Harrison Krantz, University of Arizona Steward Observatory; Eric Pearce, University of Arizona Steward Observatory; Louis Avner, University of Arizona Steward Observatory; Kris Rockowitz, University of Arizona
Keywords: Photometry, High-speed, multi-color, electron multiplying CCD, space surveillance
Abstract:
High-speed optical photometers have been used for decades to characterize man-made satellites and space debris in Earth orbit. In the 1970s and 1980s, these instruments were typically based on photomultiplier tubes (PMT) and provided single-color, or in some cases simultaneous multicolor, photometric data with high time resolution. The original GEODSS PMT photometers were designed to collect photometry on deep space satellites at rates up to 1 kHz. CCDs have since displaced the use of PMTs in photometers in the astronomical community and the GEODSS system. CCDs offer higher quantum efficiency and two-dimensional imaging arrays, but at a lower speed than PMTs. The latest developments and introductions of commercially available Electron-Multiplying CCD (EM-CCD) imagers is driving a renaissance in this field with several new instruments in development.
Chimera is a high-speed photometer with simultaneous three-color photometry in the Sloan r (562-695 nm), i (695-844), and z (826-920 nm) bands. The optical design provides well-corrected fields of view of 9.7 arcmin in the z band and 6.0 arcmin in r and i bands on the Steward Observatory 61 Kuiper telescope at Mt. Lemmon. The wide field of view facilitates acquisition and tracking of rapidly moving satellites and allows for a variety of photometric calibration methods. The optical design uses a wide-field collimator, two dichroic beam splitters, and three re-imagers. Chimera utilizes three Princeton Instruments Pro-EM HS cameras, which provide data at rates up to 228 Hz in full frame mode. Rates over 1000 Hz are possible by defining photometric regions of interest (ROIs). A highly-modified version of Michael Mommerts photometric pipeline (PP), originally developed for near-Earth asteroid photometry, is used for data processing. A real time graphic user interface is under development to allow real-time data quality assessment and period determination during data collections.
In space surveillance, the optical signature characteristics of rapidly rotating satellites necessitate the use of high-speed multicolor photometers. Satellite photometric analysis takes advantage of reflections off flat surfaces of the satellite. The duration of these flashes are as short as a few ms. The high frame rate of Chimera will allow detailed study of the temporal profile of these reflections, which will allow assessment of the quality and characteristics of the reflective surfaces. The simultaneity of the multicolor measurements ensures that data unambiguously refer to the same surface in the same orientation.
In this paper, we document the optical and opto-mechanical design of Chimera and assess the first light performance of the instrument and its cameras and characterize the operational modes of our new instrument. While the unique electron multiplication feature of EM-CCDs provides high frame rates with low noise, other noise sources, which are generally negligible with traditional CCDs, must be considered including dark noise and clock induced charge (CIC). We also present the first-light results of Chimera on a sampling of SSA targets, including multicolor observations of SL-12 rocket bodies we previously surveyed in the SWIR and satellites with distinctive specular signatures to demonstrate the capabilities of the instrument.
Date of Conference: September 11-14, 2018
Track: Optical Systems Instrumentation