseconds.

Because of manufacturing considerations, the four finer-pitch grids (1-4) are round and the five coarser-pitch grids (5-9) are square.  All are approximately 10cm by 10 cm.


Photo of Grid 7. The vertical bars are the supports. The 918 micron slit/slat structure runs horizontally.