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GPS performance could degrade but won't fail, Air Force says
- — 22 May, 2009 06:40
The Global Positioning System in use by the U.S. military, as well as millions of motorists globally as they navigate roadways, is not in danger of going down, although there is some risk of degraded performance as reported by a government accountability group, an Air Force colonel said in a Twitter forum.
"No, the GPS will not go down," said Col. Dave Buckman, command lead for position, navigation and timing at the Peterson Air Force Space Command in Colorado. However, citing an earlier report by the Government Accountability Office, the investigative arm of Congress, Buckman added, "GAO points out, there is potential risk associated with a degradation in GPS performance."
Buckman commented during a one-hour session yesterday on the command's Twitter page. A transcript of the questions and answers appears on the command's Web site.
GPS, now comprised of 31 operational satellites, is a free service provided by the U.S. government. Nearly $6 billion is alloted over the next five years to provision new GPS satellites and ground control facilities, according to government records.
Buckman is the command's subject matter expert on the GPS program, which has been under the stewardship of the U.S. Air Force and the command since its inception in the 1970s. A short statement on the command's site attempts to assure the public that the GPS system is secure.
"The current GPS constellation has the most satellites and the greatest capability ever," the statement says. "We are committed to maintaining at least our current level of service, while striving to improve service and capability through on-going modernizaton efforts. The Air Force will continue to pursue an achievable path maintaining GPS as the premier provider of positioning, navigation and timing for the military and civilian users around the world."
Buckman's Twitter comments came in response to GAO testimony May 9 before a subcommittee of the U.S. House Committee on Oversight and Government Reform, which questioned GPS's future performance.
"It is uncertain whether the Air Force will be able to acquire new satellites in time to maintain current GPS service without interruption," Christina Chaplain, director of GAO acquisition, said in her testimony.
In another tweet, Buckman admitted there have been space command problems in upgrading GPS, including a satellite launched in March that is still not fully deployed above Earth. The satellite, SVN-49, has been sending "unusual performance data," Buckman said, but the command is troubleshooting it and "making good progress." Buckman and officials at the space command could not be reached for further details.
However, a blogger on the InsideGNSS (Global Navigation Satellite System) Web site in early May said the SVN-49's problems could prevent it from being declared healthy for months, if ever.
Buckman also said two satellite programs are underway to update the fleet of GPS satellites. "Agree w/GAO there's a potential risk, but GPS isn't falling out of the sky - we have plans to mitigate risk and prevent a gap in coverage," he added.
He also said it is "very unlikely" that users will notice a decline in GPS accuracy. The next satellite designed to maintain the current group is set to launch in August, he added.
The GAO reported that 31 satellites are being used when only 24 are required to keep the GPS service for civil, commercial and military users above a 95% probability of staying within acceptable performance standards.
Defense Department officials predict that several satellites in the constellation will reach the end of their operational life faster than they will be replaced, meaning the probability of maintaining 24 operational satellites falls below 95% during fiscal year 2010 through the end of 2014, the GAO said.
From October 2011 to October 2012, the probability of maintaining 24 GPS satellites drops to as low as 80%, the GAO said.
In her testimony, the GAO's Chaplain said there could be "wide-ranging impacts" on GPS users with gaps in capability, including a decrease in the accuracy of precision-guided munitions using GPS to strike their targets. That would require using larger munitions or more munitions to hit the same target, GAO said. Also, airlines might have to delay, cancel or reroute flights, and E-911 services could lose accuracy.
In several tweets, Buckman responded: "Going below 24 won't happen ... there's only a small risk we will not continue to exceed our performance standard ... Since 1995, GPS has never failed to exceed performance standards."
To minimize potential disruptions, the GAO recommended that the defense secretary appoint a single authority to oversee development of GPS, including space, ground control and user equipment, to ensure that all the parts are synchronized and that potential disruptions are lessened.
Officials at the oversight committee and the GAO said it is too early for a committee response.
Wireless carriers that provide GPS to customers are aware of the state of the GPS system and recent concerns raised by the GAO, said John Walls, vice president of public affairs for CTIA in Washington, an industry group representing many carriers.
Walls noted that there is less than a 5% chance of a satellite problem, but should one occur, the accuracy of the location of a person using 911 from a wireless phone might be reduced, or it might take longer to identify a customer's location. Still, Walls noted that several satellites could be out of service "without causing significant problems for most wireless applications."
One wireless analyst, Jack Gold at J. Gold Associates, said the GAO report might be received by the public as more serious than it is. "Obviously GPS is something people rely upon, but we have to be careful we don't overstate the case," he said.
GPS satellites would not fall from the sky, but their radio transponders could fail and it might take 18 months to prepare and launch a replacement, Gold said. When the transponders in the satellites fail is also hard to predict.
Gold said average drivers with GPS devices could probably rely effectively upon only four GPS satellites, but the U.S. military needs 24 or more to make precise calculations. The GAO report is probably more of an alarm to remind people of the importance of GPS, he reasoned.
"It's not just the U.S. that relies on GPS," he noted. "It's the entire world."