New Approaches to Externally Occulted Coronagraphs

Friday, 19 December 2014
Douglas M Rabin, Phillip C Chamberlin, Joseph M Davila and Neerav Shah, NASA Goddard Space Flight Center, Greenbelt, MD, United States
The rapidly advancing capabilities of low-cost space platforms prompts us to reconsider concepts for externally occulted solar coronagraphs. Placing the occulter on a separate platform offers superior diffraction control but requires an analysis of alignment and separation tolerances that is different from that applied to conventional architectures. New forms of occulter (e.g., an inflatable sphere or ellipsoid) have potential advantages such as low mass and fabrication cost, simple deployment, and less stringent demands on the relative alignment of the platforms. However, the diffraction behavior of occulters that incorporate curved surfaces (Buffington 2000) is less explored than for edge-type occulters. We illustrate the new possibilities by calculating the performance of some candidate systems using an analytic framework adapted from radio wave propagation (Vogler 1985) and alignment tolerances based on a recent concept for a two-platform guidance, navigation, and control system.