Showing papers by "Daniel J. Hoppe published in 2013"

Starshade optical edge modeling, requirements, and laboratory tests

Abstract: In conjunction with a space telescope of modest size, a starshade can be used as an external occulter to block light from a target star, enabling the detection of exoplanets in close orbits. Typically, the starshade will be placed some 50,000 km from the telescope and the system oriented so that the sun is on the opposite side of the shade to the telescope, but somewhat away from the line of sight. A small amount of sunlight can scatter from the edges of the shade directly into the telescope. Since the photon rate from an earthlike exoplanet might be only a few photons per minute, it is desirable that the scattered sunlight is also near this level. We have built an analytical model of the performance of starshade edges for both specular and Lambertian surfaces and derived requirements for properties such as reflectivity and radius of curvature. A computer model was also developed to show the appearance of the sunlight from the starshade and assess the contrast with the exoplanet. A commercial electromagnetism code was also used to investigate aspects of the results. We also constructed a scatterometer with which various test edges were measured and derived the likely performance if used in a starshade. We discuss these models and give the principal results.

Multi-step Ka/Ka dichroic plate with rounded corners for NASA's 34m Beam Waveguide antenna

Abstract: A multi-step Ka/Ka dichroic plate (Frequency Selective Surface (FSS)) is designed, manufactured and tested for use in NASA's Deep Space Network (DSN) 34m Beam Waveguide (BWG) antennas. The proposed design allows ease of manufacturing and ability to handle the increased transmit power (reflected off the FSS) of the DSN BWG antennas from 20kW to 100 kW. The dichroic is designed using HFSS and results agree well with measured data considering the manufacturing tolerances that could be achieved on the dichroic.