By Joey Roulette

WASHINGTON (Reuters) -The secretive Russian satellite in space that U.S. officials believe is connected to a nuclear anti-satellite weapon program has appeared to be spinning uncontrollably, suggesting it may no longer be functioning in what could be a setback for Moscow's space weapon efforts, according to U.S. analysts.

The Cosmos 2553 satellite, launched by Russia weeks before invading Ukraine in 2022, has had various bouts of what appears to be errant spinning over the past year, according to Doppler radar data from space-tracking firm LeoLabs and optical data from Slingshot Aerospace shared with Reuters.

Believed to be a radar satellite for Russian intelligence as well as a radiation testing platform, the satellite last year became the center of U.S. allegations that Russia for years has been developing a nuclear weapon capable of destroying entire satellite networks, such as SpaceX's vast Starlink internet system that Ukrainian troops have been using.

U.S. officials assess Cosmos 2553's purpose, though not itself a weapon, is to aid Russia's development of a nuclear anti-satellite weapon. Russia has denied it is developing such a weapon and says Cosmos 2553 is for research purposes.

Russia, a storied space power that launched the first man in space in 1961, has for decades been locked in a security race in space with the U.S. that, in recent years, has intensified and seeped into public view as Earth's orbit becomes a hotspot for private sector competition and military technologies aiding ground forces.

The Cosmos 2553 satellite has been in a relatively isolated orbit some 2,000 km above Earth, parked in a hotspot of cosmic radiation that communications or Earth-observing satellites typically avoid.

LeoLabs in November detected what appeared to be errant movements with the satellite using Doppler radar measurements from its global network of ground stations. The company in December upgraded its assessment to "high confidence" that it was tumbling based additional radar data and imagery of the satellite taken by another space company, Darren McKnight, a Senior Technical Fellow at LeoLabs, told Reuters.

Russia's Ministry of Defense did not return a request for comment.

"This observation strongly suggests the satellite is no longer operational," the Center for Strategic and International Studies, a Washington-based think tank, said of LeoLabs' analysis in its annual Space Threat Assessment due for release on Friday and shared with Reuters.

The satellite earlier showed signs of odd behavior. Slingshot, whose global telescope network has been tracking the spacecraft since its February 5, 2022, launch, detected movements in May 2024.

"Slingshot noted that the object's brightness became variable, indicating a potential tumble," a company spokesperson said.

But according to Slingshot's latest observations, Cosmos 2553 appears to have stabilized, according to Belinda Marchand, the company's Chief Science Officer.

EYES ON ORBITING OBJECTS

Commercial space-tracking services are relatively young but fast-evolving and in high demand as the number of civil and military satellites in space soars.

The U.S. Defense Department and other countries' militaries, keen on avoiding military miscalculation, have made better eyesight in orbit a high priority to better distinguish between various types of spacecraft maneuvers and whether objects are civil or military assets.

U.S. Space Command, which tracks objects in space and has condemned Russian military satellites in the past, did not immediately return a request for comment.

Cosmos 2553 is one of dozens of Russian satellites in space with suspected ties to its military and intelligence programs. The country has viewed SpaceX's Starlink, a formidable constellation of thousands of satellites, as a legitimate military target as Ukrainian troops use the service in conjunction with weapons on the battlefield.

Moscow, as well as China and the U.S., are pouring tens of billions of dollars into military space capabilities and secretively testing an array of technologies in orbit that could have hostile military uses, stirring concerns of miscalculations and laws of justifiable targeting in the event of a future space conflict.

Mallory Stewart, the former U.S. Assistant Secretary of State for Arms Control, Deterrence, and Stability under president Joe Biden, said last year that Russia is "considering the incorporation of nuclear weapons into its counterspace programs."

Three U.S. officials familiar with the intelligence said the timing of the allegations were based largely on the launch of a satellite they identified as Cosmos 2553, which escalated Washington's understanding of Russia's development in the program.

(Reporting by Joey RouletteEditing by Nick Zieminski)