Showing papers on "Guidance system published in 1996"

Surgical guidance method and system for approaching a target within a body

Abstract: A surgical guidance system includes a magnetic field generator carried by a support frame, a guidance system controller, at least one magnetic field sensor located at a surgical instrument, and a feedback display device. The guidance system indicates the position of the surgical instrument relative to a trajectory as the surgical instrument approaches a surgical target within a body. The magnetic field generator establishes a magnetic field having geometric characteristics that indicate the trajectory from an initial point to the target. The sensors detect the distinguishable orientation of the magnetic field along the trajectory, and the feedback display device indicates whether the surgical instrument is aligned or misaligned with the trajectory. The magnetic field generator is adjustable upon the support frame such that the approach angle and position of the trajectory may be selected.

Method and apparatus for sensing forward, reverse and lateral motion of a driverless vehicle

Abstract: This invention relates to a swivel caster fitted with rotational and swivel angle measurement sensors mounted to a driverless vehicle so that the lateral motion of the vehicle can be detected and accounted for by the vehicle's navigation and guidance system. A preferred embodiment of the present invention is a driverless vehicle comprising a navigation and guidance system having an angular motion sensor and a track wheel caster assembly equipped with a caster pivot sensor and a wheel rotation sensor to determine the relative position of the vehicle by taking into account substantially all movement of the vehicle along the surface upon which the vehicle is travelling. These sensors enable the navigation system to more accurately determine the vehicles current position and enable the guidance system to better guide the vehicle.

Closed-Form Optimal Guidance Law for Missiles of Time-Varying Velocity

Abstract: An optimal guidance law for missiles with time-varying velocity is investigated. The closed-form solution is derived and properties of the key variables of the solution, such as a time-to-go-like function and the time-varying guidance gain, are studied. Implementation aspects related to the computations of time-to-go and the guidance gain also are considered. Simulation studies show that the performance of the proposed guidance law is superior to that of proportional navigation or augmented proportional navigation.

Root-mean-square miss distance of proportional navigation missile against sinusoidal target

Abstract: The performance of a proportional navigation homing missile against a target performing a sinusoidal weave maneuver is evaluated. The missile's effectiveness is measured in terms of the root-mean-square miss distance over a set of engagements in which the initial phase of the target weave is uniformly distributed. Closed form solutions for the root-mean-square miss are derived for the case where the missile guidance system is modeled by a first-order lag and the lateral acceleration is unlimited. The analysis is then extended to include the effects of acceleration saturation and higher order missile dynamics. Comparisons are made between a first-order and a fifth-order guidance system, and the root-mean-square miss is determined numerically as a function of the interceptor's effective navigation gain, time constant and acceleration limit, and the target's weave amplitude and frequency. UTURE homing interceptor missiles will face new and unique challenges as the sophistication of the threat spectrum in- creases. Engagements against air targets can occur at both very low and very high altitudes, with the threats accidentally or intentionally performing weaving or spiraling maneuvers during their midcourse and terminal phases.1"4 The lateral displacement, acceleration ca- pability, and weave frequency of the target maneuver can greatly enhance the threat's ability to survive a counterattack. To counter this, the defensive missile must have sufficient lateral acceleration, guidance system time constant, and terminal homing time to achieve a high probability of intercept. Whereas the per- formance of the interceptor will be influenced by many scenario- dependent factors,5"8 a major consideration will be the fundamental response of the proportional navigation (PN) guidance system to the postulated target weave motion.9'10 In the general case, the target dynamics may involve arbitrary periodic motion in three dimensions. A useful starting point for analysis, however, is the response of the PN homing system to a single plane sinusoidal maneuver of constant amplitude and fre- quency. The phase angle of target weave, which is associated with initial conditions at the start of the missile's terminal guidance, can be treated as a random variable, uniformly distributed between 0 and 2n over a set of engagements. The missile's dynamics are approxi- mated by a simple first-order transfer function, and unlimited lateral acceleration capability is assumed. The miss distance can then be parameterized in terms of the effective PN navigation gain N, the missile time constant T, and the amplitude AT and frequency co of the target weave. This paper focuses on root-mean-square (rms) miss distance as a recommended measure of effectiveness in analyzing missile perfor- mance against weaving targets. This measure allows uncertainties in target phase characteristics to be accounted for in the terminal per- formance results. The weaving target problem was first addressed by Chadwick, 9 who determined analytical expressions for the rms miss distance of the single lag PN missile for values of N =2 and 3. Zarchan 10 employed adjoint theory and transfer function tech- niques to determine formulas for the peak miss distance against a weaving target for values of N between 3 and 6. The present paper derives general closed-form expressions for the rms miss distance against a sinusoidal target. New results are obtained for arbitrary

User-driven active guidance system

Abstract: A user-driven, active guidance system for guiding visually impaired users through obstacle filled routes of travel. The system includes an obstacle detection system, having an array of ultrasonic sensors, which detects the distance to and location of obstacles and a controller for receiving obstacle data and determining an optimal path around the obstacle so as to return the user back to the original path of travel without losing orientation or direction. The system provides active guidance by exerting physical force upon the user to intuitively direct the user around the obstacle. The system is driven by the user's motion and comprises a cane, as well as the my of ultrasonic sensors and controller supported on a pair of guide wheels.

Information guidance system based on structure configuration map

Abstract: A structure configuration map display system includes a controller for depicting and displaying a structure configuration map based on structure configuration map information. The system provides for searching and guidance relative to a structure designated as a target point. A display form corresponding to the structure information for the target point is determined and the display form of the target point is changed based on the results of that determination and is displayed so that a user can easily recognize the desired facility by its display form which corresponds to stored structure information. Also, the user can easily identify a facility as the desired facility and can obtain reliable guidance to that target point by the display form which indicates the type of the structure.

The Impact of Predictive Information on Guidance Efficiency: An Analytical Approach

Abstract: The acceptance of route guidance advice by motorists is expected, to occur only whenever such advice is experienced to be valid and reliable Three major factors may cause route guidance systems to provide motorists with unreliable advice: (1) the traffic information constituting the basis for guidance advice is inaccurate; (2) the impact of a large fraction of motorists responding to the guidance, and the subsequent overreaction that occurs, is ignored whenever the guidance advice is being set; and, (3) concentration effects may occur and induce a higher level of (unpriced) congestion when drivers are provided with better information

Strategic intercept midcourse guidance using modified zero effort miss steering

Abstract: The suitability of modified proportional navigation, or an equivalent zero effort miss formulation, for strategic intercepts during midcourse guidance, followed by a ballistic coast to the endgame, is addressed. The problem is formulated in terms of relative motion in a general, three-dimensional framework. The proposed guidance law commands thrust 1) along the line of sight unit direction and 2) along the zero effort miss component that is perpendicular to the line of sight. The latter term is scaled with a guidance gain. If the guidance law is to be suitable for longer range targeting applications with significant ballistic coasting after burnout, zero effort miss computations must account for the different gravitational accelerations experienced by each vehicle. Approximations for the true differential gravity effect, which relieve the burden for direct numerical propagation of the governing equations, are considered. Approximations considered are constant, linear, quadratic, and linearized inverse square models. Theoretical results are applied to a numerical engagement scenario, and the resulting performance is evaluated in terms of the miss distances determined from nonlinear simulation.

Optimal Planar Evasive Aircraft Maneuvers Against Proportional Navigation Missiles

Abstract: A comparative study of evasive strategies of an aircraft against a missile with fixed, gravity-limited, proportional navigation is conducted for both subsonic and supersonic confrontations. A complete point-mass aircraft model and a variable-mass missile model that includes missile dynamics are used. No linearization is required in the analysis, and all motion is constrained to a horizontal plane. Sequential quadratic programming is used to solve the optimal control problem. Numerical results are presented for an early model of the F-4 fighter aircraft. In particular, the effects of varying the aircraft/missile initial velocity ratio, the missile initial heading angle, and the missile guidance time constant are determined.

Dynamic inertial coordinate system maneuver detector and processing method

Abstract: A maneuver detector and processing method for use in target trackers employed in weapon guidance systems, and the like, that employs multidimensional measurements and a set of inertial coordinate systems. The maneuver detector and processing method are implemented as follows. Time-delayed target position and velocity estimates of the target are maintained in a history file. These estimates are continuously updated, in that they are transformed 24 into intermediate north, east, down (NED) range Cartesian coordinate systems by correcting for aircraft motion. For each measurement time, the histories are used to predict the position and velocity of the target in an "observation-relative" inertial coordinate system aligned with the line-of-sight to the target. The error between the prediction and observation is calculated and used with the measurement accuracies to calculate a maneuver probability.

Guidewire controls for a material handling vehicle

Abstract: The present invention features a universal, manned, material handling vehicle. The material handling vehicle is capable of operating in a manned mode, a wire guidance mode, and a rail guidance mode. This manned material handling vehicle contains a steering management control system having a logic program which allows the vehicle to adapt itself to different wire control systems. That is, particular parameters, frequency and amplitude of the underlying wire guidance system can be determined. In this manner, the manned vehicle is universally adaptive to a wide variety of wire guidance systems. When in manned operation mode, should the vehicle receive a wire guidance signal, the system controller will be duly informed. When in wire guidance operation mode, should the vehicle lose or fail to receive a clear wire guidance signal appropriate to guide on, it will automatically revert to the manned operation mode. The steering management control system also monitors the weight and height of the vehicle's load. This steering management control system receives signals from the steering tiller, as well as from the guidewire embedded in the floor of the material storage facility.

A Virtual Audio Guidance and Alert System for Commercial Aircraft Operations

Abstract: Our work in virtual reality systems at NASA Ames Research Center includes the area of aurally-guided visual search, using specially-designed audio cues and spatial audio processing (also known as virtual or "3-D audio") techniques (Begault, 1994). Previous studies at Ames had revealed that use of 3-D audio for Traffic Collision Avoidance System (TCAS) advisories significantly reduced head-down time, compared to a head-down map display (0.5 sec advantage) or no display at all (2.2 sec advantage) (Begault, 1993, 1995; Begault & Pittman, 1994; see Wenzel, 1994, for an audio demo). Since the crew must keep their head up and looking out the window as much as possible when taxiing under low-visibility conditions, and the potential for "blunder" is increased under such conditions, it was sensible to evaluate the audio spatial cueing for a prototype audio ground collision avoidance warning (GCAW) system, and a 3-D audio guidance system. Results were favorable for GCAW, but not for the audio guidance system.

Development and Flight Test of Terrain-Referenced Guidance with Ladar Forward Sensor

Abstract: Military aircraft regularly conduct missions that include low-altitude, near-terrain flight to increase covertness and payload effectiveness. Civilian aircraft operate in this regime during airborne fire fighting, police surveillance, search and rescue, and helicopter emergency medical service applications. Several fixed-wing aircraft now employ terrain elevation maps and forward-pointed radars to achieve automated terrain following or terrain avoidance flight. Similar systems specialized to helicopters and their flight regime have not received as much attention. A helicopter guidance system relying on digitized terrain elevation maps has been developed that employs airborne navigation, mission requirements, aircraft performance limits, and radar altimeter returns to generate a valleyseeking, low-altitude trajectory between waypoints. The guidance trajectory is symbolically presented to the pilot on a helmet-mounted display. In this work, a wide field of view laser radar forward sensor has been incorporated into this guidance system to expand the system's operational flight envelope and to assist the pilot in obstacle detection and avoidance. The development and flight test results of this guidance system are presented. Missions to 75 ft altitude at 80 kn in the presence of unmapped natural and man-made obstacles were achieved while the pilot maintained situational awareness and tracking of the guidance trajectory.

Evaluation of compliance rates and travel time calculation for automatic alternative route guidance systems on freeways

Abstract: This study outlines the concept of extending an available simulation model for evaluation of freeway route guidance systems using the compliance rates of drivers with alternative route recommendations based on measurements from the freeway subnetwork near Munich, Germany. The system works with variable direction signs that automatically display routing instructions to prevent congestion on the main road. The effectiveness of the system is assessed by calculating the travel times with and without an alternative route guidance system in operation. The result is a decrease in individual travel times on the main road and overall travel time savings for all traffic participants of the system. The simulation indicates a high sensitivity of diverting portions of traffic that allows an exact validation. The diverted traffic affects not only travel time and the congested area but also the destinations, which permits the use of the compliance rate as an accurate fit parameter for exact description of traffic patterns from measurement data.

Hierarchical target intercept fuzzy controller with forbidden zone

Abstract: A target intercept guidance system for directing a steerable object, such a torpedo with a guidance point. The guidance system is located at a launching vehicle and senses the bearings from the launching vehicle to a target and to the steerable object as it moves toward the target. Various error signals are then generated and classified into sensed linguistic variables using membership functions of corresponding sensed variable membership function sets based upon primary and secondary goals to become fuzzy inputs that produce fuzzy control output membership functions from a control output membership function set based upon logical manipulation of the fuzzy inputs. The control system performs this classification and selection according to sometimes competing goals of excluding the torpedo from a particular operating zone while guiding the torpedo in response to variations in a target bearing relative to the guidance point. The selected fuzzy control output membership functions are converted into an output having an appropriate form for control, subject to optional conditioning to prevent unwanted effects and assure good behavior for different tactical parameters.

Integrated boost phase and post boost phase missile guidance system

Abstract: An integrated system and method for guiding an inflight missile during its boost phase to increase the accuracy of the missile flight and increase the probability that the missile reaches its intended target. The system includes four sub-systems that each perform a separate missile guidance function, but that each are integrated to form a single guidance system. The system includes a position rectified velocity wire guidance sub-system for steering the missile to maintain the same trajectory as determined in a prelaunch solution through measuring velocity error at a given position along the path of the missile. The system also includes an ignition delay sub-system for correcting missile position along the flight path by navigating position between burnout of the given missile stage and ignition of the subsequent stage, and modifying the ignition time to correct the missile position after all missile stages are burned. The system also includes a multi-node Lambert guidance sub-system for steering the missile through a multi-node Lambert guidance control that arrives at independent solutions based on desired conditions at the target point and one or more way points; then merges the independent solutions. In addition, the system of the present invention includes a post-boost guidance sub-system for guiding the missile through post-boost guidance correction to correct residual velocity error through either a post-boost trans-stage capability or through the inherent capability of the missile.

Lateral escape guidance strategies for microburst windshear encounters

Abstract: This paper presents the outcome of a preliminary research effort involving the development of a nearoptimal lateral escape guidance technique for aircraft encountering a microburst on e nal approach. The proposed guidance technique relies either on in situ or on relatively short-range forward-look windshear detection. Simulated guidance solutions are evaluated in terms of recovery-altitude performance and robustness to uncertainty in microburst size and strength. Based on a comparison with exact open-loop optimal solutions, the employed technique of directing the aircraft toward a target recovery altitude constitutes itself as a very promising longitudinal guidance strategy. The lateral escape strategy, though very simple, also proved to be very effective, recone rming the overall benee ts of lateral escape vis-a´ -vis nonturning escape. Before a practical implementation of the guidance strategies can take place, several issues still need be addressed. This paper briee y outlines the missing elements to provide a framework for future research and development.

Flight control system for the automatic landing flight experiment

Abstract: This paper discusses the flight control system developed for the Automatic Landing FLight Experiment, ALFLEX. ALFLEX is an experimental program conducted by the National Aerospace Laboratory and the National Space Development Agency of Japan in order to investigate the automatic landing technology for a future unmanned reentry space vehicle. The ALFLEX vehicle is a dynamically similar sub-scale model of the planned Japanese HII Orbiting Plane, HOPE. Since the HOPE program is in a preliminary conceptual design phase, the ALFLEX vehicle is a scaled model of one of the proposed configurations from 1992 research. The vehicle bare airframe is statically unstable in the pitch axis. In the lateral-directional axes, it has negative weather cock stability and strong dihedral effect, which introduce severe instability. The airframe's instability and the landing performance requirement drive the flight control system design to be one of the key technologies in the HOPE program. Since the vehicle's maximum L/D is approximately 4, it needs the same landing guidance technique as lifting body research vehicles and the Space Shuttle. This paper discusses the flight control design and the design methods applied to ALFLEX, and discusses lessons learned so far. The results from a preliminary flight test are briefly introduced. The series of automatic landing flights are scheduled for the middle of 1996, at Woomera, Australia, and will verify the guidance, navigation and control design. *Head, Control Qualification Lab., member AIAA Senior research engineer, Flight Research Division *^Research engineer, Control Research Division § Associate senior engineer, Winged Space Vehicle Office ^Engineer, Winged Space Vehicle Office *Asistant manager, Nagoya Aerospace Systems **Asistant manager, Nagoya Aerospace Systems Copyright © 1996 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Introduction Automatic landing technology for reentry space vehicles has a long history starting from the lifting body flight experiment at Edwards, California and the US Space Shuttle which demonstrates excellent technology achievement by NASA, e.g. References 1) to 6). Japan has a plan to develop a reentry space vehicle called HOPE, H II Orbiting Plane. Since the HOPE vehicle is unmanned and autonomous, it depends heavily on recent computer technology for flight control. The development project is still in the research phase, and the National Aerospace Laboratory and the National Space Development Agency of Japan are collaboratively conducting research programs in order to develop key technologies for the unmanned reentry vehicle. Among them, ALFLEX, Automatic Landing FLight Experiment, is a research program for the subsonic flight control and automatic landing technology. 7) Technology to be developed in the program breaks down as follows: (1) Integrated navigation system design for automatic landing (2) Automatic landing guidance system design (3) Subsonic flight control system design (4) Subsonic aerodynamics prediction and verification ALFLEX is a research program to study and evaluate design methods to match up-to-date hardware, such as modern computers, sensors and actuators. In the ALFLEX program, however, special hardware has not been developed. Instead, commercially proven avionics and off-the-shelf components are used. An exception is a pseudo-satellite differential GPS system (DGPS), for which the NASDA Tsukuba Space Center developed an onboard receiver and ground system. The DGPS, however, is not a flight critical component, and mainly gives engineering data for off-line analysis in order to use it for a future mission. ALFLEX is a scale model experiment of a future 15 ton reentry space vehicle, HOPE. The vehicle airframe is designed to be dynamically similar to the planned space vehicle. Also the guidance, navigation and control system for ALFLEX is designed to be as similar as possible. Fig. 1 shows three side views of the vehicle, and Fig. 2 shows the primary onboard equipment. The model's length scale is 37 %. In order for HOPE to land on a standard size runway, the runway length specification for ALFLEX is set as 1000 m. According to the similarity rule, where acceleration and mass density are equal for the real and model vehicles, the model's time scale is 60.8%, and the model's velocity scale is 60.8%. The model vehicle's mass should be 5.07%, corresponding to 760 kg; however, it is actually 796 kg, slightly in excess of this figure. The ALFLEX vehicle is released at an altitude of 1500m from a helicopter with a velocity of 46.3m/s (90kt) EAS, the maximum speed for the helicopter's hanging load flight capability. The release altitude is determined in order to achieve an equilibrium flight condition on the glide slope, where approximately 500m altitude will be lost before accelerating to the glide path speed of 84m/s EAS. Ground facilities support the experiment, such as a flight data monitoring system, laser tracker and tracking radar systems. The laser tracker provides reference data for the vehicle position to evaluate the navigation system. The tracking radar provides position data for flight safety. Japanese aerospace manufacturing companies participate in the ALFLEX program. Mitsubishi Heavy Industries Ltd. supports the development of the guidance, navigation and control (GNC) system for ALFLEX. Fuji Heavy Industries, Kawasaki Heavy Industries and TOSHIBA contribute to other parts of the program. The program commenced in 1992, and will be completed with flight tests at Woomera, Australia during 1996. Guidance, Navigation and Control system Design goal The experiment's design goal is safe automatic landing. Quantitative performance requirements are defined for the GNC system design. Automatic landing performance is evaluated by the following measures. 1) Position of touch down, Xtd, Ytd 2) Attitude at touch down, 4>, 0, *P 3) Velocity at touch down, VEAS, VGND 4) Vertical velocity at touch down, Vsink 5) Side-slip angle to the ground at touch down, 6) Pitch rate at nose gear touch down, Qtd(n) 7) Maximum lateral deviation in the ground roll, Ymax 8) Stop position of ground roll, Xstop Table 1 shows the design requirements for the above parameters. Table 1: Landing performances requirement

Integrated ground collision avoidance system

Abstract: A ground collision avoidance system that is accurate and avoids nuisance warnings and displays provides an invaluable system for the preservation of life and equipment. This system improves its accuracy and performance by integrating with all other aircraft systems including guidance systems, navigation systems, digital terrain elevation databases, mission computers, and radar altimeters. Furthermore, the ground collision avoidance system provides a multiple processing path to determine numerous predicted flight paths based on a number of reasonable assumptions regarding the aircraft flight during a predetermined amount of time. By using prediction scheme a realistic estimate of the predicted flight path envelope can be determined and then this information can be used in conjunction with accurate terrain elevation databases to determine whether a ground collision condition exists. On the basis of these calculations appropriate warnings can be provided to the air crew as well as suggested maneuvers to avoid ground collision.

Aircraft turn guidance system

Abstract: An aircraft turn guidance system comprises a satellite navigation receiver connected to a turn path computer. Position, velocity and waypoint headings and distances are communicated from the satellite navigation receiver to the turn path computer. Roll angle, airframe and airspace constraints are fed to the turn path computer which computes a constant roll turn for the constraints when transitioning a waypoint from the inbound to outbound legs. The effects of wind on the airmass are computed in to account for real world conditions.

Optimal missile guidance for weaving targets

Abstract: Proportional navigation guidance is used in many tactical missiles. It is well known that sinusoidal or weave manoeuvres on the part of target can induce large miss distances for these missiles. An optimal guidance law based on sinusoidal target manoeuvre model is derived. Since the miss distance performance of this guidance law is very sensitive to the sinusoidal manoeuvre frequency, a method to accurately estimate this frequency is presented.

Route Guidance Systems: Getting it Right from the Driver's Perspective

Abstract: This paper presents a brief overview of current human factors research into route guidance systems A short description of different interface styles is given and a review of two road-based studies of three existing route guidance systems is provided A general discussion then highlights a range of issues of relevance to driver-system interfaces, drawing on results both from the studies carried out, and other research Specific aspects addressed include the content and means of presenting route guidance information, and the potential effect of interface design on driver visual behaviour and performance

Route guidance as a just-in-time multiagent task

Abstract: This article discusses a prototype of a route guidance system able to cope with both long- and short-term navigation problems. The system plans the route using a classical shortest path algorithm working on an ''on-board'' road map knowledge base, and uses information acquired through a radio channel to activate route replanning. In this case the new plan is computed not only on the basis of the car and world state at the start of the replanning, but also on replanning time duration. An estimate of car and world variations during the replanning is used to build up a route that the driver can safely perform. The system builds a local world description by integrating the information computed by a boundary detection algorithm with the information stored in the road map knowledge base. This model is used to generate a car trajectory and to supply the driver with information. Although the time spent to compute the trajectory does not allow the car to be driven at a reasonable speed, the boundary detection algo...

Multiple node lambert guidance system

Abstract: A multi-node Lambert Guidance System that controls missile velocity along a missile flight path through adjustment of missile attitude during guidance of the missile through an intercept point and one or more way points. The system utilizes a linear Lambert solution in that it is derived from a plurality of Lambert solutions each corresponding to a particular node along the prelaunch flight path solution and each including corresponding time varying weights on the accuracy at several flight path nodes. The present invention allows direct translation of guidance velocity corrections into vehicle attitude adjustment commands, and thereby avoids additional computation required in prior predictive integration guidance approaches.

The Challenge of Intercepting Spiraling Tactical Ballistic Missiles

Abstract: Intentional or unintentional spiraling maneuvers on the part of a tactical ballistic missile target can make it particularly difficult for a pursuing missile to hit. The paper presents normalized miss distance curves showing how the target spiraling frequency and amplitude along with the interceptor guidance system time constant and navigation ratio determine the miss distance for a proportional navigation guidancesystem. It is also shown how more advanced guidance techniques can be used to improve system performance against spiraling targets. Whenever possible numerical examples are used to illustrate major points.

Optimality and guidance for planar multiple-burn orbit transfers

Abstract: An analysis of the second variation for extremal orbital transfers is presented, as well as a discussion of a multipleburn guidance scheme that may be implemented for such transfers. The second variation analysis includes the examination of the conditions for free final time transfers. A continuous burn transfer is shown to have neighboring extremals through these conditions. An implicit guidance scheme is explored, which implements a neighboring optimal feedback guidance strategy to calculate thrust direction and thrust off-times. A new time-to-go formulation is introduced, which has improved performance for this transfer. This continuous burn guidance scheme is adapted to multiple-burn transfers. A two-burn guidance problem is simulated. , C a d(-) e eT f go H

New pulse-modulation technique for guidance and control of automated spacecraft

Abstract: A comprehensive approach to problems such as automated on-orbit rendezvous and soft landing on a planetary surface is presented for spacecraft employing pulse-operated (on-off) propulsion systems. Using a technique derived from robust control theory, a new class of guidance algorithms that modulate the duration and frequency of thruster firings is developed. These algorithms allow analytical characterization of transient errors, limit cycle deadband, and the set of possible terminal conditions in the design process, without the use of dynamical approximations such as linearization. With this approach, the desired performance is ensured in the presence of dynamical modeling errors with known bounds; the effects of navigational errors can be minimized to the extent that they can be bounded. A realistic application is illustrated via computer simulation of a hypothetical mission scenario, in which a robotic spacecraft equipped with an aided-inertial guidance system soft lands on the planet Mars. N missions carried out with robotic spacecraft, self-contained guidance and control are often desirable and in some cases a necessity. Although a wealth of theory exists for applications such as automated orbital transfer, rendezvous, station keeping, and soft landing, among others, much of this knowledge base presumes the use of continuous throttleable or fixed-thrust propulsion, whereas in practice many spacecraft are equipped with on-off gas jets or thrusters because of their relative simplicity and low cost. This paper describes a new technique for pulse-modulated operation of these devices intended for use in the aforementioned problems. A representative , but not exhaustive, review of previous work emphasizing mission applications is as follows. Much of the ren- dezvous literature is devoted to the determination of optimal trajec- tories and their associated thrust profiles. Both theoretical and op- erational aspects of rendezvous are discussed in the survey papers by Jezewski et al.1 and Leonard and Bergmann.2 Parten and Mayer3 and Young and Alexander4 describe the rendezvous and docking procedures developed for the Gemini and Apollo piloted missions, respectively; these procedures have also been used in Space Shut- tle missions. Automated rendezvous schemes have been proposed for the Space Shuttle5'6 but not implemented. Previous missions in- volving soft landing have all been accomplished with throttleable propulsion systems. The early work leading to the guidance algo- rithms used in the Apollo missions was performed by Cherry7 and Battin.8 The operational Apollo lunar module guidance system is described by Klumpp.9 The automated guidance schemes used by the Surveyor and Viking spacecraft were similar: the terminal de- scent system developed for the Surveyor lunar lander is described by Cheng et al.,10 and Ingoldby11 discusses the corresponding system for the Viking Mars landers. Another prevalent feature of the literature is the use of linear approximations of the spacecraft's dynamics to obtain an analyt- ically tractable problem. Given the nonlinear behavior of on-off thrusters, the closed-loop dynamics of systems employing these

Improved laser based visual landing aids and method for implementing same

Abstract: In this application are disclosed a variety of improvements to the original aircraft azimuth guidance system. These improvements provide for greater utility, effectiveness, and ease of manufacturing of the laser visual landing aid system. The laser azimuth guidance system includes lens (53), cylindrical lens (56), mask (57) and objective lens (54).

Motion tracking apparatus for driverless vehicle

Abstract: This invention relates to a swivel caster fitted with rotational and swivel angle measurement sensors mounted to a driverless vehicle so that the lateral motion of the vehicle can be detected and accounted for by the vehicle's navigation and guidance system. A preferred embodiment of the present invention is a driverless vehicle comprising a navigation and guidance system having an angular motion sensor and a track wheel caster assembly equipped with a caster pivot sensor and a wheel rotation sensor to determine the relative position of the vehicle by taking into account substantially all movement of the vehicle along the surface upon which the vehicle is travelling. These sensors enable the navigation system to more accurately determine the vehicles current position and enable the guidance system to better guide the vehicle.

Dual-mode infrared and radar hardware-in-the-loop test assets at the Johns Hopkins University Applied Physics Laboratory

Abstract: Several next-generation air defense missiles will use dual- mode guidance systems that simultaneously employ RF and IR sensors to obtain significant improvements in guidance performance. These missiles will require sophisticated hardware-in-the-loop test facilities to provide controlled signal environments to each sensor. Such test facilities allow accurate characterization of RF and IR sensors as well as the development and validation of guidance algorithms. Two approaches for dual-mode hardware-in-the-loop testing used at The Johns Hopkins University Applied Physics Laboratory (APL) are `electrically connected' and `collocated.' Each uses a common central computer to precisely coordinate RF and IR environment generators. The electrically connected approach requires disassembly of the guidance section and locating RF and IR seekers in different rooms. Extended electrical interfaces couple the seekers to the missile's guidance computer. This arrangement is well suited for development testing where flexibility is the primary concern. In the collocated configuration, disassembly of the guidance system is not needed since the RF and IR test environment generators are built into a common facility. This noninvasive configuration is useful in identifying and resolving performance issues associated with an integrated guidance system. This paper describes the capabilities and status of the collocated dual-mode Guidance System Evaluation Laboratory developed at APL.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.