On the planet's final frontier, more and more countries are beefing up their border guards.
India became the latest country to boost its defense presence in space, announcing last week plans to develop a military space program to counter the fast-growing space defense efforts of neighboring China.
India, which has an extensive civilian space satellite program, must "optimize space applications for military purposes," army Chief of Staff Gen. Deepak Kapoor said at a defense conference in New Delhi. "The Chinese space program is expanding at an exponentially rapid pace in both offensive and defensive content."
Last month, Japanese lawmakers passed a bill ending a decades-old ban on the use of the country's space programs for defense, although officials in Tokyo insist that the country has no plans to develop a military program in space.
French President Nicolas Sarkozy, in the first major review of France's defense and security policy in more than a decade, has proposed nearly doubling spending for space intelligence assets, including spy satellites, to more than $1 billion annually.
"I don't think what you are seeing is coincidental," said Wade Boese, a researcher at the Washington-based Arms Control Association. "Countries are increasingly aware of the potential for military development in space, and increasingly aware that other countries are moving ahead."
The issue of an arms race in space took on new prominence in January 2007, when China stunned Western military analysts by using a medium-range ballistic missile to shoot down a defunct weather satellite. Pentagon planners said two orbiting U.S. spacecraft were forced to change course to avoid being hit by the thousands of pieces of space debris caused by the surprise test.
China insists the exercise was not conducted for military reasons.
"We are against weaponization or an arms race in space," Zhou Wenzhong, China's ambassador to the United States, said in an interview at The Washington Times earlier this month. "This was a scientific experiment."
But in what many around the world saw as at least in part a return salvo to the Chinese action, the U.S. Navy in February shot down a wayward U.S. spy satellite over the Pacific, arguing that the action was needed to prevent the craft from crashing to Earth and spreading potentially toxic fuel.
India, which competes for influence with China even as trade relations between the two Asian giants have blossomed, made no effort to hide its concerns about Beijing's plans for space.
"With time we will get sucked into a military race to protect our space assets and inevitably there will be a military contest in space," Lt. Gen. H.S. Lidder, one of India's most senior officers, said last week in comments reported by the Indian Express newspaper and confirmed by the country's defense ministry.
"In a life-and-death scenario, space will provide the advantage," Gen. Lidder said.
Although the United States holds a vast technological and spending edge in space defense programs, the military's reliance on satellites and space-based assets exposes the United States more than any other country to military threats in space.
Nancy Gallagher and John D. Steinbruner, researchers at the University of Maryland's Center for International Studies, argue in a study that the Pentagon cannot hope to dominate space through technological and material superiority.
The United States will not be able to "outspend and out-innovate all potential rivals in space," the two argue in a "white paper" just published by the American Academy of Arts and Sciences.
Aides to Sen. Barack Obama, Illinois Democrat, and Sen. John McCain, Arizona Republican, are staking out markedly different stands on the space arms race as the presidential campaign heats up.
"We don't need more battlegrounds," Steve Robinson, an Obama campaign adviser, said in a debate at the National Space Society's annual meeting in May in Washington. "The idea of militarization of space is not something that Senator Obama is in favor of, and cooperation is better than confrontation."
Floyd DesChamps, a Senate Commerce, Science and Transportation Committee staffer representing Mr. McCain, said the senator from Arizona recognizes the need to defend U.S. space assets from hostile attack.
"The reality is that we have to protect those assets," he said.