The Thermal Earth Resource Monitoring Instrument (THERMI) has been designed to meet stringent Landsat heritage requirements with reduced size, weight and power (SWaP). The instrument design provides Earth resource monitoring through the use of two long-wave infrared bands that measure the land surface temperatures. These bands are especially valuable for monitoring water resources and water use. Instrument subsystems, including electronics, cryocooler, thermal management, optical telescope assembly, focal plane module, in-flight calibrator, and scene select mirror were studied and conceptually designed to reduce overall THERMI SWaP. Reductions in SWaP make it possible for THERMI to fit on a small satellite bus with room available for an additional optical instrument. Since mission cost historically correlates well with mass and power on-orbit, it is expected that significant cost savings will result from the predicted SWaP reductions.
The Near Earth Object Surveillance Satellite (NEOSSat) is a small satellite dedicated to finding near Earth asteroids. Its
surveying strategy consists of imaging areas of the sky to low solar elongation, while in a sun synchronous polar orbit
(dawn-dusk). A high performance baffle will control stray light mainly due to Earth shine. Observation scenarios
require solar shielding down to 45 degree solar elongation over a wide range of ecliptic latitudes. In order to detect the
faintest objects (approx 20th v mag) given a 15 cm telescope and CCD detection system, background from stray light is a
critical operational concern. The required attenuation is in the order of 10-12. The requirement was verified by analyses;
testing was not attempted because the level of attenuation is difficult to measure reliably. We report consistent results of
stray light optical modelling from two independent analyses. Launch is expected for late 2012.
The Solar Occultation for Ice Experiment (SOFIE) instrument is one of three science instruments for the Aeronomy of
Ice in the Mesosphere (AIM) mission. SOFIE is used to measure solar attenuation by mesospheric ice aerosols during
each observatory sunrise and sunset using an 8-channel (16-detector) differential absorption radiometer. It directly
views the sun and compares the near UV to the mid-IR spectral response during exo-atmospheric and endo-atmospheric
measurements. Deposition of molecular films can degrade the reflectance and transmittance of SOFIE's optics. During
on-orbit performance, it may be possible for the extended solar exposure to promote photochemical deposition and
darkening effects in the UV. This paper will review the methods used to derive and verify contamination control
budgets for particulate and molecular contamination during the fabrication and testing of the SOFIE instrument.
Reported results include the molecular surface cleanliness throughout integration and test as well as outgassing
measurements using internal and external quartz crystal microbalances. This information provides important baseline
data for future correlation of instrument outgassing and potential photo-deposited contamination effects should they
occur during on-orbit solar exposure
The Optical Navigation Camera (ONC) is part of NASA's Mars Reconnaissance Orbiter (MRO) scheduled for an August 2005 launch. The design is a 500 mm focal length, F/8.3 Ritchey-Chretien with a refractive field corrector. Prior to flight, the off-axis performance of the ONC was measured at visible wavelengths in the off-axis scatter facility at the Space Dynamics Laboratory (SDL). This unique facility is designed to minimize scatter from the test setup to prevent data corruption. Testing was conducted in a clean room environment, and the results indicate that no detectable contamination of the optics occurred during testing. Measurements were taken in two time frames to correct an unanticipated stray light path, which occurred just outside of the sensor's field-of-view. The source of the offending path was identified as scatter from the edges of the field corrector lenses. Specifically, scatter from the interface between the flat ground glass and polished surfaces resulted in significant "humps" in the off-axis response centered at ± 1.5°. Retesting showed the removal of the humps, and an overall satisfactory performance of the ONC. The troubleshooting, correction, and lessons learned regarding the above stray light path was reported on in an earlier paper. This paper discusses the measurement process, results, and a comparison to a software prediction and other planetary sensors. The measurement validated the final stray light design and complemented the software analysis.
The Optical Navigation Camera (ONC) is a technical demonstration slated to fly on NASA’s Mars Reconnaissance Orbiter in 2005. Conventional navigation methods have reduced accuracy in the days immediately preceding Mars orbit insertion. The resulting uncertainty in spacecraft location limits rover landing sites to relatively safe areas, away from interesting features that may harbor clues to past life on the planet. The ONC will provide accurate navigation on approach for future missions by measuring the locations of the satellites of Mars relative to background stars. Because Mars will be a bright extended object just outside the camera’s field of view, stray light control at small angles is essential. The ONC optomechanical design was analyzed by stray light experts and appropriate baffles were implemented. However, stray light testing revealed significantly higher levels of light than expected at the most critical angles. The primary error source proved to be the interface between ground glass surfaces (and the paint that had been applied to them) and the polished surfaces of the lenses. This paper will describe troubleshooting and correction of the problem, as well as other lessons learned that affected stray light performance.
The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is a 10-channel earth limb-viewing sensor that measures atmospheric emissions in the spectral range of 1.27 μm to 16.9 μm. SABER is part of NASA's Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) mission, which was successfully launched in December 2001. Uncommon among limb-viewing sensors, SABER employs an on-axis telescope design with reimaging optics to allow for an intermediate field stop and a Lyot stop. Additional stray light protection is achieved by an innovative inner Lyot stop, which is placed conjugate to the secondary obscuration and support structure. Presented in this paper is the off-axis response of SABER as measured in the Terrestrial Black Hole off-axis scatter facility at the Space Dynamics Laboratory. The measurement was made at visible wavelengths; thus, the response is only representative of SABER's short wavelength channels. The measurement validated the stray light design and complemented the APART software model, which predicts that mirror scatter is the dominant stray light mechanism at short wavelengths. In addition, estimates of the mirror bi-directional reflectance distribution function (BRDF) were made. The off-axis response measurement indicates that SABER is an exceptional stray light suppression telescope.
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 Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is a 10-channel earth limb- viewing sensor that is to measure atmospheric emissions in the spectral range of 1.27 micrometer to 16.9 micrometer. Presented in this paper is the stray light design and analysis of SABER. Unwanted radiation from the earth and atmosphere are suppressed by the use of stray light features that are critical to mission success. These include the use of an intermediate field stop, an inner and outer Lyot stop, and super-polished mirrors. The point source normalized irradiance transmission (PSNIT) curve, which characterizes the sensor's off-axis response, was computed using the stray light analysis program APART. An initial calculation of the non-rejected radiance (NRR) due to emissions and scatter from the earth and atmosphere was made using the PSNIT data. The results indicate that stray light will not impede the mission objectives.
An off-axis scatter facility was developed to support the Space Dynamics Laboratory in a number of earth limb measurement programs where the off-axis performance of the sensors was critical to the validity of the data. The facility was developed from three fundamental assumptions. (1) Careful control of any light scattered from the optical system being measured to make certain that it did not return to re-enter the system and corrupt the measurement. (2) Use of black specular surfaces in a unique shape to direct and attenuate scattered light. (3) Utilization of clean room technology to filter air to reduce scattering from particulates in the air and to prevent dust from degrading the specularity of the special surfaces. Therewithal analyses of atmospheric and surface scattering showed that surface scattering effects could be suppressed below atmospheric scattering limits by use of properly shaped specular walls. Analysis of measurements made in the facility demonstrated that the measurements were limited by Rayleigh scattering from the air molecules in the facility and not from dust or water droplets in the air nor from scattering from any chamber surfaces. Measurements of the Cassini narrow field camera showed a noise floor at 2.8E-12 of on-axis response.
The wide-field infrared explorer (WIRE) is a cryogenically cooled infrared telescope designed to study the evolution of galaxies. Presented in this paper is the stray light design and analysis of WIRE. Unwanted radiation from off-axis sources such as the moon, and thermal emissions from the aperture shade are suppressed by the use of key stray light design features. These include the placement of the aperture stop at the secondary mirror, tapering of the main baffle vanes, and use of ring baffles for the secondary obscuration and outer ring. Details concerning the issues of baffle design, mirror scatter, and non-optical component scatter are provided. The point source transmission (PST) curve, which characterizes the sensor's off-axis response, and the aperture shade thermal contribution were computed using the stray light analysis program APART. The results indicate that the stray light impact on the WIRE mission is minimal.
This paper describes the design of a 10-channel infrared (1.27 to 16.9 micrometers ) radiometer instrument known as SABER (sounding of the atmosphere using broadband emission radiometry) that will measure earth-limb emissions from the TIMED (thermosphere- ionosphere-mesosphere energetics and dynamics) satellite. The instrument telescope, designed to reject stray light from the earth and the atmosphere, is an on-axis Cassegrain design with a clam shell reimager and a one-axis scan mirror. The telescope is cooled below 210 K by a dedicated radiator. The focal plane assembly (consisting of a filter array, a detector array, a Lyot stop, and a window) is cooled to 75 K by a miniature cryogenic refrigerator. The conductive heat load on the refrigerator is minimized by a Kevlar support system that thermally isolates the focal plane assembly from the telescope. Kevlar is also used to thermally isolate the telescope from the spacecraft. Instrument responsivity drifts due to changes in telescope and focal plane temperatures as well as other causes are neutralized by an in-flight calibration system. The detector array consists of discrete HgCdTe, InSb, and InGaAs detectors. Two InGaAs detectors are a new long wavelength type, made by EG&G, that have a long wavelength cutoff of 2.33 micrometers at 77 K.
The stray light analysis of the sounding of the atmosphere using broadband emission radiometry (SABER) instrument on the thermosphere-ionosphere-mesosphere energetics and dynamics (TIMED) mission is discussed. Relevant mission objectives and operating conditions are stated to define the stray light problem. Since SABER is an earth limb viewing sensor, the telescope must be designed for large off-axis rejection. Described are the key design features which make the instrument well suited for its mission. Representative point source transmittance (PST) curves computed using the commercial stray light program APART are presented. Nonrejected radiance (NRR) values computed using APART generated PST curves and LINEPACK generated curves for the total radiance from the earth and the atmosphere are given. A method for computing NRR from the earth and the atmosphere using line-of-sight radiance profiles versus tangent height is described. Computed NRR values demonstrate that the effect of stray light on SABER's measurement capability is negligible.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.