A development and test approach for an electro-optics and tracking beam control system is described. The objective is to verify and test the performance of the Space Shuttle based Starlab experiment. Starlab will provide an on-orbit demonstration of acquisition, tracking and pointing (ATP) dynamics. This paper presents the test used to measure performance with laboratory testing of the computerized system. The Starlab Pointing Control System incorporates an advanced flight computer design. This computer intermeshes analog control loops of its mirror controlling servos. Digitally derived transformation relationships are introduced to the analog channels with solid state multiplying digital analog converters (MDACs). The control system distributes commands to a two-axis pointing gimbal and fast servo mirrors to control a line of sight that is dependent on measurements made with focal plane detectors responding to space object radiation. An approach to the system hardware and software testing has been developed. The tests include verification of optical tracking, including space object imagery and the beam control mirror servos. Flight computer software is incorporated into the computer to allow functional checkout of its algorithms. In addition, a special hardware/software test set has been developed to provide the hardware flight computer system with an emulated hardware and flight dynamic environment. The test set is a special purpose hardware system supported by an external computer for supplying an emulated interface of the Starlab actuators, sensors, and effective geometric line of sight conditions corresponding closely to the physical environment of a Starlab mission. Its primary purpose is to check out the flight computer system. Its secondary purpose is to perform 'system test' and mission simulations of the pointing control system. These tests are used to validate experiment design and support laboratory hardware integration

A pointing/roll mechanism for the Ultraviolet Coronagraph Spectrometer (UVCS) is presented along with a description of the mechanism control algorithm. The mechanism, operating in space, will angulary position the 2.1 m long, 0.7 m diameter UVCS instrument in pitch and yaw, within a 54 arc-minute half-angle cone, also allowing it to rotate +/- 179.75 degree(s). After considerable design effort, an optimum mechanical solution was achieved which meets all scientific requirements as well as weight, volume, and power budgets. Evolution of the mechanism is presented along with the design status.

A study has been conducted about attitude control and pointing of an optical instrument (a Schmidt-type telescope) connected to the space station via a tether 2 to 10 km long, mounted on a platform. The tether plays a multifunctional role, including elastic suspension and data and power transmission. It will insulate the platform from dynamic noise, light, and other pollution from the space station. Furthermore, stabilization and active attitude control will be achieved by moving the attachment point of the tether with respect to the platform itself. A bi- dimensional model of this system has been realized and tested in the laboratory. The measurement and control concept that works on the basis of a computer vision system is discussed. The system is used to stabilize a platform floating on an air table attached to a fixed point through a tether, via a closed loop position control circuit. This is achieved through a CCD camera (768 X 512 pixels), an image processing software, and a dc motor with encoder which controls the attitude of the platform moving its attachment point. The tracking function is realized via a multiple windows technique using an algorithm based on the linearized equations of motion of the platform. The performance of the overall system is presented. An analysis of system characteristics with respect to a real application is carried out. In particular, the possibility of achieving stabilization and active attitude control of such a system by moving the attach point of the tether has been investigated.

The Sled Tracking System (STS) represents the successful merger of several technologies, including IR and visual sensors, real-time image processing, and real-time data processing and control. STS was developed to solve the dynamics of tracking seat ejection and vehicle tests at the Air Force's High Speed Test Track Facility at Holloman AFB, New Mexico. The system has the ability to track vehicles at transverse speeds exceeding Mach 1, while ignoring momentary loss of track due to background clutter. STS can discriminate among up to four seats sequentially ejected from a single vehicle and track only the event of interest. The system also maintains the track point of interest in the primary sensor's field-of-view while tracking an offset aim point and transitions from a transverse trajectory to a vertical trajectory while maintaining track through seat-mannequin separation and chute deployment. This paper discusses the hardware and software architectures implemented to solve these problems.

White Sands Missile Range has developed a Launch Area Theodolite (LAT) optical tracking system that provides improved Time-Space-Position-Information (TSPI) for the new class of hyper-velocity missiles being developed by the Army. The LAT system consists of a high- performance optical tracking mount equipped with an 8-12 micrometers Forward Looking Infrared (FLIR) sensor, a newly designed full-frame pin-registered 35-mm film camera, and an auto- focused 50-in. focal length lens. The FLIR has been integrated with the WSMR in-house developed statistical based automatic video tracker to yield a powerful system for the automatic tracking of missiles from a short standoff distance. The LAT has been designed to replace large fixed-camera arrays for test programs on short-range anti-tank missiles. New tracking techniques have been developed to deal with angular tracking rates that exceed one radian in both velocity and acceleration. Special techniques have been developed to shock the tracking mount at the missile launch to match the target motion. An adaptive servo control technique allows a Type III servo to be used to compensate for the high angular accelerations that are generated by the placement of the LAT mounts along the missile flight path. An automated mode selection adjustment is employed as the missile passes a point perpendicular to the tracking mount to compensate for the requirement to rapidly decelerate the tracking mount and keep the target in the field-of-view of the data camera. This paper covers the design concept for a network of eight LAT mounts, the techniques of automatic video tracking using a FLIR sensor, and the architecture of the servo control algorithms that have allowed the LAT system to produce results to a degree never before achieved at White Sands Missile Range.

Laser Tracker II has essentially one moving part. A double-gimbaled mirror directs two laser beams to a cooperative target. The mirror catches the return beams and an optical image for test information. The receivers for the return beams are image dissectors. During the test the dissectors sense a change in target position and generate an error signal to drive the mirror. To produce real-time three-dimensional position data, the tracker uses range, azimuth, and elevation readings. This raw data is shipped through the real-time control microcomputer system to a minicomputer which is also used to operate the tracker. A second minicomputer is used to produce finished trajectory data.

A first-phase demonstration of the capabilities and limitations of an optical correlator in a realistic environment has been completed. The testing was divided into several areas, from gathering laboratory data to a fully functional helicopter-delivered demonstration airframe. The basic research performed has led to three fully fieldable test units which have proven to be rugged and dependable under normal test range conditions. The units were transportable and required no realignment of the optics. Two of the test systems were modular in construction while the third was a 'solid optic' design having optical paths and components contained within a solid glass construction. Two flights have been completed so far, and in both cases the target was identified and tracked, and an airframe guided to target impact.

The Airborne Seeker Evaluation Test System (ASETS) is an airborne platform for development, test, and evaluation of air-to-ground seekers and sensors. ASETS consists of approximately 10,000 pounds of equipment, including sixteen racks of control, display, and recording electronics, and a very large stabilized airborne turret, all carried by a modified C- 130A aircraft. The turret measures 50 in. in diameter and extends over 50 in. below the aircraft. Because of the low ground clearance of the C-130, a unique retractor mechanism was designed to raise the turret inside the aircraft for take-offs and landings, and deploy the turret outside the aircraft for testing. The turret has over 7 cubic feet of payload space and can accommodate up to 300 pounds of instrumentation, including missile seekers, thermal imagers, infrared mapping systems, laser systems, millimeter wave radar units, television cameras, and laser rangers. It contains a 5-axis gyro-stabilized gimbal system that will maintain a line of sight in the pitch, roll, and yaw axes to an accuracy better than +/- 125 (mu) rad. The rack-mounted electronics in the aircraft cargo bay can be interchanged to operate any type of sensor and record the data. Six microcomputer subsystems operate and maintain all of the system components during a test mission. ASETS is capable of flying at altitudes between 200 and 20,000 feet, and at airspeeds ranging from 100 to 250 knots. Mission scenarios can include air-to-surface seeker testing, terrain mapping, surface target measurement, air-to-air testing, atmospheric transmission studies, weather data collection, aircraft or missile tracking, background signature measurements, and surveillance. ASETS is fully developed and available to support test programs.

Optimization of an infrared missile seeker requires designing the detector, optics, scanner, control system, and signal processing hardware to 'best' meet the mission performance and physical packaging requirements. 'Best' is usually defined in terms of maximum signal-to-noise ratio and/or minimum acquisition time for various target ranges, target signatures, and atmospheric conditions. This paper presents simulation and experimental results from optimization studies of a gimbal-scanned infrared seeker. The optimization criterion is maximization of the SNR for small targets in the presence of large background variations. The experimental hardware consists of a multi-element detector array, an inertially stabilized gimbal scanned by the gimbal control system, a sensor digital signal processor, and a system computer. The system permits varying the detector angular subtense, scan rate, scan angle, sensor gain, sensor dynamic range, and the acquisition algorithms. The hardware, which includes an imaging radiometer for collecting target signature data, is integrated in a pod flown on a P-3 aircraft. Theoretical optimum values for the variable parameters are derived for generic target conditions by laboratory and computer simulations. Experimental performance of the seeker as a function of the variable parameters is measured and compared to the simulation values. 'Real world' optimization criteria and problems limiting the seeker performance are discussed.

TV- or FLIR-based electro-optical (EO) sensors are used for target acquisition in an airborne scenario. The TV sensor typically consists of an optical unit, a solid-state camera, and a visual monitor for image display. Target size, sensor resolution, atmosphere, platform disturbances, etc, are some of the important factors to be considered for designing an EO sensor for an airborne mission. A TV-based target acquisition system has been designed and developed. The resolution of the optical unit has been measured with the help of a TV resolution test chart and by experimentally evaluating the modulation transfer function (MTF). This technique has been extended for the measurement of MTF of the sensor (including video monitor). The sensor resolution deteriorates considerably due to base motions of the carrying platform. The degradation of sensor MTF due to airframe motion and angular vibration has been experimentally studied, and the results are presented. Present study enables the designer to predict the sensor performance for a given airborne scenario. Anomaly between the present values and the results reported earlier is indicated. Design considerations of an airborne sensor are also discussed briefly.

The design of a new, all-digital control system for sub-arc second satellite tracking is described. This design is currently being reduced to practice for a large ground-based tracking telescope. Topics discussed include selection of overall control system architecture, the use of auxiliary inertial feedback elements for jitter reduction, sensor noise characterization, selection of bandwidth, hardware selection, and performance prediction. Experimental work is being conducted to support the development of this control system on a Contraves KINETO tracking system. A comparison of results (primarily tracking jitter and pointing accuracy) between a standard KINETO and the new control system is provided, as well as extrapolation of these results to the final system.

The beacon tracker and point ahead single system described previously has been installed and integrated with the optical tracking system. The analysis and results of bench and system integration tests are provided, including servo jitter as a function of illumination level and tracking ability.

The Relay Mirror Experiment (RME) has successfully demonstrated long-range, low-jitter tracking and pointing capabilities appropriate for ground-based laser (GBL) propagation. The RME program includes (1) a passively maneuverable, free-flying low-orbit spacecraft with a laser diode beacon and spoiled retroreflectors as acquisition aids; (2) a payload experiment package (PEP) consisting of sensors, optics, steerable mirrors, and control electronics. This subsystem accomplishes GBL tracking and pointing and the associated positioning of a space-based relay mirror sufficiently to relay an infrared beam between two ground sites. Design considerations for the control system included base motion disturbance and calibration; (3) two GBL sites each a tracking and pointing exercise in itself, using a combination of sensors and acquisition and tracking capabilities. One site includes a beam relay scoring capability.

The Augmented Tracking and Acquisition System (ATAS) provides the tracking acquisition aids, line-of-sight stabilization, and active closed-loop beam centering functions at two ground-based laser tracking sites for the Relay Mirror Experiment (RME). Simultaneous, steady illumination of the RME spacecraft with both ground beacons allows for successful beam relay between the two sites off of the orbiting mirror. Described in this paper is an overview of the functions, control system architectures, major subsystem components (steering mirrors and sensors), and mission operation of the ATAS subsystems. A brief discussion of ATAS evolution is included to show that versatility is needed for success.

An objective of the Wideband Angular Vibration Experiment (WAVE) is to measure optical bench vibrations of the Relay Mirror Experiment (RME) laser beacon tracker. The WAVE sensor package measures six degrees of freedom of optical bench base motion over a frequency band of 1-1,000 Hz. The WAVE package is comprised of 16 sensors: three angular displacement sensors, six magnetohydrodynamic (MHD) angular rate sensors, and seven linear accelerometers. Redundant angular measurements allow the qualifying of the MHD sensor for space operation. The noise floor of the angular measurements, integrated over the full frequency band, is less than 0.1 (mu) rad in each axis. Measurements taken while tracking an internal self-check laser diode indicate that vibrations from attitude control system horizon scanners, reaction wheel, and excited structural modes in the beacon tracker optical assembly dominate the base motion environment. Most of the vibrations are narrow band with amplitudes on the order of 10.0 nanoradians. Coherence analysis between WAVE sensors and unrejected quad cell errors indicates that track performance during self-check is limited by base motion.

The Relay Mirror Experiment (RME) is a research program to determine the pointing accuracy and stability levels achieved when a laser beam is reflected by the RME satellite from one ground station to another. This paper reports the results of using a video tracker augmented with a quad cell signal to improve the RME ground station tracking system performance. The video tracker controls a mirror to acquire the RME satellite, and provides a robust low bandwidth tracking loop to remove line of sight (LOS) jitter. The high-passed, high-gain quad cell signal is added to the low bandwidth, low-gain video tracker signal to increase the effective tracking loop bandwidth, and significantly improves LOS disturbance rejection. The quad cell augmented video tracking system is analyzed, and the math model for the tracker is developed. A MATLAB model is then developed from this, and performance as a function of bandwidth and disturbances is given. Improvements in performance due to the addition of the video tracker and the augmentation with the quad cell are provided. Actual satellite test results are then presented and compared with the simulated results.

The Relay Mirror Experiment is a space experiment in which an IR laser beam is propagated from one ground station, the Laser Source Site (LSS), to an orbiting relay mirror and back to another ground station, the Target Scoring System (TSS). A sparse array of 37 telescopes senses the position of the relayed beam at the second ground station for purposes of scoring the pointing capability of the relay mirror. Data from these telescopes is processed to determine the position of the beam as a function of time. These signals contain the effects of atmospheric turbulence on both the uplink and downlink of the IR beam. Spectral and correlation analysis is used on the telescope data to minimize the effects of atmospheric turbulence, as well as other environmental effects.

In the Relay Mirror Experiment (RME), three laser beams are propagated from ground-to- space and retroreflected; two argon-ion laser beams at 488 and 514 nm and a Nd:YAG laser beam at 1.06 micrometers wavelength. The full-angle 1/e2 divergences of the argon beams are operated in the 60-90 (mu) rad range while the Nd:YAG beam is in the 30-60 (mu) rad range. Uplink irradiances at the RME spacecraft (s/c) and retroreflected irradiances at the ground have been measured. The high correlation (>=0.8) between the s/c signals and retroreflected signals indicate that uplink scintillation dominates the retroreflected signal. Likewise high correlation between ground sensors separated by distances much greater than the atmospheric coherence length rO confirms that uplink scintillation is dominant over downlink scintillation. The temporal power spectrum of the scintillation shows a roll-off above 700 Hz which is steeper than theoretical predictions. The profile of the beam mean irradiance and the normalized standard deviation ((sigma) I) of the scintillation were measured by stepping the beam across the s/c in a square 7 X 7 array. These data show moderate scintillation on-axis ((sigma) I equals 0.5) and increases dramatically for off-axis pointing exceeding 0.6 1/e2 radius ((sigma) I >= 1). These data will be compared to predictions from analytic models for gaussian beams developed by R. Sasiella and J. Shelton of MIT/LL.

A sensor suite has been developed for the task of ground target acquisition that includes human perception in the sensor fusion optimization. The presentation to the operator has been chosen to be visual imagery of the target in its background clutter (this maximizes quantity of information presentable to the operator, while quality is determined by sensor capabilities and pre-display processing). The resulting composite display is natural and intuitive, increasing the amount of data that can be displayed and easily comprehended without operator confusion. Three spectral bands for imaging sensors have been selected for this suite: near-IR (.9-1.5 micrometers ), mid-IR (3-5 micrometers ), and far-IR (8-12 micrometers ). These are highly mature technologies, each with quality imaging capability and unique target signature exploitation capabilities.

A technique is developed for fusing asynchronous data from two dissimilar sensors, where one sensor provides data at a high rate relative to the other. The idea is to obtain a least-squares estimate of the high data rate sensor data at the time when the other sensor observation is taken. A previously developed synchronous data fusion algorithm is then used to fuse the time aligned data for updating the target state estimates. The case of fusing data from an optical sensor that provides periodic data at a high rate and a radar that provides quasi-periodic data at a low data rate is considered. The performance of a track filter utilizing this data fusion approach is shown via simulation to provide results that are similar to those obtained by the standard sequential data processing approach that requires significantly more computations.

A number of acquisition, tracking, and classification algorithms have been developed to deal with various image processing problems in the laboratory. Typically these are too complicated to implement in a low-cost, real-time processor. Using image data in many real-time applications requires a system with very high data rates, low power dissipation, and a small packaging volume. A processor architecture suitable for these applications have been developed, and a co-occurrence matrix target detection algorithm adapted and demonstrated in computer simulation and real-time hardware. A histogram or gray-level distribution is often used to select a threshold for image segmentation. This is often inadequate, as the histograms tend to be noisy and exhibit many small peaks. Co-occurrence matrix based segmentation allows homogeneous regions of an image to be identified and separated from a cluttered background. Results are shown for target segmentation using representative infrared imagery and real-time hardware.

Using microchannel plate intensifiers, focal array imagers, and a computer driven image processing system, images of laser induced fluorescence of selected targets can be obtained. Operating in a mode similar to Landsat imaging, a laser fluorescent imager can obtain information on concealed targets as well as material contamination at ranges up to 30 m.

Imaging autotracker technology is an area vital to numerous current and future Army programs. As advancements in infrared detector technology provide sensors with higher resolution and increased sensitivity, parallel advancements in target tracker technology will be required in order to achieve full benefit from these new generation devices. Key technical areas being researched include algorithms for terminal aim point selection, automatic reacquisition of low signature targets in high clutter, and continuous tracking of intermittently or partially obscured targets in dirty battlefield conditions. Research on improved tracking processors and devices for real-time algorithm implementation is being done in conjunction with the algorithm studies. This paper presents an overview of this work with particular emphasis on terminal homing autotracker technology.

Fuzzy logic is a discipline which seeks to provide a framework for imitating human-like thought processes, or 'approximate reasoning.' In this paper a fuzzy logic approach is taken to the problem of multitarget tracking in clutter. Fuzzy logic methods are used to evaluate returns for processing by a Kalman filter modified to treat target source uncertainty. The method is developed and demonstrated with a noise-driven simulation and an actual sequence of infrared images.

The accurate calculation of optical flow fields or displacement estimate fields in real-world imagery can be useful for detecting military targets. A new Kalman filter based low-level displacement estimation algorithm is derived. The gain matrix of the estimator turns out to be the Kalman gain matrix, which is dependent on the image statistics. A procedure is developed in which the gain matrix of the estimator is not chosen heuristically, but is calculated based on the statistics of the image. The optical flow fields obtained from this estimator is accurate, and is convergent faster compared to the previous pel recursive based algorithms.

After the stage of pointlike target tracking, the tracker comes to the stage of area target tracking. This paper considers the situation in which the FLIR image contains a number of targets. The targets are compact. The image segmentation is achieved by considering not only the global gray-level distribution but also the spatial distribution of target pixels. After the global gray-level statistics in the whole image, a recursive merging algorithm, a hierarchical clustering on the gray level and spatial position, is applied to segment the image into a multiple gray-level image. To make full use of the whole scene scan, a four direction code method is used to depict the edges of target regions. And to save more execution time, the useful features, including structure feature and geometry feature, are calculated by the four direction code expression at the same time. Thus the target edge description and the useful features calculation are finished in the same whole scene scan of the segmented image. A changing index table which describes targets and their features within the segmented image is set up. The index table is updated at each scene to depict the changing content of the image. During the time in which the image gets into a comparable stable state, a target recognition procedure may be applied to find the interested target, and the threatening value of each target is considered. An adaptive gate is assigned to each interested target.

To achieve robust and efficient object recognition, particularly from real outdoor images, methods to reduce clutter and extract salient information of objects need to be developed. Towards this end, the authors present a technique to rank and extract salient contours from a 2-D image acquired by a passive sensor. The goal is to find important contours corresponding to possible objects. The method presented starts with edgels from an edge detector and assigns a saliency measure to linked edgels (contours) based on length, smoothness, and contrast. For length the authors use the number of edgels in the contour; for smoothness they use average change of curvature; and for contrast, the edge magnitude. Contours are ranked by saliency and the more salient contours selected. This method is tested on several real outdoor images of objects in cluttered and occluded conditions. Excellent results are obtained. Performance of this technique is evaluated in the context of a recognition system that matches 2-D image corners with 3-D model vertices. Graphs, using corners on the object of interest and clutter are used to demonstrate the appropriateness of saliency ranking. Curves are plotted to display the percentage of object corners to all image corners for the top few salient contours. Extracting the more salient contours increases the ratio of image corners on the object to all image corners, reducing the search space for the corner matching step in recognition.

A parallel algorithm for detecting moving targets by imaging sensors and estimating their trajectories is proposed. The algorithm uses the temporal continuity of the smooth trajectories of moving targets and successfully detects and simultaneously tracks all the target trajectories by mapping them from the image sequence onto a single target frame. The algorithm makes use of the spatial consistency of intensity of a target within a short time period, resulting from the continuous 3-D trajectory, to detect the existence of the target. The basic steps of the algorithm, applied to a target frame, involve: 2-dimensional filtering to suppress noise and remove background clutter; target trajectory detection to identify moving targets in the form of linear lines for targets moving with constant speed or parabolas for the accelerating targets using Hough transform; and target following to determine the kinematics of the detected targets and associate targets between successive target frames. The global parallelism of the algorithm stems from the fact that all processing steps involve traditional image processing and pattern recognition techniques for which many parallel implementations exist.

In automatic assembly tasks guided by vision it is necessary to determine the position x,y and the orientation of a given element of the target. This work describes the image processor used to evaluate the shift of the target every 20 ms and thus to obtain a better guidance dynamic response.

The paper presents a new high-accuracy automatic target tracking algorithm which does not involve image segmentation. The method constructs a function which is based on local gray- level information. The function can evaluate the deviation vector between the target's center and the tracking window center and then automatically adjust the tracking window iteratively towards the target's center to achieve automatic target tracking. The algorithm can achieve high tracking accuracy. It is not sensitive to noise and is not restrained by the movement pattern of the target. As the method does not use segment processing, it provides better real- time quality, a short processing period, and is very easily implemented. The implementation by the microcomputer image processing system demonstrates that the method is especially practical for infrared images and works well for infrared images in complex environment.

The method presented is based on iterating the tracking window center towards the center of the target. The algorithm doesn't require the target inside the tracking window initially. The tracking window can then be adjusted iteratively towards the center of the target and achieve high tracking accuracy within only one frame of the image. In the process of executing several frames of target image tracking, it can evaluate some movement parameters and some physical parameters of the target. In addition, this algorithm is not restrained by the pattern of the target movement, and has a short processing period, good real-time quality, and insensitiveness to noise. Computer IP system simulations show that the algorithm works well for a variety of targets, and the center tracking error is less than 0.2 pixel per frame under the middle SNR condition.

Stability and robustness in control systems are commonly achieved by designing signal compensators and filters composed of the system's passive parameters in analog or digital form. The passive compensators are generally used to frequency shape the active state variables in the control system. If wideband loops are required when the plant contains nonlinearities and high-order dynamics, the use of fixed frequency, passive parameter compensators to obtain stability may not be tractable. In such systems, however, control stability can be achieved by manipulating the active state variables themselves. This paper presents the general concepts of state equalization, a control system stabilization technique which utilizes the differing characteristics of the active state variables to achieve the desired stability in systems containing nonlinear resonant plants. The technique, conceived in the mid- seventies, is used in several fielded weapon system. One of the applications is used to illustrate the use and advantages of the state equalization technique.

This paper discloses the new stabilization approach (patent pending) where miniature, low-cost, linear accelerometers are used (instead of gyros) to sense three-dimensional angular motion. The platform-control system uses the measured angular accelerations to generate movement commands for the gimbal servo motors. This counter-rotates the sensing device to stabilize its Line- of-Sight (LOS). Two control strategies are presented: one for the case where the accelerometers are placed on the stabilized element; the other for the case where the accelerometers measure vehicle motion. In the second case, gimbal motion is governed by counter-rotation setpoints. Setpoint generation is based on a stabilization criteria that projects the angular acceleration vectors of the platform and the vehicle onto a common reference frame and equates the resultant to zero. This provides a system of equations that can be solved to calculate the necessary gimbal motion (setpoints) to counteract vehicle motion. Test results for a proof-of-concept unit are also provided, demonstrating the feasibility of stabilizing sensor LOS with linear accelerometers. The technique to extract angular information from the output of linear accelerometers is also discussed.

Two new models for 'slip-stick' friction are presented. One, called the 'bristle model,' is an approximation designed to capture the physical phenomenon of sticking. This model is relatively inefficient numerically. The other model, called the 'reset integrator model,' does not capture the details for the sticking phenomenon, but is numerically efficient and exhibits behavior similar to the model proposed by Karnopp in 1985. All three of these models and the Dahl model are preferable to the classical model which poorly represents the friction force at zero velocity. Simulation experiments show that the Karnopp model, the Dahl model, and the new models give similar results in two examples. In a closed-loop example, the classical model predicts a limit cycle which is not observed in the laboratory. The Karnopp model, the Dahl model, and the new models, on the other hand, agree with the experimental observation.

Fine-steering mirrors (FSM) have been used for many years to provide accurate pointing and image motion compensation. The major limitation to the device is the flexure suspension system. These flexures limit the angular travel of the mirror and represent a single-point failure if they break, thus requiring careful design to reduce stress. To eliminate these design and performance issues, Ball Aerospace has developed a magnetically suspended fine-steering mirror (MSFSM). This mechanism eliminates the need for the flexure suspension system and requires acceptable amounts of power by using high-efficiency electromagnetic actuators. Other benefits include the elimination of destabilizing suspension bending modes and the ability to control telescope focus and collimation with this single device. This paper discusses a 6-DOF MSFSM, completed in 1990, that matches the operational capabilities of high- performance flexure-mounted FSMs. It addresses the critical design issues, servo control algorithms, and the device's performance capabilities and limitations.

The accuracies required for modern tracking systems far exceed the capability of most manufacturing processes. In addition, the stability and flexure of real engineering material further limit the as-built accuracy. This paper discusses the various types of static errors which exist in tracking mounts, and the extent to which they can be modeled.

A precision tracking system can function in some applications with very limited absolute accuracy, but all applications require smooth motion. This paper addresses the sources of dynamic motion error which are built into the device itself. The methods of measuring these errors are discussed, and techniques for identifying the various sources. These are illustrated with some examples from precision tracking mounts. An important error source is motor torque ripple, a position-dependant variation in torque gain constant. New techniques in brushless servo motor excitation have resulted in dramatic reductions in torque ripple. An overview of this type of drive system is also presented.

A 1-kHz control system for precision position control of a two-axis gimballed mirror is presented. The control system is unique in that it uses the state estimator's position estimates to excite the Inductosyn position transducers. Also presented is a concise algorithm for proximate time optimum control within available motor torque (or alternatively, maximum gimbal acceleration) and maximum allowable gimbal rate. The newly developed Inductosyn excitation/reduction scheme and proximate time optimum algorithm are successfully demonstrated on hardware designed, constructed, and tested by Contraves USA, where accuracies better than 4 arc seconds were measured.

The components of an open loop all-fiber optical gyro are described together with the gyro performance

In many high-resolution photographic and photoelectronic imaging systems, resolution is limited by image motion and vibration and, as a result, the high-resolution capability of the sensor may be wasted. In normal reconnaissance and robotics the sensor moves during the exposure. Some of the resulting image motion can be removed by mechanical compensation, but not all of it. The residual motion blurs the image, and usually this blur becomes the limiting factor for many high-quality imaging systems. The ever-increasing altitudes and coverage requirements of modern imaging have put a premium on high resolution. An application of this paper is the recovery of the original image by inverse filtering that depends on the modulation transfer function (MTF) of the real-time relative motion between the object and the imaging system. An original method developed here for numerically calculating MTF for any type of image motion is the basis of the paper.

The control system requirements for a night vision pilotage system (NVPS) are not well understood. Terms such as 'good control' and 'no objectionable overshoot' are common when referring to control system response. Understanding the pilot's performance is key to the design of NVPS systems. The pilot's head motions become the 'target dynamics' for the NVPS to track and, as a result, are the foundation for the requirements of a pilotage system. Mission success and pilot survival depend on presenting the right image at the right time. To date, extensive research has revealed only portions of a suitable head motion model. Most studies focus on average human performance while this system requires performance at the extremes. Additional information gleaned from the references include several heuristic block diagram 'models' describing the eye and head coupled vision system. While the blocks were not defined in empirical terms that lend themselves to direct simulation and thus system synthesis, the information assembled does provide valuable insight into the dynamics of the human vision system. The above form the basis of the model presented here. This paper presents the important points and conclusions from reference materials and provides a quantitative guide for design of NVPS control systems. Additionally, a single-axis model is presented that provides a framework for additional study. This model incorporates the significant delays, models a head motion tracker, and provides a proper head motion model for the case whereby the pilot's eyes are assumed fixed with respect to the head. Results using this model are presented.

Profiling scan velocity in linear and rotational machines (cameras and gimbal sets in particular) is common practice. Typically, these are given as trapezoidal profiles that ramp up from zero to a desired velocity, then ramp down to zero velocity at some later time. These profiles tend to be unidirectional, making implementation at the trapezoidal approach straightforward. The task is somewhat more complicated if one desires bidirectional operation. Consider the case where the displacements are identical for either direction, and scan velocities are dependent on scan direction. If cycle rate, the time required to perform a scan and return to the starting position, is a concern, the interaction between the scan profile and system dynamics needs to be considered. Tradeoffs, such as peak accelerations and settling times, and the type of controller need to be among the considerations. This paper presents some interesting results from these considerations, including a set of equations that may be implemented for either trapezoidal or sinusoidal profiles. It examines these in light of cycle rate requirements, and presents analytical results generated from Advanced Continuous Simulation Language (ACSL).

A newly developed laser range scanner which can identify and locate targets attached to a satellite is described. This identification can be performed even with the sun shining directly into the sensor. The sensor makes use of two high-speed galvanometers to address individual pixels in a high-resolution large field of view. Specular reflections and background illumination problems are eliminated by proper signal processing and an optical interference filter. Very fast tracking of the object is implemented using Lissajous-type scanning figures.

The suggested system allows an exhaustive, very low cost evaluation of an optical, anti- aircraft fire control system (FCS) before doing tests on real targets. The reliability of the results is guaranteed by using a real FCS in the test loop. Furthermore, the test loop includes gunner, operating environment, target motion, and gun performance simulation. The testing equipment is founded on an 80386-based personal computer provided with I/O interfaces toward the external world and an image processing board to generate and move a synthesized target. All the devices (computer and add-on cards) are easily available on the market. This fact contributes to lowering the cost of the whole system. The interface between the man (the gunner) and the machine is not modified at all. A TV monitor is needed to display the aiming errors, i.e., the position of the synthesized target in the optics field of view. Therefore, aiming is done by moving the FCS in order to minimize the error shown on the monitor. The simulation program sends all the parameters it needs (i.e., laser range) to the real FCS. All the software was developed using high-level programming languages run in real-time. In particular ACSL (Advanced Continuous Simulation Language, by Mitchell and Gauthier Associates), and the FORTRAN were used to get some benefit from powerful graphics and data-logging tools. Moreover, C language routines were written to manage low-level interfaces and timing problems. The use of high-level languages allowed the reduction in the time spent developing the software.

The output algorithmic control with identified model is presented in a computational implementation introducing restriction requirements. The case of multiple inputs multiple outputs is discussed in a practical application of a final approach of an aircraft.