WASHINGTON – A Russian military satellite launched in March has made at least 11 close approaches to the rocket upper stage that released it into orbit, according to a spokesman for the U.S. Air Force.

Such maneuvering capability is consistent with, but not necessarily indicative of, an on-orbit anti-satellite weapon.

Air Force officials previously said they were closely watching the satellite, and independent space tracking experts and policy analysts have joined the vigil. The maneuvers started in April, and the most recent occurred in early July, experts said, adding that in at least one case the satellite appears to have nudged the upper stage to a higher orbit.

In a response to questions from SpaceNews, Air Force Capt. Nicholas Mercurio, a spokesman for U.S. Strategic Command’s Joint Functional Component Command (JFCC) for Space, said that in addition to its dance with the upper stage, the satellite, known as Kosmos 2504, on one occasion approached an unidentified piece of orbital debris. It has not approached any active satellites, he said.

Kosmos 2504, which launched along with three communications satellites aboard a Rockot vehicle from Russia’s Plesetsk Cosmodrome, is being watched carefully by Strategic Command’s Joint Space Operations Center at Vandenberg Air Force Base, California.

Lt. Gen. Jay Raymond, commander of the 14th Air Force and of the JFCC for Space, said in April that the service was “keeping a close eye on” the satellite, whose maneuvers are similar to another Russian satellite launched last year, also along with three communications satellites on a Rockot vehicle. That satellite is known as Kosmos 2499 but is often informally referred to as Object E.

Object E’s movements were described in a broader classified briefing on space threats to congressional defense committees earlier this year, a Capitol Hill source said.

Both satellites have been the subject of widespread speculation among space tracking experts and policy analysts. They are among the reasons that U.S. Defense Department officials have been sounding alarms over the past year or two about threats to U.S. space systems from China and Russia.

T.S. Kelso, senior research astrodynamicist for AGI’s Center for Space Standards and Innovation, said via email July 13 that Kosmos 2504, the one launched in March, has “maneuvered extensively.”

In interviews with SpaceNews, experts noted that the satellite is maneuvering at extremely low speeds, which is necessary to safely make close approaches — often referred to in military parlance as proximity operations — with other objects.

After one such encounter, the Rockot launcher’s Breeze KM upper stage appeared to have moved to a slightly higher orbit, the observers said. It is unclear if the satellite intentionally or unintentionally nosed the rocket body to the higher orbit, or whether the approach was part of some kind of docking experiment, they said.

The Air Force and U.S. State Department referred questions about the satellite to the Russian Foreign Ministry. E-mails sent to the Russian embassy here were not returned.

Senior officials in the Defense Department have said repeatedly that Russian leaders claim to have an anti-satellite weapon.

At the very least, said John Sheldon, director of the George Marshall Institute, a think tank here, the maneuvers demonstrate that these “capabilities are in the hands of countries that could give us trouble in the future.”

Sheldon said while there is no proof that the satellites’ maneuvers are offensive in nature, if they were part of a routine or otherwise benign inspection mission, “then why not say so?”

But another expert cautioned that capability does not necessarily reveal intent.

“Is a knife a weapon or a way to cut a steak?” said Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics.

McDowell said he believes the satellites are part of a technology development effort in proximity operations. “It would be surprising if they weren’t doing experiments in proximity operations,” he said.

Brian Weeden, technical adviser at the Secure World Foundation, a nonprofit organization dedicated to space sustainability, points to similarities between the Kosmos 2499 and 2504 satellites and a Russian anti-satellite system known as Naryad that was developed in the 1980s.

Like the newer satellites, the Naryad launched together with military communications satellites to an altitude above 1,000 kilometers, he said.

But Weeden said it is unclear how the technologies the newer satellites are demonstrating could be used offensively.

On-orbit inspection technology is not unusual. In recent years the Air Force and Defense Advanced Research Projects Agency have experimented with on-orbit rendezvous and proximity operations.

Most recently, in 2014, the Air Force launched the Geosynchronous Space Situational Awareness Program, a two-satellite system operating in a “near-geosynchrous orbit regime” to provide accurate tracking and characterization of man-made orbiting objects. Air Force officials publicly disclosed the previously classified program in February 2014 and acknowledged that the satellites would perform rendezvous and proximity maneuvers to allow close-up looks at spacecraft in geosynchronous orbits, some 36,000 kilometers above Earth’s surface.