73 results about "Star tracker" patented technology

A closed-loop LRF pointing technology to measure the range of a target satellite from a chaser satellite for rendezvous is provided that includes several component technologies: LOS angle measurements of the target satellite on a visible sensor focal plane and the angles' relationships with the relative position of the target in inertial or LVLH frame, a relative navigation Kalman filter, attitude determination of the visible sensor with gyros, star trackers and a Kalman filter, pointing and rate commands for tracking the target, and an attitude controller. An analytical, steady-state, three-axis, six-state Kalman filter is provided for attitude determination. The system and its component technologies provide improved functionality and precision for relative navigation, attitude determination, pointing, and tracking for rendezvous. Kalman filters are designed specifically for the architecture of the closed-loop system to allow for pointing the laser rangefinder to a target even if a visible sensor, a laser rangefinder, gyros and a star tracker are misaligned and the LOS angle measurements from the visible sensor are interrupted.

A method of determining the attitude of a spinning spacecraft is provided. The method includes stabilizing the spacecraft, initializing the attitude of the spacecraft using star tracker data, and estimating the attitude of the spacecraft.

A method of and apparatus for determining and controlling the inertial attitude of a spinning artificial satellite without using a suite of inertial gyroscopes. The method and apparatus operate by tracking three astronomical objects near the Earth's ecliptic pole and the satellite's and/or star tracker's spin axis and processing the track information. The method and apparatus include steps and means for selecting preferably three astronomical objects using a histogram method and determining a square of a first radius (R₁²) of a track of a first astronomical object; determining a square of a second radius (R₂²) of a track of a second astronomical object; determining a square of a third radius (R₃²) of a track of a third astronomical object; determining the inertial attitude of the spin axis using the squares of the first, second, and third radii (R₁², R₂², and R₃²) to calculate pitch, yaw, and roll rate; determining a change in the pitch and yaw of the artificial satellite; and controlling on-board generated current flow to various orthogonally-disposed current-carrying loops to act against the Earth's magnetic field and to apply gyroscopic precession to the spinning satellite to correct and maintain its optimum inertial attitude.

Various embodiments of the present invention provide methods, systems, apparatus, and computer program products for providing integrated attitude determination and attitude control for slewing of a satellite. In one embodiment a method is provided. The method comprises after receiving a repointing request, selecting a guide star sample comprising one or more guide stars from a guide star catalog; determining current attitude information; selecting and retrieving at least one point spread function (PSF) image from a PSF library; estimating an expected position for at least one guide star, the at least one guide star being one of the guide stars of the guide star sample; acquiring at least one star tracker image; calculating a cross-correlation function (CCF) to determine shifts in position of the at least one guide star compared to the expected position; and determining updated current attitude information based at least in part on the determined shifts in position.

A method of and apparatus for determining and controlling the inertial attitude of a spinning artificial satellite without using a suite of inertial gyroscopes. The method and apparatus operate by tracking three astronomical objects near the Earth's ecliptic pole and the satellite's and/or star tracker's spin axis and processing the track information. The method and apparatus include steps and means for selecting preferably three astronomical objects using a histogram method and determining a square of a first radius (R₁²) of a track of a first astronomical object; determining a square of a second radius (R₂²) of a track of a second astronomical object; determining a square of a third radius (R₃²) of a track of a third astronomical object; determining the inertial attitude of the spin axis using the squares of the first, second, and third radii (R₁², R₂², and R₃²) to calculate pitch, yaw, and roll rate; determining a change in the pitch and yaw of the artificial satellite; and controlling on-board generated current flow to various orthogonally-disposed current-carrying loops to act against the Earth's magnetic field and to apply gyroscopic precession to the spinning satellite to correct and maintain its optimum inertial attitude.

A method of estimating the alignment of a star sensor (20) for a vehicle (12) includes generating star tracker data. A vehicle attitude and a star sensor attitude are determined in response to the star tracker data. A current alignment sample is generated in response to the vehicle attitude and the star sensor attitude. A current refined estimate alignment signal is generated in response to the current alignment sample and a previously refined estimate alignment signal via a vehicle on-board filter (38).

The invention relates to the modification to the tracking method of the star tracker. The process includes: it gets the reference star map of the K+1 frame by the star mapping; the every star in the star map collected by the (K+1) frame is matched to the star in the reference star map of the K+1 frame; the character is to map the star by the threshold value mapping; while it searches the star by the zone catalogue; in the matching process, it arrays the sequence firstly then to match. The computing of the invention cost the short time, so it has the high speed.

The invention relates to the space technology, and to the improvement of the star sensor calibration method. The invention uses the calibration system which including air cushion platform, single-star starlight simulator, star tracker, two-dimensional axial turntable platform and data-processing computer, its steps being: establishing point spread function model, establishing a centroid algorithm formula, establishing a centroid algorithm pixel frequency error model, and data acquisition. The invention provides a more practical point spread model; improving satellite sensor calibration precision; the calibration model is simple and easy to calculate.

The invention provides a method for correcting the influence of atmospheric refraction on the precision of a star sensor, which comprises the following steps: according to the optic axis orientation of an image of the star sensor, calculating the zenith distance of the optic axis orientation of the star sensor; recognizing the star image coordinates of fixed stars in the viewing field of the starsensor by using a star map recognition algorithm; calculating the zenith distances of the recognized fixed stars in the viewing field of the star sensor; decomposing an atmospheric refraction value into an X-axis direction component and a Y-axis direction component under an image space coordinate system of the star sensor; and subtracting the deviation delta X and delta Y (arising from the atmospheric refraction value) from all successfully-recognized star images of the fixed stars, thus calculating attitude quaternions. When the influence of atmospheric refraction is eliminated, the star sensor can provide high-precision navigation information for shipborne, missile-mounted and airborne aircraft and other aircraft which carry out low-altitude flying; and after carriers adopt atmospheric-refraction-corrected high-precision navigation information, a basis is provided for planning a better navigation path for the carriers, thereby further reducing the fuel consumption of the carriers and improving the efficiency.

Methods and apparatus automatically determine a location, such as of an aircraft or spacecraft, by matching images of terrain below the craft, as captured by a camera, radar, etc. in the craft, with known or predicted terrain landmark data stored in an electronic data store. A star tracker measures attitude of the camera. An additional navigation aiding sensor provides additional navigational data. Optionally, a rangefinder measures altitude of the camera above the terrain. A navigation filter uses the attitude, the additional navigational data, and optionally the altitude, to resolve attitude, and optionally altitude, ambiguities and thereby avoid location solution errors common in prior art terrain matching navigation systems.

The invention discloses an accuracy measurement system for a star sensor. The accuracy measurement system comprises a fixer and a star sensor accuracy measurement unit, wherein the fixer is used for fixing the star sensor to make a main shaft of the star sensor aligned with a zenith; the star sensor accuracy measurement unit is used for measuring the accuracy of a navigation star; a test startingmoment T is input into the star sensor; a direction vector under a J2000.0 rectangular coordinate system is determined according to declination, right ascension and apparent motion parameters of the navigation star under a J2000.0 coordinate system; the direction vector is converted into the direction vector under an epoch ecliptic coordinate system and then converted into a direction vector (VCRFT) under a celestial sphere coordinate system; the direction vector of the navigation star under the celestial sphere coordinate system is changed into a direction vector (VTRF) under an earth-fixed coordinate system; and based on the direction vector (VTRF) under the earth-fixed coordinate system, the accuracy of the star sensor is obtained. According to the accuracy measurement system provided by the invention, the star sensor is fixedly connected to the earth by using the accuracy of rotation of the earth, and the main shaft of the star sensor is aligned with the zenith for observation.

A chip scale star tracker that captures plane-wave starlight propagating in free space with a wafer-thin angle-sensitive broadband filter-aperture, and directs the light into a waveguide structure for readout. Angular information about the star source is determined from characteristics of the starlight propagating in the waveguide. Certain examples include internal propagation-constant-based baffling to elimination stray light from extreme angles.

A star tracker has an electronically steerable point of view, without requiring a precision aiming mechanism. The star tracker can be strapped down, thereby avoiding problems associated with precision aiming of mechanical devices. The star tracker images selectable narrow portions of a scene, such as the sky. Each stellar sighting can image a different portion of the sky, depending on which navigational star or group of navigational stars is of interest. The selectability of the portion of the sky imaged enables the star tracker to avoid unwanted light, such as from the sun.

A method for the automatic correction of alignment errors in individual star trackers (R, S) of star tracker systems (1) is provided. The correction of orientation errors is necessary whenever it is not possible to mount the star trackers of the star tracker system on a shared stable block of a platform. Orientation errors can arise due to installation deviations and deformation of the platform, for instance, caused by mechanical loads or temperature fluctuations. A star tracker (R) that is attached in a very stable manner to the platform serves as the reference tracker. The orientation that it measures constitutes the reference information. An error signal and an orientation matrix are derived from the measured orientation of the other star trackers, thereby effectuating the correction of the coordinate systems of the star trackers that are to be corrected, and thus of their measured quantities. The resulting orientation as the starting quantity of the star tracker system is then calculated on the basis of the orientation information of the reference tracker and of the other star trackers. The linking of the measured results of the individual star trackers can take place on the level of the star vectors of a star catalog, on the level of preprocessed tracker signals or on the level of the quaternions and/or on the level Euler angles.

A star tracker determines a location or orientation of an object, such as a space vehicle, by observing unpolarized light from one or more stars or other relatively bright navigational marks, without imaging optics, pixelated imaging sensors or associated pixel readout electronics. An angle of incidence of the light is determined by comparing signals from two or more differently polarized optical sensors. The star tracker may be fabricated on a thin substrate. Some embodiments have vertical profiles of essentially just their optical sensors. Some embodiments include micro-baffles to limit field of view of the optical sensors.

A navigation system includes a star camera having a field of view. The star camera includes a sun shields that selectively block portions of the star camera's field of view, to prevent unwanted light, such as light from the sun or moon, reaching image sensors of the star cameras. Some sun shields include x-y stages or r-θ stages to selectively position a light blocker to block the unwanted light. Some sun shields use positionable partially overlapping orthogonally polarized filters to block the unwanted light. Some sun shields use counter-wound spiral windows that are selectively rotated to block the unwanted light. Some sun shields a curved surface that defines a plurality of apertures fitted with individual mechanical or electronic shutters.