Precise starshade stationkeeping and pointing with a Zernike wavefront sensor

Starshades, large occulters positioned tens of thousands of kilometers in front of space telescopes, o er one of the
few paths to imaging and characterizing Earth-like extrasolar planets. However, for the starshade to generate
a su ciently dark shadow on the telescope, the two must be coaligned to just 1 meter laterally, even at these
large separations. The principal challenge to achieving this level of control is in determining the position of the
starshade with respect to the space telescope.
In this paper, we present numerical simulations and laboratory results demonstrating that a Zernike wavefront
sensor coupled to a WFIRST-type telescope is able to deliver the stationkeeping precision required, by measuring
light outside of the science wavelengths. The sensor can determine the starshade lateral position to centimeter
level in seconds of open shutter time for stars brighter than eighth magnitude, with a capture range of 10 meters.
We discuss the potential for fast (ms) tip/tilt pointing control at the milli-arcsecond level by illuminating the
sensor with a laser mounted on the starshade. Finally, we present early laboratory results.