Proceedings Volume 2810

Space Sciencecraft Control and Tracking in the New Millennium

E. Kane Casani, Mark A. Vander Does
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Proceedings Volume 2810

Space Sciencecraft Control and Tracking in the New Millennium

E. Kane Casani, Mark A. Vander Does
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 28 October 1996
Contents: 7 Sessions, 25 Papers, 0 Presentations
Conference: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation 1996
Volume Number: 2810

Table of Contents

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Table of Contents

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  • Sciencecraft
  • Autonomy
  • Microinstruments
  • New and Proposed Technology Advancements for Tracking and Control
  • Advancements in Guidance and Mapping
  • Star Trackers, Mission Design, and Performance I
  • Star Trackers, Mission Design, and Performance II
  • Sciencecraft
  • Autonomy
Sciencecraft
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Kuiper Express: a sciencecraft
David H. Rodgers, Leon Alkalai, Patricia M. Beauchamp, et al.
The Kuiper Express is a mission to achieve the first reconnaissance of one of the primitive objects that reside in the Kuiper Belt. The objects in the Kuiper Belt are the remnants of the planetesimal swarm that formed the four giant planets of the outer Solar System. These objects, because they are far from the Sun, have not been processed by solar heating and are essentially in their primordial state. This makes them unique objects and their study will provide information on the composition of the solar nebula that cannot be extracted from a study of other objects in the Solar System. The Kuiper Express is a sciencecraft mission. A sciencecraft is an integrated unit that combines into a single system the essential elements (but no more) necessary to achieve the science objectives of the mission, including science instruments, electronics, telecommunications, power, and propulsion. The design of a sciencecraft begins with the definition of mission science objectives and cost constraint. An observational sequence and sensor subsystem are then designed. This sensor subsystem in turn becomes the design driver for the sciencecraft architecture and hardware subsystems needed to deliver the sensor to its target and return the science data to the earth. Throughout the design process, shared functionality, shared redundancy, and reduced cost are strongly emphasized. The Kuiper Express will be launched using a Delta vehicle and will use solar electric propulsion to add velocity and shape its trajectory in the inner Solar System, executing two earth gravity-assist flybys. It will also execute flybys of main belt asteroids, Mars, Uranus, and Neptune/Triton en route to its target in the Kuiper belt, where it will arrive about ten years after launch. It will use no nuclear power. The surface constituents and morphology of the objects visited will be measured and their atmospheres will be characterized. The cost of the detailed design, fabrication, and launch of the Kuiper Express is consistent with the $150M limit set by the NASA Discovery Program.
Sciencecraft process
Patricia M. Beauchamp, Leon Alkalai, Robert H. Brown, et al.
In this paper, the authors propose a new process for the development and operation of unmanned vehicles for the exploration of space. We call the vehicle (and the process used to create it) sciencecraft. A Sciencecraft is an integrated unit that combines into a single system those elements (but no more) which are necessary to achieve the science objectives of the mission, including science instruments, electronics, telecommunications, power, and propulsion. the design of a sciencecraft begins with the definition of the mission science objectives. This is followed by the establishment of measurement goals and the definition of a critical data set. Next an observational sequence is developed, which will provide the data set. This step is followed by the design of the integrated sensor system that will make the observations. The final step in the development of a sciencecraft is the design of the hardware subsystems needed to deliver the sensor to its target and return the science data to the earth. This approach assures that the sciencecraft hardware design and overall architecture will be driven by the science objectives and the sensor requirements rather than the reverse, as has historically been the case. Throughout the design process, there is an emphasis on shared functionality, shared redundancy, and reduced cost. We illustrate the power of the sciencecraft approach by describing the Planetary Integrated Camera Spectrometer (PICS), an integrated sensor system in which the 'sciencecraft' process has been applied to the development of a single subsystem, which integrates multiple functionalities. PICS is a case-in-point where the sciencecraft process has been successfully demonstrated. We then describe a sciencecraft mission for exploration of the outer Solar System, including flybys of Uranus, Neptune, and an object in the Kuiper Belt. This mission, called the Kuiper Express, will use solar electric propulsion to shape its trajectory in the inner solar system and will use no nuclear power. The Kuiper Express is an example of how the sciencecraft approach can return 'voyager class science at ten cents on the dollar.'
Autonomy
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Autonomous optical navigation for interplanetary missions
Shyam Bhaskaran, Joseph E. Riedel, Stephen P. Synnott
The automation of interplanetary spacecraft is becoming increasingly desirable to meet various mission requirements. A prototype autonomous spacecraft which will flyby an asteroid and comet is slated for flight in mid-1998 as part of NASA's New Millennium Program. This spacecraft will navigate by using optical data taken by the onboard camera to determine its orbit, and use this information to predict its future trajectory and make necessary course corrections. The basic navigation data available from the camera are star-relative astrometric observations of solar system bodies which can be used to determine line-of-sight vectors to those objects. The directional sightings are obtained by determining the precise centers of the object and stars in the image. During interplanetary cruise, centerfinding is performed by using two pattern matching techniques inherited from the Galileo mission. Near-encounter images are processed with a separate algorithm employing image modeling and brightness centroiding. This paper describes the image processing algorithms, and the results of a ground-based test of the algorithms using real data.
Technology cooperation between NOAA and NASA in the New Millennium Program
Edward Howard, Gerald Dittberner, Steven Kirkner
We at NOAA have conducted several, early requirements studies over the past two years to better define the next generation of environmental satellites at geostationary orbit -- the GOES program. While much work remains to be done, we believe that we must use current and future technology in smarter ways to lower future satellite costs. At the same time, such technology should let us increase measurement performance and add new, required products. NASA has a program called the New Millennium Program (NMP) whose goal is to lower spacecraft and mission costs by testing technology in space. NOAA is a strong believer in this program, and we have participated from the start in its development. This paper describes the types of technology that NOAA may use in future GOES programs and that have been discussed and shared with NASA's New Millennium Program. In addition to technology needs, we mentions several benefits from the New Millennium Program on how to improve space program development.
Autonomous vision in space on an Advanced Stellar Compass platform
John Leif Joergensen, Allan Read Eisenman, Carl Christian Liebe
The Orsted Star Imager comprises the functionality of an advanced stellar compass (ASC), i.e. it is able to autonomously solve 'the lost in space' attitude problem, as well as determine the attitude with high precision in the matter of seconds. The autonomy makes for a high capability for error rejection and fault recovery, as well as 'graceful degradation' at radiation, false object or thermal loads. The instrument was developed from Concept to flight model within 3 years. The instrument surpasses the initial specifications for all parameters, for precision, computational speed and fault detection and recovery by orders of magnitude. This was accomplished by the use of advanced high level integrated chips in the design, along with a design philosophy of maximum autonomy at all levels. The instrument tracks all stars in the field of view, which enables a variety of applications not normally associated with conventional star trackers. Initially, this paper gives a general description of the ASC, including its primary specifications and performance levels. Some of the more promising of the advanced applications are then discussed, along with test-results and methodologies. The diversity of the advanced applications are vast, as depicted by the topics addressed, namely: (1) Detection and tracking of distant non-stellar objects (e.g. meteors). (2) Delta-V correction, for encounter phases. (3) Tracking of selected objects (e.g. guidance for other instruments). (4) Mass estimation via pellet ejection. (5) Complex object surface tracking (e.g. space docking, planetary terrain tracking). All the above topics have been realized in the past, either by open loop, or by man-in-the-loop systems. By implementing these methods or functions in the onboard autonomy, a superior system performance could be achieved by means of the minimal loop delay. But also reduced operations cost should be expected.
Implementing autonomous planetary remote sensing
Stewart L. Moses, Kenneth Rourke, Joseph Freitag, et al.
Future planetary exploration missions will be marked by dramatic increases in the amount of remote sensing data that can be acquired per dollar of mission cost, despite improvements in the instrumentation to retrieve data. However, planetary distances will continue to limit the amount of data that can be returned to Earth and communications will be a major factor influencing spacecraft mass, power, and ultimately cost. Remarkable advancements in spacecraft onboard data processing, fortunately, offer a solution to the downlink constriction while simultaneously reducing spacecraft operation costs on the ground by enabling autonomous and adaptive scientific data acquisition. This paper presents an approach to enhancing future space mission capabilities. We have chosen hyperspectral imaging as an example of a remote sensing technique that generates a large volume of data from a single instrument and is amenable to onboard processing and adaptive scientific data acquisition. Specific advanced hardware and software technologies from NASA and industry can be adapted to provide a feasible spacecraft implementation.
Microinstruments
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Ka-band tiny transmitter for the New Millenium Program
A. Lance Riley, Michael Grimm, Dmitrios Antsos, et al.
The size, mass and cost of telecommunications systems on deep space missions have increased at almost an exponential rate over the last thirty years. Great cost and size reduction of these systems can be achieved by reducing the cost and size of the transponder component of the radio subsystem. An advanced technology X- and Ka-band (8 and 32 GHz) tiny transmitter is being developed at JPL for the New Millennium program and is described in this paper. The tiny transmitter is the first phase of development of the tiny transponder which will incorporate recent advancements in miniaturization and flexibility of radio systems by utilizing digital radio techniques. These techniques incorporate digital technology and algorithms to perform many functions which have traditionally been performed by analog circuits and allow the complexity of the rf portion of the radio to be minimized. The tiny transponder will be able to meet the needs of almost all deep space missions presently being planned for launch after the year 2000.
Silicon bulk micromachined vibratory gyroscope for microspacecraft
Tony K. Tang, Roman C. Gutierrez, Jaroslava Z. Wilcox, et al.
This paper reports on the design, modeling, fabrication, and characterization of a novel silicon bulk micromachined vibratory rate gyroscope and a 3-axes rotation sensing system using this new type of microgyroscopes designed for microspacecraft applications. The new microgyroscope consists of a silicon four leaf clover structure with a post attached to the center. The whole structure is suspended by four thin silicon cantilevers. This device is electrostatically actuated and detects Coriolis induced motions of the leaves capacitively. A prototype of this microgyroscope has a rotation responsivity (scale factor) of 10.4 mV/deg/sec with scale factor nonlinearity of less than 1%, and a minimum detectable noise equivalent rotation rate of 90 deg/hr, at an integration time of 1 second. The bias stability of this microgyroscope is better than 29 deg/hr. The performance of this microgyroscope is limited by the electronic circuit noise and drift. Planned improvements in the fabrication and assembly of the microgyroscope will allow the use of Q-factor amplification to increase the sensitivity of the device by at least two to three orders of magnitude. This new vibratory microgyroscope offers potential advantages of almost unlimited operational life, high performance, extremely compact size, low power operation, and low cost for inertial navigation and altitude control.
Application of APS arrays to star and feature tracking systems
Christopher C. Clark, Orly Yadid-Pecht, Eric R. Fossum, et al.
Reducing mass and power demands from engineering and science image sensors, while improving system capability, remains a driving force in the development of Sciencecraft components. The Jet Propulsion Lab (JPL) is developing advanced concepts for future spacecraft celestial trackers by incorporating active pixel sensor (APS) array technology into star and feature tracker designs. We describe fundamental APS array properties and characteristics, and discuss recent progress in APS designs directly applicable to next generation trackers. A description of a new regional electronic shutter design providing extremely high dynamic range and local shuttering capability is given along with test results from a prototype device. A new star and feature tracker concept enabled by this regional shuttering capability is described.
Student Nitric Oxide Explorer
Stanley C. Solomon, Charles A. Barth, Penina Axelrad, et al.
The Student Nitric Oxide Explorer (SNOE) is a small scientific spacecraft designed to launch on a PegasusTM XL vehicle for the Student Explorer Demonstration Initiative. Its scientific goals are to measure nitric oxide density in the lower thermosphere and to analyze the solar and magnetospheric influences that create it and cause its abundance to vary dramatically. The SNOE ('snowy') spacecraft and instrumentation is being designed and built at the University of Colorado Laboratory for Atmospheric and Space Physics (LASP) by a team of scientists, engineers, and students. The spacecraft is a compact hexagonal structure, 37' by 39', weighing approximately 280 lbs. It will be launched into a circular orbit, 550 km altitude, 97.5 degrees inclination for sun-synchronous precession at 10:30 AM ascending node. It is designed to spin at 5 rpm with the spin axis normal to the orbit plane. It carries three instruments: an ultraviolet spectrometer to measure nitric oxide altitude profiles on the limb, a two-channel ultraviolet photometer to measure auroral emissions in the nadir, and a five-channel solar soft x-ray photometer. An experimental GPS receiver is also included. The spacecraft structure is aluminum, with a center platform section for the instruments and subsystems. Static solar arrays are supported by a truss system. A spacecraft microprocessor handles all subsystem, instrument, and communications functions in an integrated fashion, including command decoding, attitude control, instrument commanding, data storage, and telemetry. The spacecraft is scheduled for launch in early 1997 and will be operated by students at LASP. For more information on the SNOE project, please visit http://lasp.colorado.edu/snoe/.
Fiber optic interferometer with tuning diode laser for gravity field measuring
Igor G. Goncharov, Alexander P. Grachev, Constantin A. Scvorchevsky, et al.
This paper discusses the remote sensing based on a GaAs diode laser with an external dispersive cavity (DL EDC). The scheme provides continuous generation on a single longitudinal mode of external cavity and the generation line-width less than 1 kHz or generation on a broad mode of internal laser cavity. This source of coherent radiation provided the work of fiber-optic accelerometer, which also is fiber-optic sensor of gravity field. The fiber-optic gravimeter includes fiber-optic interferometers of Mach- Zhender and has possibility to measure value and direction of gravity field's vector in three-dimensional space. Resolution of phase shift on level 10E-3 rad gives the possibility to measure the change of value of gravity field's vector on level 10E-6*g (where g - acceleration of free fall).
New and Proposed Technology Advancements for Tracking and Control
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Scannerless terrain mapper
John T. Sackos, Bart D. Bradley, Carl F. Diegert, et al.
NASA-Ames Research Center, in collaboration with Sandia National Laboratories, is developing a scannerless terrain mapper (STM) for autonomous vehicle guidance through the use of virtual reality. The STM sensor is based on an innovative imaging optical radar technology that is being developed by Sandia National Laboratories. The sensor uses active flood- light scene illumination and an image intensified CCD camera receiver to rapidly produce and record very high quality range imagery of observed scenes. The STM is an all solid- state device (containing no moving parts) and offers significant size, performance, reliability, simplicity, and affordability advantages over other types of 3-D sensor technologies, such as scanned laser radar, stereo vision, and structured lighting. The sensor is based on low cost, commercially available hardware, and is very well suited for affordable application to a wide variety of military and commercial uses, including: munition guidance, target recognition, robotic vision, automated inspection, driver enhanced vision, collision avoidance, site security and monitoring, and facility surveying. This paper reviews the sensor technology, discusses NASA's terrain mapping applications, and presents results from the initial testing of the sensor at NASA's planetary landscape simulator.
Optical alignment monitoring and stabilization using a liquid crystal television (LCTV)
Maintenance of laser beam alignment in optical systems is highly desirable for effective operation. In this paper, a LCTV-based alignment preserving scheme is discussed. We show that a laser beam can be aligned automatically to an accuracy of less than plus or minus 2 micrometer using a LCTV with an average pixel pitch of 85 micrometer. Due to simplicity and low cost, the proposed scheme is attractive for use in laser based optical systems that are used on airborne platforms.
Advancements in Guidance and Mapping
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Active pixel sensors for autonomous spacecraft applications
Phil M. Salomon, Eric R. Fossum, Christopher C. Clark, et al.
Over the foreseeable future, the size and scope of spacecraft missions will change dramatically. No longer will we see the large, expensive, and complex spacecraft that characterized the past decades. Successful as they were, they represent a technology and approach which is not supportable in today's economic environment. The new millennium will require smaller spacecraft with a more focused set of mission goals and flying on-board sensors having greatly reduces size and weight and a greater range of capabilities. The need for additional autonomy will be created by the greater number of small spacecraft operating and the need to reduce the expenses of mission operations. Thus the emphasis on newly developed instruments for guidance and target image processing will stress enhancing instrument capabilities, minimizing size and power requirements, and maintaining the reliability that has been achieved over the past years. Toward these goals, we believe the new APS-based generation of sensors will provide the basis for achieving these goals.
Beamwidth and transmitter power adaptive to tracking-system performance for free-space optical communication
The basic free space optical communication system includes at least two satellites. In order to communicate between them, the transmitter satellite must track the beacon of the receiver satellite and point the information optical beam in its direction. Optical tracking and pointing systems for free space suffer during tracking from high amplitude vibration due to background radiation from interstellar objects such as sun, moon, earth and stars in the tracking field of view or mechanical impact from satellite internal and external sources. The vibrations of the beam pointing increase the bit error rate and jam communication between the two satellites. One way to overcome this problem is to increase the satellite receiver beacon power. However this solution requires increased power consumption and weight. These two factors are disadvantageous in satellite development. Considering these facts, we derive a mathematical model of a communication system that adapts optimally the transmitter beamwidth and the transmitted power to the tracking system performance. Based on this model, we investigate the performance of a communication system with discrete level optical phased array transmitter telescope gain. An example for a practical communication system between a low earth orbit satellite (LEO) and a geostationary earth orbit satellite (GEO) is presented. From the results of this work it is seen that a four level adaptive transmitter telescope is sufficient to compensate for vibration amplitude doubling. The benefits of the proposed model are less required transmitter power and improved communication system performance.
Star Trackers, Mission Design, and Performance I
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CCD star tracker for attitude determination and control of a satellite for a space VLBI mission
Kazuhide Noguchi, Koshi Sato, Ryouichi Kasikawa, et al.
This paper presents design and performance of a high- precision star tracker which has been developed for use in the attitude determination and control system of MUSES-B spacecraft; the space segment of space VLBI program called VSOP (equals VLBI Space Observation Program). The MUSES-B is being prepared for launch in September 1996. The attitude control system is required to fulfill an overall pointing accuracy of 0.01 degrees (3 sigma) of an 8 meter-diameter VLBI antenna mounted on the spacecraft. The onboard attitude determination system is based on a reset type Kalman filter that assures the overall attitude determination accuracy of 19 arcseconds, using outputs from the star trackers and the gyroscope-based inertial sensors. For this purpose, the star tracker is designed to provide star position detection accuracy of 4 arcsec random (1 sigma) plus 15 arcsec bias error. This paper describes the design of the STTs, the performance analyses, and ground test results of the Protoflight Model.
On-orbit performance of TOPEX/POSIEDON star trackers
Tooraj Kia, Gene A. Hanover
The primary objective of the TOPEX/POSIEDON satellite is to monitor the world's oceans for scientific study of ocean circulation leading to weather and climate prediction, coastal storm warning and maritime safety. TOPEX/POSIEDON was launched on August 10, 1992 from the Kourou Space Center in French Guyana on a nominal circular orbit with an altitude of 1336 Km with a 66 degree inclination. Selection of this orbit imposed challenging requirements on the on- board electronics. At this altitude, South Atlantic Anomaly (SAA) covers a large area. During many orbits the satellite may spend up to 40 minutes in the SAA region, all the time being bombarded by heavy protons and other charged particles. The on-board electronics were required to endure an estimated total dose radiation of 70 KRAD, with an RDM of 2, over the prime mission life of three years. In addition to the total dose radiation requirement, the spacecraft is required to perform within specifications in-spite of the heavy protons present at this orbit. TOPEX/POSIEDON is the first NASA satellite to carry two CCD based star trackers on a long duration mission. TOPEX/POSIEDON star trackers, known as advanced star tracker (ASTRA), were designed and built by Hughes Danbury Optical Systems (HDOS). These trackers have experienced single-event upsets and possible radiation induced radiation changes in their characteristics. One of the trackers has been in an in-operable state since being hit by a suspected SEU in November 1992. The second tracker has also had anomalies indicative of an SEU, but has managed to recover and is performing within the TOPEX specifications. JPL has been monitoring and evaluating the performance of these star trackers, during the last forty months. The data show change in certain tracker characteristics such as the magnitude of the detected stars, the background counts and the hot pixel data. This paper addresses the CCD tracker performance and the change in their characteristics in the high radiation environment.
Space qualification of HDOS' HD-1003 Star Tracker
Lawrence W. Cassidy
HDOS'HD-1003 Star Tracker is now in production for a variety of NASA and DoD space programs. It owes its success to its unique combination of small size (only seven pounds, 190 cu. in.) and high performance. Deliveries of the production tracker began in early 1996. Environmental qualification was completed in July 1996, and the first space flight is imminent aboard NASA's SSTI spacecraft. This paper provides a brief overview of the HD-1003 design and mission applications, and highlights qualification test results that establish HD-1003 as the premier multi-star tracker for future space programs.
Star Trackers, Mission Design, and Performance II
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Philosophy of design for low cost and high reliability
John Leif Joergensen, Allan Read Eisenman, Carl Christian Liebe
The Orsted Star Imager, comprises the functionality of an advanced stellar compass (ASC), i.e. it is able to autonomously solve 'the lost in space' attitude problem, as well as determine the attitude with high precision in the matter of seconds. The autonomy makes for a high capability for error rejection and faulty recovery, as well as graceful degradation at radiation, false object or thermal loads. The instrument was developed from concept to flight model within 3 years. The instrument surpasses the initial specifications for all parameters. For precision, computational speed and fault detection and recovery by orders of magnitude. This was accomplished, by the use of advanced high level integrated chips in the design, along with a design philosophy of maximum autonomy at all levels. This approach necessitates a prototyping facility, capable of extensive component screening. This screening addresses topics such as chip technology and thermo-mechanical propeties, as well as radiation sensitivity. The purpose of this facility is to reduce costs, by generating early information concerning whether specific components have the ability to survive space environs. This paper describes the development philosophy and the development process. Starting with the system specifications and its derived design drivers. Via the design process, iteration levels and the specifications and capability of the prototyping facility. Ending with the final system design. During this, actual choices of IC- levels and system flexibility are addressed.
Attitude intercalibration of the star imager and the spherical compact sensor magnetometer for the Oersted geomagnetic satellite mission
Torben Risbo, Nils Olsen
The main instrument for mapping of the Earth's magnetic field onboard the Danish geomagnetic satellite Orsted is the 'gondola' consisting of a compact spherical coil fluxgate vector magnetometer (CSC) and a star imager (SIM). The SIM gives the attitude relative to the rectascension-declination system by taking a snapshot of the sky, the CSC measures the magnetic field vector in the instrument coordinate system. The attitude relation (gondola quaternion) between the star camera system and the magnetometer system is a fundamental instrument constant to be determined by calibration with arc seconds accuracy. This intercalibration has been carried out at the geomagnetic observatory at Brorfelde, Denmark. Snapshots of the sky were taken simultaneously with measurements of the Earth's magnetic field made by the CSC magnetometer and the observatory variometer. The SIM attitude obtained in the celestial coordinate system is transformed to the local terrestrial system. The observatory magnetic field observations are transformed to the SIM coordinate system. By comparisons with the CSC readings the orthogonal transformation between the two instrument systems is determined. If the instrument assembly is turned around in the known ambient geomagnetic field the procedure is equivalent to a thin shell calibration in a test coil system, and hence the magnetometer constants can be determined, too. Results from the calibration of the Orsted magnetic instrument are presented.
Algorithms onboard the Oersted microsatellite stellar compass
Carl Christian Liebe, John Leif Joergensen
One of the state-of-the-art attitude determination instruments for spacecraft applications is an advanced stellar compass (ASC or a star tracker). It is able to determine the attitude of a spacecraft relative to the stars with an accuracy better than 1 arcsecond (4.8 microradian). This is achieved utilizing a CCD camera and a powerful microcomputer. The microcomputer analyzes the CCD images using an onboard software star catalogue. The objective of the Danish Oersted microsatellite is to measure the magnetic field of the earth. The field is measured with a very accurate vector magnetometer. The accurate vector measurements must be related to some celestial coordinate system. The only instrument capable of doing so with the required accuracy is an ASC. Therefore the Oersted microsatellite is equipped with an ASC, which is discussed in this paper. The design of the ASC is novel compared to conventional star trackers, because it is able to make the initial attitude acquisition autonomously (lost in space). This is achieved utilizing pattern recognition of star constellations in the CCD image and a preflight compiled version of the star catalogue. The technique is described and the performance analyzed. Also, the ASC is more accurate than conventional star trackers. A conventional star tracker typically tracks 2 - 10 stars in a single frame, whereas the ASC tracks up to 200 stars, yielding more accurate attitude estimates with similar lens configuration. The accuracy, the performance and the high sky coverage of this new approach are discussed.
Astronomical performance of the engineering model Oersted Advanced Stellar Compass
Allan Read Eisenman, John Leif Joergensen, Carl Christian Liebe
The Danish geomagnetic microsatellite, Orsted, is an autonomous sciencecraft which is scheduled for a May 1997 launch into polar orbit. It is produced by a consortium of universities, industry and government and is Denmark's first national spacecraft. NASA support includes JPL real sky evaluation of its star tracker, the advanced stellar compass (ASC). The ASC features low cost, low mass, low power, low magnetic disturbance, autonomous operation, a high level of functionality and the high precision. These features are enabled by the use of advanced optical and electronic design which permit the direct integration of the ASC and the science payload. The ASC provides the required attitude information for its associated vector magnetometer and the sciencecraft. It consists of two units, a CCD based camera head and a data processing unit with a powerful microcomputer. The microcomputer contains two large star data bases which enable the computer to recognize star patterns in the field-of-view, to quickly solve the lost-in- space acquisition problem and to derive the attitude of the ASC camera head. The flight model of the camera head has a mass and a power consumption of 127 grams (without baffle) and 0.5 W, respectively. Typical, beginning-of-life, relative measurement precision in pitch and yaw are in the order of two arcseconds (1 sigma) or better have been achieved in the tests and are substantiated.
Analysis of the NEAR star tracker flight data
Thomas E. Strikwerda, H. Landis Fisher
The NEAR spacecraft uses a star tracker for precision attitude determination and employs techniques for autonomous star identification and tracking. Outdoor test data and flight data have been analyzed to characterize the performance. Both types of data show good agreement in general with calibration data. Results from the outdoor tests were used to improve models of the tracker in simulations used for software development and test. This paper briefly describes the guidance and control system and star tracker, simulations, and star catalogs. The remainder of the paper discusses the analysis of the flight data and compares the performance results with calibration data.
Sciencecraft
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EO-1: NASA's first new millennium earth orbiting mission
Bernard D. Seery, D. Bryant Cramer, Christopher M. Stevens, et al.
One of the key charges to NASA's Mission to Planet Earth (MTPE) is to ensure the continuity of future Landsat data. The New Millennium Program's (NMP) first Earth orbiting flight will validate technologies contributing to the reduction in cost of Landsat follow-on missions. The centerpiece is an advanced land imager (ALI) instrument. The EO-1 imaging system will also incorporate alternative and innovative approaches to future land imaging, including two different hyperspectral imaging techniques. One of these is a hyperspectral wedge spectrometer and the other is a miniature hyperspectral grating spectrometer.
Autonomy
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Remote agent prototype for spacecraft autonomy
Barney Pell, Douglas E. Bernard, Steve Chien, et al.
NASA has recently announced the New Millennium Program (NMP) to develop 'faster, better, cheaper' spacecraft in order to establish a 'virtual presence' in space. A crucial element in achieving this vision is onboard spacecraft autonomy, requiring us to automate functions which have traditionally been achieved on ground by humans. These include planning activities, sequencing spacecraft actions, tracking spacecraft state, ensuring correct functioning, recovering in cases of failure and reconfiguring hardware. In response to these challenging requirements, we analyzed the spacecraft domain to determine its unique properties and developed an architecture which provided the required functionality. This architecture integrates traditional real-time monitoring and control with constraint-based planning and scheduling, robust multi-threaded execution, and model-based diagnosis and reconfiguration. In a five month effort we successfully demonstrated this implemented architecture in the context of an autonomous insertion of a simulated spacecraft into orbit around Saturn, trading off science and engineering goals, and achieving the mission goals in the face of any single point of hardware failure. This scenario turned out to be among the most complex handled by each of the component technologies. As a result of this success, the integrated architecture has been selected to control the first NMP flight, Deep Space One, in 1998. It will be the first AI system to autonomously control an actual spacecraft.