Error analysis for the Global Positioning System: Difference between revisions

Revision as of 19:22, 2 August 2011

Revision as of 06:04, 18 August 2011

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Selective Availability is still a system capability of GPS, and could, in theory, be reintroduced at any time. In practice, in view of the hazards and costs this would induce for U.S. and foreign shipping, it is unlikely to be reintroduced, and various government agencies, including the [[FAA]],<ref>{{cite web|url=http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/faq/gps/index.cfm#ad3|title=GNSS - Frequently Asked Questions - GPS: Will SA ever be turned back on?|publisher=FAA|accessdate=2007-12-17|date=June 13, 2007}}</ref> have stated that it is not intended to be reintroduced.

One interesting side effect of the Selective Availability hardware is the capability to add corrections to the outgoing signal of the GPS [[caesium|cesium]] and [[rubidium]] [[atomic clocks]] to an accuracy of approximately 2&nbsp;×&nbsp;10⁻¹³<!-- What units? Hz? kHz? MHz? Answer: This is a dimensionless ratio. For example, 1 s/ 5 trillion s gives one in five trillion.-->. This represented a significant improvement over the raw accuracy of the clocks.{{Citation needed|date=March 2007}}

On 19 September 2007, the [[United States Department of Defense]] announced that future [[GPS modernization|GPS III]] satellites will not be capable of implementing SA,<ref>{{cite web | url = http://www.defenselink.mil/releases/release.aspx?releaseid=11335 | title = DoD Permanently Discontinues Procurement Of Global Positioning System Selective Availability | publisher = DefenseLink | date = September 18, 2007 | accessdate = 2008-02-20}}</ref> eventually making the policy permanent.<ref>{{cite web | url = http://pnt.gov/public/sa/ | title = Selective Availability | publisher = National space-based Positioning, Navigation, and Timing Executive Committee | accessdate = 2008-02-20}}</ref>