Satellite-watchers say a Russian object that was put into orbit six months ago has been behaving strangely, sparking worries that the craft is conducting a test run for anti-satellite warfare.

The object carries several designations — 2014-28E, or Cosmos 2499, or NORAD object 39765. It popped up in space along with three military communication satellites after a Russian Rokot-Briz launch in May, and at the time, experts assumed it was just a piece of space debris.

But since that time, 2014-28E moved into a different orbit and then maneuvered back into a position near the launch vehicle's spent Briz-KM upper stage, according to reports circulating among satellite observers. In the latest issue of his report on satellites and launches, astrophysicist Jonathan McDowell says the object "made a final burn to complete its rendezvous" on Nov. 9.

Such observations have gotten a wider spotlight thanks to reports appearing this week in The Financial Times and The Washington Post.

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The maneuvers could mean Russia has resumed testing techniques that would enable satellites to approach and observe other satellites, or even disable or destroy them. The Soviet Union looked into concepts for inspector satellites and a satellite killer (known in Russian as "Istrebitel Sputnikov") as far back as the 1950s, and Russia has continued to work on elements of a potential anti-satellite system.

The fact that Russia has said so little about 2014-28E only deepens the mystery.

"The possibility that these kinds of activities are preparing a major and unpleasant strategic surprise for U.S. military capabilities warrants a lot of attention, and a lot of questions for Moscow," NBC News space analyst James Oberg said in an email.

Oberg suggested that the Pentagon already knows more about the project than outside satellite-watchers do. "Presumably, U.S. military observers have seen the same thing, but in even greater detail," he said.

NASA and the U.S. military have been conducting experiments in satellite rendezvous technologies for more than a decade. The Air Force notched successes with its XSS-11 program, while NASA's DART program ended in failure. More recently, the Air Force launched an experimental maneuvering satellite called ANGELS, or Automated Navigation and Guidance Experiment for Local Space.

China, too, has been conducting exercises in satellite maneuvering with its Shiyan, Chuangxin and Shijian spacecraft. Chinese officials have characterized those exercises as tests for space debris collection or satellite maintenance, but outside experts worry that the technology could be used against other satellites.

Concerns about anti-satellite weapons sparked an international debate over the prospects of a "Pearl Harbor" attack in outer space several years ago, and the newly reported test could cause the controversy to flare up again.

"The payoff in building such weapons isn't so much as a tool to make a space sneak attack, it's to raise doubts in the minds of American military leaders about the survivability of their space assets," said Oberg, who wrote a book about space power theory for military planners. "In the past, U.S. space-based systems have been justifiably praised as 'force multipliers' for surface combatants. So any development that reduces that 'multiplication factor,' by placing doubt in its owners' minds, is a bargain 'force reducer.' It then can sway critical deployment and engagement decisions in a real crisis."