The mission of the High-Altitude Balloon Experiment (HABE) is to acquire supporting data, validate enabling technologies, and resolve critical acquisition, tracking, and pointing (ATP) and fire control issues in support of future space-based precision pointing experiments. The use of high-altitude balloons offers a relatively low-cost, low-vibration test platform, a recoverable and reusable payload, worldwide launch capability, and a 'near- space' emulation of the future space systems operational scenarios. The HABE platform design is based on several previous spacecraft designs, and includes coarse gimbal pointing, infrared and visible passive tracking, active fine tracking, internal auto alignment and boresighting, and precision line-of-sight (LOS) stabilization functions. A broad overview of the HABE balloon and payload system is presented, and the similarities and differences between high-altitude balloon and spacecraft design approaches are discussed. The special design features and operational conditions for ATP experiments aboard high-altitude balloon platforms are reviewed with HABE used as a design reference.
This paper describes a new formulation of the equations of motion for a system of connected rigid bodies. The bodies may either be hinge or slide connected. The connection topology is assumed to be that of a tree. Starting with the Newton-Euler equations of motion, the equations are transformed into a new system of equations using generalized velocity coordinates (both translational and rotational). The selection of these generalized coordinates is what sets this development apart from others. Constraint forces and/or torques that do not work are isolated and eliminated from the equations of motion. The generalized velocities are reduced to a minimum set. The vector operator equations of motion give a set of nonlinear differential equations that are amenable to standard numerical integration techniques.
An experiment was performed during the summer of 1992 to measure the changes in the roundtrip time of flight of laser light due to horizontal gradients in the atmosphere. Dual laser frequencies were used to range from a fixed telescope ground system to an array of corner cubes mounted on an aircraft. The aircraft flew circular paths at slant ranges of 20 to 25 kilometers around the ground facility. To maximize the number of two color returns from the aircraft, both an acquisition and a closed loop tracking scheme were developed. A Global Positioning System (GPS) receiver placed onboard the aircraft relayed its position to the ground via a radio downlink; when this data was extrapolated in time, it gave telescope acquisition pointing angles to within 1 degree of truth. Closed loop tracking was then achieved by digitizing the image of a down-looking infra-red beacon which was viewed through a camera mounted on the telescope. The X-Y coordinates of the beacon in the camera field of view were sent to the telescope computer to continuously track the image. Stable tracking was achieved on each of the three experiment nights for over 90 minutes with tracking errors within the required 200 microradian limit. Enough two color waveform data was obtained to analyze the horizontal changes in the atmospheric delay.
Engineers at the Naval Air Warfare Center Weapons Division (NAWCWPNS), China Lake, Calif., have modeled air-to-air missile seekers and their components within a larger missile engagement simulation framework. At China Lake, seeker simulation tools historically have been specific to individual seeker components. However, recent advances in computational power have allowed a team to develop a simulation that analyzes entire seeker systems as they behave on the missile airframe, both before launch and during flyout to the target. The tool is called the Infrared Seeker Trade-Off Requirements Model II (IRSTORM II). IRSTORM II is a modular seeker engagement simulation that incorporates some of the country's best IR modeling work in missile flyouts, IR target signatures and imagery, optics, detectors, and signal processing. Currently in Phase III development, this simulation is ever-evolving, and this report describes the work done in Phase II and the plans for future improvement.
Proc. SPIE 1950, Comparative study of tracking performance in an airborne tracking radar simulator using global positioning system versus monopulse radar techniques, 0000 (1 October 1993); doi: 10.1117/12.156611
This paper attempts to address the tracking accuracy between the two systems under test. A monopulse radar model was developed to theoretically calculate the would-be measured angle and angle variances. Essentially, measurements of the target's angle, angle variances, range and range rate from the monopulse radar receiver of an aircraft are assessed against the tracking performance of an airborne simulator which uses the time, space, position information (TSPI) delivered from a global positioning system (GPS) system. The accuracy of measurements from a monopulse radar primarily depends on the signal-to-noise ratio (SNR), distance from target in this case, but information received from the GPS Space Vehicle would be virtually jamfree, and independent of distance. Tracking using GPS data however requires good data link between airborne participants. The simulation fidelity becomes an issue when the target is in close range track. The monopulse random slope error and target glint become significant, while the resolution from GPS data links remains the same.
In this paper, we first describe the generic pointing and tracking problems in a general dynamical system/state-space context. Then, we analyze the information-theoretical aspects of the various uncertain signals in those problems, and establish some fundamental performance limitations those uncertainties induce, using various results and principles of modern control theory. It is shown that the introduction of 'waveform models' for uncertain signals, leading to an extended-state formulation of pointing and tracking problems, is the most effective rational means of coping with those fundamental limitations.
The pointing system described in this paper was originally developed as part of the Hard X-ray Imaging Telescope (XRT) built by the University of Birmingham for flight on the Spacelab-2 mission in 1985. The primary scientific objective of the XRT was the imaging of extended celestial X-ray sources in the energy band 2.5 - 30 kev using the coded-aperture technique. In order to maximize the observing time available to the XRT the instrument was provided with an independent pointing mount. The performance parameters of the pointing system were determined by the requirements of the XRT and resulted in the development of a two- axis gimbal system capable of supporting a moving mass of 280 kg and providing an inertial pointing stability of 20'. The mechanical configuration of a balanced payload with gimbal support bearings rated to withstand the launch environment without off-loading was chosen to enhance reliability and minimize development costs. The electrical configuration is based around duel redundant torque motors and synchros on each axis. The control loop is closed via redundant Intersil IM6100 microprocessors. The control software uses a novel algorithm to estimate gimbal rates from timing transition data from the synchros.
The objective of the infrared search and track (IRST) demonstrator program is to develop demonstration hardware which will be capable of long range detection and tracking of air targets in an airborne environment. This paper describes each of the major subsystems of the IRST equipment, which comprises the pointing system, the thermal imaging system and the signal processing system. The various modes of operation are described which provide the capability to search for, detect and track multiple targets; to display imagery of a selected target and to provide passive ranging information. The equipment will be flown in an experimental Tornado aircraft and the installation and proposed trials are also described. In conclusion, the future capability of the hardware is outlined and several upgrade paths identified.
A 3-dimensional kinematic ranging algorithm for IRSTs is described, capable of real-time operation at greater than 25 Hz. The algorithm implements two 2-dimensional extended Kalman filters to estimate range in azimuth and elevation which are then combined to give the 3-dimensional range. Also included are algorithms for target manoeuvre detection and for determining the confidence of the range estimate. Simulation results for the algorithm are presented, which show that accuracies of better than 20% can be achieved at long range, depending on the measurement accuracy.
A technique is developed to steer the transmit laser beam for free-space laser communications (lasercom) using a 2-dimensional acousto-optic (AO) Bragg cell deflector. Important characteristics of the AO Bragg deflector include high angular resolution, fast switching speed, high electrical and optical efficiency, and high reliability with no moving parts. A demonstration transmitter terminal was developed to steer a laser over a range of 360 degree(s) X 36 degree(s). Several unique capabilities are provided by the AO deflector which are not possible with conventional steering mirrors. For example, multiple simultaneous beams can be independently steered anywhere within the total steering range. Also, the AO deflector can produce variable defocus (zoom) that increases the divergence of the beam to over 10 times the diffraction-limited beam width. A direct-digital- synthesizer (DDS) was developed to produce stable and fast switching frequencies for input to the AO deflector. All of the beam control and diagnostic functions for the demo transmitter are provided by a menu-driven PC486-33 computer program.
One of the most apparent types of motion in real times systems is acceleration. In this paper the effects of this kind of motion are considered for two important areas, image quality and target acquisition. Comparison between effects of linear and acceleration motion is presented in the first section. The problem of acceleration motion is very critical for airborne photography in hostile territory. There are two opposing considerations when flying over hostile territory. On the one hand the pilot must fly fast so he will not revealed or attacked by the enemy. On the other hand he must fly slowly so the degradation process on the image quality will not be so severe. Mathematical tools developed recently permit quantitative analysis of effects of acceleration on image quality and acquisition of the target.
This paper describes the Advanced Modulator Tracker (AMT), a real-time video tracker capable of tracking targets such as boosting rockets and satellites. The AMT has been developed as an in-house project by the USAF Phillips Lab for Acquisition, Tracking, and Pointing (ATP) experiments, and is based on Datacube's parallel-piped Image Processing hardware and Imageflow software. The current version of the AMT uses Datacube's MaxVideo-20, MaxScan, and Max860 boards. The AMT is capable of performing centroid, edge and correlation tracking on two separate video inputs simultaneously, with real-time video switching of input images, real-time histogram computation and preprocessing of input images. The AMT has the ability to automatically acquire the target under track, adjust its threshold and adjust its gate size. The AMT can be used for any ground, air, or space-based video tracking applications.
This paper describes tree real-time video edge tracking algorithms for use in tracking targets such as boosting-rockets and satellites. These algorithms are referred to as the Maximum intercept method. Single modified-Hough transform method, and the Double modified-Hough transform method. These algorithms assume knowledge of the angle associated with the edge that you wish to track. Two methods of obtaining the best edge angle from which to track are presented. These edge tracking algorithms and edge- angle determination methods evolved throughout the development of the Advanced Modular Tracker (AMT). The AMT is a real-time video tracker with sophisticated mode logic and is described in another paper. The AMT will be the primary tracker for the High Altitude Balloon Experiment (HABE) being performed by the USAF Phillips Laboratory for the Strategic Defense Initiative Organization (SDIO).
This study considers a satellite-mounted sensor in a 1000-km circular orbit. The sensor is initially placed North, South, East, or West of a ballistic target, at a variety of initial ranges from 500 km to over 3000 km. The initial angle between the sensor and target velocity vectors is varied, from near zero degrees to roughly 180 degrees, in steps of 30 degrees. The tracking algorithm used is a standard Kalman filter. The track errors as a function of track time for several track data rates (once every 2 to 20 seconds) are examined. The error is defined to be the maximum eigenvalue of the covariance matrix. Both the current covariance matrix and the matrix propagated to impact are studied. The study is done for a variety of angular measurement errors, from one microradian to over 100 microradians. The best tracking performance seldom occurs when the target and sensor velocity vectors are crossing, as might be intuitively expected. The track error is very nearly linear with angular error. While increasing the data rate improves tracking performance, doubling the data rate does not improve performance nearly as much as doubling the total track time. The tracking performance does not automatically degrade with inithi range, as might be expected. Once a good track is obtained, further updates to the track can be very infrequent (less than once per 100 seconds), and the track will still improve steadily with time. Stereo tracking, as might be expected, offers dramatically better results than mono tracking.
In tracking maneuvering targets, the detection of the start and the end of a maneuver time is a prerequisite to maintaining good track quality. The paper addresses the issue of maneuver detection using information from an image sensor. Contrary to existing image sensor based tracking methods, the proposed approach is very attractive from computational and storage points of view.
The problem of observability when tracking a target with noisy angles measurements by a single observer is addressed. Necessary and sufficient conditions on the observer maneuver to ensure the target observability are developed for the constant velocity target motion case.
The objective of this paper is to examine the performance of the sequential approach and an asynchronous data fusion approach to target tracking as defined for two dissimilar sensors. First, analytical expressions for evaluating the performance of these two approaches were derived. Then, these expressions were applied to the fusion of data from a multi-tasking radar and an optical sensor. It is assumed that the data rate of the optical sensor is much higher than the radar's. Overall, it was found that the sequential and data fusion approaches have reasonably similar performance for this case. However, the computational advantage of the fusion approach makes it more attractive than the sequential approach.
The potential applications for machine vision are increasing faster than the costs are decreasing. The ability to follow moving objects is a key to machine vision and is the foundation to tracking. The principles of inspection or machine control are essentially unchanged, but the temporal environment introduces increased memory and bandwidth requirements for host processors, and increased performance requirements for the feature extraction processors. Recent developments in hardware are allowing more robust tracking systems at increasingly affordable prices. We'll explore these topics are greater length in the text which follows.
The Joint European Telescope for X-ray astronomy, JET-X, is one of the core instruments in the scientific payload of the Russian Spectrum-Roentgen-Gamma high energy astrophysics mission. JET-X consists of two co-aligned x-ray imaging telescopes, each with a spatial resolution of better than 20 arcseconds. Cooled x-ray sensitized CCDs in the focal plane of each telescope are designed to provide imaging with 150 eV spectral resolution over the energy band 0.3 - 10 keV. A typical observation of 105 seconds comprises many short (2.5 second) CCD exposures, thus enabling the detection and energy determination of individual photon events. If the full imaging resolution of the instrument is to be realized, a post facto, time-resolved attitude reconstruction of the telescope's pointing direction will be required, so that the effects of thermal distortion within the telescope structure and attitude drift of the spacecraft can be corrected when combining the multiple x-ray images obtained during an observation. JET-X will therefore generate its own aspect solution through pointing measurements with a purpose- designed Attitude Monitor: a cooled, slow-scan CCD TV camera with data processing electronics.
A development of a medium accuracy, CCD based starsensor, intended for use on the new generation of communication satellites is in progress. The sensor aims at an accuracy of 0.06 degree(s) in a FOV of 30 degree(s) X 40 degree(s). The sensor is designed to detect stars with a brightness of mvia <EQ + 2.5 during its whole lifetime of at least 10 years. A breadboard of this starsensor, called Pattern Recognition System (PRS) was built and verified and the manufacturing of an EQM is ongoing now. Intended to be versatile in applications for telecommunication and other missions, a unit is developed which is adaptive and has low recurring cost. The PRS concept is based on new MPP CCD technology. This technology brings passive thermal control without Peltier elements within reach. The electronics accommodated inside the PRS sensorheads is miniaturized by large scale integration by using a Field Programmable Gate Array (FPGA) and Surface Mount Technology (SMT). For cost reasons no microprocessor was implemented. This paper describes the main design features of the PRS, the selection and testing of appropriate CCD, performance characteristics of the system and test results obtained from the PRS breadboard system.
This paper introduces a spiral guidance law for intercepting missiles or satellites. The law is termed spiral because it directs the kill vehicle (KV) along a spiral-shape trajectory. The guidance law has two important features: (1) it directs the KV along a trajectory that makes target range observable to an angle-only (passive) sensor, and (2) it does not require the KV's thrust to be throttled. The second feature permits the use of divert motors that burn at a fixed predetermined rate, such as fixed-impulse solid-fuel divert motors.
Electrical noise in gimbal control loops can directly impact gimbal drift and Line-of-Sight motion in electro-optic systems. When electrical noise saturates the control loop, the loop operates non-linearly, and changes the loop's ability to reject disturbances. Should the requirement for this loop noise stay below the saturation point for adequate gimbal control? This paper provides an avenue to study Line-of-Sight stabilization performance in the presence of saturating loop noise. The rate feedback device is a two-axis piezoelectric gyro that senses gimbal structural flexure and linear vibrations.
The performance of image registration algorithms for IR images depends on different system parameters such as SNR, gain, offset, image variance etc. in a very complex fashion. A statistical approach has been adopted to predict the performance of image registration algorithms , classical Correlation and Mean Absolute Difference algorithms, in terms of probability of correct registration as a function of different system parameters. Considering the complexity of the problem, some simplifying assumptions have been made regarding the random nature of different images as well as criteria function values which may not be strictly true for real environments. This analysis helps in understanding the sensitivity of different algorithms to different system parameters. This in turn helps to compare the performance of different registration algorithms in differe nt environments. A scheme for choosing adaptive threshold to meet constraints as probability of false hit and probability of miss, has also been proposed