Analysis of External Occulters in the Presence of Defects Philip Dumont* a , Stuart Shaklan a , Eric Cady b , Jeremy Kasdin b , Robert Vanderbei b a Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Los Angeles, CA, USA 91109 b Princeton University, Princeton, NJ, USA 08544 ABSTRACT Fifty meter-class external occulters have been proposed to detect earth-like planets. The THEIA concept 1 , a forty-meter diameter occulter with twenty ten-meter petals has the necessary nominal performance to achieve this goal. This paper examines whether this design is robust against expected manufacturing and deployment errors. The development of a numerical algorithm that represents the mask defects as a collection of rectangular apertures mitigates the problems associated with modeling diffraction phenomena produced by an occulter with characteristic physical dimensions that span five orders of magnitude. The field from each of these rectangles, which is proportional to a two-dimensional sinc function at the telescope, is added to the diffracted field from the nominal occulter. Results for a set of representative defects are presented. A single-petal, single-defect error budget, based on a minimum contrast of 10 -12 at 75 or 118 milli-arcseconds from the host star from 0.3 μ to 0.9 μ, is quoted. A Monte Carlo-type simulation that predicts the performance of the occulter in the presence of random combinations of all of the error demonstrates that the system contrast can maintained to better than 10 -11 from 0.3 μ to 0.9 μ if the values in the error budget can be achieved. Keywords: Planet finding, external occulter, near-field diffraction 1. INTRODUCTION The maturity of methods for detecting Jupiter-class extra-solar planets has motivated the development of concepts that will enable detection and characterization of Earth-class planets. The external occulter concept, first proposed by Spitzer 2 , has, recently, been resurrected and morphed into implementations that are capable of achieving this goal 3,4 . Designing an occulter that will achieve the necessary suppression of the light from the host star over a bandpass sufficiently wide to enable characterization is, admittedly, a non-trivial exercise. Nevertheless, several implementations have been proposed that appear to meet these requirements. However, we must ask how robust these implementations are to the types of mask imperfections that will surely result in the process of manufacturing and deploying the occulter. We must also understand the performance degradation that results from station keeping and mask orientation errors. This paper summarizes the results of a study that has tried to answer these questions. Although we have chosen the THEIA concept as the baseline 1 against which to evaluate our algorithms, the techniques can be used to assess similar designs. 2. DESCRIPTION OF STUDY Achieving and maintaining the contrast required to detect Earth-like planets around nearby starts places stringent requirements on the implementation of any TPF external occulter concept. The occulter must be capable of producing a broadband deep suppression of the field from the host star in the geometric shadow of the mask. The geometric width of the shadow must be large enough to accommodate a telescope with an aperture size that is sufficient to collect the number of planet photons necessary to achieve the SNR required for detection. These top-level requirements flow down to a set of mission and mask design requirements that include mask dimensions, mask feature sizes, the distance from the mask to the telescope, and the telescope diameter. Techniques and Instrumentation for Detection of Exoplanets IV, edited by Stuart B. Shaklan, Proc. of SPIE Vol. 7440, 744008 · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.824633 Proc. of SPIE Vol. 7440 744008-1