Barnes Engineering Company

Edo Corporation, Barnes Engineering Division

Other

Robert C Savoca

Gerald Falbel

Seymour C Spielberger

Todd J Bednarek

Carlo E Zaffanella

A staring horizon sensor is mounted on an orbiting satellite has one or more linear infrared detector arrays having the horizon being detected imaged thereon. The arrays are each connected in cyclic repetitive alternating polarity patterns for generating at least two output signals which are offset in phase. The output signals are processed to locate the position of the horizon on the arrays. The repetitive pattern interconnection of the elements in the arrays provide a focal plane data compression which reduces the bandwidth as well as the complexity of the processing electronics. In addition, interconnecting the detective elements in repetitive alternating polarity groups having a spatial frequency greater than the spatial frequency of the thermal variation of the horizon minimize any error due to the earth's thermal variations.

Staring horizon sensor

A multiple detector array is positioned in a satellite orbiting the earth for determining the attitude of the satellite with respect to the earth by detecting the earth's horizon. The multiple array of spaced detectors are mounted on a horizon sensor with a space detector viewing space, a horizon detector, with a field of view straddling the horizon and outer space space, a detector viewing the earth, and a gradient detector viewing the earth. Individual signals from these detectors are amplified and processed such that any gradients between the two earth viewing detectors are used to provide radiance compensation to correct for radiance errors in sensing the true position of the horizon.

Method and apparatus compensating for radiance variations in horizon

Continuous positional information for an orbiting body such as a spacecraft, satellite, or the like with respect to a reference body, for example, the sun, is provided by a first continuous sensor which continually views the sun from the orbiting body and generates electrical signals which provide two axis information on the orbiting body's position. Analog sensors of this type have low accuracy because of transfer function non-linearity, degradation due to environmental aging, or radiation effects and others. A second periodic sensor is directed at the reference body to provide periodic positional updates. These updates are used as references to which the instantaneous output of a continuous sensor are compared so that error associated with the output of the continuous sensor can be eliminated to the accuracy of the calibration. The first continuous sensor preferably utilizes a first and second double triangle detector arranged to form first and second rectangles each having a slot aperture mounted thereon for projecting a line image normal to each rectangle. The first and second double triangle detectors are arranged orthogonally with respect to each other. An algorithm is used to accurately locate the position of the slit shadows on the first and second detectors on the continuous sensor, and thus provide a continuous position for the reference body such as the sun. The second periodic sensor has a patterned detector mask positioned over a very small area detector for producing periodic positional updates which information can be used to correct the continuous sensor errors and provide an accurate analog sun position sensor.

Analog sun sensor

A horizon sensor orbiting the earth views the earth's horizon in at least two points in the earth's summer and winter hemisphere and calculates pitch and roll information therefrom. The summer pitch and roll information is calculated at intervals long with respect to pitch and roll rates, but short with respect to weather variation. The pitch and roll information is then periodically corrected during a predetermined correction interval using the summer hemisphere pitch and roll information.

Method for reducing radiance errors in earth sensors

At geosynchronous and other high altitudes a dual cone scanner has been a convenient way of determining both pitch and roll utilizing a single horizon sensor positioned on an orbiting spacecraft whose attitude is to be determined. However, for large roll angles, one of the scans may leave the earth or reference body defeating the purpose of the sensor. In accordance with the present invention, a third cone angle is scanned between the original two, thereby providing two good scans preserving the pitch and roll attitude information, even if one of the scans has rolled off of the reference body.

Tri-scan horizon sensor

A scanning sensor having a radiation detector is mounted on a spacecraft or satellite orbiting the earth. The scanner is pointed in such a way with respect to the orbit plane of the satellite that the instantaneous field of view of the detector crosses the region between the lower and upper limits of the travel of a celestial body in a year in order for the radiation detector of the earth sensor to encounter the celestial body at least once per orbit. Electrical signals based on the horizon crossing and the presence of a celestial body in the field of view of the detector are generated and used to derive Yaw, Pitch and Roll attitude information for the satellite with respect to the earth.

Scanning earth sensor using the sun's position for determining yaw

A conical scanner having a detector is mounted on a spinning satellite with the scaner axis directed normal to the satellite spin axis for scanning the detector over a great circle passing through the poles of the spin axis of the satellite and producing horizon crossing information of the bodies in the scanning path of the scanner. The scan rate of the conical scanner is synchroized with the spin rate of the satellite and then by slightly increasing or decreasing the scan rate of the conical scanner, successive crossings are precessed through the field of view of the detector for determining the orientation of the satellite with respect to the earth or other celestial body such as the sun or the moon with great accuracy. When the satellite is operated at high spin rates, the conical scanner is operated at a slower rotational speed allowing gaps between successive scans which are filled by precessing the conical scanner to fill in the gaps after several satellite rotations.

High-accuracy attitude sensor for spin stabilized satellite

A horizon sensor which senses the horizon and produces a signal which indicates orientation with respect thereto is provided for scanning the horizon or distant line of discontinuity in optical radiation by a detector sensitive to such radiation and using the signals generated by the detector in crossing the line of discontinuity in optical radiation for attitude control of moving bodies. A scanner for the detector has two successive reflecting elements in optical alignment with the detector for reflectively applying predetermined optical radiation from a scanned field of view which includes the line of discontinuity in optical radiation. Reststrohlen mirrors which absorb and transmit predetermined laser radiation and reflect said predetermined optical radiation comprise the two successive reflecting elements which perform the scanning for protecting the horizon sensor from laser radiation damage by preventing the application of the laser radiation from reaching the detector or other sensitive components of the horizon sensor.

Laser radiation protected horizon sensor with successive reststrahlen

Three axis attitude information is provided by a horizon sensor for a spin stabilized satellite having an optical system on the spinning member viewing normal to the spin axis with a linear array of detectors in its focal plane which scans a zone around the earth. The detectors are self scanned and sensitive to visible and UV light and respond to the sun illuminated crescent of the earth, moon, stars or other illuminated bodies. Accordingly, a linear array of detectors mounted on a rotating portion of the satellite views a line in space which scans a zone on the celestial sphere and from the position of two celestial objects within this zone such as the earth and the sun, and the known time, pitch, roll and yaw can be established. The system also has an automatic alignment feature in which the array can be accurately aligned with the spin axis and any misalignment can be determined from orbital data and corrections made in flight. With the wide 360.degree. scan it is not necessary to sense the earth to determine attitude and having knowledge of the time and ephemeris data the position of any two objects such as the sun and the moon, a star or a planet is sufficient.

Fan scan horizon sensor for a spin stabilized satellite

Pitch and roll attitude information of an orbiting body is provided by sensing the discontinuity of optical radiation in a scan field of view between the reference body and outer space using a scanner which simultaneously scans two concentric conical paths through the field of view about the same axis of rotation of the orbiting body. The scanner comprises a scanning mirror split into two halves which are tilted through an angle with respect to each other and are also displaced in phase with respect to each other about the axis of rotation. The scanner may also be a prism having angled faces on opposite sides of the optical axis of the scanner which are also displaced in phase. Either scanner results in having a detector view two instantaneous fields of view simultaneously. An infrared detector receiving the radiation from these two fields of view produces signals which can be used to determine pitch and roll attidue as well as altitude on each scan which identifies four points around the horizon. This is all accomplished using but a single conical scanner.

Dual field horizon scanner

A radiation detector is scanned over two fan fields of view by first and second cylindrical lenses spaced about the axis of rotation of a common optical element positioned on the axis of rotation. The optical element is rotated about the optical axis by a motor or the rotation of the orbiting body on which the scanner is mounted. In one form the common optical element is a chisel mirror having the first and second cylindrical lenses positioned on opposite sides thereof and tilted at an angle of 45.degree. with respect to the axis of rotation producing two fan fields which are 180.degree. apart in phase. As an alternative the common optical element may comprise a cylinder having the second cylindrical lens positioned along with a bevelled reflective upper surface for producing a vertical fan field. The cylindrical lenses and common optical element may be incorporated in a conical scanner employing an infrared detector which systems can be combined to produce yaw, pitch, roll, attitude information in a single horizon sensor head.

Yaw sensing conical scanner horizon sensor

A hand-held radiometer for non-contact temperature measurement of objects is provided with a probe which is adapted to be mounted on the optical barrel of the radiometer to permit the radiometer to which it is attached to provide contact temperature measurements. The probe comprises a thin plastic film of low thermal mass which is shaped on one end thereof to be easily deformed when brought into contact with a specimen whose temperature is desired to be measured. The inner surface of the plastic film has a high emissivity, and a retainer means is provided on the other end of the thin plastic film for mounting the probe on the optical barrel of the radiometer.

Growing community of inventors

Ridgefield, CT, United States of America

Robert C Savoca