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    Re: GPS Maybe Not as Healthy as Thought
    From: Richard B. Langley
    Date: 2009 May 22, 17:19 -0300

    Some news reports have been more measured:
    Quoting frankreed@HistoricalAtlas.com:
    > I've read the GAO report all the way through and also the Air Force replies on the
    > matter. I think this issue has been over-blown by the media. They're quoting the
    > first page summary of the report, and like most GAO reports, it's intentionally
    > dire.
    > For marine navigation, the potential reduction in active GPS satellites is not likely
    > to be noticeable. Marine users have the best conditions for GPS signal acquisition.
    > From a boat at sea, a GPS receiver can generally "see" the whole sky and reduced
    > numbers of satellites will rarely matter (unless there is a major program delay, see
    > below, which would not have a practical impact until about 2014).
    > The one market that may be adversely affected, sooner rather than later, is "urban
    > canyon" navigation since those users benefit most from the excess satellite capacity
    > which currently exists (far from being in trouble, the US GPS constellation currently
    > has EXCESS capacity). These are the car navigation and mobile phone location
    > services, for example, which are becoming dramatically more popular with each passing
    > year. Since these services are already impaired in environments like this where GPS
    > signals propagate poorly, if at all, this report will probably encourage more rapid
    > adoption of alternative location services like SkyHook (that's the one based on
    > triangulation of home and business Wi-Fi signals). The challenge is to make the
    > hand-off between GPS and other services seamless and invisible to the end-user.
    > There are two issues raised in later sections of the GAO report which are serious and
    > more relevant than the supposed increased risk in 2010. The first of these is the
    > potential decline in service that could result if there is a serious delay in the
    > launches of the next series of satellites, the GPS-III satellites. If they're delayed
    > by two years, then there could be a serious disruption in the US GPS signals starting
    > around 2014 and lasting for as long as seven years. Have a look at figures 4 and 5 in
    > the GAO report. Although GAO reports are intentionally pessimistic, I believe that
    > the low probability of having a full GPS constellation around 2017 is realistic. That
    > is, it's realistic IF there is a significant delay in the GPS-III program. But note
    > that the EU's Galileo system as well as the Russian GLONASS systems are expected to
    > be fully operational in this period. So this isn't an issue for global navigation
    > directly; it's an issue for US-pre-eminence in the satellite navigation business, and
    > it's an issue for the US military which would be loath to rely on a non-US
    > position-finding system. Beyond the specifics of the GAO report, the US Air Force
    > claims that they already have procedures lined up which would extend the lives of
    > existing satellites (mainly by powering down other military hardware on the
    > satellites) and so even this supposed gap could potentially be covered.
    > The second significant problem outlined in the GAO report applies only to the US
    > military. They haven't funded receivers to take advantage of the new satellites'
    > capabilities. There are details in the report.
    > To sum up, the "sky is falling" media reports are misleading. The GPS system is not
    > on the verge of failure in 2010. However, it is on the verge of disappointing, to
    > some extent, the rapidly growing commercial market for its services in urban areas
    > because the current excess capacity is considered temporary, and there are some
    > significant issues for the US military. So unless there is some major collapse in the
    > system unrelated to the issues in the GAO report, there do not appear to be any
    > significant issues for marine navigation with the single exception that marine users
    > may need to upgrade to systems capable of picking up signale from multiple satellite
    > constellations (GPS, GLONASS, Galileo, Beidou/Compass) at a somewhat earlier date
    > (c.2014) if the worst predictions in the GAO report are borne out.
    > -FER
    > PS: There are a couple of distinct reports on GPS from the GAO. The longer of them is
    > linked here.

    > > > > > =============================================================================== Richard B. Langley E-mail: lang@unb.ca Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ =============================================================================== --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavList-unsubscribe@fer3.com -~----------~----~----~----~------~----~------~--~---

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