DDA 36th Meeting, 10-14 April 2005
Session 13 The Quest for Precision
Oral, Wednesday, April 13, 2005, 3:05-5:45pm

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[13.01] Laser Ranging to Vulnerable Targets

P. J. Shelus, B. E. Schutz, C. E. Webb, R. L. Ricklefs, H. J. Rim, S. P. Yoon, J. G. Ries (CSR, University of Texas at Austin)

Entering a new century, we also enter a new phase of laser ranging. There are now a number of satellites that fire laser pulses toward the surface of the object about which they orbit. These are satellites like MOLA, orbiting Mars, and Earth-orbiting satellites, like ICESat and ADEOS. Like other satellites, they require precision tracking and some tracking comes from the laser ranging network. However, with sensitive downward looking detectors, instrumentation could be harmed by incoming radiation. Also, with some missions, target specific restrictions become an important issue for routine laser ranging. For example, precision orbit determination (POD) for ICESat is performed using GPS data from on-board instrumentation. But, SLR observations provide a verification of GPS-based results. We use ICESat, under carefully managed SLR operations, to test logistics for target-specific restrictions. Several stations, MLRS, Zimmerwald, Graz, and the NASA MOBLASís, have automatic elevation-initiated laser cut-off. They observe ICESat under the restriction that ranging not be performed when ICESat has an elevation greater than 70 degrees. Further, ICESat performs active off-nadir pointing. Even though ICESat may be at an elevation less than 70 degrees as seen from a station, it might still be possible for a station to shoot up the barrel. Communications must exist between ICESat operations and cooperating SLR stations to assure that ranging is not performed when ICESat may be pointed at that station. Finally, because of the spottiness of SLR data for ICESat, with operational outages and the fact that only a sub-set of the SLR network is used for ICESat ranging, predictions based only upon SLR data might not satisfy tracking requirements. For that, we prepare SLR predicts using data from ICESatís on-board GPS navigation files. Here, we expand upon these points, present the pit-falls encountered, review the SLR data obtained, and assess the successes. We acknowledge NASA support.


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