XRS-2 was a new generation of X-Ray Spectrometer. It was to measure the spectrum of celestial objects in the "soft" X-ray range (200 to 10,000 eV), to much higher resolution than has been possible up to now.
XRS-2 was the prime instrument aboard the Japanese Suzaku (formerly Astro-E2) spacecraft, launched July 10, 2005. Suzaku is a joint project of NASA and the Japanese space science agency ISAS. Since October 2003, ISAS has been part of the Japanese space agency JAXA
XRS-2 would have, for the first time, provide both high resolution and high throughput in one instrument.
High Resolution means measuring the spectrum at many different frequencies (or energies). The detectors used in XRS-2 have a spectral resolution about 6eV (20 times better than typical solid-state detectors). This allows us to see much finer detail in the spectrum.
High Throughput means measuring nearly all of the X-rays that hit the detector. This allows us to measure the spectra of even very faint sources.
XRS-2 failed shortly after launch. An investigation of the failure is underway.
XRS-1 (which was just called "XRS" at the time) was part of the ASTRO-E spacecraft. ASTRO-E was launched February 10, 2000. Unfortunately, there was a problem with the first stage rocket motor, and the spacecraft didn't achieve orbit. It fell back to Earth and burned up. In July 2001, NASA approved a new mission, Astro-E2, which was a rebuild of Astro-E and was launched July 10, 2005. After launch, it was renamed Suzaku.
Suzaku has several improvments over the original ASTRO-E mission. For starters, the XRS-2 detectors have twice the spectral resolution and operate effectively over a wider range of energies. The X-ray focusing mirrors are improved as well. In addition, a mechanical cooler has been added to the system, which will extend its life from 2 years to somewhere between 2.5 and 3 years.