The X-ray microcalorimeter instruments on the Astro-E2 and Constellation-X X-ray observatories

X-ray microcalorimeter arrays are well suited to address key problems in high-energy astrophysics. The Japan/US Astro-E2 mission will deploy a 32-pixel array of microcalorimeters with 6 eV resolution. This mission is scheduled for launch in 2005. Beyond Astro-E2, NASA is formulating the Constellation-X mission to provide a dramatic increase in collecting area with four separate spacecraft each with large area optics and 1 k-pixel calorimeter arrays providing an energy resolution of 2–4 eV.We will describe the microcalorimeter instrumentation on these missions and mention some of their scientific objectives.