A facet of the NASA Greenland Ice Sheet mapping experiment is the requirement for precise navigation and positioning of the aircraft. In order to establish baseline elevational measurements it is necessary to reoccupy ifight tracks several times to ensure the validity of the survey. The Airborne Oceanographic Lidar1 (AOL) was operated in a scanning mode from an a!titude of 400 m so the survey swath width is '200m thus the real-time navigational requirement is +1-50 m to provide for at least a 50% swath overlap on repeated passes. We developed the GPS Flight Management System (GFMS) using the Global Positioning System (GPS). The GFMS inputs GPS position data to a PC which generates _ aircraft automatic pilot steering commands and a cockpit display including 1) course deviation indicators for cross-track error and altitude, 2) flight plan and waypoint map overlay oriented to the aircraft and 3) other mission pertinent numerical data.
A joint NASA-Langley/Honeywell flight test project evaluating a differential Global Positioning System (GPS)Ilnertial Navigation System (INS) as an approach/landing aid was completed in November 1990. The test objective was to acquire a system performance data base and to demonstrate automatic landing using an integrated differential GPS/INS with radar altimeter aiding for vertical axis guidance. A NASA Boeing 737 testbed was used to evaluate the differential GPSIINS performance which included real-time comparison against MLS-derived position. This paper presents an overview and summary of the results from that flight test and discusses the application and benefits of the integrated INS/GPS to future space vehicles.
Collision avoidance involves the detection of impending collisions of an aircraft with either another aircraft or the ground from radar data and the timely alert of the danger to the pilot or air-traffic controller. The challenge is to provide sufficient warning (timely detections) with minimal false alarms. Radar measurement uncertainties degrade collision detection performance and must be accounted for in the algorithm design. This paper describes a method which uses statistical decision theory to control both missed or late detections and false alarms. The key to the technique is the mathematical description of the aircraft corridor uncertainty region. The corridor uncertainty region is derived from the position and velocity confidence ellipsoid associated with the aircraft radar track via a mapping from six dimensional space to three. By careful choice of the mapping, the minimum volume corridor uncertainty region is derived. This allows for the definition of the optimal collision avoidance decision rule. Since the method is based solely on the statistical properties of an aircraft's position and velocity track, it may be adapted to a variety of collision avoidance or guidance problems involving a radar or beacon-type sensors such as Mode C or Mode S.
Low cost interferometric fiber optic gyros (both polarization maintaining and depolarized types) having bias drift less than one degree/hr over wide temperature ranges are reported. The depolarized fiber gyros exhibit significantly lower sensitivity to temperature transients than the polarization maintaining fiber gyros.
We have demonstrated a novel solid-state ring laser gyroscope by actively modelocking a pair of InGaAsP diodes in an external ring cavity. We observe no evidence of gain competition or frequency locking between the counterpropagating optical pulse trains circulating in the cavity to within the limit of our experimental resolution.
A feasibility study was conducted of a prototype electrostatically suspended micromechanical two-axis gyroscope on a microchip, which is expected to find many applications in commercial, aerospace, and military sectors. Particular attention is given to the microfabrication techniques used for this device, the specifications and the configuration of the gyroscope, the configurations of the motor and the sensor, the electromechanical design, and the control and electronics design. Results of the feasibility study were very promising.
A model is developed which explains the lock-in growth phenomenon in ring laser gyros (RLGs), based on the concept of a 'burn-in' reflection grating proposed by Chao et al. (1984). It is suggested that a 'burn-in grating' is produced by the photoinduced refractive index modulation of the dielectric mirror stack. Experimental results supporting the burn-in grating model are presented, including lock-in growth and recovery measurements, second-order optical nonlinear activity measurements confirming electrooptic activity, and high- and low-intensity laser-induced damage measurements.
A star sensor simulator was developed, which models the characteristics of the star, the background, the sensor's windows, the telescope, the detector, the electronics, and the environment, generating data which are similar to data received from a real star sensor. The simulated data are then processed to reveal the star sensing capability. The paper discusses the requirements of the star sensor simulator, the models used, and the simulator design and presents representative simulations.
The fact that a spacecraft traveling through the 'vacuum' of space conforms to the classical Keplerian ellipse has recently been disproven. It is now well known that such a vehicle is acted on by many external forces such as drag in the rarefied particle atmosphere, solar wind and particle impact. This paper discusses the development of sensors and sensor systems to measure these minute forces of acceleration/deceleration. Four systems will be discussed: a 10 exp -4 g system, a 10 exp -6 g system, a 10 exp -(6-8) g system and a 10 exp -9 g system. The design of each system will be explained along with the advantages/disadvantages of each. Various applications unique to each system will be discussed. Configurations, design schemes, test plans and calibration procedures, both in the ground laboratory and inflight, will be presented. The current design/development/operational status of each system will be examined and future plans discussed. Application to aerodynamic studies and vernier guidance, navigation, and vehicle control will also be examined.
Hercules Defense Electronics Systems, Incorporated has applied millimeter wave technologies to a variety of guidance and control problems. This presentation documents the development and integration of an autonomous millimeter wave seeker to the AGM-65(D) (Maverick) air- to-ground missile. The resulting system was successfully demonstrated to search a large area for potential targets, prioritize detections, and guide the missile to the target during recent free-flight tests.
The paper describes the design and performance of the Coherent Launch Site Atmospheric Wind Sounder (CLAWS), which is a test and demonstration program designed for monitoring winds with a solid-state lidar in real time for the launch site vehicle guidance and control application. Analyses were conducted to trade off CO2 (9.11- and 10.6-microns), Ho:YAG (2.09 microns), and Nd:YAG (1.06-micron) laser-based lidars. The measurements set a new altitude record (26 km) for coherent wind measurements in the stratosphere.
The design of a newly designed ladar system (called LADAR) using a diode-pumped Q-switched Nd:YLF laser operating at 1.32 micron is described, and images obtained with the LADAR are presented together with the performance results of signal processing algorithms. It is shown that the system is able to obtain a range image of a target at 2 km, obtain intensity image information, and implement target detection and identification algorithms.
Recent advances in tunneling-tip technology, magnetic materials, and microfabrication techniques allow development of a new class of improved magnetometers. The sensor utilizes changes in Young's modulus of amorphous magnetic alloys resulting from their excellent magnetoelastic properties. Changes in applied magnetic field cause resonant frequency changes of a sputtered, electrostatically excited Metglass cantilever. Resonant cantilever position is measured by a second, electrostatically controlled cantilever holding a tunneling-tip that tracks the Metglas cantilever. The phase relationship between the exciting signal and the position is fed back to maintain the excitation frequency at the moving resonant peak. In this way the resonant frequency is measured, and the field is inferred from the frequency. The 'Q' of the Metglas cantilever is increased to very high levels using closed loop control of cantilever dynamics, producing extraordinary resolution.
The features and the components of a new microscale guidance, navigation, and control (GN&C) system for future space systems are discussed. An approach is described for the utilization of new microengineering technologies for achieving major reductions in the GN&C system's mass, size, power, and costs. The micro-GN&C system and the component concepts include microactuated adaptive optics, micromachined inertial sensors, fiberoptic data nets with light-power transmission, and VLSI microcomputers. The GN&C system will be applied in microspacecraft, microlanders, microrovers, remote sensing platforms, interferometers, and deployable reflectors.
Microactuators ideally produce large output forces per unit chip area. This requires processing procedures which lend themselves to structures with large structural heights. Processing which also produces large edge acuities is required for low friction, low wear sliding bearing surfaces. Both attributes are accommodated in a processing sequence which uses thick photoresist technology, X-ray exposure, and metal plating together with a surface micromachined sacrificial layer. The end results are thick precision metal structures which can be assembled to achieve submicron tolerances in sliding bearing surfaces. The process has been used to fabricate rotational planar magnetic micromotors with low friction. Linear reluctance drives with spring returns have also been achieved and are in the testing phase.
An important new approach for vehicle guidance and control is based on the use of compact, low-mass, low-cost sensors integrated with the vehicle structure. Many advantages of this approach lead to new capabilities. However, the development of compact guidance and control sensors leads to a variety of fundamental physical problems associated with sensor sensitivity and noise. For example, as sensor size is reduced, it becomes necessary to improve the sensitivity of the sensor signal detection mechanism. These challenges to sensor development will be described. Recent developments at JPL, based on new position sensor principles such as electron tunneling, have produced a series of novel, ultra-high sensitivity micro-sensors and micro-instruments. Included among the applications demonstrated, are a high sensitivity micro-accelerometer and micro-seismometer. In this paper, the fundamental limits of conventional position sensors will be discussed and a new position sensor for advanced accelerometers will be described.
The paper describes the integration of sol-gel ferroelectric thin films into micromachined sensors and optical detectors, devices which are based on the piezoelectric and pyroelectric effects in Pb(Zr(x)Ti(1-x))O3 and PbTiO3 thin films, respectively. The ferroelectric and surface-micromachining technologies are described, which are compatible with 3-micron CMOS technology. At 297 K and a chopping frequency of 50 Hz, the measured blackbody voltage responsivity of a pyroelectric element with an active area of 7 x 10 exp -4 sq cm was 4.2 x 10 exp 4 V/W and the measured normalized detectivity was 1.0 x 10 exp 9 cm sq-rt Hz/W.
The feasibility of using polycrystalline CVD diamond films as temperature sensors in harsh aerospace environment associated with hypersonic flights was tested using patterned diamond resistors, fabricated on flat or curved oxidized Si surfaces, as temperature sensors at temperatures between 20 and 1000 C. In this temperature range, the measured resistance was found to vary over 3 orders of magnitude and the temperature coefficient of resistance to change from 0.017/K to 0.003/K. After an annealing treatment, the resistance change was reproducible within 1 percent on the entire temperature range for short measuring times.
An empirical study was conducted to determine the ability of naive subjects to sample information from different display configurations. Simple line drawings circumscribed areas shaped like squares, rectangles, `Ts,' `Ls,' and `+,' among others. Each such `area' was presented for one second followed after a brief interstimulus interval (ISI) by a 12-letter (3 X 4) matrix. The subjects' task was to report all the letters that would have been surrounded by the area, if the line drawing of the area were superimposd on the letter matrix. The effects of display configuration on attentional sampling performance were thus assessed for an arbitrary set of 36 configurations. The results indicated that single, spatially contiguous areas could be monitored better than separate areas, and simple configurations were better than more complex ones. These results have implications for Heads-up Displays (HUDs) and for the optimal spatial configuration of salient gauges and instruments within a vehicle or airplane cockpit.
Generally, dashboard information display devices can be divided into active and passive ones, i.e., emitting or modulating light. The thin film electroluminescent display devices belong to the former category. The new concept electroluminescent dashboard information display devices conceived by the author are presented in this paper. In this case, a DC and an AC power supply voltage are simultaneously applied. As a result, the DC voltage is essentially reduced to about 25 V DC. The electroluminescent information display device was prepared by vacuum methods on a glass substrate in the form of tri-electrode structure.
A novel interconnection assembly method was developed for the electron gun of airborne CRTs, which makes it possible for the connectors to be connected and disconnected repeatedly (as opposed to soldering as in the conventional method) to provide access to the tube and its interconnecting cable harness. Environmental tests were conducted on one series of CRTs, which included electrical and environmental conditions which would be experienced in a worst-case aircraft cabin environment, including the altitude, humidity, thermal shock, vibration, and mechanical shock.
A cockpit revolution is in the making. Many of the much ballyhooed, much promised, but little delivered technologies of the 70s and 80s will finally come of age in the 90s, just in time to complement the data explosion coming from sensor and processing advances. Technologies such as helmet systems, large flat panel displays, speech recognition, color graphics, decision aiding, and stereopsis are simultaneously reaching technology maturities that promise big payoffs for the third generation cockpit and beyond. The first generation cockpit used round dials to help the pilot keep the airplane flying right side up. The second generation cockpits used multifunction displays and the HUD to interface the pilot with sensors and weapons. What might the third generation cockpit look like? How might it integrate many of these technologies to simplify the pilot's life and most of all: what is the payoff? This paper examines tactical cockpit problems, the technologies needed to solve them, and recommends three generations of solutions.
An airborne 3-D computer image generation system (CIGS) is a modular avionics box that receives commands from and sends status information to other avionics units. The CIGS maintains a large amount of data in secondary storage systems and simultaneously drives several display units. Emerging requirements for CIGS include: advanced avionics system architecture requirements and BIT/fault tolerance; real-time operating systems and graphic interface languages in Ada; and geometric/pixel processing functions, rendering system, and frame buffers/display controllers for pictorial displays. In addition, podded sensors (FLIR, LLTV, radar, etc.) will require multiplexing of high-resolution sensor video with graphics overlays. A combination of head-down AMLCD flat panels, helmet-mounted display (HMD), and Head-Up Display (HUD) will require highly parallel graphics generation technology. Generation of high-resolution, real-time 2-D/3-D displays with anti-aliasing, transparency, shading, and motion, however, emphasizes compute-intensive processing. High-performance graphics engines, powerful floating point processors, and parallel architectures are needed to increase the rendering speed, functionality and reliability, while reducing power, space requirements, and cost. The CIGS of the future will feature special high speed busses geared toward real-time graphics processing. The CIG system will be multi-channel, will have a high addressable resolution to drive HUD, 3-D displays in 4-pi-steradian virtual space, and 3-D panoramic displays; and will include fiber optics video distribution between CIG and display units. The head-down display (HDD) is by far the most complex display in that both background and overlay display elements are required. The background is usually generated from terrain/cultural features data. Terrain data is used to generate 2-D map backgrounds or 3-D perspective views duplicating or substituting for the pilot's out-the-window view. Performance of 150,000 to 500,000 3-D triangles/second is needed. Gouraud shading, ambient-diffuse lighting models, and anti-aliasing are required. For the year 2000, a single large and very high-resolution display surface covering the entire instrument panel is required.
The paper describes the structure and technology of active matrix liquid crystal displays (AMLCDs) and discusses the advantages of the AMLCD technology ocmpared with CRT technology. AMLCDs use microelectronic thin film transistors (TFTs) to produce bright, full-color images equal to those of CRTs in clarity and resolution. At the same time, color AMLSDs alleviate many problems associated with color CRTs, such as poor reliability in a severe environment, modest color performance in high ambient light, poor mean time between repair (five times less than that of AMLCDs), relatively great weight, and poor volumetric efficiency. The paper considers the AMLCD electronics and discusses the development of self-scanned poly-Si AMLCDs with integrated row and column (data and select line scanners) circuitry and 5-bit grey shade drivers. The integration of row and column and gray scale circuitry on glass will dramatically increase compactness and reliability and decrease AMLCD panel costs.
A prototype thin film electroluminescent (TFEL) display unit (DU) for a control display unit (CDU) design and development was initiated in FY90. Features of the display include high brightness and contrast, sunlight readability, night vision goggle compatibility, light weight, low power, automatic brightness control based on ambient light conditions, modular design, ease of assembly and test, and high reliability. The display contains an integral switch and lightplate that is night vision goggle compatible. The unit was designed for cockpit CDU applications, but can be easily converted for other display needs. The scope of this task was to design and build an ANVIS-compatible, sunlight-readable TFEL CDU DU engineering evaluation unit to replace an existing cathode ray tube (CRT) DU in the V-22 CDU. In order to accomplish that task it was necessary to learn interface, drive, and improved packaging techniques. The electronics were very straight forward using large scale integration (LSI) components. The CDU is mounted in the instrument panel in standard cockpit avionics mounting rails, utilizing quarter turn captive fasteners. The CDU is cooled by natural convection. The TFEL display unit weighs 4.3 pounds compared to 7.8 pounds for the CRT version. Surface mount was a requirement for the drive card due to size constraints. Elastomeric connectors were used to interface the driver board to the glass. The approach uses as much proven design as possible, but makes use of state-of-the-art display technology to provide a low power display unit with outstanding characteristics. The TFEL CDU DU tasks completed during 1991-92 included design and development of: (1) controller and RS-170 digitizer board, (2) high voltage-switching or pre-driver board, (3) row and column driver circuitry for gray scale (double-sided surface mount using sample Supertex HV38 gray-shade column drivers and TI high-voltage row drivers); (4) high and low voltage power supplies; and bezel and packaging. Performance of the TFEL DU, functions and operation of the TFEL CDU DU and key board unit (KBU), and aircraft interfaces are described.
The in-cockpit swath centerline identifier (SCI) for aerial applicators uses differentially corrected global positioning system (GPS) signals to determine precise ground track of an aircraft and provide guidance to the pilot for flying patterns for aerial application of materials such as pesticides, herbicides, and fertilizers. Cross track distance from the swath centerline is provided by a heads up light bar display while detailed navigation, position, and status information is provided on an alphanumeric display on a panel mounted console. This system provides straight line guidance when executing a swath and turn-in guidance when proceeding from one swath to the next. It provides a record of the swaths which were sprayed and logs all of the associated navigation and operational data, including time. In addition, it provides navigation information from base to the fields, between fields, and return. The SCI eliminates the need for flaggers while providing improved accuracy of application. Reduced exposure to liability and improved quality control results as the position, altitude, time, and spray status are logged for post flight analysis. The SCI has been used in commercial agricultural applications. Demonstrations of the SCI showed better precision than anticipated.
The Laser Centerline Localizer (LCL) and the laser Glideslope Indicator (LGI) use a series of low power, but highly visible laser beams to illuminate approach corridors for carrier flight operations. By taking advantage of the ability to precisely shape and direct visible laser beams and by encoding the illuminated paths using color and temporal frequency, direct visual signals which provide a positive on course signal as well as an indication of the direction and degree of deviation from the proper approach are seen by the pilot. The LCL provides centerline guidance and the LGI provides descent guidance. This laser visual landing aid (LVLA) system provides the pilot with significantly improved visual cues to aid in the safe landing of the aircraft. The LCL and LGI units have been constructed and field tested. The ability to guide pilots from a range of over 15 miles has been demonstrated.
The Scanning Laser Aircraft Surveillance System (SLASS) uses two scanning infrared laser beams to illuminate retroreflectors located on aircraft landing gears and hook to determine very precisely the azimuthal, ascension, yaw, roll, and pitch angles of the aircraft in the approach corridor. The range, approach velocity, and aircraft type are also determined. Aircraft configuration is determined by the presence or absence of each return signal, and aircraft type is identified with an encoded sequence of retroreflectors on one landing gear. The position of the aircraft is determined by the time in the scan that the beam encounters the retroreflectors.
In the future, aviation aircrews will likely operate in an environment that is saturated with electromagnetic energy emitted from a variety of sources. Lasers serving many applications, such as rangefinding and guidance, will be included in this environment. Eye damage from laser sources is possible, but laser irradiation below levels necessary to produce eye damage may still degrade visually guided human performance. It is important to understand how, and to what extent, visually mediated human performance is affected by low-level laser glare. To this end, we have conducted some initial laboratory studies in which we have systematically varied level of glare and cockpit windscreen characteristics while subjects, who were seated in a cockpit familiarization trainer, performed a visual search task. The search task required subjects to scan a complex visual scene projected on a screen and report the location of one small target disk randomly placed among larger background disks. In a series of studies, we have shown that windscreen characteristics and ambient illumination can interact with laser- induced glare to disrupt visual search performance. We have also shown that lens opacity, an opaqueness of the lens that increases with age, may interact with laser glare and degrade visual search performance more in older individuals. Laser light intensities well below the eye injury threshold may effectively disrupt visually guided performance.
General Dynamics has been developing an Autonomous Rendezvous Docking and Landing (ARD&L) system that utilizes cruise missile technologies. In November 1990 the Autonomous Rendezvous and Docking (AR&D) system was first demonstrated for members of NASA's Strategic Avionics Technology Working Group (SATWG). This simulation utilized prototype hardware from the Cruise Missile and Advanced Centaur Avionics systems. The objective was to show that all the accuracy, reliability, and operational requirements established for a spacecraft to dock with Space Station Freedom could be met by the proposed system. Rapid prototyping techniques were used to evaluate the proposed system in a real time, hardware in the loop simulation of the rendezvous and docking reference mission. The simulation is currently being upgraded to test an Autonomous Approach and Landing (AA&L) system. Both systems use inertial guidance and control systems supplemented by the Global Positioning System (GPS) and an Image Processing System (IPS), for target recognition and tracking. The IPS includes a general purpose multiprocessor computer and a selected suite of sensors that will provide the required relative position and orientation data. Graphic displays can provide the astronaut/operator with realtime guidance and navigation data with enhanced video or sensor imagery.
A rugged, miniaturized, optical cross-correlator that recognizes a single object is particularly suitable for performing a single-vision function, such as pattern recognition for semi- autonomous navigation, landing, and docking of vehicles to a pre-designated landing mark. The optical cross-correlator, with a video input from a simple imaging system and the output of the optical correlation plane processed using the standard star tracker software, produces sufficient information for a spacecraft's terminal homing navigation system to complete a docking maneuver.
The development of the coated Contrast Enhancement Filters, the coated narrow band-pass absorbing optical filters designed for P43 CRT color shadow mask displays and flat panel displays is discussed. Particular attention is given to the properties and applications of several series of Contrast Enhancement Filters, including filters designed to meet special day-night application.