Isabella T. Lewis

Star tracker stellar compass for the Clementine mission

The Clementine mission provided the first ever complete, systematic surface mapping of the moon from the ultra-violet to the near-infrared region. More than 1.7 million images of the moon, earth and space were returned from this mission. Two star tracker stellar compasses (star tracker camera + stellar compass software) were included on the spacecraft, serving a primary function of providing angle updates to the guidance and navigation system. These cameras served as a secondary function by providing a wide field of view imaging capability for lunar horizon glow and other dark-side imaging data. This 290 g camera using a 576 X 384 FPA and a 17 mm entrance pupil, detected and centroided stars as dim and dimmer than 4.5 mv, providing rms pointing accuracy of better than 100 (mu) rad pitch and yaw and 450 (mu) rad roll. A description of this light-weight, low power star tracker camera along with a summary of lessons learned is presented. Design goals and preliminary on-orbit performance estimates are addressed in terms of meeting the missions primary objective for flight qualifying the sensors for future Department of Defense flights.

Near-infrared camera for the Clementine mission

The Clementine mission provided the first ever complete, systematic surface mapping of the moon from the ultra-violet to the near-infrared regions. More than 1.7 million images of the moon, earth, and space were returned from this mission. The near-infrared (NIR) multi- spectral camera, one of two workhorse lunar mapping cameras (the other being the UV/visible camera), provided approximately 200 m spatial resolution at 400 km periselene, and a 39 km across-track swath. This 1.9 kg infrared camera using a 256 X 256 InSb FPA viewed reflected solar illumination from the lunar surface and lunar horizon in the 1 to 3 micrometers wavelength region, extending lunar imagery and mineralogy studies into the near infrared. A description of this lightweight, low power NIR camera along with a summary of lessons learned is presented. Design goals and preliminary on-orbit performance estimates are addressed in terms of meeting the missions primary objective for flight qualifying the sensors for future Department of Defense flights.

HiRes camera and lidar ranging system for the Clementine mission

Lawrence Livermore National Laboratory developed a space-qualified high resolution (HiRes) imaging LIDAR (light detection and ranging) system for use on the DoD Clementine mission. The Clementine mission provided more than 1.7 million images of the moon, earth, and stars, including the first ever complete systematic surface mapping of the moon from the ultra-violet to near-infrared spectral regions. This article describes the Clementine HiRes/LIDAR system, discusses design goals and preliminary estimates of on-orbit performance, and summarizes lessons learned in building and using the sensor. The LIDAR receiver system consists of a HiRes imaging channel which incorporates an intensified multi-spectral visible camera combined with a laser ranging channel which uses an avalanche photo-diode for laser pulse detection and timing. The receiver was bore sighted to a lightweight McDonnell-Douglas diode-pumped Nd:YAG laser transmitter that emitted 1.06 micrometer wavelength pulses of 200 mJ/pulse and 10 ns pulse-width. The LIDAR receiver uses a common F/9.5 Cassegrain telescope assembly. The optical path of the telescope is split using a color-separating beamsplitter. The imaging channel incorporates a filter wheel assembly which spectrally selects the light which is imaged onto a custom 12 mm gated image intensifier fiber-optically coupled into a 384 multiplied by 276 pixel frame transfer CCD FPA. The image intensifier was spectrally sensitive over the 0.4 to 0.8 micrometer wavelength region. The six-position filter wheel contained 4 narrow spectral filters, one broadband and one blocking filter. At periselene (400 km) the HiRes/LIDAR imaged a 2.8 km swath width at 20-meter resolution. The LIDAR function detected differential signal return with a 40-meter range accuracy, with a maximum range capability of 640 km, limited by the bit counter in the range return counting clock. The imagery from the HiRes is most useful for smaller scale topography studies, while the LIDAR data is used for global terrain and inferred gravity maps.

Visible Imaging Fourier Transform Spectrometer: Design and Calibration

We present details of the design, operation and calibration of an astronomical visible-band imaging Fourier transform spectrometer (IFTS). This type of instrument produces a spectrum for every pixel in the field of view where the spectral resolution is flexible. The instrument is a dual-input/dual-output Michelson interferometer coupled to the 3.5 meter telescope at the Apache Point Observatory. Imaging performance, and interferograms and spectra from calibration sources and standard stars are discussed.

Clementine longwave infrared camera

The Clementine mission provided the first ever complete, systematic surface mapping of the moon from the ultra-violet to the near-infrared regions. More than 1.7 million images of the moon, earth, and space were returned from this mission. The long-wave-infrared (LWIR) camera supplemented the UV/visible and near-infrared mapping cameras providing limited strip coverage of the moon, giving insight to the thermal properties of the soils. This camera provided approximately 100 m spatial resolution at 400 km periselene, and a 7 km across- track swath. This 2.1 kg camera using a 128 X 128 mercury-cadmium-telluride (MCT) FPA viewed thermal emission of the lunar surface and lunar horizon in the 8.0 to 9.5 micrometers wavelength region. A description of this lightweight, low power LWIR camera along with a summary of lessons learned is presented. Design goals and preliminary on-orbit performance estimates are addressed in terms of meeting the missions primary objective for flight qualifying the sensors for future Department of Defense flights.

UV/visible camera for the Clementine mission

This article describes the Clementine UV/Visible (UV/Vis) multispectral camera, discusses design goals and preliminary estimates of on-orbit performance, and summarized lessons learned in building and using the sensor. While the primary objective of the Clementine Program was to qualify a suite of 6 light-weight, low power imagers for future Department of Defense flights, the mission also has provided the first systematic mapping of the complete lunar surface in the visible and near-IR spectral regions. The 410 g, 4.65 W UV/Vis camera uses a 384 X 288 frame-transfer silicon CCD FPA and operates at 6 user-selectable wavelength bands between 0.4 and 1.1 micrometers . It has yielded lunar imagery and mineralogy data with up to 120 m spatial resolution (band dependent) at 400 km periselene along a 39 km cross-track swath.

Cross-dispersion infrared spectrometry (CDIRS) for remote chemical sensing

The advent of high performance infrared detector arrays together with recent advances in coarse grating fabrication now makes possible the design and fabrication of infrared spectrometers that cover the mid-IR atmospheric windows at high resolution with no moving components. For applications involving small sources at large distances this instrument approach can provide a substantial increase in sensitivity over Fourier transform spectrometers at the same resolution and spectral coverage. We describe the design evolution of the LLNL cross dispersive infrared spectrometer (CDIRS) remote chemical sensors operating in the two atmospheric windows from 2.3 microns to 4.2 microns. The spectral and mechanical performance of the first generation 1 meter focal length prototype echelle grating spectrometer (EGS) is presented. A second generation cryogenic (150 K) spectrometer (mini-EGS) utilizes a high dispersion silicon immersion grating to provide a compact design. This instrument will be flown in the winter of 1995 as part of the instrumentation suite for the DOE airborne multisensor pod system (AMPS) effluent research program.

Stray-light reduction in a WFOV star tracker lens

Lawrence Livermore National Laboratory (LLNL) has recently developed a wide-field-of- view (28 degree(s) X 44 degree(s)) camera for use as a star tracker navigational sensor. As for all sensors, stray light rejection performance is critical. Due to the baffle dimensions dictated by the large field angles, the 2-part sunshade/baffle configuration commonly seen on space- born telescopes is impractical. Meeting the required stray light rejection performance (of 10-7 Point Source Transmittance, (PST)) with a 1-part baffle required iterative APART modeling (APART is an industry standard stray light evaluation program), hardware testing, and mechanical design correction. This paper presents a chronology of lens and baffle improvements that resulted in the meeting of the stray light rejection goal outside the solar exclusion angle of the baffle stage. Comparisons with APART analyses are given, and future improvements in mechanical design are discussed. Stray light testing methods and associated experimental difficulties are presented.

Design of a mid-IR immersion echelle grating spectrograph for remote sensing

We describe the design of a silicon immersion grating spectrograph for the remote detection of chemicals in the atmosphere. The instrument is designed to operate in the two atmospheric windows from 2.3 to 2.5 and 2.8 to 4.2 microns at a resolution of 0.1 cm-1. This is achieved by cross dispersing a high order silicon immersion echelle (13.5 grooves/mm) and a first order concave grating operating in a reflective configuration to generate a 2D spectrum in the image plane with diffraction limited performance.