Keith Peacock

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.

An overview of the NEAR multispectral imager‐near‐infrared spectrometer investigation

The combined MSI-NIS investigation on NEAR consists of a Multi-Spectral Imager (MSI) and a Near-Infrared Spectrometer (NIS). MSI covers the spectral range from 0.4 to 1.1 μm in seven narrow passbands and one broad filter. MSI has a field of view of 2.25° by 2.90° and will achieve an image scale of about 3 m/pixel at the surface of Eros. NIS covers the spectral interval from 0.8 to 2.6 μm: the range between 0.804 and 1.506 μm is measured by a 32-element Germanium detector; a 32-element Indium-Gallium-Arsenide detector observes wavelengths between 1.348 and 2.600 μm. The instrument has a selectable field of view of either 0.38°×0.76° or 0.76°×0.76°. A spatial resolution of about 300 m (100 times coarser than MSI) can be achieved at Eros. A major goal of the MSI-NIS investigation is to determine the fundamental global properties of Eros, including spin state, size, and shape. Precise size and shape measurements are necessary to determine an accurate volume and thereby a mean density from mass measurements. MSI-NIS spectral data will be combined with abundance determinations of key rock-forming elements obtained by the X ray/gamma ray spectrometers (XGRS) to infer the distribution of minerals on Eros and constrain models of the asteroids geochemical evolution. On approach to Eros, a search will be made for satellites: objects as small as 12 m (some 100 times smaller than Idas Dactyl) could be detected.

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.

Near Infrared Spectrometer for the Near Earth Asteroid Rendezvous Mission

The Near-Infrared Spectrometer (NIS) instrument on the Near-Earth Asteroid Rendezvous (NEAR) spacecraft is designed to map spectral properties of the mission target, the S-type asteroid 433 Eros, at near-infrared wavelengths diagnostic of the composition of minerals forming S asteroids. NIS is a grating spectrometer, in which light is directed by a dichroic beam-splitter onto a 32-element Ge detector (center wavelengths, 816–1486 nm) and a 32-element InGaAs detector (center wavelengths, 1371–2708 nm). Each detector reports a 32-channel spectrum at 12-bit quantization. The field-of-view is selectable using slits with dimensions calibrated at 0.37° × 0.76° (narrow slit) and 0.74° × 0.76° (wide slit). A shutter can be closed for dark current measurements. For the Ge detector, there is an option to command a 10x boost in gain. A scan mirror rotates the field-of-view over a 140° range, and a diffuse gold radiance calibration target is viewable at the sunward edge of the field of regard. Spectra are measured once per second, and up to 16 can be summed onboard. Hyperspectral image cubes are built up by a combination of down-track spacecraft motion and cross-track scanning of the mirror. Instrument software allows execution of data acquisition macros, which include selection of the slit width, number of spectra to sum, gain, mirror scanning, and an option to interleave dark spectra with the shutter closed among asteroid observations. The instrument was extensively characterized by on-ground calibration, and a comprehensive program of in-flight calibration was begun shortly after launch. NIS observations of Eros will largely be coordinated with multicolor imaging from the Multispectral Imager (MSI). NIS will begin observing Eros during approach to the asteroid, and the instrument will map Eros at successively higher spatial resolutions as NEARs orbit around Eros is lowered incrementally to 25 km altitude. Ultimate products of the investigation will include composition maps of the entire illuminated surface of Eros at spatial resolutions as high as ∼300 m.

Multi-Spectral Imager on the Near Earth Asteroid Rendezvous Mission

A multispectral imager has been developed for a rendezvous mission with the near-Earth asteroid, 433 Eros. The Multi-Spectral Imager (MSI) on the Near-Earth Asteroid Rendezvous (NEAR) spacecraft uses a five-element refractive optical telescope, has a field of view of 2.93 × 2.25°, a focal length of 167.35 mm, and has a spatial resolution of 16.1 × 9.5 m at a range of 100 km. The spectral sensitivity of the instrument spans visible to near infrared wavelengths, and was designed to provide insight into the nature and fundamental properties of asteroids and comets. Seven narrow band spectral filters were chosen to provide multicolor imaging and to make comparative studies with previous observations of S asteroids and measurements of the characteristic absorption in Fe minerals near 1 µm. An eighth filter with a much wider spectral passband will be used for optical navigation and for imaging faint objects, down to visual magnitude of +10.5. The camera has a fixed 1 Hz frame rate and the signal intensities are digitized to 12 bits. The detector, a Thomson-CSF TH7866A Charge-Coupled Device, permits electronic shuttering which effectively varies the dynamic range over an additional three orders of magnitude. Communication with the NEAR spacecraft occurs via a MIL-STD-1553 bus interface, and a high speed serial interface permits rapid transmission of images to the spacecraft solid state recorder. Onboard image processing consists of a multi-tiered data compression scheme. The instrument was extensively tested and calibrated prior to launch; some inflight calibrations have already been completed. This paper presents a detailed overview of the Multi-Spectral Imager and its objectives, design, construction, testing and calibration.

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.

The Optical Variability Of The Ocean Surface From CZCS Imagery

Coastal Zone Color Scanner (CZCS) results have been used to measure the optical varia-bility of the ocean over large areas. The properties of Jerlov type I waters of areas of the North Atlantic are compared with the types II and III waters of the North Pacific. Several techniques are used to quantify the variability. Radiance variations show the reflectance changes over large and small areas and demonstrate the striking difference between types I and III waters. Color index variations (in which the color index is the ratio of radiances in two spectral bands) have been computed for small areas such as warm core rings and for large ocean areas containing different water masses. Spectral band relationships, which display the radiance at one wavelength against the radiance at another wavelength or against the color index, show a great diversity which makes it difficult to generalize the data. Spectra show the spatial variability of radiance and color for a selection of north-south and east-west tracks covering a range of water types. The results indicate that the color and radiance variations have very diverse characteristics from region to region.

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.

Four-meter lunar engineering telescope

The 16-meter diffraction limited lunar telescope incorporates a primary mirror with 312 one-meter segments; 3 nanometer active optics surface control with laser metrology and hexapod positioners; a space frame structure with one-millimeter stability; and a hexapod mount for pointing. The design data needed to limit risk in this development can be obtained by building a smaller engineering telescope on the moon with all of the features of the 16-meter design. This paper presents a 4.33-meter engineering telescope concept developed by the Summer 1990 Student Program of the NASA/JHU Space Grant Consortium Lunar Telescope Project. The primary mirror, made up of 18 one-meter hexagonal segments, is sized to provide interesting science as well as engineering data. The optics are configured as a Ritchey-Chretien with a coude relay to the focal plane beneath the surface. The optical path is continuously monitored with 3-nanometer precision interferometrically. An active optics processor and piezoelectric actuators operate to maintain the end-to-end optical configuration established by wave front sensing using a guide star. The mirror segments, consisting of a one-centimeter thick faceplate on 30-cm deep ribs, maintain the surface figure to a few nanometers under lunar gravity and thermal environment.

Selected configuration tradeoffs of contour optical instruments

Abstract The Comet Nucleus Tour (CONTOUR) is a low-cost NASA Discovery mission designed to conduct three close flybys of comet nuclei. Selected configuration tradeoffs conducted to balance science requirements with low mission cost are reviewed. The tradeoffs discussed focus on the optical instruments and related spacecraft considerations. Two instruments are under development. The CONTOUR Forward Imager (CFI) is designed to perform optical navigation, moderate resolution nucleus/jet imaging, and imaging of faint molecular emission bands in the coma. The CONTOUR Remote Imager and Spectrometer (CRISP) is designed to obtain high-resolution multispectral images of the nucleus, conduct spectral mapping of the nucleus surface, and provide a backup optical navigation capability. Tradeoffs discussed are: (1) the impact on the optical instruments of not using reaction wheels on the spacecraft, (2) the improved performance and simplification gained by implementing a dedicated star tracker instead of including this function in CFI, (3) the improved flexibility and robustness of switching to a low frame rate tracker for CRISP, (4) the improved performance and simplification of replacing a visible imaging spectrometer by enhanced multispectral imaging in CRISP, and (5) the impact on spacecraft resources of these and other tradeoffs.