Detection of a geostationary satellite with the Navy Prototype Optical Interferometer

J. T. Armstrong; R. B. Hindsley; H. R. Schmitt; F. J. Vrba; J. A. Benson; D. J. Hutter; R. T. Zavala

doi:10.1117/12.858283

21 July 2010 Detection of a geostationary satellite with the Navy Prototype Optical Interferometer

J. T. Armstrong, R. B. Hindsley, H. R. Schmitt, F. J. Vrba, J. A. Benson, D. J. Hutter, R. T. Zavala

Proceedings Volume 7734, Optical and Infrared Interferometry II; 77343C (2010) https://doi.org/10.1117/12.858283
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

We have detected a satellite via optical interferometry for the first time, using a 16 m baseline of the Navy Prototype Optical Interferometer (NPOI) to observe the geostationary communications satellite DirecTV-9S during the "glint" seasons of February-March 2008 and 2009 when the sun-satellite-NPOI geometry was favorable for causing specular reflections from geostationary satellites. We used the US Naval Observatory Flagstaff Station 1 m telescope to generate accurate positions for steering the NPOI. Stars are the easiest targets for optical/infrared interferometers because of their high surface brightness. Low surface brightness targets are more difficult: if they are small enough not to be resolved out by typical baselines, they are likely to be too faint to produce detectable fringes in an atmospheric coherence time. The 16 m NPOI baseline, the shortest available at the time of our observations, resolves out structures larger than ~ 1.5 m at the geostationary distance, while a typical size for the solar panel arrays is 2 m x 30 m. Our detection indicates that a small fraction of the satellite glinted, not surprising given that the solar panels are not accurately flat. Our fringe data are consistent with a two-component image consisting of a 1 to 1.3 m higher surface brightness component and a significantly larger lower surface brightness component. The brightness of the glints (2.^m 4 and ~ 1.^m 5 for the two detections in March 2009) and the size scale suggest that the compact component has an albedo of 0.06 to 0.13, while the larger-scale component is much darker, if circular geometry is assumed.

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J. T. Armstrong, R. B. Hindsley, H. R. Schmitt, F. J. Vrba, J. A. Benson, D. J. Hutter, and R. T. Zavala "Detection of a geostationary satellite with the Navy Prototype Optical Interferometer", Proc. SPIE 7734, Optical and Infrared Interferometry II, 77343C (21 July 2010); https://doi.org/10.1117/12.858283

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