Satellites too reliable for GPS’ (and U.S.’) good

Aviation International News » November 2006
November 9, 2006, 5:40 AM

GPS Satellite SVN-15 will celebrate its 16th birthday in space this month, and by next spring it will have circled the earth 12,000 times (roughly twice a day), continuously transmitting navigation signals to us. That’s amazing performance, especially considering that its original orbital life was expected to be 7.5 years. As the last remaining member of the USAF’s early Block II GPS space vehicles, Number 15 is a great tribute to the engineers who designed it. However, its reliability is creating some obstacles for the engineers who designed newer-generation satellites.

The Block IIs were the second generation of GPS satellites, and over time they have been replaced by progressively more advanced Block IIAs, then IIRs and IIRMs. Eventually, even more improved IIF space vehicles will follow, with Block IIIs to come much later. There are 30 satellites of various vintages in the GPS constellation, including one of the new Block IIRMs launched on September 25.

The 16th anniversary of the satellite is a mixed blessing, because as long as the satellite–and other old-timers like it–keeps flying, DOD policy decrees that more capable satellites can’t be sent up to replace them. SVN-15’s onboard systems are therefore controlled by pre-1990 computer technology. But DOD’s policy means that the latest Block IIF versions, which will transmit a third civil frequency to counter ionospheric “noise”–the major source of GPS position errors–will have to wait in the wings a little longer.

Just how much longer is hard to tell. GPS satellite life-expectancy forecasts presented by the USAF at the Institute of Navigation’s GNSS Conference in Fort Worth in September predicted SVN-15’s demise in early/midsummer next year.

And the Block IIA satellites that followed it into space appear equally tenacious. All 15 of them have now exceeded their predicted 7.5-year orbital lives, with three exceeding 14 years and three more pushing that date. However, a USAF spokesman described 13 of those 15 as “one component away from navigation mission failure,” and 12 were forecast to die by 2010.

Europe Gets a Leg Up
Unfortunately, the unexpected longevity of the older satellites hampers more than GPS modernization. It could also have a potentially negative effect on U.S. space superiority. The DOD’s budget is currently under severe pressure, making GPS modernization–the Block III constellation in particular–less of a priority for the agency. DOD officials have described Block III as incorporating major advances over all the earlier Block II variants in power, accuracy, jamming resistance and several other performance-enhancing features. But it has always cautiously downplayed GPS-III’s planned competitive advantage over Europe’s Galileo navigation satellites, scheduled to be in worldwide operation by 2010.

In 2002 the USAF expected the first Block III launch in 2005, with all earlier satellite versions replaced by Block IIIs in 2011. Those dates have slipped gradually, and now the most recent forecast predicts the first launch for 2014, and with the completely renewed constellation date now estimated as not before 2018.

Reportedly, the delay comes partly from efforts to reduce the cost of these new satellites, which is speculated to have been first estimated at between two and three times that of their predecessors. Boeing and Lockheed Martin are the USAF’s chosen competitors for the Block III development and production contract. That contract was scheduled to have been awarded earlier this year but instead both firms were given “risk reduction” study contracts, said to be a Pentagon euphemism for “get those prices down.” The final contract award is now expected in early 2008.

Meanwhile, the gap between the new GPS III constellation and Galileo seems
to be slowly widening, with European spokesmen at the Fort Worth conference expressing confidence in their 2010 start date–a view now shared by some U.S. industry observers. Helping the Europeans is the fact that Galileo’s satellites are not burdened with anti-radiation shielding to protect against enemy nuclear attacks in space, as well as other military requirements such as the ability to immediately detect, pinpoint and report atomic weapons test explosions anywhere on earth.

Freed from these constraints, four of Galileo’s smaller satellites can be launched in a single rocket, compared to a single GPS space vehicle. One high-level space scientist, who preferred to remain anonymous, told AIN at Fort Worth that there could be a “substantial shift of allegiance” from GPS to Galileo if the European constellation becomes fully operational “even just a couple of years” before GPS III. In this, he was echoing the sentiment of the U.S. Defense Research Board that “Galileo could marginalize GPS to an expensive system only for military use.”

Galileo’s arrival won’t affect the performance of current GPS units although, unlike future receivers designed to use both GPS and Galileo–and perhaps Russia’s glonass satnav system–they won’t be able to take advantage of the new capabilities the European system will offer. But if Galileo enters operation more or less on schedule, and the time to full GPS III operation can’t be shortened, the U.S. might find itself in full catch-up mode for several years.

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