Sources within the U.S. government and outside experts said there was no immediate evidence pointing to the preparations for the type of satellite or rocket launches used by China for past anti-satellite tests at lower orbits.

But they said Beijing could test its anti-satellite weapons in other ways that would be harder to detect, such as by jamming a satellite’s signals from the ground or issuing a powerful electromagnetic pulse from one satellite to disable another.

China could also maneuver two satellites very close together at higher orbits, replicating actions it has already taken in lower orbits in August 2010 and November 2010. Such activities could be used to perform maintenance or test docking capabilities for human spaceflight, but could clearly be used for more destructive purposes as well, they said.

The United States has continued to test its own anti-satellite capabilities. In February 2008, a missile fired from a U.S. Navy cruiser in the north Pacific destroyed an ailing American satellite in orbit.

The U.S. government said the satellite’s toxic fuel posed a risk upon re-entry of the earth’s atmosphere. Skeptics said the test was a message to China.

Any further anti-satellite test by China would be troubling, especially if it occurred at higher altitudes, said Bruce MacDonald, a former White House official who is now a senior director at the U.S. Institute of Peace.

The United States operates its fleet of Global Positioning System (GPS) satellites in medium earth orbit about 11,000 miles above the surface of the earth, while U.S. military communications and early missile warning satellites are located in geostationary orbit 22,000 miles above the equator.

Brian Weeden, technical adviser for the nonprofit Secure World Foundation and a former Air Force space and missile expert, said a Chinese anti-satellite test at those higher orbits would put U.S. satellites at risk.

“Some critical U.S. assets in that region have been assumed for the most part to be safe from those kind of attacks,” he said. “Such tests would signal that they’re not.”

(Additional reporting by Mark Hosenball in Washington and Terril Yue Jones in Beijing; editing by Warren Strobel and Philip Barbara)