There were two types of detectors on board ASCA: two Gas Imaging Spectrometers (GIS) and two Solid-state Imaging Spectrometers (SIS), each behind its own X-ray Telescope. Although the GISs were excellent instruments it was the SIS detectors that astrophysicists were most excited about. At the heart of the SIS's are X-ray sensitive CCD chips, and while CCDs may seem common these days, since there is one in every digital camera and smartphone around, ASCA was the pioneer in the use of CCDs for X-ray astronomy. CCDs are now routine in X-ray astronomy satellites.
