Imaging other Earths with secondhand spy satellites and starshades
Michael Bottom
California Institute of Technology

The gift of unused spy satellites to NASA for the WFIRST mission has presented an incredible opportunity for a broad range of astrophysics, from elucidating the nature of dark energy to exoplanet detection. The positioning of WFIRST at Lagrange point 2, with its gentle gravity gradients and benign thermal environment, has allowed NASA to set a goal of making WFIRST "starshade ready" -- that is, ready for a 30-meter wide, flower-shaped spacecraft to rendezvous 50,000 km away and block out stars, allowing for imaging and spectroscopy of neighboring Earth-like planets. I will discuss the scientific potential of the starshade mission and describe the technical challenges that must be overcome to make it possible. First I will discuss our work towards developing a photon-counting, flight-ready detector capable of sensing photon rates of a few per hour, typical of Earth-like exoplanets. I will end with the challenge of formation flying, as the starshade and WFIRST must be kept aligned to within just one meter at these very large separations. I will present analytic, numerical, and experimental work on the optical formation sensing and control framework for the starshade, demonstrating centimeter-level accuracy in position sensing and robust control with high observing efficiency.