White-light demonstration of one hundred parts per billion irradiance suppression in air by new starshade occulters

Abstract

A new mission concept for the direct imaging of exo-solar planets called the New Worlds Observer (NWO) has been proposed. The concept involves flying a meter-class space telescope in formation with a newly-conceived, speciallyshaped, deployable star-occulting shade several meters across at a separation of some tens of thousands of kilometers. The telescope would make its observations from behind the starshade in a volume of high suppression of incident irradiance from the star around which planets orbit. The required level of irradiance suppression created by the starshade for an efficacious mission is of order 0.1 to 10 parts per billion in broadband light. This paper discusses the experimental setup developed to accurately measure the suppression ratio of irradiance produced at the null position behind candidate starshade forms to these levels. It also presents results of broadband measurements which demonstrated suppression levels of just under 100 parts per billion in air using the Sun as a light source. Analytical modeling of spatial irradiance distributions surrounding the null are presented and compared with photographs of irradiance captured in situ behind candidate starshades.

Limits on achievable intensity reduction with an optical occulter: comment

“…Schindhelm et al [16] and Leviton et al [15] both studied starshades that have petals fully formed out to the precalculated truncation distance. There was no discernible diffraction from the tips as predicted.…”

Analysis of exoplanet light curves with the New Worlds Observer

“…Important studies have also begun on issues such as formation flying , Leitner et al (2007)), scatter off the starshade (Arenberg et al (2007a)) and tolerances ). Additional studies on starshade performance , Leviton et al (2007), Lo et al (2007)) and science simulations (Schindhelm et al (2005)) are available.…”

“…Introductory lab tests of starshades have been conducted recently in air byLeviton et al (2007) and weak vacuum (~1 torr) bySchindhelm et al (2007). These tests have used a basic heliostat setup to illuminate a starshade with broadband light and measure suppression and contrast ratios.…”

Advanced speckle sensing for internal coronagraphs

“…This goal is tantalizingly close to our grasp, and could be achieved within our lifetime. Instruments have been designed and to some extent tested, 2,3,4,5,6 that are capable of direct detection-blocking the light from a nearby star and revealing the faint light of any planets orbiting around it. In this directly detected exoplanet light, we can observe atmospheric absorption lines, including biomarkers that provide evidence of life on that exoplanet.…”