Ever since China claimed success in the secretive launch of an experimental spacecraft, experts have been pondering over what it could be and what it did in space.
The spacecraft - mounted on a Long March 2F rocket - was launched from the Jiuquan Satellite Launch Centre in northern China on 4 September and safely returned to Earth after two days in orbit.
"The successful flight marked the country's important breakthrough in reusable spacecraft research and is expected to offer convenient and low-cost round-trip transport for the peaceful use of space," state-run Xinhua News Agency said on 6 September in a brief report.
But unlike recent Chinese high-profile space missions, very few details have emerged about the vehicle and no visuals have been released.
Chinese authorities have been tight-lipped about the nature of the short-duration excursion and what technologies were tested.
The exact launch and landing times were not revealed, nor was the landing site although it is thought to be the Taklamakan Desert, which is in northwest China.
"There are many firsts in this launch. The spacecraft is new, the launch method is also different. That's why we need to make sure there is extra security," a military source told South China Morning Post (SCMP).
An official memo circulating on social media also warned staff and visitors to the launch site not to film the lift-off or discuss it online, according to SCMP.
The launch of the vehicle may have come as a surprise - there was no official announcement prior to the launch - but China has been working on such technology for the past decade. Three years ago, China said it would launch a space vessel in 2020 that "will fly into the sky like an aircraft" and be reusable.
Now then -- this could be something exceptional. The rumours are that inside this exceptional payload fairing atop a CZ-2F is a CASC spaceplane, launching from Jiuquan Friday. Source: 俊了个锅 via 林晓弈。 https://t.co/qs6VRfzQoP https://t.co/OESvzyDyEl pic.twitter.com/ZPnpwAIfyO— Andrew Jones (@AJ_FI) September 3, 2020
A reusable spacecraft - as the name implies can undertake multiple trips to space - thereby potentially lowering the overall cost of launch activity. A traditional one-off spacecraft - costing tens of millions of dollars - is practically rendered useless after a single mission.
The experimental vessel reached an altitude of about 350km, which is in line with China's previous crewed flights. The spacecraft also released an unknown object into the orbit before returning to Earth.
Jonathan McDowell, an astronomer at Harvard Smithsonian Centre for Astrophysics, says the aim of the mission was likely to test out the vehicle's systems such as power, temperature, stability and to prove it could re-enter and land correctly.
Once the testing is complete, such a vehicle could be used to launch and repair satellites, survey the Earth, as well as take astronauts and goods to and from orbit, possibly to a planned future Chinese space station.
Comparisons to US' X-37 space plane
The Chinese craft's size and shape remain unclear but it is widely believed to be some sort of uncrewed space plane similar to the X-37B Orbital Test Vehicle operated by the US Air Force.
The recent mission could be linked to the Shenlong - or divine dragon - space plane project, which has been in development for some time, according to reports. A second Chinese reusable space plane called Tengyun, or cloud climber, is also in the works.
If confirmed as a space plane, China would become only the third country to have successfully launched such a vehicle into orbit after the US and the former Soviet Union.
The European Space Agency is working on its own reusable orbital vehicle called Space Rider, while India is also said to be developing a space shuttle-like craft.
The X-37B, resembling a miniature space shuttle, has been in orbit since late May following its launch on its sixth assignment. Very little is known about the X-37B's missions, prompting speculation that the planes could be used for spying activity or testing space weapons.
Similarly, the lack of publicity has given rise to speculation that the Chinese spacecraft could also possibly have some military use.
"The secrecy, I am sure, is just because it is a military project," adds McDowell, who has been closely following the mission.
There is little distinction between China's civilian and military space programmes which fuels suspicions about Beijing's space ambitions.
"It is reasonable to assume that what's being tested has some military applications, probably new satellite equipment and spying technologies," notes Bleddyn Bowen, a space policy academic at the University of Leicester.
"We'll have to wait and see how many future flights like this China may conduct to see whether it will match the scale of X-37B," he told the BBC.
China's state-run outlet Global Times, citing observers, did say that the country should have the capability to strike anywhere on Earth within half an hour, just as the X-37B does.
China's growing space ambitions
Whatever its purpose, the reusable system marks yet another milestone for China's ambitious space programme, and comes weeks after the launch of Tianwen-1, China's latest attempt to reach Mars.
China has poured significant funding into its space efforts, and last year became the first country to send an uncrewed rover to the far side of the Moon.
President Xi Jinping has also thrown his support behind the country's space endeavours and the Chinese state media regularly cast the "space dream" as one step in the path to "national rejuvenation".
Earlier this year it also completed the network of satellites for its BeiDou navigation system, an alternative to the US GPS system. China is also working toward sending astronauts to the Moon and, eventually, Mars.
"If this really is a space plane, and not just a reusable capsule like Dragon, then it represents a big step forward in China's space technology as winged re-entry is really hard to do," notes McDowell.
"China was way behind in space but has been gearing up its space programme on all fronts and is now catching up fast. The spacecraft launch is just another reflection of that."
Bleddyn Bowen adds the spacecraft launch is "just another part of China becoming a comprehensive space power that utilises space technology for the purposes of war, development, and prestige like all others".