Optoelectronic sensor systems are being developed for use in maintaining fixed relative orientations of two scientific- instrument platforms that are in relative motion. In the original intended application, the platforms would be two spacecraft flying in formation and separated by a long baseline. In principle, sensor systems of this type could also be used in terrestrial applications for maintaining alignments between moving instrument platforms. The sensor system would utilize beacon laser beams that would be transmitted by the platforms in the normal course of scientific measurements. The frequency of the returned laser beam would differ by about 5 MHz. On each platform, the transmitted laser beam and the laser beam bounced off the other platform would be focused onto a quadrant photodetector, where the interference between the laser beams would give rise to sinusoidal (beat-frequency) signals on all four quadrants. The differences among the phases of the beat-frequency signals in the quadrants would depend on, and would be used to determine the angle between, the wave fronts of the outgoing and incoming laser beams.
This work was done by Carl Liebe, Alexander Abramovici, Jacob Chapsky, Daniel Shaddock, Charles Harb, and Frank Dekens of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-40610
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Sensors for Pointing Moving Instruments Toward Each Other
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Overview
The document is a New Technology Reporting Form from the Jet Propulsion Laboratory (JPL) at the California Institute of Technology, detailing a novel pointing sensor technology developed for spacecraft. This technology addresses the challenge of accurately determining the relative orientation of spacecraft that are positioned at vast distances from one another, which is crucial for missions like the Laser Interferometer Space Antenna (LISA).
The core innovation involves using laser beams as optical beacons emitted from each spacecraft. These beams are Doppler-shifted due to the relative motion of the spacecraft, creating a beat signal of approximately 5 MHz when the outgoing and incoming beams interact. This interaction generates sinusoidal signals across four quadrants of a quad cell, with the phase differences in these signals indicating the angle of the wavefront, thus allowing for precise measurement of the spacecraft's orientation relative to one another.
The document outlines the motivation behind this technology, emphasizing the necessity for high accuracy in locking the orientation of multiple spacecraft for scientific measurements. Traditional methods of tracking spacecraft involve imaging optics to lock their positions, but this new sensor technology offers a more effective solution by measuring the angle of the laser wavefront.
The report also discusses the development status of the technology, noting that while a prototype has been built and tested, further development is needed to demonstrate its capabilities at realistic power levels. The technology is not intended for commercial semiconductor applications but is aimed at scientific uses, particularly in space missions involving formation flying of spacecraft.
Additionally, the document highlights the collaborative nature of the project, mentioning contributions from various JPL personnel and plans for future disclosures at conferences. It indicates that the technology has not yet been published or presented outside of JPL, but there are intentions to share findings with the broader scientific community.
In summary, this document presents a significant advancement in spacecraft orientation technology, with potential applications in future NASA missions, particularly those requiring precise formation flying and coordination between multiple spacecraft.
