Geospace Electrodynamic Connections (GEC) Mission

1. The GEC mission has been in the formulation phase as part of NASA’s Solar Terrestrial Probe program for nearly 5 years. It is to be launched after the Magnetosphere Multiscale Mission. It is a challenging multi-satellite mission of 3 spacecraft with each spacecraft carrying sufficient propulsion fuel to make extensive deep dipping campaigns to the lower boundary of outer space. This is where the neutral atmosphere begins to play the dominant role in the dissipation of magnetosphere energy and in the creation of electric currents that close the magnetosphere current network. The three spacecraft will be launched from a single launch vehicle into high inclination, ~2000X ~200 km orbits (i.e., a pearls-on-a-string configuration). They will have the capability to change orbit separations to study multiple scaled structures. They also will have the exciting capability to dip to 130 km or lower, in coordinated campaigns with ground based measurements, to explore for the first time in situ the electrodynamic connections of the atmosphere to the magnetosphere. The spacecraft, identically instrumented, will measure the ionosphere/atmosphere composition, temperatures and concentrations, magnetic and electric field and energetic particle distributions, providing a complete picture of the underlying physics. Focused, deep dipping campaigns (e.g., over a radar station, or in the auroral region) will measure the atmosphere’s impact on the electrodynamics as a function of altitude. This will lead to complete understanding of how the collisionally-coupled charged and neutral particle constituents in the ionosphere- thermosphere boundary layer respond to electromagnetic inputs from space. With its multiple spacecraft, the mission will determine how the spatial variations and persistence of the electrodynamic drivers relate to the neutral responses. And importantly, by making measurements of both the field and particle distributions it can be determined how the responses evolve and feed back on the magnetosphere drivers. Current understanding of the effect of the solar wind on planetary atmosphere environments is at the point where complex, multi-scaled phenomena are recognized to be key elements of the interactions. To understand these effects in situ measurements from multi-satellite missions are the only viable approaches. This holds also for the exploration of the lower boundary of geospace and, coining an analogous term, the lower boundary of “planetospace” for other planetary bodies. These upper atmosphere/lower ionosphere regions, are where ultimately the energy and momentum of the solar wind are converted into atmospheric energy and momentum and where horizontal electric currents complete the circuits generated by the solar wind interaction. GEC’s goal to penetrate deep into the Earth’s upper atmosphere and to explore for the first time with in situ measurements the complexity of the transition of Earth’s upper atmosphere to outer space, is of paramount value to both NASA’s science and exploration initiatives. Besides the technical experience and knowledge it will gather by penetrating and gathering ambient measurements in a region with large aerodynamic torques and consequent heating of the spacecraft, it will also provide first-hand information on the atmosphere-plasma interactions that are the final low-altitude links in the dynamical coupling of the Sun’s solar wind to planetary atmospheres. From a Space Weather perspective this region includes the electrical currents and atmospheric perturbations that affect terrestrial ground-based power systems, radio communication and satellite drag. The same basic processes occur in other planetary atmospheres. A mission dedicated to providing comprehensive in situ measurements in the region where the neutral atmosphere begins to take preeminent control of the plasma dynamics and with multiple spacecraft to separate the spatial/temporal scales, has yet to be flown. GEC will fulfill this role. For GEC Science Definition Team Report and recent update see: http://stp.gsfc.nasa.gov/missions/gec/gec.htm Geospace Electrodynamic Connections (GEC) Mission

2. Geospace Electrodynamic Connections (GEC) Science Objectives • Determine how the collisionally coupled charged and neutral atmospheric constituents in the ionosphere/thermosphere boundary layer respond to electromagnetic inputs imposed from space. • Determine how the spatial variations and persistence of the electrodynamic drivers relate to the neutral atmosphere responses • Delineate how, and under what conditions the responses evolve and feed back on the drivers Mission Description(Launch next decade) • Example Mission Design - 3 identical spacecraft: pearls-on- a-string configuration - Delta II Launch (3000 kg total to 2000 km X ~200 k, 83 degree inclination orbits) - Each spacecraft carries fuel (~100kg) for extensive deep dipping campaigns to <130 km and for changing orbit separations - Two year baseline mission • Flight System Concept - Electromagnetically clean spacecraft - Aerodynamic design - Three axis stabilized, ram facing instrument platform Measurement Strategy • Measure, in situ, the motion,temperature and composition of the ionosphere and neutral atmosphere, the energetic particle distributions and the electric/magnetic fields. • Have coordinated dipping campaigns of all spacecraft to 130 km or lower to determine altitude effects of neutral atmosphere on the dynamics. • Change relative spacings of spacecraft to study key spatial- temporal scales. • Enhancing Technology Development • No engineering show-stoppers • Formation Flying • Enhanced propulsion efficiency • Aerodynamic Spacecraft design • Light weight,low cross-seciton E-field booms • Momentum unloading system that minimally affects the measurements.