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Instrument: LRA : Laser Retroreflector Array |
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Associated Platforms OSTM/JASON-2 JASON-1 TOPEX/POSEIDON Spectral/Frequency Information Wavelength Keyword: Visible Number Channels: 1 Channel Spectral/Frequency Coverage/Range: 532 nm (primary) Wavelength Keyword: Near Infrared Number Channels: 1 Channel Spectral/Frequency Coverage/Range: 1064 nm (secondary) Related Data Sets View all records related to this instrument Description The Laser Retroreflector Array (LRA) is used to calibrate the other location systems on the satellite with a very high degree of precision. The ability to determine a satellites precise position on orbit is critical in interpreting altimetry data used for measuring ocean surface topography. LRA is a totally passive reflector designed to reflect laser pulses back to their point of origin on Earth. It consists of nine 39 millimeter quartz corner-cube reflectors arrayed on a circular structure on the satellites nadir side (facing Earth). A corner-cube reflector is a special type of mirror that always reflects an incoming light beam back in the direction from which it came. The retroreflectors are optimized for a wavelength of 532 nm (green), providing a field of view of about 100ý. The eight equally spaced peripheral cubes are oriented at 50 degrees with respect to NADIR. The array structure is aluminum alloy and the corner cubes are constrained to allow for the differential thermal expansion of the structure and the quartz corner cubes. The LRA is an array of mirrors onboard the satellite that provides a target for laser-tracking measurements from ground stations. By analyzing the round-trip time of the laser beam, it is possible to determine precisely where the satellite is on its orbit. The laser-tracking data are analyzed to calculate the satellites altitude to within a few mm; however, because there are a small number (1015) of ground stations and the laser beams are sensitive to weather conditions, it is not possible to track the satellite continuously using the LRA alone. That is why other location systems are needed on board the satellite. Key LRA Facts Heritage: TOPEX/Poseidon Function: Laser-tracking targets Configuration: 9 corner cubes: 1 nadir looking, 8 arrayed azimuthally in truncated cone FOV: 110ý w/1.5 arcsec dihedral angle per cube Dimensions: Each cube is 163-mm diameter ý 66-mm height Mass: 0. 8 kg Duty Cycle: 100% Thermal Operating Range: -65ý to 95ý C Online Resources http://god.tksc.jaxa.jp/ad2/lrra/main.html http://sealevel.jpl.nasa.gov/technology/instrument-lra.html Instrument Logistics Instrument Start Date: 2002-01-15 Instrument Owner: USA/NASA JAXA Instrument Start Date: 1992-09-23 Instrument Stop Date: 2005-10-09 |
