Advanced microdevices for the exploration of the solar system have become increasingly important in the current environment of fiscal constraints and payload size limitations. The Discovery-class missions being proposed for future exploration, while being clearly responsive to this environment, will require highly miniaturized and efficient instruments based on these advanced devices. Several instrument concept developments are continuing at Ames Research Center in support of specific exobiology science goals in future solar system studies on candidate Discovery and other missions. Developments include highly miniaturized metastable ionization detectors for gas chromatography that weight as little as 1 - 2 grams with sensitivities of 10-14 mol/second and an advanced ion mobility spectrometer that has near-universal sensitivity and weighs as little as 200 grams. New chemical sensors based on solid-state pyroelectric devices are being studied and developed that weigh a few milligrams and, for example, have a sensitivity of 0.1 ppm for H2O2. Advanced X- ray diffraction and fluorescence instruments for crystallographic and geochemical measurements on unprepared soil and rock samples are under test. A stable isotope laser diode spectrometer for determination of 12C/13C and 18O/16O isotope ratios on Mars at fractional percent accuracies has been breadboarded. Finally, advanced computational methods are being applied to new instrument concepts allowing new, less complex, and thus, smaller instruments.
Microsensors will play key roles in Planetary Exploration in the future because of their low mass, and the low power consumption that usually results. Ruggedness also almost always improves with decrease in size. The trend toward smaller, simpler, and more highly integrated spacecraft requires instrument and sensor miniaturization.
Superconducting transition-edge infrared microbolometers have been fabricated by silicon micromachining using an epitaxial YLa.05Ba1.95Cu3O7-x (YBCO) film on a epitaxial yttria-stabilized zirconia buffer layer on silicon. The low thermal conductance of the micromachined structures combined with the sharp resistance change at the superconducting transition results in very sensitive infrared detectors. The broadband response of these thermal detectors makes them particularly useful at wavelengths longer than the typical operating range of semiconductor detectors ((lambda) greater than about 20 micrometers ) at moderately high temperatures (T approximately 70 K and higher). The use of standard silicon processing promises low-cost monolithic integration of the readout electronics for arrays of these devices. Preliminary measurements are reported here on a device 140 micrometers X 105 micrometers in size with a detectivity, D*, of 8 +/- 2 X 109 cm Hz1/2/Watt, and NEP of 1.5 X 10-12 Watts/Hz1/2 at 2 Hz and 80.7 K. This value of D* exceeds the highest previously reported D* for a YBCO transition-edge bolometer, and is comparable to the highest reported D* for a thermal detector operating at greater than about 70 K. The thermal time constant for this device was 105 +/- 20 msec.
This study investigates the use of diffractive optical components for efficient, mode-matched optical fiber-to-waveguide coupling. In this study a single element, with diffractive lenses on both back and front surfaces, is designed, fabricated, and tested. The element transforms the optical beam profile exiting a laser diode from a divergent, elliptical mode profile into a collimated beam of circular mode shape. The output beam shape and optical efficiency of the diffractive element are measured. Test results agree favorably with expected values.
A new technology for infrared optical filters is presented. We have produced a band pass filter consisting of a thin (12.4 micrometers ) Si wafer with cross-shaped metal patterns deposited on both sides. The crosses, with 6 micrometers arms, have been formed by direct-write electron- beam lithography on 1000 angstroms Al film. The filter is mounted on a 0.2 mm thick Si frame with 0.25 cm2 window, but it also can be bonded to detectors so that the filter and the detector temperature are the same. Due to the high index of refractive in Si, this filter is more tolerant to converging beams than interferometric filters made of metal meshes stretched in air that have been reported previously. When placed into an F/3 converging beam, the filter has a bandpass characteristic centered at 70 micrometers wavelength with width at half maximum (delta) (lambda) /(lambda) equals 7%. The transmission maximum is 44%. At present the band pass is limited by the non-uniformity of the available substrates. The out-of-band rejection need improving which can be achieved using additional non-interferometric filters with wider band pass made with similar technology. Another way of improving the performance is integrating the metal patterns onto the detector which will make it frequency selective. Extending the interference filter technology to shorter wavelengths is difficult due to the onset of absorption in the metal layers.
Phase holograms have been created on the surface of a thin film of poly-methyl methacrylate (PMMA, Plexiglas) by direct-write electron beam (E-Beam) lithography. The process involves delivering a patterned exposure dose followed by partial development with a strong developer. The patterned dose derives from arbitrary computer-calculated holograms, which must be corrected for the sensitivity characteristic of the PMMA and for the effective point-spread function of the E-Beam.
A high speed Hartmann wavefront sensor was designed and built for measuring refractive index variations in supersonic air flows. The device contained a lenslet array which formed an array of spots on the focal plane of a high speed camera. Spot motion at the focal plane is directly related to fluctuation of wavefront tilt in the corresponding subaperture. Both refractive and diffractive (binary optic) lenslet arrays were fabricated for the Hartmann sensor. The long focal length needed to meet resolution requirements placed tight tolerances on the wedge error in the refractive lenslets and the cement interface mounting the lenslets to the substrate lens. In spite of the use of state-of-the-art interferometric alignment techniques for assembling the refractive lenslet array, the diffractive lenslet array demonstrated superior alignment and performance. In this application binary optics demonstrated significant advantages over conventional optics. In addition to performance issues, binary optics allows reduced weight and reduced number of elements. For airborne and space applications these advantages translate into significant cost savings.
The instrumentation requirements for a spacecraft mission to Pluto include miniaturization, low power, high reliability, radiation tolerance, and low cost as well as significant science data return. To address these needs, we are developing a prototype, integrated, hybrid, focal plane assembly that can be used to acquire multi-spectral, visible-light images during the flyby. This focal plane integrates a four-channel CCD, clock drives, analog processing, and digital data conversion into a miniature assembly. This paper discusses our design and how it addresses the needs of NASA's space science program.
The Array of Low Energy X-ray Imaging Sensors (ALEXIS) satellite is Los Alamos' first attempt at building and flying a small, low cost, rapid development, technology demonstration and scientific space mission. The ALEXIS satellite contains the two experiments: the ALEXIS telescope array, (which consists of six EUV/ultrasoft x-ray telescopes utilizing multilayer mirrors, each with a 33 degree field-of-view), and VHF ionospheric experiment called BLACKBEARD. The spacecraft is controlled exclusively from a ground station located at Los Alamos. The 113-kg ALEXIS satellite was launched by a Pegasus booster into a 750 X 850 km, 70 degree inclination orbit on April 25, 1993. Due to damage sustained at the time of launch, ground controllers did not make contact with the satellite until late June. By late July, full satellite operations had been restored through the implementation of new procedures for attitude control. Science operations with the two onboard experiments began at that time. This paper will discuss our experience gained in launching and managing this small scientific and technology demonstration satellite.
This paper discusses the design, and implementation of a miniaturized electronic system for the Planetary Integrated Camera Spectrometer (PICS). The PICS electronics demonstrate the application of Field Programmable Gate Arrays (FPGAs) and of analog hybrid technology to space flight multi-spectral systems. A discussion of the electronic system design illustrates how signals from a multi-sensor instrument containing an UV CCD, two visible CCDs, and a near-IR focal plane assembly can be processed through a common set of electronics. Following the system design discussion, the actual electronic design will be presented. Each miniaturized module will be discussed as to functionality and performance. The test setup for bench checkout of a cooled CCD and an IR FPA, including results with breadboard electronics and with the hybrids are also described.
New advances in the areas of microelectronics and micro-mechanical devices have created a momentum in the development of lightweight, miniaturized, electro-optical space subsystems. The performance improvements achieved and new observational techniques developed as a result, have provided a basis for a new range of Small Explorer, Discovery-class and other low-cost mission concepts for space exploration. However, the ultimate objective of low-mass, inexpensive space science missions will only be achieved with a companion development in the areas of flight optical systems and sensor instrument benches. Silicon carbide (SiC) is currently emerging as an attractive technology to fill this need. As a material basis for reflective, flight telescopes and optical benches, SiC offers: the lightweight and stiffness characteristics of beryllium; glass-like inherent stability consistent with performance to levels of diffraction-limited visible resolution; superior thermal properties down to cryogenic temperatures; and an existing, commercially-based material and processing infrastructure like aluminum. This paper will describe the current status and results of on-going technology developments to utilize these material properties in the creation of lightweight, high- performing, thermally robust, flight optical assemblies. System concepts to be discussed range from an 18 cm aperture, 4-mirror, off-axis system weighing less than 2 kg to a 0.5 m, 15 kg reimager. In addition, results in the development of a thermally-stable, `GOES-like' scan mirror will be presented.
The need for miniaturization in advanced science sensor systems has led to the development of a new image sensor technology, the active pixel image sensors (APS). The development of CMOS APS technology allows the integration of timing and control electronics, imaging detector arrays, signal chains and analog-to-digital conversion on a single integrated circuit. The impact on the imaging system is to reduce power by approximately 1000X over existing systems--from tens of watts to tens of milliwatts. This paper will describe the development of this technology and its application to future space science sensor systems.
This paper describes a type of cosmic ray detector suitable for the construction of a small, low power space-based instrument to detect the energy and isotope of energetic nuclei, such as those produced by solar flares. The detector is similar to previous types of silicon PIN detectors where the fully depleted body of the wafer comprises the intrinsic region of the PIN structure. The novel aspect of this detector is that the one surface is divided into a 2D array of pixels, and that the collected holes are divided between a row and a column collector in each pixel, yielding both dimensions of position information from this side of the detector. In a conventional PIN detector, both sides are divided into stripes, and each side provides 1D information. A single large area collector on the opposite side of this new detector is used to determine the energy of the incident nucleus. This scheme requires only a single precision pulse-height amplifier connected to the broad area contract, rather than one for each strip, as in the conventional scheme, resulting in a significant reduction in the mass, power and complexity of the readout electronics. The design, fabrication, and operation of such a detector is discussed. Initial particle tests show a prototype to be functional. The projected power saved by using such as detector is presented.
Proc. SPIE 2267, Dual-theodolite real-time computation method used during the optical alignment of the Excitation by Electron Deposition (EXCEDE) III rocket payload, 0000 (23 September 1994); doi: 10.1117/12.187473
Phillips Laboratory and Systems Integration Engineering developed a two-theodolite, reflecting-surface technique for measuring the lines of sight (LOS) of sensors in rocket payload modules. A flat mirror, keyed to one theodolite provides a stable and adjustable reference by which the angular separation of sensor LOS's can be measured and referenced to the rocket's coordinate system. The rocket's Attitude Control System and external launch pad geodetic survey points are referenced to the vehicle's geometry using this procedure.
Hughes Danbury Optical Systems (HDOS) has developed several concepts for hyperspectral remote sensing of the earth and major and minor planets. The basic instrument is an imaging prism spectrometer located on an orbiting platform. The spectrometer slit is imaged by a telescope on the planetary surface and pushbroom scanned across it. The prism spectrometer disperses the observed slit image and reimages it in the multiple spectral bands onto a 2D focal plane array. Extensive use is made of Application Specific Integrated Circuits (ASICs) for signal processing in order to reduce power and weight. The baselined focal plane array is a 320 (image) X 210 (spectral) InSb detector. This detector provides high quantum efficiency for photons spanning the spectral range from the band gap limit of 5.4 micrometers to the ultraviolet. Various spectral ranges and spectral resolutions may be selected by appropriate choice of the prism and design of the spectrometer optics. These concepts for a spaceborne imaging prism spectrometer rely heavily on HDOS's HYDICE heritage. HYDICE (HYperspectral Digital Imaging Collection Experiment) is a prism imaging spectrometer being developed by HDOS for the Naval Research Laboratory. HYDICE will fly in a Convair aircraft and pushbroom scan the earth in 210 spectral colors between 0.4 micrometers and 2.5 micrometers . The heritage for the miniaturized electronics in the HDOS Miniature Star Tracker program.