Ongoing Evolution of the Geospace Electrodynamic Connections (GEC) Mission

NASA's planned Geospace Electrodynamic Connections (GEC) mission is composed of several identical spacecraft in eccentric (~2000 km to below ~200 km) orbits, with 83 degree inclinations. GEC observations, complemented by land-based measurements, will delineate the complex spatial and temporal scale ionosphere/thermosphere processes associated with the energy and momentum transfer between the magnetosphere, ionosphere, and thermosphere. GEC will provide the key in situ plasma and neutral particle measurements needed to complete our understanding of the effects of the upper atmosphere on magnetosphere-ionosphere coupling. To best accomplish its science goals, the technical design must strive to minimally disturb the environment, maximize the number of spacecraft, have the ability to traverse the lower ionosphere, and efficiently manage a pearls-on-a-string spacecraft constellation with variable spacecraft separations. Initial industry studies of the mission demonstrated that an ambitious 4-spacecraft mission with deep dipping capability to ~ 130 km is challenging given NASA's cost cap. Therefore some of the mission constraints were changed to provide an affordable mission concept that still meets the major science goals. Spacecraft accommodation studies, performed by industry in 2003, have now provided mission designs that are consistent with the cost and weight constraints and have highlighted major mission challenges. Preliminary plans are for NASA to issue a GEC Announcement of Opportunity (AO) in 2004 for launch in about 2009.