Focal plane geometry

In order to compute a joint HRMA-ACIS simulation we must be able to relate the rays produced by the HRMA simulators and propagate them back to the point of contact with the ACIS CCD detectors. The problem we want to solve consists of the following: given a photon emerging from the HRMA from a given direction, we want to determine which CCD the photon will hit and the pixel coordinates of the event. Our input information is the direction of the incoming photons (in terms of three direction cosines) from an arbitrary point outside the mirror. This information will be provided by the ASC program SAOSAC (see the XRCF Phase 1 report). The problem consists of finding the (unique) intersection of the ray trajectory with the CCD surface, taking into account the tilt of the latter with respect to the HRMA optical axis. The MARX program, provided by the ASC, is a convenient tool which includes this calculation.
 

• CCD geometry
• Ray projection on ACIS