China's space plane releases another mystery object into orbit

China's reusable space plane has released another unknown object into Earth's orbit. 

The experimental orbital plane, named Shenlong, which means "divine dragon" in Chinese, has been in orbit for 168 days. Space activity tracker Jonathan McDowell first spotted the spacecraft's recent activity on May 24. The new object has since been cataloged as 59884 (International designator 2023-195G) by the U.S. Space Force space domain awareness teams, SpaceNews reported. 

"This object could be a subsatellite deployment, or it could be a piece of hardware ejected prior to end of mission and deorbit (the space plane's first flight did something similar)," McDowell, who is an astronomer from the Harvard-Smithsonian Center for Astrophysics, said in a post on X (formally Twitter). "Will be interesting to see if the plane maneuvers or lands soon."

Related: China launches secret space plane on 3rd-ever mission 

Another possible explanation is the space plane released the object for proximity and recapture maneuver tests, similar to those completed during its second flight, which launched in 2022 and spanned 276 days in Earth's orbit. 

The reusable space plane is currently conducting its third mission, which launched aboard a Long March 2F rocket from the Jiuquan Satellite Launch Center on Dec. 14, 2023. While China has maintained strict secrecy surrounding the spacecraft, a launch report suggested the mission would conduct reusable technology verification and space science experiments to provide technical support for the peaceful use of space, according to SpaceNews.

This is not the first object ejected from Shenlong during this mission. Only four days after its December launch, the robotic spaceplane placed six mysterious objects into Earth's orbit that appeared to emit signals. The spacecraft has also performed maneuvers to alter its orbit during this third flight.

Despite the lack of images or descriptions of the spacecraft, it has been suggested that Shenlong could be similar in size and function to the U.S. Air Force's X-37B spaceplane. Both reusable spacecraft offer the potential for reduced costs and increased frequency of future missions.