On December 30, 1995, NASA launched the RXTE (Bruno B. Rossi X-Ray Timing Explorer) satellite, which takes measurements from emissions originated from cosmic X-ray sources - especially analyzing the timely variation of X-ray emission.
One of the instruments of this satellite is an ASM (All-Sky Monitor), designed and manufactured by the Massachusetts Institute of Technology (MIT, USA). It observes the long term (from hours to years) behaviour of the brightest targets in the starry sky, observing 80% of it every one and a half hours. At the same time it can observe if any new X-ray object has appeared and alerts the other instruments to research them.
ASM instrument is still active today. X-ray astronomy has been able to extensively utilise the results produced by the ASM. For this reason the ASM is one of the most referred instruments in the field.
Oxford Instruments Analytical Oy has manufactured the position sensitive gas filled multiwire proportional counters for the ASM detectors.
These ASM detectors still work by producing results after 16 years from the launch of RXTE staellite!
See more of RXTE project:
The Rossi X-Ray Timing Explorer Project