Louis Lischwe, Delft University of Technology; T.P.G. Wijnen, Delft University of Technology; M. Rodenhuis, Leiden University
Keywords: Spectropolarimetry, Satellite Identification, Non-Resolved Object Characterization, Instrumentation, GEO Satellites, Spectral Analysis, Linear Polarization
Abstract:
The exponentially increasing number of Earth orbiting satellites, as well as the pronounced importance for space military operations, impose new challenges on a functional Space Domain Awareness (SDA). A key factor for an effective SDA is the successful identification of an Earth orbiting satellite, or object in general. Current methods are usually limited to either time resolved photometry, spectrometry, or polarimetry. In this paper we present the Spectropolarimeter for Satellite Identification (SSI), whose design combines these detection methods with the aim to provide a unique ‘fingerprint’ of the satellite, thereby expanding the range of satellite identification methods.
The SSI combines a dual channel spectrometer with off-the-shelf polarization optics. Using a combination of an achromatic quarter wave retarder, a highly chromatic multiple order retarder, a polarizing beam splitter, and two linear polarizers, all operating in the visible spectrum, a sinusoidal modulation of the linear polarization information is imprinted onto the measured spectrum. The amplitude of the signal scales with the degree of linear polarization and the phase with the angle of linear polarization. Furthermore, by using a dual channel setup, the intensity spectrum is obtained for the full spectrograph resolution. Since the full linear spectropolarimetric information is obtained in a single measurement, differential effects and drifts are strongly reduced, which simplifies the calibration. The spectrally resolved linear polarization information provides a unique approach for satellite identification, combining material and geometric response.
We will take measurements with the SSI using the 800 mm Ritchey-Chrétien AZ800 telescope from the Netherlands Organisation for Applied Scientific Research (TNO) at The Hague Waalsdorp. We will attempt to identify a satellite by correlating the retrieved spectropolarimetric data from different observations of the same satellite, while also reliably discriminating it from measurements of other satellites. We expect the phase angle to have a major influence on the measured spectropolarimetric data and therefore on the ability to identify the satellite.
The proof of concept to use linear channeled spectropolarimetry for satellite identification with the SSI will open up the way for further technical refinement of the instrument, an extension to low Earth orbit satellites, and the possible addition of phase angle resolved spectropolarimetric measurements to further improve the concept of a satellite`s spectropolarimetric ‘fingerprint’.
Our work is part of a collaboration between Leiden Observatory and Delft University of Technology commissioned by the Royal Netherlands Air Force.
Date of Conference: September 27-20, 2022
Track: Non-Resolved Object Characterization