PRAGUE, Czech Republic — The new U.S space policy encourages government use of foreign satellite navigation systems to enhance GPS service and places a priority on using customs controls and other means to curb the spread of GPS jamming devices, a U.S government official said.

Anthony J. Russo, director of the U.S. National Coordination Office for Space-based Positioning, Navigation and Timing, said the United States has done an about-face in the past few years in its attitude toward new satellite navigation systems.

“We’ve gone from discouraging other services and hoping GPS was the standard, to a sort of peaceful, side-by-side co-existence, and now toward actively looking to use those foreign services as part of our solution,” Russo said here Sept. 28 during the 61st International Astronautical Congress.

Russia, whose Glonass system was on the brink of collapse in the mid-1990s, has rebuilt the constellation, an effort expected to return Glonass to global operations by early 2011. China’s Compass/Beidou system, while still far from full development, appears to be moving forward. Europe’s Galileo constellation faces continued financial stress, but an initial 18 satellites under construction are scheduled to be in orbit by 2014.

In addition to these global constellations, all in medium Earth orbit, India and Japan have embarked on large regional satellite navigation efforts.

How far each system’s owners are willing to go to make their satellites compatible with the others remains unclear. Some experts say more needs to be done. Bradford Parkinson, one of the original developers of GPS and now a professor at California’s Stanford University, said the goal should be that the systems adopt a policy of interchangeability, meaning a Galileo satellite, for example, could be used as part of the GPS constellation if the need arose.

Parkinson said he remains concerned that, despite the current health of GPS — 31 operational satellites in orbit for a constellation that needs only 24 — the risk of system degradation remains.

“GPS-2F is late. The first 2F was launched in May, but when will we see the next 11?” Parkinson asked. “GPS-3 is ahead of schedule, but the schedule is not for launch until 2014 or 2015. Galileo is delayed, and when will it be certifiable? Glonass has a [satellite] longevity problem, and China’s intentions with Compass are not clear. It is imperative that we avoid system ‘brown-outs,’ meaning a diminution of the number of satellites in orbit.”

Russo said that despite these concerns, the risk of performance erosion in the near future is “very low.” He said the next-generation GPS-3 is moving through its critical-design phase and toward production faster than expected.

Russia’s Glonass, while still requiring more annual launches than the GPS system because of the relatively short life expectancies of the spacecraft, is moving toward a new design that will increase Glonass service life from five years to seven and eventually to nine years.

Europe’s planned Galileo system is still apparently far from being able to finance the planned 30-satellite constellation. Four in-orbit test satellites are scheduled for launch in late 2011, and 14 spacecraft are under construction and scheduled for launch between 2012 and 2014.

The European Commission is still lacking the equivalent of several hundred million dollars to launch the full constellation and may not have the necessary funds before its new budget cycle in 2014. When the full constellation, and a fully operational ground segment, will be ready is unknown.

“It has been decided to use a staggered approach, with a limited infrastructure based on 18 satellites and a limited ground-segment configuration,” said Didier Faivre, head of the navigation department at the 18-nation European Space Agency, which is under contract to the European Commission to develop the Galileo infrastructure.

An 18-satellite system, he said, would allow Galileo to offer its planned open service, similar to GPS’s and using the same frequency, as well as its search-and-rescue service and a “limited” version of the Public Regulated Service, a government-only frequency equivalent to the U.S. GPS military code.

Berry Smutny, chief executive of OHB System of Bremen, Germany, which is building 14 Galileo satellites, urged European governments to order the full constellation and said work also needs to begin on designing the second-generation Galileo.

“Before you launch the last of the first generation, you must have a very clear picture of the next generation,” Smutny said. The GPS development, in which satellites are modernized regularly even before jumping from one generation of GPS spacecraft to another, is a good model to follow, he said.

Peter B. de Selding was the Paris bureau chief for SpaceNews.