Astro-H (formerly known as "NeXT") is a facility-class mission to be launched on a JAXA H-IIA into low Earth orbit. The Astro-H mission objectives are to:

• trace the growth history of the largest structures in the Universe
• provide insights into the behavior of material in extreme gravitational fields
• determine the spin of black holes and the equation of state of neutron stars
• trace shock acceleration structures in clusters of galaxies and SNRs
• investigate the detailed physics of jets.

Achieving these objectives requires the Soft X-ray Spectrometer, which combines a lightweight Soft X-ray Telescope (SXT) paired with a X-ray Calorimeter Spectrometer (XCS), providing non-dispersive 7 eV resolution in the 0.3-10 keV bandpass.

Three additional scientific instruments extend the bandpass to produce an observatory with extraordinary new capabilities. The Hard X-ray Imager (HXI) will perform sensitive imaging spectroscopy in the 5-80 keV band; the non-imaging Soft Gamma-ray Detector (SGD) extends Astro-H’s energy band to 300 keV; and the Soft X-ray Imager (SXI) expands the field of view with a new generation CCD camera.

Astro-H will be Japan's sixth X-ray astronomy mission, and will be primarily developed at the Institute of Space and Astronautical Science of Japan Aerospace Exploration Agency (ISAS/JAXA) in collaboration with U.S. (NASA/GSFC) and Japanese institutions.

NASA has started the process of selecting science advisors for the Astro-H mission, who will be added as US members to the international science working group. In addition, a Guest Observer Program including a Guest Observer Facility and Guest Observer funding has been proposed to NASA, and will be evaluated at a later date.