Tardy, but Twice as Precise: A New Generation of GPS IIF satellites due for launch


Senior Member
Feb 23, 2009
Tardy, but Twice as Precise

With New GPS Satellites, U.S. Seeks To Double Resolution

By William Matthews
Published: 22 March 2010

The U.S. Air Force is preparing for a May launch of the first of a new generation of Global Positioning System satellites.

If it occurs on time - it's years behind schedule - the launch will come about a year after a government study sparked widespread concern by warning that the aging GPS satellites could begin to fail later this year.

Having too few of these satellites could reduce the ability of precision-guided bombs to hit their targets, could force aircraft to reroute or delay long-distance flights, and could diminish the accuracy of GPS signals available to troops fighting in urban areas or in mountainous terrain, the Government Accountability Office (GAO) reported to Congress.

The Air Force, which operates GPS satellites, plays down the likelihood of degraded GPS service, but other GPS experts say the possibility is real.

The new satellite - a GPS IIF - is the first of 12 Boeing-built satellites scheduled to be launched over the next several years. A second IIF launch is expected later this year if all goes well with the first one.

As their numbers increase in orbit, the accuracy of GPS should also improve, said Ken Torok, vice president of Boeing's navigation and communications systems division.

The GPS IIF is designed to be twice as accurate as its predecessors. Thus, when most of the IIFs are in orbit, they should be able to locate a receiver on earth with accuracy of less than 3 meters, compared with less than 6 meters with the current GPS constellation.

Greater accuracy is a product of advanced atomic clocks in the new satellites, Torok said. GPS works by accurately measuring the time it takes for positioning signals to travel from several satellites in space to a GPS receiver on Earth. Software in the receiver measures the time from three or more satellites and then calculates its location.

The more accurate the time measurement, the more precise the location.

IIF satellites offer other improvements as well for military and civilian users.

The satellites' military signal - "M-code" - is formatted in a way that enables it to penetrate jamming better than the signals from current satellites, Torok said. And variable power feature enables operators to increase signal power to punch through jamming if that becomes necessary, Torok said.

The IIF satellites have greater capability to receive updated software in space. They carry enough onboard memory to update both the GPS system and the satellite's operating system. Current satellites have only limited updating capability, Torok said.

New ground-based control equipment for the GPS system uses more automation to fly the satellites and manage the constellation. The automation reduces operating costs, he said.

The IIFs are designed to operate at least 12 years in space but are expected to last longer than that, Torok said. Extended life among satellites is not uncommon. At least one of the current GPS satellites is still going after 19 years.

The current GPS constellation includes 30 satellites. The Air Force says the system's "requirement" is for just 24 and that there is little danger of the constellation falling below that number. But other GPS experts say 24 satellites can't provide the level of accuracy that's available with 30, and the requirement should be raised to 30.

Rival global positioning systems being set up by Europe and China are designed for 30 satellites.

"We really need IIF launched and on orbit," said Bradford Parkinson, an aeronautics and astronautics professor at Stanford University and a GPS pioneer more than three decades ago.

Even so, "IIF will not take us out of the woods," he said. "Any significant degradation from the current 30-satellite coverage" is likely to mean "brownouts" in which GPS service in some locations is poor or lost.

"While we have a good chance of keeping at 24 [satellites], we have virtually no prospect of maintaining 30 in the near term. GPS-IIF will help fill the gap, but it is not enough," he said.

"We desperately need to vigorously pursue GPS III to avoid dropping below 24," he said. GPS III is the generation of satellites after GPS-IIF that's being developed by Lockheed Martin.

The first GPS III is to be launched in 2014, according to Lockheed. But in light of the delays that plagued the IIF and most other satellite programs, the GPS III schedule may be unrealistic, the GAO warned.

Getting the first GPS IIF to the launch pad was a challenge. Work on IIF satellites began more than a decade ago and was plagued by "congenital defects due to bad procurement practices imposed" by the Air Force, Parkinson said.

There were other troubles, too, according to the GAO. They included "a loss of expertise in building the GPS satellites on the contractor side, lax program oversight and technical problems." As a result, the first IIF is 3½ years late and IIF program costs more than doubled, climbing from $729 million to $1.7 billion.

As important as GPS is to the military - it's used to navigate aircraft, ships and vehicles, to guide foot soldiers and smart bombs, and to track supplies - it is also critical for civilian uses.

Airliners steer by it, many drivers use it instead of paper maps, cell phones link to it, farmers use it to manage crops, and surveyors and cartographers depend on it. GPS tracks packages in transit and puts accurate time stamps on automated teller machine transactions.

So keeping the GPS constellation intact is important.

"I have attended the reviews of launch readiness of IIF as a member of the Independent Review Team and we have reasonably high confidence in the current design," Parkinson said.

Boeing concurs, said Torok. "We feel confident about the IIF program now."



Senior Member
Feb 23, 2009
The new satellites apparently have better resistance to jamming with variable power and a precision/PRN code of unknown length transmitted at 5.115 MHz. Also a module for L5 signals, the new 'safety of life' signal for better commercial, aeronautical and maritime navigation. As well, longer design-lives, estimated at 12 years and drastically lower operating costs.

The (CST) consolidated system test to validate launch vehicle, ground-control procedures and equipment was completed in 2009 and the satellite is due for take off in the coming few weeks!
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