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For many of us space is a bit of a mystery - but it's just become even more mysterious...

On Sunday, the United States Airforce launched an Atlas V rocket into orbit, carrying an X-37B space plane.

Yep, space plane!

The strange thing about this space plane, is that its mission is top secret! No one, apart from a tiny handful of top military experts, know what the aircraft is tasked with doing.

The plane was launched from Cape Canaveral in Florida on Sunday - it was supposed to launch on Saturday but the weather was too bad.

Rockets can only launch if the weather is clear as wind or cloud can put the safety of the launch at risk.

What we do know is that the aircraft, also known as an Orbital Test Vehicle (OTV), will deploy a satellite into orbit and also test power-beaming technology.

The small plane is unmanned, which means there are no astronauts on board the vehicle - it is controlled remotely from Earth.

It is able to fly back down to earth and land on a runway like a standard airplane, meaning it can be re-launched over and over.

The launch was dedicated to the front line workers and those affected by the coronavirus pandemic. A message including the words "America Strong" was written on the side of the rocket.

This is the sixth time the plane has been to space.

The Pentagon - the top military building where America's most senior military officials work - has revealed very few details about the aircraft's missions in the past.

"This X-37B mission will host more experiments than any other," Secretary of the Air Force Barbara Barrett said earlier this month.

She said one of the experiments will test the effect of radiation on seeds and other materials.

Although it is often referred to as a spy plane, the US Air Force has never confirmed if the rocket is monitoring other countries or satellites. Some experts have previously said it would be difficult to monitor other satellites.

We may never know what the secret mission really is...