Past spacecraft and instruments that participated in GCN include Array of Low Energy X-ray Imaging Sensors (ALEXIS), BeppoSAX, the Imaging Compton Telescope (COMPTEL) on CGRO, the X-Ray/Gamma-Ray Spectrometer (XGRS) on NEAR Shoemaker, the High Energy Transient Explorer (WMM and SXC), the Rossi X-ray Timing Explorer (PCA and ASM) and Ulysses.