The X-ray XMM-Newton space telescope in October 12th, 2021 completed its 4000th orbit around the Earth with a billion kilometers travelled so far!
XMM-Newton is an European Space Agency X-ray satellite launched in December 10th of 1999. The mission was initially planned for two years but has been extended several times till today operating already 22 years. Initially, it was named X-ray Multi-Mirror Mission, though the name XMM-Newton was given in honor of Sir Isaac Newton. Its main objective is to observe the sky in the soft X-ray regime (0.2-15 keV) and explore distant X-ray sources for long time periods, such as active galactic nuclei that contain super0massive black holes in their very center.
The satellite with a weight of almost four tons is orbiting the Earth in an elliptical orbit (eccentricity is e=0.68) with a period of 48 hours. The apogee and the perigee of the orbit are at 114,000 and 7,000 km, respectively. It is characterized by a high position accuracy and stability, since the control of its orientation is handled precisely with two sets of four small thruster and four momentum wheels. XMM-Newton constitutes of three X-ray co-aligned telescopes, an optical telescope and, in total, three instruments that provide high sensitivity and good angular and spectral resolution with a moderate energy resolution (E/∆E∼20−50). These are: a) the European Photon Imaging Camera (EPIC), for X-ray imaging and moderate resolution spectroscopy b) the Reflection Grating Spectrometer (RGS), for high-resolution X-ray spectroscopy in the 0.35 2.5 keV range and, c) the Optical Monitor (OM), for optical/UV imaging and spectroscopy.