Carrier‐phase ranging measurements from Global Positioning System (GPS) and low‐Earth‐orbiting Iridium telecommunication satellites are integrated in a precision navigation system named iGPS. The basic goal of the system is to enhance GPS positioning and timing performance, especially under jamming. In addition, large satellite geometry variations generated by fast‐moving Iridium spacecraft enable rapid estimation of floating cycle ambiguities. Augmentation of GPS with Iridium satellites also guarantees signal redundancy, which enables Receiver Autonomous Integrity Monitoring (RAIM). In this work, parametric models are developed for iGPS measurement error sources and for wide‐area corrections from an assumed network of ground reference stations. A fixed‐interval positioning and cycle ambiguity estimation algorithm is derived and a residual‐based carrier‐phase RAIM detection method is investigated for integrity against single‐satellite step and ramp‐type faults of all magnitudes and start‐times. Predicted overall performance is quantified for various ground, space, and user segment configurations.

Preliminary space flight results of attitude determination using GPS are presented from a spacecraft in low Earth orbit. Relative position measurements accurate to the sub‐centimetre level are made among multiple GPS antennas mounted on the space vehicle. A Trimble Navigation TANS Quadrex (a GPS receiver specially adapted for attitude determination by Stanford University) is used as a differential carrier phase sensor for the flight. Four GPS antennas are mounted on the zenith face of RADCAL, a polar orbiting, gravity‐gradient‐stabilized Air Force Space Test Program Satellite, built by Defense Systems, Inc. The four antennas are equally spaced about the perimeter of the 30 inch diameter cylindrical spacecraft bus. The Quadrex receiver measures the phase of the L‐band GPS carrier (1575 MHz) at each of up to four antennas for up to six GPS satellites simultaneously. From these measurements, an initial assessment of attitude determination in space is performed in post‐processing. For RADCAL, the attitude solution is greatly overdetermined. In a preliminary evaluation of system performance, the system accuracy is determined through measurement self‐consistency. Analysis of the attitude motion in the context of a gravity gradient dynamic model yields further insight into the system performance.

Attitude determination using GPS carrier phase has been applied successfully to aircraft in experiments by a number of researchers. In an effort to formally characterize its accuracy and bandwidth performance, a GPS attitude determination system was flight tested against an inertial navigation unit, (INU). Based on completely separate physical principles, this testing provides an independent means of evaluating overall performance.For the flight experiments, a twin-engine turboprop transport aircraft was outfitted with a specially designed attitude determination receiver. A strap-down ring laser gyro INU was operated in the main cabin as the independent reference. For system evaluation, a number of test maneuvers were executed, including pitch angles to + 30 deg and bank angles to ? 60 deg. Performance in moderate turbulence was measured. The impact of structural flexure during aircraft maneuvering was evaluated.

No abstract

This paper describes how differential GPS (DGPS) and miniature, low-cost Integrity Beacon pseudolites were used to carry out 110 successful automatic landings of a United Airlines Boeing 737 aircraft. These autopilot-in-the-loop flight tests using GPS Integrity Beacons (low-power, ground-based marker beacon pseudolites placed under the approach path) furnished evidence that GPS can provide the full performance necessary to meet the stringent specifications of Category III. The built-in geometrical redundancy provided by Integrity Beacon ranging is coupled with centimeter-level accuracy to provide the system integrity. This integritycalculated to be better than one part in a billion probability of missed detectionis achieved independently from ground-based monitors using receiver autonomous integrity monitoring @AIM).