Edward Hugo Darlington

CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) on MRO (Mars Reconnaissance Orbiter)

CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) is a hyperspectral imager that will be launched on the MRO (Mars Reconnaissance Orbiter) spacecraft in August 2005. MRO’s objectives are to recover climate science originally to have been conducted on the Mars Climate Orbiter (MCO), to identify and characterize sites of possible aqueous activity to which future landed missions may be sent, and to characterize the composition, geology, and stratigraphy of Martian surface deposits. MRO will operate from a sun-synchronous, near-circular (255x320 km altitude), near-polar orbit with a mean local solar time of 3 PM. CRISM’s spectral range spans the ultraviolet (UV) to the mid-wave infrared (MWIR), 383 nm to 3960 nm. The instrument utilizes a Ritchey-Chretien telescope with a 2.12° field-of-view (FOV) to focus light on the entrance slit of a dual spectrometer. Within the spectrometer, light is split by a dichroic into VNIR (visible-near-infrared, 383-1071 nm) and IR (infrared, 988-3960 nm) beams. Each beam is directed into a separate modified Offner spectrometer that focuses a spectrally dispersed image of the slit onto a two dimensional focal plane (FP). The IR FP is a 640 x 480 HgCdTe area array; the VNIR FP is a 640 x 480 silicon photodiode area array. The spectral image is contiguously sampled with a 6.6 nm spectral spacing and an instantaneous field of view of 61.5 μradians. The Optical Sensor Unit (OSU) can be gimbaled to take out along-track smear, allowing long integration times that afford high signal-to-noise ratio (SNR) at high spectral and spatial resolution. The scan motor and encoder are controlled by a separately housed Gimbal Motor Electronics (GME) unit. A Data Processing Unit (DPU) provides power, command and control, and data editing and compression. CRISM acquires three major types of observations of the Martian surface and atmosphere. In Multispectral Mapping Mode, with the gimbal pointed at planet nadir, data are collected at frame rates of 15 or 30 Hz. A commandable subset of wavelengths is saved by the DPU and binned 5:1 or 10:1 cross-track. The combination of frame rates and binning yields pixel footprints of 100 or 200 m. In this mode, nearly the entire planet can be mapped at wavelengths of key mineralogic absorption bands to select regions of interest. In Targeted Mode, the gimbal is scanned over ±60° from nadir to remove most along-track motion, and a region of interest is mapped at full spatial and spectral resolution. Ten additional abbreviated, pixel-binned observations are taken before and after the main hyperspectral image at longer atmospheric path lengths, providing an emission phase function (EPF) of the site for atmospheric study and correction of surface spectra for atmospheric effects. In Atmospheric Mode, the central observation is eliminated and only the EPF is acquired. Global grids of the resulting lower data volume observation are taken repeatedly throughout the Martian year to measure seasonal variations in atmospheric properties.

Ultraviolet and visible imaging and spectrographic imaging instrument

The Ultraviolet and Visible Imaging and Spectrographic Imaging experiment consists of five spectrographic imagers and four imagers. These nine sensors provide spectrographic and imaging capabilities from 110 to 900 nm. The spectrographic imagers share an off-axis design in which selectable slits alternate fields of view (1.00° × 0.10° or 1.00° × 0.05°) and spectral resolutions between 0.5 and 4 nm. Image planes of the spectrographic imager have a programmable spectral dimension with 68, 136, or 272 pixels across each individual spectral band, and a programmable spatial dimension with 5, 10, 20, or 40 pixels across the 1° slit length. A scan mirror sweeps the slit through a second spatial dimension to generate a 1° × 1° spectrographic image once every 5, 10, or 20 s, depending on the scan rate. The four imagers provide narrow-field (1.28° × 1.59°) and wide-field (10.5° × 13.1°) viewing. Each imager has a six-position filter wheel that selects various spectral regimes and neutral densities. The nine sensors ut lize intensified CCD detectors that have an intrascene dynamic range of ~ 10(3) and an interscene dynamic range of ~ 10(5); neutral-density filters provide an additional dynamic range of ~ 10(2-3). The detector uses an automatic gain control that permits the sensors to adjust to scenes of varying intensity. The sensors have common boresights and can operate separately, simultaneously, or synchronously. To be launched aboard the Midcourse Space Experiment spacecraft in the mid-1990s, the ultraviolet and visible imaging and spectrographic imaging instrument will investigate a multitude of celestial, atmospheric, and point sources during its planned 4-yr life.

Special sensor ultraviolet spectrographic imager: an instrument description

We describe the Special Sensor Ultraviolet Spectrographic Imager (SSUSI). This instrument consists of a scanning imaging spectrograph (SIS) whose field-of-view is scanned from horizon to horizon and a nadir-looking photometer system (NPS). The SIS produces simultaneous multispectral images over the spectral range 1 150 to 1800A. The NPS consists of three photometers with filters designed to monitor the airglow at 4278A and 6300A and the terrestrial albedo near 6300A. SSUSI will fly on the DMSP Block 5D3 satellites S-16 thru S-19. The instruments will be calibrated at the Applied Physics Laboratorys Optical Calibration Facility.

In-flight performance of MESSENGER's Mercury Dual Imaging System

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched in August 2004 and planned for insertion into orbit around Mercury in 2011, has already completed two flybys of the innermost planet. The Mercury Dual Imaging System (MDIS) acquired nearly 2500 images from the first two flybys and viewed portions of Mercurys surface not viewed by Mariner 10 in 1974-1975. Mercurys proximity to the Sun and its slow rotation present challenges to the thermal design for a camera on an orbital mission around Mercury. In addition, strict limitations on spacecraft pointing and the highly elliptical orbit create challenges in attaining coverage at desired geometries and relatively uniform spatial resolution. The instrument designed to meet these challenges consists of dual imagers, a monochrome narrow-angle camera (NAC) with a 1.5° field of view (FOV) and a multispectral wide-angle camera (WAC) with a 10.5° FOV, co-aligned on a pivoting platform. The focal-plane electronics of each camera are identical and use a 1024×1024 charge-coupled device detector. The cameras are passively cooled but use diode heat pipes and phase-change-material thermal reservoirs to maintain the thermal configuration during the hot portions of the orbit. Here we present an overview of the instrument design and how the design meets its technical challenges. We also review results from the first two flybys, discuss the quality of MDIS data from the initial periods of data acquisition and how that compares with requirements, and summarize how in-flight tests are being used to improve the quality of the instrument calibration.

Design and fabrication of the New Horizons Long-Range Reconnaissance Imager

The LOng-Range Reconnaissance Imager (LORRI) is an instrument that was designed, fabricated, and qualified for the New Horizons mission to the outermost planet Pluto, its giant satellite Charon, and the Kuiper Belt, which is the vast belt of icy bodies extending roughly from Neptunes orbit out to 50 astronomical units (AU). New Horizons is being prepared for launch in January 2006 as the inaugural mission in NASAs New Frontiers program. This paper provides an overview of the efforts to produce LORRI. LORRI is a narrow angle (field of view=0.29°), high resolution (instantaneous field of view = 4.94 μrad), Ritchey-Chretien telescope with a 20.8 cm diameter primary mirror, a focal length of 263 cm, and a three lens field-flattening assembly. A 1024 x 1024 pixel (optically active region), back-thinned, backside-illuminated charge-coupled device (CCD) detector (model CCD 47-20 from E2V Technologies) is located at the telescope focal plane and is operated in standard frame-transfer mode. LORRI does not have any color filters; it provides panchromatic imaging over a wide bandpass that extends approximately from 350 nm to 850 nm. A unique aspect of LORRI is the extreme thermal environment, as the instrument is situated inside a near room temperature spacecraft, while pointing primarily at cold space. This environment forced the use of a silicon carbide optical system, which is designed to maintain focus over the operating temperature range without a focus adjustment mechanism. Another challenging aspect of the design is that the spacecraft will be thruster stabilized (no reaction wheels), which places stringent limits on the available exposure time and the optical throughput needed to accomplish the high-resolution observations required. LORRI was designed and fabricated by a combined effort of The Johns Hopkins University Applied Physics Laboratory (APL) and SSG Precision Optronics Incorporated (SSG).

Calibration of the New Horizons Long-Range Reconnaissance Imager

The LOng-Range Reconnaissance Imager (LORRI) is a panchromatic imager for the New Horizons Pluto/Kuiper belt mission. New Horizons is being prepared for launch in January 2006 as the inaugural mission in NASAs New Frontiers program. This paper discusses the calibration and characterization of LORRI. LORRI consists of a Ritchey-Chretien telescope and CCD detector. It provides a narrow field of view (0.29°), high resolution (pixel FOV = 5 μrad) image at f/12.6 with a 20.8~cm diameter primary mirror. The image is acquired with a 1024 x 1024 pixel CCD detector (model CCD 47-20 from E2V). LORRI was calibrated in vacuum at three temperatures covering the extremes of its operating range (-100°C to +40°C for various parts of the system) and its predicted nominal temperature in-flight. A high pressure xenon arc lamp, selected for its solar-like spectrum, provided the light source for the calibration. The lamp was fiber-optically coupled into the vacuum chamber and monitored by a calibrated photodiode. Neutral density and bandpass filters controlled source intensity and provided measurements of the wavelength dependence of LORRIs performance. This paper will describe the calibration facility and design, as well as summarize the results on point spread function, flat field, radiometric response, detector noise, and focus stability over the operating temperature range. LORRI was designed and fabricated by a combined effort of The Johns Hopkins University Applied Physics Laboratory (APL) and SSG Precision Optronics. Calibration was conducted at the Diffraction Grating Evaluation Facility at NASA/Goddard Space Flight Center with additional characterization measurements at APL.

Compact reconnaissance imaging spectrometer for Mars (CRISM): characterization results for instrument and focal plane subsystems

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) will launch in 2005 on the Mars Reconnaissance Orbiter (MRO) mission, with its primary science objective to characterize sites with aqueous mineral deposits hyperspectrally at high spatial resolution. CRISM’s two Offner relay spectrometers share a single entrance slit with a dichroic beamsplitter. The IR focal plane contains a 640 (spatial) x 480 (spectral) HgCdTe FPA with a 980 nm to 3960 nm spectral bandpass. It is cooled to 110 K to minimize dark current, and coupled to a 28 mm long cold shield to minimize thermal background. The spectrometer housing is cooled to -90 C for the same reason. A three-zone IR filter consisting of two broadband filters and a linear variable filter overlays the IR focal plane, eliminating multiple grating orders and providing additional attenuation of the thermal background. The visible focal plane contains a 640 (spatial) x 480 (spectral) silicon photodiode array, with a 380-1050 nm spectral bandpass occupying approximately 106 rows of the detector. A two-zone filter comprised of two different Schott glasses eliminates multiple grating orders. The two focal planes together cover 544 spectral channels with a dispersion of 6.55 nm/channel in the VNIR and 6.63 nm/channel in the IR. The optics and focal planes are gimbaled, and a pre-programmed slew can be used to remove groundtrack motion while superimposing a scan across a target. CRISM will operate in two basic modes: a scanning, high resolution mode to hyperspectrally map small, targeted areas of high scientific interest, and a fixed, nadir-pointed, lower resolution pixel-binned mode using selected wavelength channels to obtain near-global coverage to find targets. Preliminary performance of the CRISM instrument is presented, and is compared with prior system design predictions.

Ultraviolet and visible imaging and spectrographic imaging (UVISI) experiment

The ultraviolet and visible imaging and spectrographic imaging (UVISI) experiment consists of five spectrographic imagers and four imagers. These nine sensors provide spectrographic and imaging capabilities from approximately equals 110 nm to approximately equals 900 nm. The spectrographic imagers (SPIMs) share an off-axis parabolic design in which selectable slits (1.00 degree(s) X 0.10 degree(s) or 1.00 degree(s) X 0.05 degree(s)) provide spectral resolutions between approximately equals 0.5 nm and approximately equals 4.0 nm. SPIM image planes have programmable spectral dimensions with 68, 136, or 272 pixels and programmable spatial dimensions with 5, 10, 20, 40 pixels. A scan mirror sweeps the slit through a second spatial dimension and generates a spectrographic image once every 5, 10, or 20 seconds. The four imagers provide narrow-field and wide-field viewing. Each imager has a six-position filter wheel that selects various spectral regimes and neutral densities. Each of the nine sensors use intensified CCD detectors that have an intrascene dynamic range of approximately equals 103 and an interscene dynamic range of approximately equals 105; neutral density filters provide an additional dynamic range of approximately equals 102-3. An automatic gain control adjusts the intensifiers to scenes of varying intensity. UVISI also includes an image processing system that uses the raw data from any single imager to acquire and track targets of various sizes, shapes, and brightnesses. The image processor relays its results to a master tracking system that uses the UVISI data (as well as other data) to point the satellite in real time. UVISI will be launched on the MSX satellite in late 1994 and will investigate a multitude of celestial, atmospheric, and point sources during its planned five-year lifetime.

Study of Low Illumination Sensing Aids Applicable to Lunar Landing

An assessment of the potential use of low illumination sensing aids as a means to facilitate manned lunar landing in dimly lit regions, such as near the poles, terminator, and the lunar dark side has been performed. A number of natural and artificial illumination sources were considered: starlight, earthshine, sunlight reflected from high altitude terrain, light emitted by the landing rocket plume and artificial lamps. In addition, thermal emissions from the surface were considered. Various sensors were modeled, including CCDs in the visual and near infrared bands, low light goggles, long wavelength IR sensors, and the unaided human eye. It was found that in regions illuminated by scattered sunlight or earthshine mature CCD or low light goggle technology is adequate. Regions on the lunar dark side are more problematic as the temperatures are too low for practical thermal IR sensors and surface contrast may be inadequate for hazard avoidance using artificial sources of illumination.

The CONTOUR remote imager and spectrograph

Abstract The Comet Nucleus Tour (CONTOUR) is a NASA Discovery mission to study the diversity of comet nuclei. Top level mission goals include imaging the nuclei of several comets at resolutions up to 4 m / pixel , acquiring spectral information in both the visible and infrared (IR), and obtaining detailed compositional measurements of the gas and dust. The CONTOUR Remote Imager and Spectrograph (CRISP) instrument, under development at The Johns Hopkins University Applied Physics Laboratory, achieves the primary imaging and spectral mapping objectives. CRISP includes a visible imager and 10-position filter wheel to survey the visible spectrum from 400 to 800 nm and provide high-resolution images of the nucleus. An imaging spectrograph, utilizing a 256×256 HgCdTe array and yielding a spectral resolution of 7 nm , analyzes the infrared IR spectrum from 800 to 2500 nm . A Stirling cycle refrigerator cools the IR array to cryogenic operating temperatures. The imager and spectrograph share a common optical path that includes a scan mirror to actively track the comet nucleus during approach and fly-by. An overview of the CRISP instrument is presented.