A formation flying technology vision

Collision Probability with Gaussian Mixture Orbit Uncertainty

Integrating Passive Millimeter Wave camera (PMMW), Global Positioning System (GPS), and Differential Global Positioning System (DGPS) provides a pilot with a visual precision approach and landing in inclement weather conditions conceivably down to CAT III conditions. A DARPA funded, NASA Langley managed Technology Reinvestment Program (TRP) consortium consisting of Honeywell, TRW, Boeing, and Composite Optics Corporations is demonstrating the PMMW camera. The TRW developed PMMW camera displays the runway through fog, smoke, and clouds in day or night conditions. The Global Air Traffic Program Office entered into a Cooperative Research and Development Agreement (CRDA) with Honeywell to demonstrate DGPS. The Honeywell developed DGPS provides precision navigational data to within 1 m error where GPS has 100 m of error. In inclement weather the runway approach is initiated using GPS data until a range where DGPS data can be received. The runway is presented to the pilot using the PMMW image viewed via a Heads Up Display (HUD) or Head Mounted Display (HMD). At a range where DGPS data is available, a precise runway and horizon symbology is computed in the Flight Display Computer and overlaid on the PMMW image. Image processing algorithms operate on the PMMW image to identify and highlight obstacles on the runway. The integrated system provides the pilot with an enhanced situation awareness of the runway approach in inclement weather. When a DGPS ground station is not available at the landing area, image processing algorithms (again operating on the PMMW image) generate the runway and horizon symbology. GPS provides the algorithm with initial conditions for runway location and perspective. The algorithm then locates and highlights the runway and any obstacles on the runway. Honeywell Technology Center is performing research in the area of integrating the PMMW, DGPS, and GPS technologies to provide the pilot with the most necessary features of each system; namely: visibility, accuracy, obstacle detection, runway overlay, horizon symbology and availability.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The main component of Global Positioning System (GPS) positioning error results from time and space varying conditions of radio wave propagation, which depend on atmospherics, disturbances in the satellite constellation, orbit stability, and also due to the U. S. military intentionally such as Selective Availability (SA), among other things. The error caused by the transmitter and receiver operation precision or time-measurement accuracy is negligible. A method for GPS precision enhancement commonly used by civil users is the Differential GPS (DGPS). If DGPS service is interrupted, it will lead to the degraded navigation performance. This paper focuses on applying a Π-Σ Neural Network (PSNN) model to predict Pseudo-Range Corrections (PRC) for DGPS. A low cost commercial module (Rockwell single-frequency GPS receiver) is employed to represent the improvement in DGPS. Experimental results show the proposed NN can online predict the PRC precisely when the PRC signal is lost for a short period of time.

Spacecraft formation flying has received an enor- mous amount of attention over the past few years as a promising alternative to monolithic- and often large- space structures. Balanced optimal energy control of such distributed space systems guarantees maximum lifetime for these missions and hence is of great importance in mission feasibility studies. In this paper, an optimal control strategy for two and three spacecraft distributed space systems that are commanded to attain new relative coordinates, is proposed, guaranteeing balanced energy consumption among the spacecraft. We will delineate on the relevant mission scenarios both in deep space as well as in close proximity to a gravitational force field as in Earth's orbit. Index Terms— Formation flying, balanced energy reconfig- urations, optimal control

The capabilities of Ashtech XII for differential GPS (Global Positioning System) are discussed. Differential algorithms and communication protocols to exchange differential information between receivers are included in the internal software of the receiver. Hence, there is no need for external computers to provide the protocol link. The all-in-view capability of the receivers makes them suitable for reference stations as well as remotes. Integration of ASHTECH XII with the vehicle tracking system (VTS) is presented. Differential GPS messages are transferred via the VTS communication link. The integration of the VTS and differential GPS has resulted in an accurate vehicle tracking and positioning system called differential GPS/VTS.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Global Positioning system (GPS) is used for navigation and associated tasks in wide variety of applications. One of the primary modes of GPS operation is differential GPS. Differential GPS allows more accurate positioning than stand-alone GPS. Many new applications are possible because of the increased accuracy obtained through differential GPS. In this paper the techniques and methods of differential GPS along with the algorithms are discussed which are providing more accurate and precise positioning in recent trends of communication. The purpose of the paper is to introduce the principles of differential GPS theory, and to provide a background for more advanced material.

In recent years the importance of real-time positioning and navigation with the Global Positioning System (GPS) has grown rapidly. Starting from the establishment of differential GPS (DGPS) reference stations for marine and land navigation, new users and applications have emerged that resulted in a high demand for the establishment of a high-density network of reference stations around the world. Many countries have established their own DGPS service, which is either governmentally or commercially owned. These services are referred to as Local Area DGPS Systems (LADGPS). However, the costs for the establishment and maintenance of a dense network of reference stations are very high. Therefore Wide Area DGPS Systems (WADGPS) are being developed to overcome the main drawbacks of LADGPS. In this case, only a few reference stations are used to cover a large area, such s a continent like Europe. To achieve high positioning accuracies, real-time modeling of the main error sources for long-range baselines is required as errors in the satellite orbit and ionospheric refraction do not cancel entirely in double differencing. In this article, a real-time correction model based on the Kalman filter for WADGPS and networked LADGPS services is discussed and results of field tests in a WADGPS network in Europe are presented. © 2000 John Wiley & Sons, Inc.

The difference in ionospheric delay between paths to the reference and mobile stations for differential GPS has been quantified for equatorial region. This small additional ionospheric error can be evaluated and predicted for the mobile station by means of a determined differential delay along the baseline so that accurate correction can be made for the most precise positioning. In this paper we studies the ionospheric delay on the Global Positioning System (GPS) signal due to the variation of elevation angle and variation in total electron content (TEC) and ionospheric profiles utilizing the Modified Jones 3D Ray Tracing method. The differential delay can be determined for any azimuth angle of propagation and for any baseline direction, providing the approximate difference in line-of-sight (LOS) between the stations. Result show that the variations of elevation angle and TEC give effects on the difference in delay between the two stations in differential GPS (dGPS). This analysis determined the difference in ionospheric delay expected over a short baseline so that a more accurate differential GPS correction can be made.

The Air Force Research Laboratory (AFRL) Space Vehicles Directorate is actively pursuing cryocooler and cryogenic integration research to support technology needs for the Air Force, the Missile Defense Agency (MDA, formerly the Ballistic Missile Defense Organization), and the Department of Defense (DoD). This paper presents an overview of the in-house and external applied research efforts on a number of fundamental issues toward the development of long-life strategic cryocoolers and cryogenic integration technology. External activities include Small Business Innovative Research (SBIR) development, AFRL funded activities at the National Institute for Standards and Technology (NIST), and funded research at Oxford University. In house research efforts include work on advanced regenerators for Stirling cycle cryocoolers, and continued in-house research on products from the SBIR program. Additionally, this paper examines future research trends for AF and DoD cryogenic technology.

Advanced airborne sensor technology in support of Non-Cooperative Target Identification (NCTI) programs has been the subject of ongoing programs at Wright Laboratory for several years. Capitalizing on the freedom achieved via Global Position System (GPS)/Differential Global Position System (DGPS) technologies, research, development, test and evaluation (RDT&E) organizations can detach from ground-based systems and locate their operations at a multitude of suitable locations. Utilization of GPS-based position information coupled with a single combined downlink and control facility reduces the complexity and maintenance of a range system while increasing its reliability. Establishing a transportable system further frees the experimenter to deploy to a variety of locations as required under short notice. GPS/DGPS based systems also provide a path to functions other than pure RDT&E. They may be used to provide tools for mission planning, performance monitoring, fault diagnosis, DIS/HLA and other virtual theater platforms. Mission rehearsals can take place in a virtual environment, and the results or expected outcomes integrated into actual exercises via modifications to data sources and operational mode(s). The end product is a powerful, flexible, fully mobile testbed fully supporting RDT&E requirements for Wright Laboratories, as well as other U.S. and foreign research organizations. Termed the Mobile Advanced Range Data System (ARDS) Control Station (MACS), the system has established a track record as an essential enabling technology for current test and evaluation applications. MACS is expected to have a cost-effective impact for future flight test applications as well.

A real-time integrated navigation system with 2-cm position accuracy was developed using commercial off-the shelf (COTS) equipment including inertial sensors and differential Global Positioning System (GPS) receivers, and was demonstrated for transportation applications with an emphasis on lane departure detection. A 900-MHz radiofrequency communications link transmits GPS base station range and carrier phase measurements to a GPS receiver on the vehicle. The GPS receiver calculates the vehicle position relative to the surveyed base location. The loosely coupled eight-state extended Kalman filter with 10-Hz navigation aids provides smoothed position information between 2-Hz GPS updates and provides graceful degradation in the presence of GPS blockages or communication dropouts. Currently, the navigation aids include anti-lock braking system wheel turns, electronic compass heading and pitch, and map vertical height. Data acquisition and Kalman filtering systems were developed to handle real-time processing and recording of all instrument data for further post-test system evaluation to determine the optimum configuration. An accurate rapid survey and map representation approach for measuring lane boundaries was validated using a vehicle, demonstrating inherit repeatability by the GPS positioning system. Real-time lane departure monitoring was developed. A video camera was installed to assist in accurate surveying and real-time system validation. This GPS-based positioning system is suitable for highway speeds during all weather conditions. It can be extended to other collision avoidance, drowsy driver awareness, advanced curve or intersection warnings, SOS, tracking, automated control, fast precision road mapping, and traffic management applications.

FAA and NASA have established a joint program to evaluate the technical feasibility of using guidance from the satellite-based NAVSTAR Global Positioning System (GPS) for Category I11 (CAT 111) precision approaches. A combination of analyses, simulation tests and flight tests will be used to evaluate Differential GPS (DGPS) techniques for CAT I11 applications. Emphasis will be placed on meeting accuracy and integrity requirements for a complete DGPS-based CAT I11 autoland capability. Contractors will be requested to supply the ground and airborne equipment for computing the DGPS-based aircraft position and velocity. Contractors will also provide their own aircraft completely equipped with a DGPS-based capability. Feasibility will be demonstrated by meeting either sensor accuracy requirements for Instrument Landing System (ILS) CAT I11 applications or Total System Error (TSE) requirements currently under development. Additionally, the existing FAA Advisory Circulzus for CAT 11, CAT I11 and autoland approaches should be used as a guide for system development. It is expected that meeting TSE requirements would place less demand on the performance of the DGPS-based sensor than meeting ILSwves an based navigation sensor requirements. This paper ,' overview of the DGPS CAT I11 system architecture, requirements and demonstration program.

In order to resolve the problem that DGPS (differential global positioning system) can not be used in the HIL (hardware-in-loop) simulation of aerocraft, but only simulated by math modeling, a method how to use DGPS in HIL simulation was brought forward on the base of GSS7700GPS simulator and NovAtel DGPS receiver. The DGPS simulation system configuration fig of aerocarft was shown.The trial data of single GPS and DGPS was acquired and plotted in the table. Comparing single GPS trial data with DGPS trial data, it improved that DGPS has more positioning accuracy than single GPS. The method realized that the whole DGPS out-of-doors running process could be simulated realistically in static environment of laboratory. The accuracy and reliability of DGPS simulation of aerocraft were improved greatly by using the method.

PRISMA is a technology demonstration mission for satellite formation flying and in-orbit servicing. The space segment comprises the fully maneuverable Main minisatellite and the smaller Target satellite in a low Earth orbit at 700-km altitude. A key mission objective is to demonstrate onboard, fully autonomous, robust, safe, and precise formation flying of spacecraft. This is accomplished by spaceborne global positioning system navigation, guidance, and control functionalities for the maintenance of the relative motion between the two spacecraft. An innovative estimation approach employs a common Kalman filter for the absolute states of Main and Target, which accounts for the interdependency of absolute and relative navigation without the need for an explicit relative state. As a result, the onboard navigation system provides absolute and relative orbit information in real time with a position accuracy of 2 and 0.1 m, respectively. The formation control achieves accuracies of a few tenths of meters with minimum usage of thrusters. The guidance and control concept is detailed with emphasis on a relative eccentricity and inclination vector separation strategy. The paper derives estimates of the expected relative orbit control performances based upon realworld simulations using typical global positioning system receiver and propulsion system characteristics.

Application of Systems Engineering to USAF Small Business Innovative Research (SBIR)