The Stellar Imager (SI): A revolutionary large-baseline imaging interferometer at the sun-earth L2 point

The Stellar Imager (SI) is a far-horizon or "Vision" mission in the NASA Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 0.1 milliarcsec and thus baselines on the order of 500 meters. These requirements call for a large, multi-spacecraft (>20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. SI's resolution (several 100 times that of HST) will make it an invaluable resource for many other areas of astrophysics, including studies of AGN's, supernovae, cataclysmic variables, young stellar objects, QSO's, and stellar black holes. In this paper, we present an update on the ongoing mission concept and technology development studies for SI. These studies are designed to refine the mission requirements for the science goals, define a Design Reference Mission, perform trade studies of selected major technical and architectural issues, improve the existing technology roadmap, and explore the details of deployment and operations, as well as the possible roles of astronauts and/or robots in construction and servicing of the facility.