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A Chinese "reusable experimental spacecraft," believed to be the country's top-secret spacecraft, has landed back on Earth after more than eight months in orbit - the latest development in a largely secret race between the United States and China to perfect such technology.
The Chinese spacecraft was launched into orbit last December, two weeks before the latest launch of the U.S. military's Boeing X-37B unmanned spacecraft. It was the third known mission of such a Chinese spacecraft.
About 268 days later, the spacecraft returned to an unnamed landing site, according to a brief Sept. 6 announcement by state news agency Xinhua, which called the test mission a "complete success."
China's development of the spacecraft, about which little is known, follows years of efforts to overtake the US, long the world's leading space power, for dominance in space and beyond.
Here's what we know - and don't know - about the Chinese spacecraft.
What is a spacecraft - and isn't it old technology?
The term "spaceplane" often conjures up NASA's Space Shuttle, which flew 135 missions from 1981 to 2011, carrying astronauts into orbit and helping build the International Space Station. It can also refer to the Soviet Union's ill-fated Buran space shuttle, which completed one successful unmanned flight in 1988 before being retired.
But the newer craft currently being tested in orbit by the U.S. and China are reportedly smaller than the shuttle and unmanned. The U.S. X-37B is operated by the military, while China has not said whether the program believed to be tied to its recently landed spacecraft is civilian or military.
Spacecraft are generally reusable vessels that resemble both an airplane and a spacecraft in that they can fly in Earth's atmosphere and into space. Both the Chinese spacecraft that recently returned to Earth and the U.S. X-37B, which has flown seven missions since its debut in 2010, are launched into space on rockets but land on runways like airplanes, experts say.
Spacecraft are valued for their potential to carry out diverse missions in space and to help countries respond quickly to developments in space, while also improving the technology for reusable spacecraft, which could be used for more regular human space travel in the future.
"It's no surprise that the Chinese are extremely interested in our spacecraft, and we're extremely interested in theirs," U.S. Space Force chief of operations Gen. Chance Saltzman told reporters at a conference in December.
"It's a capability - the ability to put something into orbit, do a number of things, bring it back home and see the results is powerful."
What do we know about the Chinese space program?
Not too much.
China has never disclosed what specific technologies the spacecraft tested, nor released any photos of it, since it began operating in orbit in 2020.
A video shared on the social media account of state-backed space company China Aerospace Science and Technology Corporation announcing the spacecraft's Sept. 6 landing featured a banner instead of images, with the text reading: "It is too advanced to be shown."
Even the name of the spacecraft that landed on Earth has not been confirmed by the Chinese government, although observers suspect it is the "Shenlong" spacecraft, which has been in development for twenty years.
Other space projects developed in China in recent years have been publicly and officially described as civilian projects. However, Shenlong's official purpose has not yet been confirmed, experts say.
It is also unknown whether this is the same vehicle or another in the same series that completed two previous missions - the first in 2020 lasted two days and the second that began in 2022 lasted 273. Analysts believe they all ended with landings at the secretive Lop Nur military facility in Xinjiang, in the far northwest of the country.
An official announcement after the Dec. 14 launch said the spacecraft would "carry out reusable technological verification and space science experiments as planned, and provide technical support for the peaceful use of space."
But space observers can - using open-source data, imaging and positioning measurements - monitor what the vehicle has been doing in space, including tracking the launch of what they call a suspected "sub-satellite" in late May and apparent attempts to maneuver around the object. That follows similar exercises during previous test missions.
"This ability to maneuver close to another object could be used for inspection of space assets or potentially clearing space debris from orbit. But it could also be used for more sinister purposes, including intercepting signals or physically damaging other spacecraft," said Juliana Suess, a space security researcher at the London-based defense think tank Royal United Services Institute, or RUSI.
Are there military applications?
The development of Chinese spacecraft comes at a time when more and more countries are paying attention to the ever-closer connection between security on Earth and in space. They are competing for so-called counterspace technologies that have the potential to disrupt or even destroy adversaries' space assets.
China has been explicit in recent announcements about the peaceful purposes of the spacecraft and its other space missions, but analysts say the country is among the world powers developing counterspace capabilities.
The state media announcement of the spacecraft landing said it would "pave the way for easier and cheaper return methods for the peaceful use of space in the future."
Analysts say there is no evidence the Chinese spacecraft are designed to serve as space weapons, but that information and capabilities obtained during the missions could be dual-use.
"Anything China learns from deploying its spacecraft, regardless of their primary purpose, will benefit its counterspace efforts," said Clayton Swope, deputy director of the Aerospace Security Project at the Center for Strategic and International Studies think tank in Washington.
"In addition to developing space technologies, it allows China to develop its muscle memory for operating in space. It is worrying how China can apply that knowledge to counterspace weapons," he said.
How does this compare to the American space plane X-37B?
It is difficult to compare the Chinese space plane with the American X-37B, due to the high level of secrecy surrounding both programs.
The X-37B has outlasted the Chinese spacecraft by several years, and has remained in orbit for significantly longer. This record was set during its sixth mission, lasting 908 days before returning to Earth in November 2022.
The U.S. Space Force, which oversees the X-37B, describes it as a reusable, unmanned spacecraft that "strengthens the United States' future in space by conducting technology experiments that accelerate the development of next-generation capabilities."
The latest mission includes testing in new areas of the orbit, experimenting with space domain awareness technologies to monitor objects in space and studying the effects of radiation on NASA materials, including plant seeds, the military said.
But observers have also raised questions about the spacecraft's activities, including the deployment of several small satellites.
The level of secrecy surrounding the deployment of these satellites "could indicate they are part of a covert intelligence program, but it could also indicate the testing of offensive technologies or capabilities," the independent US Secure World Foundation noted in a recent report, while pointing to "similar behavior in terms of covert deployment" from the Shenlong spacecraft.
Observers also note that China is likely using the US program as a benchmark for its own program.
"The fact that they now have a reusable spacecraft shows how far they've come (and) the fact that it was in the air for so long and came back safely," said Brendan Mulvaney, director of the China Aerospace Studies Institute, a U.S. Air Force think tank, referring to China's claim of a successful mission earlier this month.
"That means they are putting in the time, effort and investment to make it work. China is the undisputed No. 2 in space power and is seeking to close the gap with the U.S. in military, commercial and scientific areas, all at the same time," he said.
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