Definitions for "MIDEX"
NASA's Mid-Class Explorer.
Medium-class Explorer or MIDEX is a medium-sized (defined by definition and development costs not exceeding $140M) spacecraft that carries one or more science instruments. Compare to SMEX and UNEX; see also Explorer.
Mid-sized Explorer: A continuing line in NASA's budget dedicated to low-cost ($70 million) missions in space physics and astrophysics.