Mark F. Larsen

Wide-field Infrared Survey Explorer science payload update

The Wide Field Infrared Survey Explorer is a NASA Medium Class Explorer mission to perform a high-sensitivity, high resolution, all-sky survey in four infrared wavelength bands. The science payload is a 40 cm aperture cryogenically cooled infrared telescope with four 10242 infrared focal plane arrays covering from 2.8 to 26 μm. Mercury cadmium telluride (MCT) detectors are used for the 3.3 μm and 4.6 μm channels, and Si:As detectors are used for the 12 μm and 23 μm wavelength channels. A cryogenic scan mirror freezes the field of view on the sky over the 9.9-second frame integration time. A two-stage solid hydrogen cryostat provides cooling to temperatures less than 17 K and 8.3 K at the telescope and Si:As focal planes, respectively. The science payload collects continuous data on orbit for the seven-month baseline mission with a goal to support a year-long mission, if possible. As of the writing of this paper, the payload subassemblies are complete, and the payload has begun integration and test. This paper provides a payload overview and discusses instrument status and performance.

Wide-field Infrared Survey Explorer science payload overview

The Wide Field Infrared Survey Explorer is a NASA Medium Class Explorer mission to perform and all-survey in four infrared wavelength bands. The science payload is a cryogenically cooled infrared telescope with four 10242 infrared focal plane arrays covering from 2.8 to 26 microns. Advances in focal plane technology and a large aperture allow an all-sky survey to be performed with high sensitivity and resolution. Mercury cadmium telluride (MCT) detectors, cooled to 32 K, are used for the two midwave channels, and Si:As detectors, cooled to < 8.3 K, are used for the two long wavelength channels. Cooling for the payload is provided by a two-stage solid hydrogen cryostat providing temperatures <17K and < 8.3K at the telescope and Si:As focal planes, respectively. The science payload supports operations on orbit for the seven month baseline mission with a goal to support a 13 month extended mission if available. This paper provides a payload overview and discusses instrument requirements and performance.

Characterization of flight detector arrays for the wide-field infrared survey explorer

The Wide-field Infrared Survey Explorer is a NASA Midex mission launching in late 2009 that will survey the entire sky at 3.3, 4.7, 12, and 23 microns (PI: Ned Wright, UCLA). Its primary scientific goals are to find the nearest stars (actually most likely to be brown dwarfs) and the most luminous galaxies in the universe. WISE uses three dichroic beamsplitters to take simultaneous images in all four bands using four 1024×1024 detector arrays. The 3.3 and 4.7 micron channels use HgCdTe arrays, and the 12 and 23 micron bands employ Si:As arrays. In order to make a 1024×1024 Si:As array, a new multiplexer had to be designed and produced. The HgCdTe arrays were developed by Teledyne Imaging Systems, and the Si:As array were made by DRS. All four flight arrays have been delivered to the WISE payload contractor, Space Dynamics Laboratory. We present initial ground-based characterization results for the WISE arrays, including measurements of read noise, dark current, flat field and latent image performance, etc. These characterization data will be useful in producing the final WISE data product, an all-sky image atlas and source catalog.

Temperature-dependent linearity calibration for the SPIRIT III radiometer

A temperature-dependent linearity correction function is derived using ground calibration data for the spatial infrared imaging telescope (SPIRIT III) radiometer. First, a small-signal analysis is used to derive linearity correction functions for each array at several focal plane temperatures. These functions are used to derive a single temperaturedependent linearity correction function for each array. The arrays exhibit some detector-dependent nonlinearity. A temperature- and detectordependent linearity correction function is developed by modifying the temperature-dependent array-average linearity correction function so that the half-scale nonlinearity is correct for each detector in the array. Using the nonuniformity correction (NUC) coefficient of variation (COV) as a metric, this temperature- and detector-dependent linearity correction function results in a COV between 0.35 to 2.6% for all arrays, depending on the array and integration mode.

Estimated performance of the Wide-field Infrared Explorer (WIRE) instrument

The Wide-Field IR Explorer (WIRE) is a small spaceborne cryogenic IR telescope being readied for launch in September 1998. Part of NASAs Small Explorer program, WIRE will carry out a deep pointed survey in broad 24 and 12 micron passbands designed primarily to study the evolution of starburst galaxies and to search for protogalaxies. The strategy for the WIRE survey and its stare-and-dither technique for building up long exposure times are described. An overview of the WIRE instrument is presented, with emphasis on the results of ground characterization and expected on-orbit performance of the WIRE optics and the Si:As focal plane arrays. The result of the ground characterization demonstrate that WIRE will meet or exceed the requirements for its science objectives. A brief overview is given of the primary and additional science that will be enabled by WIRE.

Impact of the SPIRIT III sensor design on algorithms for background removal, object detection, and point-source extraction

This paper describes background removal, point source detection, and position and irradiance extraction data processing algorithms that have been developed for the Spatial Infrared Imaging Telescope (SPIRIT) III design. The SPIRIT III sensor is the primary instrument on the Midcourse Space Experiment (MSX) satellite and is scheduled for launch in early 1996. The sensor consists of an off-axis reimaging telescope, and, among other instruments, a six-band scanning radiometer that covers the spectrum from midwave infrared to longwave infrared. The radiometer has five arsenic-doped silicon (Si:As) focal plane detector arrays with 8 X 192 pixels. The angular separation between adjacent pixels is 90 (mu) rad. A single axis scan mirror can operate at a constant 0.46 deg/sec scan rate to give programmable fields of regard of 1 X 0.75, 1 X 1.5, and 1 X 3 degrees or can remain fixed. Scanned images are non-uniformly sampled because of non-linear scan mirror motion, array misalignment, optical distortion, detector readout ordering, and satellite rotation. In addition, three of the five arrays contain multiple cross-scan aligned columns of pixels that five scanned images that have spatially overlapping in- scan data. Algorithms for processing data sampled on a uniform grid, such as data obtained from a CCD array, are enhanced and applied to the SPIRIT III radiometer where scanned images are non-uniformly sampled and have spatially overlapping data. The performance of these algorithms are evaluated with point source data acquired during ground measurements.

Algorithms for calibration and point-source extraction for a LWIR space-based sensor

The Midcourse Space Experiment (MSX) satellite is scheduled for launch in early 1996. The Spatial Infrared Imaging Telescope (SPIRIT) III sensor, the primary instrument of MSX, covers the spectrum from the midwave infrared to the longwave infrared. The SPIRIT III instrument is cryogenically cooled and consists of an interferometer and a five-band scanning radiometer with a spatial resolution of 90 (mu) rad. This paper describes the unique algorithms and software implementation developed to support the SPIRIT III radiometer. The algorithms for converting raw radiometer counts to calibrated counts and then to engineering units are described. The standard process (raw counts to corrected counts) consists of dark offset correction, linearity correction, integration mode normalization, non-uniformity correction, field of regard non-uniformity correction, and bad pixel processing. The algorithm to convert corrected counts to point source engineering units consist of pixel position tagging (non-uniform grid), color coalignment, distortion correction, background subtraction, correction for spacecraft attitude, and position and amplitude determination. The algorithms implemented in the software must produce goniometric estimates to within 5 (mu) rad (0.05 pixel) and radiometric results to within 1 percent. The results of the algorithms are demonstrated in this paper.

The Wide-field Infrared Survey Explorer (WISE) beamsplitter assembly

The design, fabrication and testing of the BeamSplitter Assembly (BSA) of the Wide-field Infrared Survey Explorer (WISE) instrument are discussed in the paper. The BSA splits the WISE telescope optical output beam into 4 spectral wavelength bands: 2.8-3.8, 4.1-5.2, 7.5-16.5, and 20-26 μm. The BSA also provides focus adjustments to focus the WISE instrument prior to launch. The methods used to focus WISE are also discussed in this paper. Funding for and management of the WISE program were provided by the NASA Jet Propulsion Laboratory.

Pre-launch characterization of the WISE payload

The Wide-field Infrared Survey Explorer (WISE), launched on December 14, 2009, is a NASA-funded Explorer mission that is providing an all-sky survey in the mid-infrared with far greater sensitivity and resolution than any previous IR survey mission. The WISE science payload is a cryogenically cooled infrared telescope with four 1024x1024 infrared focal plane arrays covering from 2.8 to 26 μm, which was designed, fabricated, and characterized by Utah State Universitys Space Dynamics Laboratory. Pre-launch charaterization included measuring focus, repeatability, response non-linearity, saturation, latency, absolute response, flatfield, point response function, scanner linearity, and relative spectral response. We will provide a brief overview of the payload, discuss the overall characterization approach, review several pre-launch characterization methods in detail, and present selected results from ground characterization and early on-orbit performance.

Lessions learned in WISE image quality

The Wide-Field Infrared Survey Explorer (WISE) mission launched in December of 2009 is a true success story. The mission is performing beyond expectations on-orbit and maintained cost and schedule throughout. How does such a thing happen? A team constantly focused on mission success is a key factor. Mission success is more than a program meeting its ultimate science goals; it is also meeting schedule and cost goals to avoid cancellation. The WISE program can attribute some of its success in achieving the image quality needed to meet science goals to lessons learned along the way. A requirement was missed in early decomposition, the absence of which would have adversely affected end-to-end system image quality. Fortunately, the ability of the cross-organizational team to focus on fixing the problem without pointing fingers or waiting for paperwork was crucial in achieving a timely solution. Asking layman questions early in the program could have revealed requirement flowdown misunderstandings between spacecraft control stability and image processing needs. Such is the lesson learned with the WISE spacecraft Attitude Determination & Control Subsystem (ADCS) jitter control and the image data reductions needs. Spacecraft motion can affect image quality in numerous ways. Something as seemingly benign as different terminology being used by teammates in separate groups working on data reduction, spacecraft ADCS, the instrument, mission operations, and the science proved to be a risk to system image quality. While the spacecraft was meeting the allocated jitter requirement , the drift rate variation need was not being met. This missing need was noticed about a year before launch and with a dedicated team effort, an adjustment was made to the spacecraft ADCS control. WISE is meeting all image quality requirements on-orbit thanks to a diligent team noticing something was missing before it was too late and applying their best effort to find a solution.