FOR the past 678 record-breaking days, a large robotic plane owned by the US Air Force has been floating around space in low-earth orbit.

Despite the unique accomplishment, the space plane remains shrouded in secrecy and the goals and purpose of the mission are a mystery to the public — fuelling intense speculation and conspiracy theories, including concern that it is helping to usher in the weaponisation of space.

The weaponisation of space has been a major issue for governments as far back as the 1960s.

“Whoever has the capability to control space will likewise possess the capability to exert control of the surface of earth,” US Air Force chief of staff Thomas White told the press in 1957.

The international community has worked hard to ensure space remains a place absent of military-style weapons but some fear the secrecy around X-37B could open a “backdoor” to a new kind of celestial arms race among the world powers.

The plane is officially known as the X-37B Orbital Test Vehicle. The unmanned, heat-shielded craft is about nine metres long and three metres tall.

It gets launched on the back of a rocket and once in space deploys a solar array, allowing it to stay in orbit for long periods of time.

The spacecraft has made a total of four missions since April 2010 with the fourth and current mission launching on May 20, 2015. When it returns to Earth it uses its small wings to glide down and make an autonomous runway landing.

Despite the long term nature of the project, very little information has leaked about the X-37B. For a long time intense speculation surrounded the spacecraft with reports claiming the plane could be a unique space bomber with the potential to be equipped with nukes or a satellite meant to spy on, or covertly disrupt, other satellites.

In 2015, MIT researcher Subrata Ghoshroy from the Bulletin of Atomic Scientists — the group of scientists who control the doomsday clock — published a paper suggesting the X-37B was a worrying “backdoor” to the weaponisation of space.

“The X-37B illustrates the United States’ continuing interest in militarising space and, possibly, weaponising it in the future,” he wrote.

This idea has been a popular one among conspiracy theorists.

Officially, the only role the Pentagon acknowledges is that the space plane is used to conduct experiments on new technologies. Given the size of the plane and the longevity of its missions, it’s likely that the X-37B is carrying out quite a number of highly classified experiments for the US military. One of those is believed to be the testing of a new propulsion system called a Hall Thruster, an engine technology that has been touted for its potential to help get us to Mars.

On the more speculative side of things, it could be testing new communication technologies as well as various military applications such as deploying certain weapons from low Earth orbit.

It’s also been suggested it could serve as a prototype for a “space ambulance” for astronauts aboard the International Space Station.

“The X-37B remains in orbit,” said an Air Force spokesperson at the Pentagon on Monday.

“We are extremely proud of its performance and its contributions to advancing space technologies.”

But while the Pentagon remains tight-lipped about the X-37B, other major powers such as Russia and China have been scrambling to come up with their own answer to America’s secretive mission.

China has previously voiced suspicion over the Pentagon’s X-37B via its state-run media.

“Industry analysts said the spacecraft could be a precursor to an orbiting weapon, capable of dropping bombs or disabling enemy satellites as it circles the globe,” China’s state-run Xinhua news agency wrote in June 2012.

Last year, A Russian military official claimed the Kremlin was working on a similar plane to the X-37B but was promising to put nuclear weapons on the impending spacecraft.

Lt. Col. Aleksei Solodovnikov, an instructor at the Russian Strategic Missile Forces Academy in St. Petersburg is reportedly overseeing the plane’s development.

“The idea is that the bomber will take off from a normal home airfield to patrol Russian airspace,” he said, according to the state-run Sputnik News.

“Upon command, it will ascend into space, strike a target with nuclear warheads and then return to its home base.”