The Spaceborne Infrared Atmospheric Sounder for Geosynchronous Earth Orbit (SIRAS-G) is an infrared imaging spectrometer concept being developed to address future Earth observation from both low-earth and geosynchronous orbit. SIRAS-G is now in its second year of development as part of NASA's Instrument Incubator Program. The SIRAS-G approach offers lower mass and power requirements than heritage instruments while offering enhanced capabilities for measuring atmospheric temperature, water vapor, and trace gas column abundances at improved spatial resolution. The system employs a wide field-of-view hyperspectral infrared optical system that splits the incoming radiation to several grating spectrometer channels. Combined with large 2-D focal planes, this system provides for simultaneous spectral and high-resolution spatial imaging. In 1999, the SIRAS team built and tested the SIRAS LWIR spectrometer also under NASA's Instrument Incubator Program (IIP-1). SIRAS-G builds on this experience with a goal of producing a laboratory demonstration instrument operating in the MWIR including the telescope, a single spectrometer channel, focal plane and active cooling subsystem. In this paper, we describe the on-going development of this instrument concept, focusing on aspects of the optical design, fabrication and testing of the demonstration instrument, performance requirement predictions and potential future scientific instrument applications.
BATC is developing the Spaceborne Atmospheric Infrared Sounder for Geosynchronous Earth Orbit (SIRAS-G) under NASA's 2002 Instrument Incubator Program. SIRAS-G represents a new approach to infrared imaging spectrometry suitable for Earth observation from geosynchronous orbit. SIRAS-G is an instrument concept with lower mass and power requirements than contemporary instruments that offers enhanced capabilities for measuring atmospheric temperature, water vapor, and trace gas column abundances in a compact package. In addition, the SIRAS-G concept is adaptable to airborne, low-Earth orbit and geosynchronous deployment. SIRAS-G employs a wide field-of-view hyperspectral infrared optical system that splits the incoming radiation to four separate grating spectrometer channels. Combined with large 2-D focal planes, this system provides simultaneous spectral and high-resolution spatial imaging designed to measure infrared radiation in 2048 spectral channels with a nominal spectral resolution (l/Dl) of between 700 and 1400. Design parameters and the associated basic design trades for a SIRAS-G laboratory demonstration instrument are presented in this paper. Results of completed instrument design analyses along with instrument performance predictions are included. Using these performance predictions, we offer a comparison of current technology with SIRAS-G's capabilities for measuring atmospheric temperature, water vapor profiles, and trace gas column abundances.
The Aspect Camera Assembly (ACA) is a 'state-of-the-art' star tracker that provides real-time attitude information to the Advanced X-ray Astrophysics Facility (AXAF), and provides imaging data for 'post-facto' ground processing. The ACA consists of a telescope with a CCD focal plane, associated focal plane read-out electronics, and an on-board processor that processes the focal plane data to produce star image location reports. On-board star image locations are resolved to <EQ 0.8 arcsec, and post-facto algorithms yield <EQ arcsec star location accuracies. The protoflight ACA has been built, along with a high accuracy vacuum test facility. Image position determination has been verified to <EQ 0.2 arcsec accuracy. This paper is a follow-on paper to one presented by the author at the AeroSense '95 conference. This paper presents the 'as built' configuration, the tested performance, and the test facility's design and demonstrated accuracy. The ACA has been delivered in anticipation of a 1998 shuttle launch of AXAF.
The Aspect Camera Assembly (ACA) is a state-of-the-art star tracker that provides real-time attitude information to the Advanced X-Ray Astrophysics Facility-Imaging (AXAF-I), and provides imaging data for post-facto ground processing. The ACA consists of a telescope with a charge coupled device (CCD) focal plane, associated focal plane read-out electronics, and an on-board processor that processes the focal plane data to produce star image location reports. On-board star image locations are resolved to 0.8 arc-sec, 1 (sigma) and post-facto algorithms yield 0.2 arc-sec, 1 (sigma) star location accuracy. A high- fidelity ACA breadboard was built along with a high accuracy test facility. In air, image position determination has been verified to 0.2 arc-sec, 1 (sigma) accuracy. This paper presents the system requirements and a description for the ACA. A design description is included for both the ACA and the test facility, and performance results are presented.
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