Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant
to many astrophysical problems. ACCESS, “Absolute Color Calibration Experiment for Standard Stars”, is a
series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in
the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from
the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration
accuracy of 1% and a spectral resolving power of 500 across the 0.35−1.7μm bandpass. Achieving a calibration
accuracy of 1% not only requires an accurate calibration transfer from the detector standards to the instrument,
but it also requires characterization and stability of the detector as well as a thermal background that contributes
less than 1% to the flux per resolution element in the near-infrared (1.7μm) spectral region of the ACCESS
bandpass. This paper describes the thermal mechanical design for achieving a low thermal background across
the ACCESS spectral bandpass.
Several studies have shown that a geostationary hyperspectral imager/sounder can provide the most significant value increase in short term, regional numerical prediction weather models over a range of other options. In 1998, the Geostationary Imaging Fourier Transform Spectrometer (GIFTS) proposal was selected by NASA as the New Millennium Earth Observation 3 program over several other geostationary instrument development proposals. After the EO3 GIFTS flight demonstration program was changed to an Engineering Development Unit (EDU) due to funding limitations by one of the partners, the EDU was subjected to flight-like thermal vacuum calibration and testing and successfully validated the breakthrough technologies needed to make a successful observatory. After several government stops and starts, only EUMETSAT’s Meteosat Third Generation (MTG-S) sounder is in operational development. Recently, a commercial partnership has been formed to fill the significant data gap. AsiaSat has partnered with GeoMetWatch (GMW)1 to fund the development and launch of the Sounding and Tracking Observatory for Regional Meteorology (STORMTM) sensor, a derivative of the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) EDU that was designed, built, and tested by Utah State University (USU). STORMTM combines advanced technologies to observe surface thermal properties, atmospheric weather, and chemistry variables in four dimensions to provide high vertical resolution temperature and moisture sounding information, with the fourth dimension (time) provided by the geosynchronous satellite platform ability to measure a location as often as desired. STORMTM will enhance the polar orbiting imaging and sounding measurements by providing: (1) a direct measure of moisture flux and altitude-resolved water vapor and cloud tracer winds throughout the troposphere, (2) an observation of the time varying atmospheric thermodynamics associated with storm system development, and (3) the transport of tropospheric pollutant gases. The AsiaSat/GMW partnership will host the first STORMTM sensor on their AsiaSat 9 telecommunications satellite at 122 E over the Asia Pacific area. GMW’s business plan is to sell the unique STORM data and data products to countries and companies in the satellite coverage area. GMW plans to place 6 STORMTM sensors on geostationary telecommunications satellites to provide global hyperspectral sounding and imaging data. Utah State University’s Advanced Weather Systems Laboratory (AWS) will build the sensors for GMW.
Ultra-spectral sounders (USS) in low earth orbit have significantly improved weather forecast accuracy in recent years, and their impact could be significantly improved with reduced revisit times. The GeoMetWatch, Inc.1 Sounding and Tracking Observatory for Regional Meteorology (STORMTM) program is designed to place a constellation of six USS units in spaced geostationary (GEO) positions around the earth. From GEO, the repeat time for a specific weather feature can be reduced to minutes, and the vertical temperature, water vapor and wind profiles can provide detailed warnings not available by any other means. The STORMTM sensor, a derivative of the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) EDU that was designed and built for NASA by Utah State University (USU) and rigorously tested in 2006, will be launched on a commercial geostationary satellite in late 2016. It combines advanced technologies to provide improved performance and reliability over the original EDU. From GEO the USS can observe surface thermal properties and atmospheric weather and chemistry variables in four dimensions. This paper provides an overview of the STORMTM instrument and the measurement concept. STORMTM’s USS will provide data of the same quality as the current LEO satellite sounders (AIRS, CrIS, and IASI) but with the ability to track storm development with soundings and images at any desired rate. Wind profiles obtained from a time sequence of STORMTM water vapor retrieval images will provide additional input to now casting and regional models.
The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS), developed for the NASA New Millennium
Program (NMP) Earth Observing-3 (EO-3) mission, has recently completed a series of uplooking atmospheric
measurements. The GIFTS development demonstrates a series of new sensor and data processing technologies that can
significantly expand geostationary meteorological observational capability. The resulting increase in forecasting
accuracy and atmospheric model development utilizing this hyperspectral data is demonstrated by the uplooking data.
The GIFTS sensor is an imaging FTS with programmable spectral resolution and spatial scene selection, allowing
spectral resolution and area coverage to be traded in near-real time. Due to funding limitations, the GIFTS sensor module
was completed as an engineering demonstration unit that can be upgraded to flight quality. This paper reviews the
GIFTS system design considerations and the technology utilized to enable a nearly two order performance increase over
the existing GOES sounder and shows its capability. While not designed as an operational sensor, GIFTS EDU provides
a flexible and accurate testbed for the new products the hyperspectral era will bring. Efforts to find funding to upgrade
and demonstrate this amazing sensor in space are continuing.
J. Elwell, G. Cantwell, D. Scott, R. Esplin, G. Hansen, S. Jensen, M. Jensen, S. Brown, L. Zollinger, V. Thurgood, M. Esplin, R. Huppi, G. Bingham, H. Revercomb, F. Best, D. Tobin, J. Taylor, R. Knuteson, W. Smith, R. Reisse, R. Hooker
The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) was developed for the NASA New Millennium
Program (NMP) Earth Observing-3 (EO-3) mission. This paper discusses the GIFTS measurement requirements and the
technology utilized by the GIFTS sensor to provide the required system performance. Also presented are preliminary
results from the recently completed calibration of the instrument. The GIFTS NMP mission challenge was to
demonstrate new and emerging sensor and data processing technologies to make revolutionary improvements in
meteorological observational capability and forecasting accuracy using atmospheric imaging and hyperspectral sounding
methods. The GIFTS sensor is an imaging FTS with programmable spectral resolution and spatial scene selection,
allowing radiometric accuracy and atmospheric sounding precision to be traded in near-real time for area coverage.
System sensitivity is achieved through the use of a cryogenic Michelson interferometer and two large-area, IR focal
plane detector arrays. Due to funding limitations, the GIFTS sensor module was completed as an engineering
demonstration unit, which can be upgraded for flight qualification. Capability to meet the next generation
geosynchronous sounding requirements has been successfully demonstrated through thermal vacuum testing and
rigorous IR calibration activities.
The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, a 10-channel infrared (1.27 - 16.9 μm) radiometer, was launched on the TIMED (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics) satellite in December 2001 from Vandenburg Air Force Base. SABER is being used to measure earthlimb emissions and to characterize infrared radiation, allowing calculation of cooling rates and determination of composition and temperature profiles in the mesosphere, lower thermosphere, and ionosphere (60-180 km). The SABER telescope is an on-axis Cassegrain design with a picket-fence tuning fork chopper at the first focus and a clamshell re-imager to focus the image on the focal plane. The telescope was designed to reject stray light from the Earth and atmosphere outside the instrument's instantaneous field-of-view (IFOV). The baffle assembly contains a single-axis scan mirror, which permits the 2 km vertical IFOV of each detector to be scanned from the Earth to a 400 km tangent height. The telescope and baffle assembly are cooled to 220 K by a dedicated radiator. The focal plane assembly is cooled to 75 K by a miniature cryogenic refrigerator. Field programmable gate arrays are used to implement state machine algorithms for control and operation of the instrument and subsystems. Although originally designed for a two-year lifetime requirement, the SABER instrument has been in continuous operation since January 2002. This paper discusses the SABER instrument design and innovations developed to achieve the required performance, along with instrument performance and lessons learned from the program.
Utah State University/Space Dynamics Laboratory, teaming with NASA Langley, has built, tested, integrated, and launched the SABER instrument. This instrument is orbiting the Earth on board the TIMED satellite, which resides in a 600 km circular orbit. SABER utilizes a pulse tube cryocooler to cool the focal plane assembly to 75K and passive radiators to cool the remaining components of the instrument. This paper will document the thermal design and modeling of the SABER instrument and compare the modeling results with acceptance testing and on orbit performance data. Preliminary on orbit data indicates that SABER is performing as modeled and is meeting all science objectives.
The SABER instrument (Sounding of the Atmosphere using Broadband Emission Spectroscopy) is a cryogenic infrared sensor on the TIMED spacecraft with stringent molecular and particulate contamination control requirements. The sensor measures infrared emissions from atmospheric constituents in the earth limb at altitudes ranging from 60 to 180 km using radiatively-cooled 240 K optics and a mechanically-refrigerated 75 K detector. The stray light performance requirements necessitate nearly pristine foreoptics. The cold detector in a warm sensor presents challenges in controlling the cryodeposition of water and other condensable vapors. Accordingly, SABER incorporates several unique design features and test strategies to control and measure the particulate and molecular contamination environment. These include internal witness mirrors, dedicated purge/depressurization manifolds, labyrinths, cold stops, and validated procedures for bakeout, cooldown, and warmup. The pre-launch and on-orbit contamination control performance for the SABER telescope will be reviewed.
The focal plane assembly of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is supported using Fiber Support Technology (FiST) which utilizes high performance fibers in tension to mechanically support and thermally isolate a cooled component from a warm environment. Details of this approach were presented in detail at SPIE meeting in Denver in 1996. The SABER team deemed it necessary to perform optical stability testing on this never-before-flown technology for supporting focal plane assemblies to determine if precise positioning could be maintained through vibration and thermal cycling. After subjecting the support system to vibration and thermal cycling, the angular orientation between the warm outer support structure and the inner cold block was measured. Since the outer support structure serves as the reference location for positioning the focal plane assembly and the cold block is where the detectors reside, it was possible to determine if FiST meets the optical stability requirements for the SABER instrument. The results from this testing are presented, discussed, and compared to the optical requirements of the SABER instrument. A brief summary of current thermal and mechanical enhancements to the system will also be discussed.
Utah State University/Space Dynamics Laboratory, teaming with NASA Langley Research Center, is currently building the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument. Stringent mass and power constraints, together with a greater than two year mission life, led to the selection of a TRW miniature pulse tube refrigerator to cool SABER's infrared detectors to the required temperature of 75 K. This paper provides an overview of the SABER thermal management plan and the challenges encountered in matching the refrigerator characteristics with instrument performance requirements under the broadly variant space environments expected for this mission. Innovative technologies were developed to keep heat loads within the limited cooling capacity of the miniature refrigerator, as well as mechanically isolating but thermally connecting the refrigerator cold block to the focal plane assembly (FPA). A passive radiator will maintain the SABER telescope at an average temperature of 230 K while a separate radiator will reject heat from the refrigerator and electronics at approximately 260 K. Significant breadboard tests of various components of the SABER instrument have taken place and the details of one of these will be discussed. The test included attaching a miniature mechanical refrigerator, borrowed from the Air Force, to the SABER FPA. This opportunity gave the SABER team a significant head start in learning about integrating and testing issues related with the TRW miniature pulse tube refrigerator. SABER is scheduled to be launched in January 2000 as the primary instrument of NASA's TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) spacecraft. The TIMED program is being managed by the Applied Physics Laboratory at Johns Hopkins University.
This paper addresses the current thermal management techniques of the Sounding of the Atmosphere using broadband emission radiometry (SABER) instrument. The SABER instrument is being developed jointly by NASA Langley and the Space Dynamics Laboratory at Utah State University. This instrument will fly on the Thermosphere-Ionosphere- Mesosphere Energetics and Dynamics spacecraft being built at the Applied Physics Laboratory at John Hopkins University. The infrared sensors on SABER must be cooled to 75 K for a 2 year period and at a 100 percent duty cycle. Because of SABER's stringent mass, size, and power constraints, the TRW miniature pulse tube refrigerator has been baselined to cool the focal plane assembly. A passive radiator will maintain the telescope at an average temperature near 230 K. Heat from the cryo-cooler and electronics will be dissipated by a separate radiator maintained at approximately 273 K. Approaches and advances in thermal management technology currently employed on the SABER instrument to ensure that heat loads and temperature ranges are met are also discussed.
Flexible thermal links play an important role int he thermal management of cryogenically cooled components. The purpose of these links is to provide a means of transferring heat from a cooled component to a cooler reservoir with little increase in temperature. The standard soldered approach although effective proves to be time consuming and contributes to added thermal impedances which degrade the performance of the link. For system with little tolerance for temperature differences between cooled components and a cooling source this is undesirable. The authors of this paper have developed a technique by which thin metal foil or braided wire can be attached to metal end blocks without any solder using the swaging process. Swaging provides a fast, simple method for providing a low thermal impedance between the foils and blocks. This paper describes the characteristics of these thermal links in terms of length, mass, thermal resistance, flexibility, and survivability.
Conventional methods for supporting cold components in optical systems and instruments often lead to excessive conductive heat loads. The need for better thermal isolation while maintaining structural rigidity motivated work on a tension system utilizing high performance fibers to support a focal plane assembly in an instrument to be flown in space. Utilizing Kevlar 49 fibers in an approach referred to as fiber support technology, we were able to reduce the conducted parasitic heat loads from 85 mW to less than 2 mW while increasing the 1st resonant frequency form about 50 Hz to 700 Hz. Various radiation suppression and wiring schemes were necessary to further reduce the total parasitic heat loads on this system. This paper outlines the details of this development effort making the use of a low input power miniature mechanical cooler possible. This approach seems consistent with the 'smaller', better, cheaper, faster' attitude of the nineties.
This paper provides an overview of the sounding of the atmosphere using broadband emission radiometer (SABER) instrument proposed by NASA Langley Research Center (LaRC) and the Space Dynamics Laboratory at Utah State University (SDL/USU). SABER is a 12-channel infrared radiometer designed to measure atmospheric emissions in the 1 to 17 micrometers spectral region. Radiometric, optical, thermal, and electronic aspects of the design are discussed.
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