IT IS annoying enough when you board a plane in New York bound for San Francisco only to end up in Los Angeles because the Bay Area is fogged in (which has happened to your correspondent twice). It would be downright unnerving if it happened because the air-traffic control system directed the plane there by mistake.
The ?NextGen? air-traffic control system, which uses GPS satellites to pin-point every plane?s precise position in the sky once a second, plus onboard radios that let each aircraft continually see (and be seen by) all others nearby, is to be rolled out in 2012 and fully implemented by 2022. Replacing today?s patchwork of ground-based air-traffic control radars that sweep a small arc of airspace every 12 seconds?and lose aircraft between scans and as soon as they go out of range?with a blanketing mesh of GPS satellite signals should allow planes travelling busy routes to steer clear of one another, while flying in tighter formations though crowded airspace. The aim is to save fuel, time and lives, while handling an ever increasing amount of air traffic (see "Unfriendly skies", November 9th 2007).
And so it would except that, due to regulatory haste and shortsightedness, GPS coverage of America could soon go dark in places and become patchy elsewhere. Not only airlines would suffer. There are over 500m GPS receivers in use throughout the United States. Motorists, mobile-phone users, boat-owners, television broadcasters, the police, the armed forces, the emergency services and even farmers would be adversely affected. The Federal Aviation Administration (FAA) reckons it would cost airlines, in particular, more than $70 billion over the next ten years if they had to find fixes to cope with a GPS blackout. A leaked report suggests the airlines' loss of GPS services would also precipitate some 800 fatalities during that period.
The ultimate source of the trouble is a decision made in 2003 by the Federal Communications Commission (FCC) to grant special dispensation to a broadband satellite operator called SkyTerra, allowing it to fill gaps in its coverage by means of ground-based transmitters. SkyTerra?s chunk of spectrum (1,525-1,559 megahertz) abutted a crucial frequency (1,575 megahertz) used by GPS satellites. However, SkyTerra?s signals being mere whispers from space and its few proposed ground stations designed to operate at low power, any threat to GPS was dismissed as highly unlikely.
Everything changed when Harbinger Capital Partners, a New York-based investment firm founded by subprime-mortgage billionaire Philip Falcone, bought SkyTerra in 2010 and renamed it LightSquared. For Mr Falcone, the attraction was three-fold: SkyTerra?s swathe of under-used frequencies; its licence to provide a nation-wide internet service; and, above all, the FCC?s waiver allowing it to use ground-based transmitters where satellite reception was poor.
Mr Falcone quickly persuaded the FCC to rewrite the former SkyTerra licence. Instead of being conditional on offering an internet service primarily by satellite, with ground stations filling in only where satellite coverage was inadequate, the revised licence accepts that the network will rely almost exclusively on terrestrial transmitters.
And not just low-powered ones for serving inner cities. The company intends to build a broadband wireless network comprising 40,000 base-stations across the United States. These stations will put out 15,000 watts apiece. Typical mobile-phone transmitters in urban areas radiate between five and ten watts. Even the 100-foot towers used in open countryside transmit no more than 60 watts.
Source: http://www.economist.com/blogs/babbage/2011/08/gps-fiasco?fsrc=rss
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