NASA's Future Missions in X-ray Astronomy
  The NASA program in X-ray astronomy has two long term goals: 1) to achieve sufficient angular resolution to image the event horizon of a black hole (0.1 micro arc sec) and 2) to achieve sufficient collecting area (50-150 sq m) and angular resolution (0.1-1.0 arc sec) to observe in detail the first black holes and galaxies at high redshift. These ambitous goals can be used to map out a series of missions and a technology program. The next major mission will be Constellation-X which will be dedicated to high resolution X-ray spectroscopy for launch in ~2010. This mission is a critical step in the roadmap to achieve these goals. Following Constellation-X NASA is considering two very ambitious vision missions: MAXIM and Generation-X that will achieve the ultimate capabilities. The modest missions Astro-E2 and Swift address more focussed science goals on a rapid development cycle and provide important pathfinders to the larger missions. 
Nicholas E. White