@prefix ns0: . @prefix skos: . ns0:resource [ ] ; ns0:altLabel [ ] ; skos:definition """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 satellite’s 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 satellite’s 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 satellite’s altitude to within a few mm; however, because there are a small number (10–15) 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 Group: Instrument_Details Entry_ID: LRA Group: Instrument_Identification Instrument_Category: Earth Remote Sensing Instruments Instrument_Class: Passive Remote Sensing Instrument_Type: Positioning/Navigation Instrument_Subtype: Laser Ranging Short_Name: LRA Long_Name: Laser Retroreflector Array End_Group Group: Associated_Platforms Short_Name: OSTM/JASON-2 Short_Name: JASON-1 Short_Name: TOPEX/POSEIDON End_Group Group: Spectral_Frequency_Information Wavelength_Keyword: Visible Number_Channels: 1 Channel Spectral_Frequency_Coverage_Range: 532 nm (primary) End_Group Group: Spectral_Frequency_Information Wavelength_Keyword: Near Infrared Number_Channels: 1 Channel Spectral_Frequency_Coverage_Range: 1064 nm (secondary) End_Group Online_Resource: http://god.tksc.jaxa.jp/ad2/lrra/main.html Online_Resource: http://sealevel.jpl.nasa.gov/technology/instrument-lra.html Sample_Image: http://argonautica.jason.oceanobs.com/images/missions/tp/image1.gif Creation_Date: 2007-04-16 Group: Instrument_Logistics Instrument_Start_Date: 2002-01-15 Instrument_Owner: USA/NASA Instrument_Owner: JAXA End_Group Group: Instrument_Logistics Instrument_Start_Date: 1992-09-23 Instrument_Stop_Date: 2005-10-09 End_Group End_Group"""@en ; skos:prefLabel "LRA"@en ; skos:inScheme ; skos:broader ; a skos:Concept . skos:prefLabel "Laser Ranging"@en ; a skos:Concept ; skos:narrower .