The US Air Force late last month disputed a General Accountability Office report concluding that the Global Positioning System used by the military and millions of motorists worldwide may be in danger of disruption unless aging satellites are replaced quickly.
"The GPS will not go down," said Col. Dave Buckman, in a forum hosted late last month on Twitter's social network. Buckman, command lead for position, navigation and timing at the Air Force Space Command in Colorado Springs, is a subject-matter expert on the GPS satellite navigation programme, which dates back to the 1970s.
The programme is funded by the US Department of Defense; the Air Force is responsible for acquiring satellites and other equipment for the system. The US government offers the GPS navigation service to commercial users at no charge.
Buckman acknowledged that there is some risk of degraded performance as a result of delays in launching new satellites, but he contended that the service is not in danger of failing. "There is 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.
In a report issued early last month, the GAO said that it is uncertain whether the Air Force can launch new satellites in time to replace older ones that are starting to fail. The report suggests that as early as next year, the number of satellites used for the service could fall below 24, which is the number of satellites necessary "to provide the level of GPS service the US government commits to." The report noted that the next new satellite is set to be launched in November, some three years behind the Air Force's original schedule.
There are now 30 operational GPS satellites, according to the Air Force.
The GAO report concluded that there is an 80% chance that the Air Force will be able to maintain the 24-satellite constellation required for full GPS service at all times between 2010 and 2014. Falling below the 24-satellite threshold could have a "wide-ranging impact" on GPS users, Christina Chaplain, director of acquisition and sourcing management at the GAO, told a subcommittee of the U.S. House Committee on Oversight and Government Reform on May 7, the day the report was released.
She said the military especially could face significant problems if GPS performance lags, noting that the accuracy of precision-guided munitions depends on a full implementation of the technology. Degraded service would require that the military use larger or greater numbers of munitions to hit the same target, she added.
Also, GPS satellite problems could affect the 911 emergency telephone system or force airlines to delay, cancel or reroute flights, the GAO said.
In a statement responding to the GAO report, Gen. C. Robert Kehler, commander of the Air Force Space Command, said he has "high confidence" that the number of GPS satellites will not drop below 24.
Wireless carriers that provide GPS service to customers are aware of the state of the Global Positioning System and of the concerns raised by the GAO, said John Walls, vice president of public affairs at CTIA, a Washington-based industry group that represents many major wireless carriers.
Walls estimated the chances of a satellite problem at about 5% and suggested that several satellites could be out of service "without causing significant problems for most wireless applications."
Jack Gold, a wireless analyst at J.Gold Associates LLC, said that while most drivers with GPS devices could get the data they need with only four GPS satellites, the military needs at least 24 to make precise calculations.
The GAO report will remind people of the importance of GPS technology, he reasoned, but the public might get the impression that the problems are more serious than they really are. "We have to be careful we don't overstate the case," he said.
The GAO recommended that a single authority be created by the Department of Defense to oversee the acquisition and development of all GPS technology, including satellites and ground control systems. The DOD agrees with the recommendation, the GAO said.