National Aeronautics and Space Administration

The Advanced Telescope for High ENergy Astrophysics (ATHENA) is an X-ray observatory planned for launch in 2034 aboard an Ariane 6 expendable launch vehicle. The mission was selected and now under development by the European Space Agency (ESA) as part of their Cosmic Vision program to address the HOT and Energetic Universe science theme. The mission is an ESA led project with contributions from institutes in Europe, United States and Japan.
ATHENA has a 12 m focal length X-ray telescope with a large effective area. X-rays are collected by two focal plane instruments: the Wide Field Imager (WFI) and X-ray Integral Field Unit (X-IFU). The observatory is placed in a halo orbit around the Earth-Sun L2 Lagrange point with a nominal mission lifetime of 5 years with possible extension of other 5 years. The L1 orbit is still evaluated as back-up option

ATHENA is a down-sized version of the abandoned NASA/JAXA/ESA International X-ray Observatory (IXO), which itself was a merger of the ESA XEUS and NASA Constellation-X mission proposals.

ATHENA includes two different detectors, the Wild Field Imager (WFI) and X-ray Integral Field Unit (X-IFU), which share optics with a single 12 m focal length X-ray telescope.
The telescope uses grazing incidence silicone pore optics to a provide 5-arcsec Half Energy Width angular resolution and an effective area ≥1.4 m2 at 1 keV, and ≥0.25 m2 at 6 keV. An Instrument Switching Mechanism, based on a set of hexapods, allows each of the two instruments to be located at the mirror focus at any given time. The same mechanism allows to defocus the mirror Point Spread Function (PSF), permitting to increase the capability of the X-IFU to observe bright X-ray sources..

The WFI detector comprises a Large Large Detector Array (LDA) and a Fast Detector (FD) both using depleted p-channel field-effect transistor (DEPFET) detector. The LDA is an array of 2x2 detectors, each with 512x512 pixels, with a time resolution in full frame of 5ms. The FD optimized for bright point sources is an array of 64x64 pixels and allows a time resolution 80 microseconds. WFI is sensitive to X-rays between 0.2 to 15 keV, an energy resolution of ≤170 eV at 7 keV, a pixel size of 2.2 arcsec and the 40″ x 40′ field of view.

The X-IFU is an X-ray calorimeter using an array of cryogenically cooled transition edge detectors. It has a 10 microsecond timing accuracy, a spectral resolution of 2.5 eV at or below 7 keV, a field of view of 5 arcmin, a pixel size of 5 arcsec and sensitive across the spectral range 0.2–12 keV.

ATHENA science goals includes: a) studying how matter assembles within galaxies and galaxy clusters, b) measuring the history of the chemical compisition of the Universe through time, c) studying acceration processing in compact objects, d) finding the earliest super-massive black holes and tracing their growth despite the obsuration of heavy dust and gas, and e)studying transient phenomena such as gamma-ray burst sources with a fast target of opportunity system.