NASA's Living with a Star Geospace Missions

Two geospace regions that are of particular importance to understand space weather, and form the focus of the Living with a Star Geospace Program, are the radiation belts and the ionosphere. Both regions strongly affect military and commercial systems and can have direct impact on individual human activities during geomagnetic storm periods. The storms pump up the radiation belts producing enhanced energetic electron populations that can damage satellite electronics and harm astronauts and cause ionospheric disturbances that affect radio communications and Global Positioning System Navigation systems. Further they can lead to shortened satellite lifetimes as well as power line outages. Despite its importance we have not yet established the connections between specific mechanisms, their phenomenology nor a predictive capability of their occurrences. The LWS Geospace spacecraft missions have been planned (via the LWS Geospace Mission Definition Team) to target the basic research problems needed to understand and form predictive models of the societal impacts of these two regions.

The missions' objectives are to a) characterize and understand the acceleration, global distribution, and variation of the radiation belt particles and b) to characterize and understand mid-latitude ionospheric variability and irregularities. Because of the spatial and temporal variations both missions consist of multiple resources. The Radiation Belt Storm Probe mission consists of a pair of satellites on low inclination eccentric orbits that measure the charged particle distributions and the magnetic and electric fields that lead to their transport and energization. One spacecraft will reside in the region that particles are transported from and the other resides in the region that the particles are transported to to form the intense radiaton belts. The Ionosphere-Thermosphere (I-T) Storm Probe mission on the other hand consists of two satellites at ~400 km, near the peak of the main ionosphere layer, in moderate inclination orbits. They are separated in local time to provide a measure of longitudinal spatial variations which contribute lead to many of the important ionosphere space weather consequences. The I-T spacecraft carry instruments to measure the thermal plasma and neutral particle distributions along with their motions. For the I-T studies an Extreme Ultraviolet radiation detector was selected for flight on the Solar Dynamics Observatory spacecraft to provide a measure of the source of the bulk of the ionosphere - photoionization. It is critically important to know the response of the ionosphere and neutral atmosphere to EUV variations in order to separate the direct solar influence from geomagnetic storm induced variations produced by high latitude magnetospheric energy inputs. And, complementing the in situ measurements remote I-T sensing is sought to provide a large-scale picture of the storm effects. The current status of these resources is that the Solar Dynamics Observatory, with the important EUV measurements, is to be launched in 2007; the RB-Storm Probes, for which NASA is now soliciting instrument proposals, is projected for a 2011 launch, followed by the I-T Storm Probes.