Saturday, January 06, 2007

Patent Application for Operating Satellites in Tundra Orbits to Reduce Receiver Buffering Requirements for Time Diversity Signals

This is a patent application for Sirius, right? Wrong. This is an XM application. Sirius operates its satellites in a Tundra Orbit, but recently applied to operate a geostationary satellite. XM satellites are in geostationary orbit. Is XM thinking about changing orbits?

This application was published by the European Patent Office late last year on November 08, 2006. It is not uncommon that after receiving a US Patent that they following up with international patent applications. Sure enough, I found this XM patent granted on August 27, 2002. So, no, XM is not changing the orbits, but they did think about the Tundra orbits at one time and perhaps they might use it for satellite radio operations in other parts of the world, if they ever decide to go international. It caught our eyes. Thought it might be related to an international operation, but on a second look, it probably doesn't mean much.

Method and Apparatus for Selectively Operating Satellites in Tundra Orbits to Reduce Receiver Buffering Requirements for Time Diversity Signals

Abstract of EP1720266
A method for controlling first, second and third geosynchronous satellites in tundra orbits in three orbital planes in a time diversity system, the time diversity system providing both an early satellite signal and a late satellite signal to receivers, the late satellite signal corresponding to a delayed early satellite signal, the satellites each traversing a common ground track having a northern loop a southern loop, and a crossover point between the northern and southern loops, the southern loop being intersected via the equator, the method comprising the steps of: powering on a first satellite that is ascending said southern loop from the equator; operating a second satellite at apogee as a lite satellite to provide said late satellite signal to said receivers; powering down a third after descending the southern loop below the equator, said third satellite having operated as an early satellite to provide said early signal to said receivers prior to reaching an orbital position near the equator; operating said first satellite as said late satellite when said first satellite reaches said crossover point, said first satellite operating as said late satellite while said first satellite traverses said northern loop; and switching operation of said second satellite from operation as said late satellite to operation as said early satellite when said second satellite traverses said crossover point to commence its descent of said southern loop.

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