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GPS and new ATC technology
From: David Farber <dave () farber net>
Date: Sat, 1 Sep 2007 13:49:25 -0400
Begin forwarded message: From: "Mike O'Dell" <mo () ccr org> Date: September 1, 2007 12:30:52 PM EDT To: David Farber <dave () farber net> Subject: GPS and new ATC technology GPS is wonderful, when it works, but it doesn't work everywhere all the time for various reasons, and not just because of hostile actions. urban canyons, natural canyons, heavy tree canopy, tunnels, and under areas with metal roofs, for a few examples. and it isn't that hard to jam a GPS signal, or at least desensitize a GPS receiver so it can't hear the real, very tiny signals from the satellites. An FAA study has concluded that before we make GPS the primary guidance system for commercial aircraft, there *must* be a reliable backup system which has very different failure modes so the likelihood of simultaneous outages (or "loss of precision") is extremely unlikely. the only existing alternative is LORAN-C, ideally augmented with "eLoran" capabilities. the existing LORAN-C infrastructure has recently been updated. new solid-state transmitters have dramatically reduced the phase noise on the signals and new cesium clocks have dramatically increased the stability. eLoran is a receiver-side technology which exploits all the work developing "all satellites in view" algorithms for GPS receivers to provide "all chains in view" capability. a modern eLoran receiver can track multiple 10s of Loran stations simultaneously, and by using quadrature antennas and knowledge of the extremely precise surveyed locations of the Loran stations, an eLoran receiver can also provide absolute heading information *without* requiring platform motion (required by single-receiver GPS for path-over-ground). further, an inexpensive eLoran receiver can also integrate a GPS receiver in the same housing, and together they can provide the absolute positioning ability of GPS ("go to Lat/Lon xxx/yyy on the other side of the world within so many meters") with the very high repeatability of Loran ("return to *this* spot precisely") and the ability to generate static absolute heading. such eLoran receivers are already down to circa $750 street price (SiTex eLoran) and that's without high volumes. The only problem is that in spite of all this, LORAN-C is an unloved stepchild with continued funding in serious jeopardy. Only a few million dollars *per year* are required to maintain and operate the just-upgraded LORAN-C infrastructure, but nobody can seem to find the funds. the US Coast Guard, who paid for much of the upgrade, is all but running bake sales to fund their existing "coastal defense" mission and doesn't have the money, and while LORAN-C is being used by the trucking industry for vehicle tracking, not to mention the identified need as a backup for GPS-based Air Traffic Control, Dept of Transportation cannot find any money under the couch cushions, either. so LORAN-C is scheduled to be shut down because they cannot maintain the system, and a navigation system that gives wrong answers is worse than no system at all.again we have an astonishing example of "penny-wise and pound foolishness"
that just boggles the mind. yeah, i now - take a number. -mo ------------------------------------------- Archives: http://v2.listbox.com/member/archive/247/=now RSS Feed: http://v2.listbox.com/member/archive/rss/247/ Powered by Listbox: http://www.listbox.com
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- GPS and new ATC technology David Farber (Sep 01)