NuSTAR (Nuclear Spectroscopic Telescope Array) is a space-based X-ray telescope that uses a conical approximation to a Wolter telescope to focus high energy X-rays from astrophysical sources, especially for nuclear spectroscopy, and operates in the range of 3 to 79 keV. It is the eleventh mission of the NASA Small Explorer satellite program (SMEX-11) and the first space-based direct-imaging X-ray telescope at energies beyond those of the Chandra X-ray Observatory and XMM-Newton. It was successfully launched on 13 June 2012, having previously been delayed from 21 March due to software issues with the launch vehicle.