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Volume 6555 Sensors and Systems for Space Applications

Richard T. Howard, Robert D. Richards April 2007

Conference Location: Orlando, FL, USA Conference Date: Monday 9 April 2007

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Front Matter

Select this Article OPEN ACCESS		Front Matter: Volume 6555 Proceedings of SPIE Proc. SPIE 6555, 655501 (2007); http://dx.doi.org/10.1117/12.738964 Online Publication Date: May 29, 2007 Full Text: \| Download PDF
	+ -	Show Abstract This PDF file contains the front matter associated with SPIE Proceedings Volume 6555, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

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Space to Ground Sensing

Select this Article		Remote sensing phase fluorimetry using mercury vapor lamp Michael A. Lundin and Matthew J. Bohn Proc. SPIE 6555, 655502 (2007); http://dx.doi.org/10.1117/12.718606 Online Publication Date: Apr 27, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Phase Fluorimetry, or Frequency Domain (FD) Fluorimetry, capitalizes on the phase delay from excitation modulation of fluorescent media and offers independence from light scatter and excitation/emission intensity variations in order to extract the sample's fluorescent lifetime. Samples which fluoresce in the UV are commonly excited with UV laser sources, which are not necessarily high power, portable devices. Mercury vapor lamps, a common source of industrial facility lighting, emit wavelengths (365 nm, 405 nm, and 436 nm) that overlap the UV/blue spectrum and may be used as an efficient and portable excitation source. Mercury vapor lamps show strong peak intensities at 120 Hz and higher harmonics, due to the modulation of facility power at 60 Hz in the United States. For this research effort, single exponential decay will be assumed and lifetime calculation will be performed by least squares analysis with corrections made for lamp intensity variations at the harmonics of facility power.

Select this Article		High-efficiency UV laser for space-based wind lidar Floyd E. Hovis and Jinxue Wang Proc. SPIE 6555, 655504 (2007); http://dx.doi.org/10.1117/12.720251 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Lidar based measurements of clear air winds from space requires a high efficiency UV laser transmitter. We have developed a prototype of the required transmitter that uses third harmonic generation from a diode pumped Nd:YAG laser to achieve the desired UV output. Our approach uses a single-frequency Nd:YAG master oscillator/power amplifier as the primary pump source. The system is diode pumped and conductively cooled for compatibility with space-based operation. We use a variation of the ramp and fire technique to injection seed the master oscillator. The space-qualifiable electronics provide user control of the injection seeding, diode pump power, and operational modes of the laser. The 1064 nm laser transmitter has been demonstrated to achieve a true system level wall plug efficiency of 6.4% for a q-switched output power of 44 W at 50 Hz. We use high efficiency doubling and sum frequency mixing of the 1064 nm pump to generate 24 W of 355 nm output. This result implies a third harmonic optical to optical generation efficiency of 55% and a system level efficiency of 3.5%. In this paper we report on the design and testing of this laser transmitter.

Select this Article		Space-based direct detection wind mission design Thomas H. Zurbuchen, Richard Walker, Charles Richey, Jane Pavlich, and Peter Tchoryk, Jr. Proc. SPIE 6555, 655505 (2007); http://dx.doi.org/10.1117/12.721798 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract There is an important need for accurate measurements of tropospheric wind altitude profiles. These wind systems have long been recognized as one of the primary unknowns limiting weather forecasting over timescales of several days. Typical measurement architectures have focused primarily on space-based approaches, using a high-powered and highly effective Light Detection and Ranging (lidar) system. This paper discusses architectures for low-altitude space missions. The architectures are analyzed in the context of a weather forecasting system for the Gulf of Mexico region during hurricane season. The architecture studies were developed by collaboration between a class of engineers who are part of the University of Michigan's new Space Engineering program and Michigan Aerospace Corporation, a University of Michigan spin-off company specializing, in part, in lidar systems.

Select this Article		Optical sensing of atmospheric emissions with Cubesats and Nanosats Gary Swenson, Purvesh Thakker, Farzad Kamalabadi, Mathew Frank, Victoria Coverstone, and Hank Voss Proc. SPIE 6555, 655506 (2007); http://dx.doi.org/10.1117/12.722662 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Small satellites and payloads in the (1-2 kg) class called Cubesats and (20-30 kg) called Nanosats have been under development at the University of Illinois since fall, 2001. The ION1 Cubesat was a 10x10x21.5 cm³ satellite with the experiment consisting of photometric remote sensing of mesospheric structures (near 94 km) in the O₂ (0,0) band airglow at 762 nm. ION1 development began in 2001 and was lost on the failed launch attempt, July 26, 2006. ION2 development began in Fall 2005, and has a remote sensing experiment to measure Hα (656.3 nm) originating in the Earth's geocorona from which column H densities can be deduced. Taylor University has led the development of a Nanosat called TEST, which was designed to study ionospheric structures. Illinois provided remote sensing payloads including a CCD camera and dual photometers. The development activity is largely implemented by a College of Engineering Interdisciplinary Design class (ENG 491), where students typically participate in the systems engineering experience for two semesters. The students (15-20 average enrollment) are responsible for the design, fabrication, and testing of the systems. This paper describes the development of these Cubesat and Nanosat systems.

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Camera-Based Sensing

Select this Article		Effects of optical artifacts in a laser-based spacecraft navigation sensor Jerry E. LeCroy, Dean S. Hallmark, and Richard T. Howard Proc. SPIE 6555, 655507 (2007); http://dx.doi.org/10.1117/12.723377 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Testing of the Advanced Video Guidance Sensor (AVGS) used for proximity operations navigation on the Orbital Express ASTRO spacecraft exposed several unanticipated imaging system artifacts and aberrations that required correction to meet critical navigation performance requirements. Mitigation actions are described for a number of system error sources, including lens aberration, optical train misalignment, laser speckle, target image defects, and detector nonlinearity/noise characteristics. Sensor test requirements and protocols are described, along with a summary of test results from sensor confidence tests and system performance testing.

Select this Article		Super resolution structured light illumination Laurence G. Hassebrook, Akshay G. Pethe, Charles Casey, Veera Ganesh Yalla, and Daniel L. Lau Proc. SPIE 6555, 655508 (2007); http://dx.doi.org/10.1117/12.719703 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract We present an eight million point structured light illumination scanner design. It has a single patch projection resolution of 12,288 lines along the phase direction. The Basler CMOS video cameras are 2352 by 1726 pixel resolution. The configuration consists of a custom Boulder Nonlinear Systems Spatial Light Modulator for the projection system and dual four mega pixel digital video cameras. The camera field of views are tiled with minimal overlap region and a potential capture rate of 24 frames per second. This report is a status report of a project still under development. We will report on the concept of applying a 1D-square footprint projection chip and give preliminary results of single camera scans. The structured light illumination technique we use is the multi-pattern, multi-frequency phase measuring profilometry technique already published by our group.

Select this Article		Multicamera phase measuring profilometry for accurate depth measurement Yongchang Wang, Kai Liu, Qi Hao, Daniel Lau, and Laurence G. Hassebrook Proc. SPIE 6555, 655509 (2007); http://dx.doi.org/10.1117/12.720068 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Structured light illumination refers to a scanning process of projecting a series of patterns such that, when viewed from an angle, a camera is able to extract range information. Ultimately, resolution in depth is controlled by the number of patterns projected which, in turn, increases the total time that the target object must remain still. By adding a second camera sensor, it becomes possible to not only achieve wrap around scanning but also reduce the number of patterns needed to achieve a certain degree of depth resolution. But a second camera also makes it possible to reconstruct 3-D surfaces through stereo-vision techniques and triangulation between the cameras instead of between the cameras and the projectors. For both of these two tasks, correspondence between points from two cameras is essential. In this paper, we develop a new method to find the correspondence between the two cameras using both the phase information generated by the temporal multiplexed illumination patterns and stereo triangulation. We also analyze the resulting correspondence accuracy as a function of the number of structured patterns as well as the geometric position of projector to cameras.

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Three-Dimensional Position and Attitude Sensing

Select this Article		Processing 3D flash LADAR point-clouds in real-time for flight applications R. Craig, I. Gravseth, R. P. Earhart, J. Bladt, S. Barnhill, L. Ruppert, and C. Centamore Proc. SPIE 6555, 65550D (2007); http://dx.doi.org/10.1117/12.720143 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Ball Aerospace & Technologies Corp. has demonstrated real-time processing of 3D imaging LADAR point-cloud data to produce the industry's first time-of-flight (TOF) 3D video capability. This capability is uniquely suited to the rigorous demands of space and airborne flight applications and holds great promise in the area of autonomous navigation. It will provide long-range, three dimensional video information to autonomous flight software or pilots for immediate use in rendezvous and docking, proximity operations, landing, surface vision systems, and automatic target recognition and tracking. This is enabled by our new generation of FPGA based "pixel-tube" processors, coprocessors and their associated algorithms which have led to a number of advancements in high-speed wavefront processing along with additional advances in dynamic camera control, and space laser designs based on Ball's CALIPSO LIDAR. This evolution in LADAR is made possible by moving the mechanical complexity required for a scanning system into the electronics, where production, integration, testing and life-cycle costs can be significantly reduced. This technique requires a state of the art TOF read-out integrated circuit (ROIC) attached to a sensor array to collect high resolution temporal data, which is then processed through FPGAs. The number of calculations required to process the data is greatly reduced thanks to the fact that all points are captured at the same time and thus correlated. This correlation allows extremely efficient FPGA processing. This capability has been demonstrated in prototype form at both Marshal Space Flight Center and Langley Research Center on targets that represent docking and landing scenarios. This report outlines many aspects of this work as well as aspects of our recent testing at Marshall's Flight Robotics Laboratory.

Select this Article		Stereo-vision-based 3D modeling of space structures Stephen Se, Piotr Jasiobedzki, and Richard Wildes Proc. SPIE 6555, 65550E (2007); http://dx.doi.org/10.1117/12.718427 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Servicing satellites in space requires accurate and reliable 3D information. Such information can be used to create virtual models of space structures for inspection (geometry, surface flaws, and deployment of appendages), estimation of relative position and orientation of a target spacecraft during autonomous docking or satellite capture, replacement of serviceable modules, detection of unexpected objects and collisions. Existing space vision systems rely on assumptions to achieve the necessary performance and reliability. Future missions will require vision systems that can operate without visual targets and under less restricted operational conditions towards full autonomy. Our vision system uses stereo cameras with a pattern projector and software to obtain reliable and accurate 3D information. It can process images from cameras mounted on a robotic arm end-effector on a space structure or a spacecraft. Image sequences can be acquired during relative camera motion, during fly-around of a spacecraft or motion of the arm. The system recovers the relative camera motion from the image sequence automatically without using spacecraft or arm telemetry. The 3D data computed can then be integrated to generate a calibrated photo-realistic 3D model of the space structure. Feature-based and shape-based approaches for camera motion estimation have been developed and compared. Imaging effects on specular surfaces are introduced by space materials and illumination. With a pattern projector and redundant stereo cameras, the robustness and accuracy of stereo matching are improved as inconsistent 3D points are discarded. Experiments in our space vision facility show promising results and photo-realistic 3D models of scaled satellite replicas are created.

Select this Article		A pose and position measurement system for the Hubble Space Telescope servicing mission Michael Balch and Dave Tandy Proc. SPIE 6555, 65550F (2007); http://dx.doi.org/10.1117/12.720302 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract As NASA develops the new space explorations systems required for the Crew Exploration Vehicle (CEV) also known as ORION, there is a growing need for hardware and algorithms to support Automated Rendezvous and Docking (AR&D) technology for both manned and unmanned flights. A new definition of space hardware is also emerging based on reconfigurable computing. Goddard Space Flight Center (GSFC) has developed a high processing bandwidth hardware platform based on the latest Xilinx Field Programmable Gate Array (FPGA) technology. This platform, called SpaceCube, incorporates the processing power of immersed PowerPC core technology with an extremely flexible I/O capability. The result is an adaptable, reconfigurable computing platform well suited for hosting computationally intensive AR&D algorithms. Advanced Optical Systems, Inc. (AOS) has developed several electro-optical sensor systems for both NASA and the Department of Defense. ULTOR^® is one such sensor technology, developed for Automatic Target Recognition (ATR) in missile guidance systems. AOS has applied ULTOR^® to target position and attitude measurements in space, commonly referred to as pose estimation. Under GSFC funding, AOS has successfully integrated ULTOR^® into the SpaceCube platform. GSFC plans to demonstrate on-station pose estimation using the integrated ULTOR^® SpaceCube system on the next shuttle mission to the service the Hubble Space Telescope.

Select this Article		Simulation tests of a lidar-based spacecraft pose determination algorithm Ronald C. Fenton, R. Rees Fullmer, and Robert T. Pack Proc. SPIE 6555, 65550G (2007); http://dx.doi.org/10.1117/12.720114 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The autonomous close-in maneuvering necessary for the rendezvous and docking of two spacecraft requires a relative navigation sensor system that can determine the relative position and orientation (pose) of the controlled spacecraft with respect to the target spacecraft. Lidar imaging systems offer the potential for accurately measuring the relative six degree-of-freedom positions and orientations and the associated rates. In this paper, we present simulation results generated using a high fidelity modeling program. A simulated lidar system is used to capture close-proximity range images of a model target spacecraft, producing 3-D point cloud data. The sequentially gathered point-clouds are compared with the previous point-cloud using a real-time point-plane correspondence-less variant of the Iterative Closest Points (ICP) algorithm. The resulting range and pose estimates are used in turn to prime the next time-step iteration of the ICP algorithm. Results from detailed point-plane simulations and will be presented. The implications for real-time implementation are discussed.

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Sensors and Systems

Select this Article		Hydra AR&D sensor suite Fred Roe and Stephen R. Granade Proc. SPIE 6555, 65550H (2007); http://dx.doi.org/10.1117/12.719328 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract AOS is designing a modular AR&D System named Hydra^® and building an initial prototype with selected (near-field and docking) capabilities and expansion capabilities to accommodate a time-of-flight and far-field sensor. Lessons learned from DART and Orbital Express have been applied to the proposed Hydra^® design. The prototype Hydra^® system design includes an AVGS sensor head and an ULTOR^® sensor head. Although the initial Hydra^® system is a ground demonstration unit, design methods and component selection provide a straightforward path for building a space-qualified Hydra^® system. The basic architectural component for Hydra^® is based on a common processing platform that can be configured to process inputs from a variety of sensors. The design consists of three elements: The sensor head or camera, which can be mounted external to the spacecraft; the processing electronics, which can be mounted internal to the spacecraft; and the Hydra^® target, which is mounted on the target spacecraft at or near the docking interface.

Select this Article		The lunar orbiter laser altimeter (LOLA) on NASA's lunar reconnaissance orbiter (LRO) mission Haris Riris, Xiaoli Sun, John F. Cavanaugh, Glenn B. Jackson, Luis Ramos-Izquierdo, David E. Smith, and Maria Zuber Proc. SPIE 6555, 65550I (2007); http://dx.doi.org/10.1117/12.719266 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The Lunar Orbiter Laser Altimeter (LOLA) instrument on NASA's Lunar Reconnaissance Orbiter (LRO) mission, scheduled to launch in October 2008, will provide a precise global lunar topographic map using laser altimetry. LOLA uses short pulses from a single laser through a Diffractive Optical Element (DOE) to produce a five-beam pattern that illuminates the lunar surface. For each beam, LOLA measures the time of flight (range), pulse spreading (surface roughness), and transmit/return energy (surface reflectance). LOLA will produce a high-resolution global topographic model and global geodetic framework that enables precise targeting, safe landing, and surface mobility to carry out exploratory activities. In addition, it will characterize the polar illumination environment, and image permanently shadowed polar regions of the lunar surface to identify possible locations of surface ice crystals in shadowed polar craters.

Select this Article		Commissioning of the CALIPSO payload Carl Weimer, Lyle Ruppert, and Justin Spelman Proc. SPIE 6555, 65550J (2007); http://dx.doi.org/10.1117/12.722420 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The CALIPSO satellite launched on April 28, 2006. It successfully entered into the Aqua (A) -train of Earth observing satellites along with its co-manifested CloudSat satellite. CALIPSO includes a Payload built for NASA by Ball Aerospace & Technologies Corp. The Payload includes three instruments for earth remote sensing: A two-wavelength polarization-sensitive lidar, a visible wide-field camera (WFC), and an infrared imaging radiometer (IIR). The commissioning and performance assessment of the satellite were successfully completed in the first ninety days after launch. This paper highlights some of the key instrument performance measured during commissioning, focusing on the lidar and wide-field camera.

Select this Article		Utilizing UV and visible sensors on micro-satellites to demonstrate target acquisition and tracking Steven Brown, Dean Wada, Ali Ghafourian, Mark Greenman, Charles Harris, Carl Howlett, Thomas Humpherys, and Vincent Nguyen Proc. SPIE 6555, 65550K (2007); http://dx.doi.org/10.1117/12.717059 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The Distributed Sensing Experiment (DSE) program is a technology demonstration of target acquisition, tracking, and three-dimensional track development using a constellation of three micro satellites. DSE will demonstrate how micro satellites, working singly and as a group, can observe test-missile boost and ballistic-flight events. The overarching program objective is to demonstrate a means of fusing measurements from multiple sensors into a composite track. To perform this demonstration, each DSE micro satellite will acquire and track a target, determine a two-dimensional direction and movement rate for each, communicate observations to other DSE satellites, determine a three-dimensional target position and velocity, and relay this information to ground systems. A key design parameter of the program is incorporating commercial off-the-shelf (COTS) hardware and software to reduce risk and control costs, while maintaining performance. Having completed a successful Critical Design Review, the program is currently in fabrication, integration, and test phase. The constellation of satellites is scheduled for launch in CY2009. This paper describes the status and capabilities of the UV and visible sensor payloads, as well as the algorithms and software being developed to achieve the DSE mission.

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Spacecraft Sensors Analysis and Results

Select this Article		DART AVGS flight results Richard T. Howard and Thomas C. Bryan Proc. SPIE 6555, 65550L (2007); http://dx.doi.org/10.1117/12.720242 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The Advanced Video Guidance Sensor (AVGS) was designed to be the proximity operations sensor for the Demonstration of Autonomous Rendezvous Technologies (DART). The DART mission flew in April of 2005 and was a partial success. The AVGS did not get the opportunity to operate in every mode in orbit, but those modes in which it did operate were completely successful. This paper will detail the development, testing, and on-orbit performance of the AVGS.

Select this Article		Miniature, light weight, coherent optical receiver system for space platforms Abhay Joshi, Don Becker, Christoph Wree, and Dan Mohr Proc. SPIE 6555, 65550M (2007); http://dx.doi.org/10.1117/12.718923 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract We have manufactured a miniaturized, light weight, high data rate, optical coherent receiver system with weight less than 37 lbs and power consumption less than 70 W. By using a coherent heterodyne method, the bench-top receiver has achieved a link rate of 2.5 Gb/s at a Bit Error Ratio of 1e-9 with a sensitivity of -40 dBm. This receiver could be used as a critical component of a free-space optical link, where the large distances and power limitations necessitate a high sensitivity. Optical communications links provide tremendous bandwidth and can achieve data rates two orders of magnitude higher that an RF communications link. Potential mass and power savings that go with using an optical system over an RF, along with the significantly higher bandwidth and reduced susceptibility to interference make them very attractive in the further development of the space environment.

Select this Article		Real-world educational experience through project-oriented graduate classes in collaboration with industry Thomas H. Zurbuchen Proc. SPIE 6555, 65550N (2007); http://dx.doi.org/10.1117/12.721744 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract There is a need for a motivated and innovative work force for the U.S. aerospace industry. The education of such engineers and scientists typically revolves around a fundamental knowledge of basic important technologies, such as the mechanics relevant to orbit-design, structures, avionics, and many others. A few years ago, the University of Michigan developed a Masters of Engineering program that provides students with skills that are not taught as part of a typical engineering curriculum. This program is focused on open problem solving, space systems, and space policy, as well as other classes that further their understanding of the connections between technologies and the nontechnical aspects of managing a space mission. The value of such an education is substantially increased through a direct connection to industry. An innovative problem-oriented approach has been developed that enables direct connections between industry and classroom teaching. The class works as a system study group and addresses problems of interest to and defined by a company with a specific application. We discuss such an application, a near-space lidar wind measurement system to enhance weather predictions, as well as the approach taken to link educational rationales.

Select this Article		High-resolution imaging with small satellites: what are the possibilities and limitations? Rainer Sandau Proc. SPIE 6555, 65550O (2007); http://dx.doi.org/10.1117/12.717570 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract High resolution mapping systems follow the trend to smaller ground sample distances (GSD) making use of the best technology available at the given time. From the 80 m GSD of ERTS in 1972, the GSD now approached 1 m and even less for civil applications. Mass and power consumption of spacecrafts and imaging instruments follow similar trends in conjunction with the immense improvements in very divers fields of technology. SAR systems are an alternative to passive optical systems; they also benefit from the technology improvements. But the most promising prospects for high resolution mapping with small satellites are connected with passive optical systems. The paper gives a MTF based metrics and analytical method to assess how far we can go with decreasing instrument size and decreasing the GSD at the same time and what features the spacecraft needs to provide. In this context the paper deals with such important parameters for topographic mapping with small satellites like spatial resolution, radiometry, pointing accuracy and stability. It is shown that the imagers as well as the spacecraft bus need to follow certain rules to allow high resolution imaging aboard of small satellites.

Select this Article		Autonomous docking experiments using the SPHERES testbed inside the ISS Simon Nolet and David W. Miller Proc. SPIE 6555, 65550P (2007); http://dx.doi.org/10.1117/12.720125 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents recent results regarding the research on autonomous docking with tumbling targets performed by the MIT Space Systems Laboratory (SSL). The objective of this research is to develop a guidance, navigation and control (GN&C) architecture that enables safe and fuel efficient docking of a thruster-based spacecraft with a tumbling target in the presence of obstacles and contingencies. Over the calendar year 2006, experiments were performed inside the International Space Station (ISS) using the SPHERES nano-satellites to validate a GN&C architecture on hardware in microgravity. A series of attitude slews, an autonomous docking maneuver with a fixed beacon and a station-keeping maneuver were among the experiments carried out in May to validate subsets of the architecture with only a fraction of the SPHERES hardware. The second set of experiments occurred in August and involved two satellites and the remaining navigation hardware. The global estimator allowing the SPHERES to navigate within the US Laboratory was validated. Multiple successful docking maneuvers between two satellites were also accomplished. In November, more complex docking scenarios were experimented, leading to the first successful autonomous docking with a tumbling target ever performed in microgravity. Results collected during key ISS experiments are presented in this paper.

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Propulsion Sensors I

Select this Article		Sensors and systems for space applications: a methodology for developing fault detection, diagnosis, and recovery John L. Edwards, Randy M. Beekman, David B. Buchanan, Scott Farner, Gary R. Gershzohn, Mbuyi Khuzadi, D. F. Mikula, Gerry Nissen, James Peck, and Shaun Taylor Proc. SPIE 6555, 65550R (2007); http://dx.doi.org/10.1117/12.718703 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Human space travel is inherently dangerous. Hazardous conditions will exist. Real time health monitoring of critical subsystems is essential for providing a safe abort timeline in the event of a catastrophic subsystem failure. In this paper, we discuss a practical and cost effective process for developing critical subsystem failure detection, diagnosis and response (FDDR). We also present the results of a real time health monitoring simulation of a propellant ullage pressurization subsystem failure. The health monitoring development process identifies hazards, isolates hazard causes, defines software partitioning requirements and quantifies software algorithm development. The process provides a means to establish the number and placement of sensors necessary to provide real time health monitoring. We discuss how health monitoring software tracks subsystem control commands, interprets off-nominal operational sensor data, predicts failure propagation timelines, corroborate failures predictions and formats failure protocol.

Select this Article		Evaluation of holographic subsurface radar for NDE of space shuttle thermal protection tiles Thomas Lu, Cooper Snapp, Tien-Hsin Chao, Anilkumar Thakoor, Tim Bechtel, Sergey Ivashov, and Igor Vasiliev Proc. SPIE 6555, 65550S (2007); http://dx.doi.org/10.1117/12.719911 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Experiments have been carried out to evaluate holographic subsurface radar (RASCAN) for non-destructive evaluation (NDE) of subnominal bond conditions between the Space Shuttle Thermal Protection System tiles and the aluminum substrate. Initial results have shown detection of small voids and spots of moisture between Space Shuttle thermal protection tiles and underlying aluminum substrate. The characteristic feature of this device is the ability to obtain one-sided radar soundings/images with high sensitivity (detecting of wire of 20 micron and less in diameter), and high resolution (2 cm lateral resolution) in the frequency band of 3.6-4.0 GHz. JPL's advanced high-speed image processing and pattern recognition algorithms can be used to process the data generated by the holographic radar and automatically detect and measure the defects. Combining JPL's technologies with the briefcase size, portable RASCAN system will produce a simple and fully automated scanner capable of inspecting dielectric heat shielding materials or other spacecraft structures for cracks, voids, inclusions, delamination, debonding, etc.. We believe this technology holds promise to significantly enhance the safety of the Space Shuttle and the future CEV and other space exploration missions.

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Propulsion Sensors II

Select this Article		Stable 600 °C silicon carbide MEMS pressure transducers Robert S. Okojie Proc. SPIE 6555, 65550V (2007); http://dx.doi.org/10.1117/12.723406 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a review of recent results of silicon carbide (SiC) piezoresistive pressure transducers that have been demonstrated to operate up to 600 °C. The results offer promise to extend pressure measurement to higher temperatures beyond the capability of conventional semiconductor pressure transducers. The development also provides three immediate significant technological benefits: i) wider frequency bandwidth (overcomes acoustic attenuation associated with pitot tubes), ii) accuracy (improved stable output at high temperature), and iii) reduced packaging complexity (no package cooling required). Operation at 600 °C provides immediate applications in military and commercial jet engines in which critical static and dynamic pressure measurements are performed to improve engine performance (i.e., reduced emission and combustor instabilities) and improved CFD code validation. The pressure sensor is packaged by a novel MEMS direct chip attach (MEMS-DCA) technique that eliminates the need for wire bonding, thereby removing some reliability issues encountered at high temperature. Generally, at 600 °C the full-scale output (FSO) of these transducers drops by about 50-65 % of the room temperature values, which can be compensated for with external signal conditioning circuitry.

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Spacecraft Platforms and Infrastructure

Select this Article		Docking and reconfiguration of modular spacecraft: preliminary SWARM testing at MSFC Nicholas R. Hoff III, Swati Mohan, Simon Nolet, and David W. Miller Proc. SPIE 6555, 65550W (2007); http://dx.doi.org/10.1117/12.719029 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract On-orbit servicing and assembly is a critical enabling technology for the advancement of large scale structures in space. The goal of the SWARM project (Synchronized Wireless Autonomous Reconfigurable Modules) is to develop and mature algorithms for autonomous docking and reconfiguration, to be used as the building blocks for autonomous servicing and assembly. Algorithms for approach, docking, and reconfiguration have been implemented and tested through a demonstration of the assembly of two telescope sub-apertures at Marshall Space Flight Center (MSFC) in July 2006. The algorithms developed for reconfiguration set the mass properties based on the configuration. Updatable parameters include the location of sensors and receivers with respect to the geometric center, thruster locations, and control gains specific to each configuration. To test these algorithms in a 2D environment, a ground testbed was developed to provide multiple docking ports and modular payload attachments. Hardware components include nodes, Universal Docking Ports, posts, sub-aperture mirrors, and a SPHERES satellite as the assembler tug. Testing at MSFC successfully demonstrated relative docking and reconfiguration. Valuable information was gained about the performance of the docking under friction, sensitivity to estimator initialization, thrust authority needed for different phases of the test, and control when CM changes during the test.

Select this Article		Autonomous precision formation flying: a proposed fault tolerant attitude control strategy Tao Jiang and K. Khorasani Proc. SPIE 6555, 65550X (2007); http://dx.doi.org/10.1117/12.719592 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Future space missions, such as those involving formation flying of multiple satellites require high operational autonomy mainly with the aim of reducing the operation costs and improving reactivity to sensed data. In particular, stringent performance requirements envisaged precision formation flying cannot be achieved by currently available technologies. One of the main challenges in achieving autonomy is the capability of fault management without extensive involvement of ground station operators. This paper uses a second order nonlinear sliding mode observer to detect actuator faults in the attitude control system of a satellite with four reaction wheels in a tetrahedron configuration. A post-processing of residuals is required to isolate and reconstruct the faults in all four reaction wheels. Furthermore, the control strategy needs to be reconfigured to recover faults. Simulation results show that the proposed strategy can detect, isolate and reconstruct reaction wheel faults in the attitude control system of a satellite.

Select this Article		SUMO/FREND: vision system for autonomous satellite grapple Jerome Obermark, Glenn Creamer, Bernard E. Kelm, William Wagner, and C. Glen Henshaw Proc. SPIE 6555, 65550Y (2007); http://dx.doi.org/10.1117/12.720284 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract SUMO/FREND is a risk reduction program for an advanced servicing spacecraft sponsored by DARPA and executed by the Naval Center for Space Technology at the Naval Research Laboratory in Washington, DC. The overall program will demonstrate the integration of many techniques needed in order to autonomously rendezvous and capture customer satellites at geosynchronous orbits. A flight-qualifiable payload is currently under development to prove out challenging aspects of the mission. The grappling process presents computer vision challenges to properly identify and guide the final step in joining the pursuer craft to the customer. This paper will provide an overview of the current status of the project with an emphasis on the challenges, techniques, and directions of the machine vision processes to guide the grappling.

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Optical Modeling and Testing

Select this Article		Quantifying an imagery system's performance with transformational mission data analysis Alisha W. Mauck Proc. SPIE 6555, 65550Z (2007); http://dx.doi.org/10.1117/12.718648 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Traditionally, the performance of an imagery intelligence collection system is quantified by a satisfaction percentage. The mission satisfaction is the number of images collected divided by the number of images requested. This paradigm assumes the information needed is generated from the collected imagery data if the data is delivered on time to the consumer. As persistent surveillance requirements become more prominent, the time sequence of data collection is increasingly important. The satisfaction percentage is not wholly descriptive of a collection system's ability to complete persistent surveillance missions. A metric of imagery data utility that is dependent on the time sequence of data collected is necessary. Booz Allen Hamilton's transformational mission analysis focuses on additional metrics to characterize satisfaction of persistent surveillance requirements. Surveillance missions are based on a need to monitor an activity or event. The observables are animate, and may require a time sequence of images. For surveillance imagery data to be useful, the system must collect the data in required sequence and deliver the information in a timely fashion. Booz Allen defines a utility score to quantify system performance against persistent surveillance missions. The utility score includes the satisfaction percentage, but is sensitive to the time dependences of data. This paper outlines a transformational approach to mission analysis. The paper introduces examples of surveillance missions, and the limited value of satisfaction percentage. It defines data relationships between imagery system capabilities and surveillance missions. Finally, it computes the utility score, and quantifies the performance of an example collection system.

Select this Article		Modeling of electro-statically actuated two-axis (tip-tilt) MEMS torsion micro-mirrors for laser beamsteering C. L. Edwards, B. G. Boone, W. S. Levine, and C. C. Davis Proc. SPIE 6555, 655510 (2007); http://dx.doi.org/10.1117/12.719282 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The availability of recently developed MEMS micro-mirror technology provides an opportunity to replace macro-scale actuators for free-space laser beamsteering in lidar and communication systems. Such an approach is under investigation at the Johns Hopkins University Applied Physics Laboratory for use on space-based platforms. Precision modeling of mirror pointing and its dynamics are critical to optimal design and control of MEMS beamsteerers. Beginning with Hornbeck's torque approach, this paper presents a first-principle, analytically closed-form torque model for an electro-statically actuated two-axis (tip-tilt) MEMS structure. An Euler dynamic equation formulation describes the gimbaled motion as a coupled pair of damped harmonic oscillators with a common forcing function. Static physical parameters such as MEMS mirror dimensions, facet mass, and height are inputs to the model as well as dynamic harmonic oscillator parameters such as damping and restoring constants fitted from measurements. A Taylor series expansion of the torque function provides valuable insights into basic one dimensional as well as two dimensional MEMS behavior, including operational sensitivities near "pull-in." The model also permits the natural inclusion and analysis of pointing noise sources such as electrical drive noise, platform vibration, and molecular Brownian motion. MATLAB and SIMULINK simulations illustrate performance sensitivities, controllability, and physical limitations, important considerations in the design of optimal pointing systems.

Select this Article		A low-cost test-bed for real-time landmark tracking Ambrus Csaszar, Jay C. Hanan, Pierre Moreels, and Christopher Assad Proc. SPIE 6555, 655511 (2007); http://dx.doi.org/10.1117/12.720183 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract A low-cost vehicle test-bed system was developed to iteratively test, refine and demonstrate navigation algorithms before attempting to transfer the algorithms to more advanced rover prototypes. The platform used here was a modified radio controlled (RC) car. A microcontroller board and onboard laptop computer allow for either autonomous or remote operation via a computer workstation. The sensors onboard the vehicle represent the types currently used on NASA-JPL rover prototypes. For dead-reckoning navigation, optical wheel encoders, a single axis gyroscope, and 2-axis accelerometer were used. An ultrasound ranger is available to calculate distance as a substitute for the stereo vision systems presently used on rovers. The prototype also carries a small laptop computer with a USB camera and wireless transmitter to send real time video to an off-board computer. A real-time user interface was implemented that combines an automatic image feature selector, tracking parameter controls, streaming video viewer, and user generated or autonomous driving commands. Using the test-bed, real-time landmark tracking was demonstrated by autonomously driving the vehicle through the JPL Mars yard. The algorithms tracked rocks as waypoints. This generated coordinates calculating relative motion and visually servoing to science targets. A limitation for the current system is serial computing−each additional landmark is tracked in order−but since each landmark is tracked independently, if transferred to appropriate parallel hardware, adding targets would not significantly diminish system speed.

Select this Article		Automated rendezvous and docking sensor testing at the flight robotics laboratory Richard T. Howard, Marlin L. Williamson, Albert S. Johnston, Linda L. Brewster, Jennifer D. Mitchell, Scott P. Cryan, David Strack, and Kevin Key Proc. SPIE 6555, 655512 (2007); http://dx.doi.org/10.1117/12.723437 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The Exploration Systems Architecture defines missions that require rendezvous, proximity operations, and docking (RPOD) of two spacecraft both in Low Earth Orbit (LEO) and in Low Lunar Orbit (LLO). Uncrewed spacecraft must perform automated and/or autonomous rendezvous, proximity operations and docking operations (commonly known as Automated Rendezvous and Docking, (AR&D).) The crewed versions of the spacecraft may also perform AR&D, possibly with a different level of automation and/or autonomy, and must also provide the crew with relative navigation information for manual piloting. The capabilities of the RPOD sensors are critical to the success of the Exploration Program. NASA has the responsibility to determine whether the Crew Exploration Vehicle (CEV) contractor-proposed relative navigation sensor suite will meet the CEV requirements. The relatively low technology readiness of relative navigation sensors for AR&D has been carried as one of the CEV Projects top risks. The AR&D Sensor Technology Project seeks to reduce this risk by increasing technology maturation of selected relative navigation sensor technologies through testing and simulation, and to allow the CEV Project to assess the relative navigation sensors.

Select this Article		New approach to analysis and new principles for optimization of remote sensing systems Asadov Hikmat Hamid, Hajizadeh Anver Tariyel, Kerimov Mahmud Jalal, and Isayev Azer Azad Proc. SPIE 6555, 655513 (2007); http://dx.doi.org/10.1117/12.718907 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The new approach to the analysis and optimization of remote sensing systems is describe. According to the proposed concept RS systems should be optimized using energetic - information criterion, which does mean that the maximal amount of information should be obtained upon fixed value of energy of input signal. The new multi - step principle of optimization is proposed. The examples of application of this principle are given. Also the principle of implicit dimensionality lowering for optimization systems with fading and generating signals is proposed. The principle was used to optimize aerospace remote sensing systems, with varying distance as for as investigated Earth's surface. Questions related with optimization of systems of active remote sensing taking into account of energetic losses of sensing signal in the investigated medium are considered. Physical model of such systems, envisaging energetic losses is considered. Theorems, optimizing grade regimes of system's output signal when correction of fading is carried out and is not carried out are proved.

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Spacecraft Modeling and Control

Select this Article		Optimal design of systems that evolve over time using neural networks Michael K. Nolan Proc. SPIE 6555, 655514 (2007); http://dx.doi.org/10.1117/12.719092 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract Design optimization is challenging when the number of variables becomes large. One method of addressing this problem is to use pattern recognition to decrease the solution space in which the optimizer searches. Human "common sense" is used by designers to narrow the scope of search to a confined area defined by patterns conforming to likely solution candidates. However, computer-based optimization generally does not apply similar heuristics. In this paper, a system is presented that recognizes patterns and adjusts its search for optimal solutions based on these patterns. A design problem was selected that requires the optimization algorithm to assess designs that evolve over time. A small sensor network design is evolved into a larger sensor network design. Optimal design solutions for the small network do not necessarily lead to optimal solutions for the larger network. Systems that are well-positioned to evolve have characteristics that distinguish themselves from systems that are not well-positioned to evolve. In this study, a neural network was able to recognize a pattern whereby flexible sensor networks evolved more successfully than less flexible networks. The optimizing algorithm used this pattern to select candidate systems that showed promise for evolution. A genetic algorithm assisted by a neural network achieved better performance than an unassisted genetic algorithm did. This thesis advocates the merit of neural network use in multi-objective system design optimization and to lay a basis for future study.

Select this Article		Modeling and control of active gravity off-loading for deployable space structures Trevor J. Bihl, Khanh D. Pham, and Thomas W. Murphey Proc. SPIE 6555, 655515 (2007); http://dx.doi.org/10.1117/12.717410 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract The mechanics of deployable space structures are examined through ground based testing to predict the structures' deployment in a microgravity environment. In order to simulate the microgravity conditions a test article would experience in space, a method of counteracting the loads and deflections induced by gravity is required. This is accomplished through various gravity off-loading methods, which introduce forces opposite and equal to the force of gravity acting upon a test article throughout its deployment. Current gravity off-loading methods are passive rail-cart systems with their movement forced due to their physical coupling with a test article; this introduces unwanted boundary conditions, such as inertia and side-loading from a test article's transverse movement. Therefore, an active gravity off-loading method is being developed that will deploy simultaneously with a test article. This method employs motorized carts with active position control based upon the lead angle of the off-loading cable. The maximum allowable lead angle is designed to be ±5°, with the intention of minimizing the forcing of the carts' longitudinal deployment. System dynamics and kinematics analytical modeling is derived. Simulated system results from the analytical system model and preliminary results from the prototype are presented.

Select this Article		The differential game barrier model for spacecraft under target maneuvering based on minimum error Qiu-hua Zhang, Jian Chen, Song-tao Sun, and Yi Sun Proc. SPIE 6555, 655518 (2007); http://dx.doi.org/10.1117/12.718910 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract This paper explores the pursuit-evasion game of two spacecrafts in low coplanar orbit under minute continuous thrust. By using differential game theory, this study verifies terminal conditions confined by controlling, target set and velocity and gives the linear game model of minimum error that is compared with nonlinear game model on sight coordinate. The terminal conditions are fixed by constructing parameter equations set, which are obtained by the optimal controlling strategy for both spacecraft. Within the linearized set of equations, there are variable parameters that are associated with the linearization process. Using differential game of kind theory, this paper obtains the expression of the barrier with the variable parameters to be established. According to extremum theory of the minimum error, the parameters to be established are achieved. This paper gives the results of theoretical derivation and numerical simulation.

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Simulation, Robotics, and Testing

Select this Article		Simulation study of a robotics-based method for on-orbit identification of spacecraft inertia properties Ou Ma, Hung Dang, and Khanh Pham Proc. SPIE 6555, 655519 (2007); http://dx.doi.org/10.1117/12.719376 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents the results of a simulation based study of a method for identifying the inertia parameters of a spacecraft on orbit. The method makes use of an onboard robotic arm to change the inertia distribution of the spacecraft system. As the result of the inertia redistribution, the velocity of the spacecraft system changes correspondingly. Since the velocity change is measurable and the inertia change of the robotic arm is precisely computable, the inertia parameters of the spacecraft body become the only unknown in the momentum equations and hence, can be identified from the momentum equations of the spacecraft system. To treat the problem as a linear identification problem, the problem has to be solved in two steps. The first step is to identify the mass and mass center of the spacecraft; and the second step is to identify the inertia tensor of the spacecraft. The advantages of this method are: 1) it does not consume fuel because the whole onboard mechanical subsystem involved is energized by solar power; 2) it requires measuring steady-state velocities only, but not acceleration and force; 3) it is not affected by any internal energy dissipation, which is very difficult to predict otherwise. The paper investigates the sensitivity of the method with respect to different arm/spacecraft mass ratios, arm motion trajectories, and velocity errors. The possible extension of the method by using a pair of two degrees of freedom solar panel mechanisms instead of a robotic arm is also discussed.

Select this Article		Online tribology ball bearing fault detection and identification B. Ling and M. M. Khonsari Proc. SPIE 6555, 65551A (2007); http://dx.doi.org/10.1117/12.719416 Online Publication Date: May 03, 2007 Full Text: \| Download PDF
	+ -	Show Abstract We present a feasibility analysis for the development of an online ball bearing fault detection and identification system. This system can effectively identify various fault stages related to the evolution of friction within the contact in the coated ball bearings. Data are collected from laboratory experiments involving forces, torque and acceleration sensors. To detect the ball bearing faulty stages, we have developed a new bispectrum and entropy analysis methods to capture the faulty transient signals embedded in the measurements. Test results have shown that these methods can detect the small abnormal transient signals associated with the friction evolution. To identify the fault stages, we have further developed a set of stochastic models using hidden Markov model (HMM). Instead of using the discrete sequences, our HMM models can incorporate the feature vectors modeled as Gaussian mixtures. To facilitate online fault identification, we build an HMM model for each fault stage. At each evaluation time, all HMM models are evaluated and the final detection is refined based on individual detections. Test results using laboratory experiment data have shown that our system can identify coated ball bearing faults in near real-time.

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Field Guide to Geometrical Optics

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