During the Cold War the U.S. and Soviet Union had a gentlemen's agreement to avoid targeting one another's geostationary satellites, which are crucial for weather forecasts, satellite TV, global communications and, of course, military intelligence and surveillance. Decades later mistrust over military intentions in space has cast fresh uncertainty over the security of the numerous geostationary satellites orbiting more than 22,000 miles above Earth's equator.

A satellite in geosynchronous orbit stays “fixed” above the same region of Earth by traveling at the same speed as the planet's rotation. From its lofty perch it can continuously observe one area or communicate with ground receivers. They are incredibly valuable for both government and commercial purposes—the satellite TV industry, which depends on geosynchronous Earth orbit (GEO) satellites, is alone worth about $95 billion annually, according to the Space Foundation. The U.S. military depends heavily on its GEO satellites for everything from early warnings about ballistic missile launches to protected communications with far-flung forces across the globe. "What the U.S. military is grappling with now is the potential for other countries to reach out and touch those satellites," says Brian Weeden, technical advisor for the Secure World Foundation in Broomfield, Colo. "And so it’s looking to how it could protect itself."

This year, the U.S. Air Force unveiled its formerly classified Geosynchronous Space Situational Awareness Program (GSSAP), which envisions a pair of maneuverable satellites, capable of operating both above and below the zone of geosynchronous Earth orbit, to monitor spacecraft and space debris throughout the entire GEO belt. The first pair of GSSAP satellites received a priority launch slot scheduled for September 2014 after U.S. officials bumped back a test flight of NASA's Orion spacecraft, the space agency’s next-generation manned spacecraft.

The Air Force satellites will complement existing ground and low Earth orbit telescopes that currently keep track of all objects in geostationary orbit by providing a much closer view of objects in that belt, Weeden explained. That would make it easier to eyeball potential antisatellite threats—a form of "neighborhood watch" deterrence that the U.S. wants other countries to know about.

Technological threats to GEO satellites are nothing new. For instance, in the 1980s the Soviet Union developed parts of its Naryad antisatellite (ASAT) system to place "kill vehicles" in orbit that could attack GEO satellites. The military project only carried out a few known launch tests, but it eventually evolved into a Russian commercial launch system called Briz-M that represents the upper stage of rockets used for launching payloads to high orbits such as GEO. China recently pushed ASAT capabilities to new heights by launching a rocket "on a ballistic trajectory nearly to geosynchronous Earth orbit" on May 13, 2013, according to U.S. military officials.

Chinese officials said the rocket carried scientific payloads for high-altitude experiments. By contrast, U.S. analysts found strong evidence suggesting the launch represented the world's first test of a direct-ascent ASAT missile system designed to intercept GEO satellites without first going into orbit, as detailed by Weeden in The Space Review. That development, coupled with the lack of a "gentlemen's agreement" between the U.S. and Chinese militaries, has left U.S. analysts worrying about whether a future political crisis might prompt China to consider a crippling strike on U.S. military satellites. "When there are situations, as currently, where trust is low between Asian countries, between China and the U.S., and increasingly between Russia and other countries, dual-use space technology can create security dilemmas," wrote Joan Johnson-Freese, professor of national security affairs at the U.S. Naval War College in Rhode Island. (“Dual-use” is the term for technologies that fit both civilian and military purposes.)

One bad day in geosynchronous Earth orbit could quickly turn into a bad day for everyone. A direct ascent ASAT weapon destroying a GEO satellite could create a swarm of space junk that proves far more dangerous to satellites in the "narrow racetrack" of GEO than in low Earth orbit, Weeden said. In one simulation of a collision between two objects in GEO, the resulting space debris spread around half of the GEO belt within a few days. Still, China may rethink such a strike as it becomes more dependent on GEO satellites in the future. The 447 operational GEO satellites currently tracked by the Union of Concerned Scientists include 177 from the U.S., 35 from China and 22 from Russia.

Of course, China may view U.S. space activities with equal suspicion. The Pentagon's Defense Advanced Research Projects Agency is currently developing small satellites under its Phoenix project capable of sidling up to a satellite in geosynchronous orbit and harvesting and reusing parts of it. Such capability could also serve the dual purpose of disassembling GEO satellites from other countries without creating much space debris. "If you sidle up to a Chinese satellite and pull the solar panels off, it's effectively an antisatellite weapon," says Micah Walter-Range, director of research and analysis at the Space Foundation in Colorado Springs, Colo.

No easy solutions exist for reducing potential threats to GEO satellites. But Weeden suggests the U.S. could start by talking more publicly about China's suspected ASAT test. That could generate international dialogue on how to handle the growing threats to GEO satellites—as long as the U.S. is also ready to frankly discuss its own ASAT capabilities.