Litton Systems, Inc.

Other

Northrop Grumman Systems Corporation

David Y Hsu

Allan J Brockstein

Samuel N Fersht

Patrick J Donoghue

Robert John Buchler

Robert D Curby

Joseph A Ratkovic

Ground targets can be passively identified on uneven terrain from an observation point elevation above a known reference point, a line-of-sight inclination angle, an azimuth angle and a digital terrain elevation database wherein actual elevations of surrounding latitude and longitude coordinates are stored and retrievable. Using the observation point's elevation above the known reference point and using the line-of-sight elevation angle from the observation point to the ground target, an initial estimate of the latitude and longitude coordinates of the ground target is made and used as an index into a digital terrain elevation database.

Passive determination of ground target location

A projectile guidance system without gyros in which the projectile has an orthogonal body coordinate system. The projectile has a triax of accelerometers providing x, y and z acceleration data measured along the x, y and z axes respectively. A GPS antenna and receiver means provides onboard GPS position and velocity data in earth referenced navigational coordinates. A computer and program means stores and accesses time indexed GPS position and GPS velocity data and transforms x, y and z axis acceleration data from body to navigation coordinates. The program means is responsive to corresponding time indexed acceleration data and to GPS velocity and position data for calculating and outputing an estimated projectile roll, pitch and yaw angle via optimal smoothing techniques with respect to local level for each time index iteration of present position to a flight control system for guiding the projectile to a predetermined location.

Projectile guidance with accelerometers and a GPS receiver

The invention is a method and apparatus for gravity vector compensation in an inertial navigation system (INS). The INS obtains its position and determines a gravity-model vector at its position using a predetermined gravity model. The deflection of vertical (DOV), the error in the direction of the gravity-model vector, is expressed in terms of a North-South (N-S) DOV component and an East-West (E-W) DOV component. Matrices of N-S DOV and E-W DOV data are stored in memory in a plurality of files for a plurality of discrete points distributed over the surface of the earth at a plurality of altitudes. The elements of a matrix of N-S DOV data or E-W DOV data have a one-to-one correspondence with a two-dimensional array of discrete contiguous points at a specified altitude above the earth's surface. Adjacent elements in a matrix correspond to (1) adjacent points on a parallel of latitude or (2) adjacent points on a half-circle meridian, a half-circle meridian terminating at the two poles of the earth. The method consists of obtaining the INS position, separately translating the N-S DOV data and the E-W DOV data from a plurality of matrices into a plurality of supermatrices, determining the N-S DOV and the E-W DOV at the INS position utilizing data from the plurality of supermatrices, and finally compensating the direction of the gravity-model vector for the N-S DOV and the E-W DOV.

Gravity vector compensation system

The invention is a method for determining gravity in an inertial navigation system which periodically produces and stores in memory position coordinates. The method comprises the steps of (a) retrieving the most recently determined position coordinates, (b) determining coordinates L.sub.u, L.sub.n, H.sub.u, and H.sub.n from the position coordinates, L.sub.u and L.sub.n being predetermined functions of geodetic latitude and H.sub.u and H.sub.n being predetermined functions of geodetic altitude, (c) determining the vertical component of gravity by substituting either or both L.sub.u and H.sub.u in a first polynomial expression, (d) determining the north-south component of gravity by substituting either or both L.sub.n and H.sub.n in a second polynomial expression, and (e) utilizing the components of gravity determined in steps (c) and (d) in the next determination of the position coordinates.

Method for determining gravity in an inertial navigation system

The navigation apparatus with improved attitude determination is intended for use on a mobile platform. It combines data from a platform inertial navigation unit and carrier phase data for a plurality of GPS satellite signals received at a plurality of receiving points on the platform for the purpose of obtaining estimates of the navigation states of the platform. The navigation apparatus comprises a processor which computes estimates of the states from inputs comprising (1) one or more measured phase double-differences calculated from the measured satellite signal carrier phases, (2) the estimated position of the platform, (3) the estimated positions of the receiving points, and (4) the positions of the satellites, a phase double-difference being defined as the difference in phase differences for signals received from two satellites and a phase difference being defined as the difference in carrier phase of a satellite signal received at two receiving points. The navigation and attitude determination solution is obtained by means of a Kalman filter process wherein the observables comprise measured phase double-differences and each predicted phase double-difference is obtained by operating on the Kalman state vector with an observation matrix defined by linearizing the equations relating the phase double-difference to the navigation states.

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Agoura Hills, CA, United States of America

David Y Hsu