Constellation-X

NASA's Constellation-X is an observatory that is in the early stages of design and planning, with a proposed for launch date of c.2009. Similar to Astro E, the prime detector instruments are expected to be X-ray micro-calorimeters, albeit with total effective area greater than any current or previous X-ray satellite ($A\sim 3\,{\rm m}^2$). The planned energy range will be $0.2-40$keV, with a spatial resolution of 6 arcsec. The large effective area is to be achieved by ``mass-producing'' and launching four separate satellite systems with their own independent mirror and detector assemblies. The combination of high spectral resolution with large effective area has raised the prospects that Constellation-X can be used for detailed iron line variability studies, including ``reverberation mapping'' between continuum and line features, as we further discuss below.