MIDEX (Medium-class Explorer)
MIDEX (Medium-class Explorer) spacecraft are fairly low-cost ($120 million to $180 million, including development, launch, and operation) NASA science satellites. The first four to be launched were FUSE (Far Ultraviolet Spectroscopic Explorer) in Jun 1999, IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) in Mar 2000, WMAP (Wilkinson Microwave Anisotropy Probe, previously known simply as MAP) in June 2001, and the Swift Gamma Ray Burst Explorer in Nov 2004. The next spacecraft in the series scheduled for launch are THEMIS in Oct 2006 and WISE (Wide-field Infrared Survey Explorer) in summer 2008. See also SMEX (small Explorers) and UnEX (university-class Explorer).