Issue 12 - October 2013

August Was a Month of “Discovery” for Starshade Technology By Mark Thomson, Doug Lisman, and David Webb On Tuesday, August 27, the Discovery Channel filmed the initial deployments of the world’s first prototype deployable Starshade, a huge deployable structure for the direct imaging of extrasolar planets, or exoplanets. The video sequences, filmed by a crew from Pioneer TV of the UK, are for an exoplanet-themed segment of “How the Universe Works,” scheduled to air in 2014. The starshade concept is comprised of an external occulter, or Starshade, flown in formation with a companion telescope, capable of launching jointly on a single launch vehicle. The Starshade is compactly stowed for launch and deploys to a very large structure of approximately 34 meters in diameter. Resembling a sunflower in shape, the Starshade consists of an opaque inner disk with flower-like petals around the circumference, shaped to control the diffraction of starlight. Accurately controlling the deployed starshade petal positions is a key performance parameter and the focus of a “Technology Development for Exoplanet Mission,” or TDEM. This effort by JPL and Astro Aerospace, a business unit of Northrop Grumman Aerospace Systems (NGAS), is led by Professor Jeremy Kasdin of Princeton University. The Starshade prototype, conceived and designed at JPL, includes an existing 12-meter-diameter AstroMesh antenna truss, modified by Astro to form the inner disk of the starshade, complimented with 4.3 meter petals, assembled at JPL by summer interns from Princeton and MIT. The fully integrated Starshade prototype has been deployed over 10 times as of September 23, 2013 at Astro’s facilities in Goleta, Ca. After each deployment, metrology data were collected and analyzed to determine the 3-D position of the hundreds of measurement targets spread across the Starshade to an accuracy of approximately 100 microns, or .004 inches. Preliminary results indicate that the truss nodes, which locate pairs of interface points at the root of each petal, deploy repeatedly over the 12-meter truss to within a radius of better than 250 microns (0.010 inches) relative to nominal. This level of structural repeatability is two times better than the requirement, which is based on achieving a worst-case minimum of 10⁹ starlight suppression in a flight system. Final results will be published after aligning the petal interface points relative to the design circle and repeating ten more deployments with metrology. To learn more about starshade technology, read the following abstracts:

STARSHADES FOR EXOPLANET IMAGING AND CHARACTERIZATION: KEY TECHNOLOGY DEVELOPMENT

VERIFYING DEPLOYMENT TOLERANCES OF AN EXTERNAL OCCULTER FOR STARLIGHT SUPPRESSION