The X-Ray Spectrometer (XRS) is a system of X-ray calorimeters that sit behind an imaging X-Ray Telescope (XRT). XRS is a spectrometer, an instrument that separates light signals into different frequencies, producing a spectrum. XRS was special because it was the first X-ray calorimeter flown on a satellite. Unfortunately, XRS lost its coolant shortly after launch, and so we were never able to see its full potential. We won't have long to wait, however, before seeing what a calorimeter can do – Astro-H, the next collaborative X-ray satellite launching around 2014, will carry one.
