The strange science of the US Air Force's top-secret space plane

For two years, an unmanned Boeing X-37B orbited the Earth. But what was the top secret mission all about?

 In the dead of night, a space plane landed at Nasa’s Kennedy Space Center after over two years in orbit. Although the US Air Force seems to be pleased with how this mission ended, it has been tight-lipped about what it was for.

At only 2.7 metres tall with a 4.2m wingspan, the unmanned Boeing X-37B orbital test vehicle looks like a smaller version of the Nasa space shuttle. It orbited the Earth for 780 days, performing secret experiments for the Air Force before returning home autonomously.

The Air Force says that these experiments “benefit the national space community” and concern areas such as advanced guidance, navigation and control, and reentry and landing. What we don’t know is why this plane was launched into space, or what it learned up there.

What is for sure, however, is that the plane has broken its own record for time in orbit, as the previous mission touched down on May 7, 2017 after 718 days. This is this fifth mission of its kind for a combined total of 2,865 days. It is the lightest orbital space plane launched to date at only 5,000kg.

“The Air Force stresses that this is primarily a reusable, robust space plane,” says Laura Forczyk, founder of the consulting firm Astralytical. “In order for it to be robust, it needs to be radiation-hardened, and in order for it to be reusable safely, it needs to be automated and be able to adjust.”

 


Reusable spacecraft have become more of a priority recently, especially with commercial enterprises such as SpaceX trying to create vehicles that can be reused indefinitely. Usually space missions involve a vehicle with parts that are either abandoned in space or thrown away once they return to Earth. With commercial spaceflight likely soon accessible to tens of thousands of people, reusable spacecraft have become an economic and environmental necessity.
The Boeing X-37 tests show the viability of being able to launch as a rocket, but land like a plane. It was sent up vertically, using the SpaceX Falcon 9 rocket, and successfully touched back down horizontally on a runway. “If it were no longer classified then I could see commercial companies integrating this into their systems,” Forczyk says.

We don’t know for sure what the military benefits of this space plane are, but there have been hints that the X-37B is able to change orbits rapidly. “It probably has thrusters on there that can lower its altitude,” says Forczyk. “It already flies pretty low, in low orbit. If it can lower its altitude even more, it can get closer, higher-resolution imagery of whatever we assume it is taking pictures of.”

Heather Wilson, former secretary of the Air Force, has hinted that the X-37B can change its orbit to dodge away from anyone trying to track it. Speaking at the Aspen Security Forum in July 2019, she said the craft can change the shape of its orbit and use the Earth’s atmosphere to maneuver. She says this means “our adversaries don't know – and that happens on the far side of the Earth from our adversaries – where it's going to come up next. And we know that that drives them nuts."

Forczyk believes that this is misleading, pointing out that amateur skywatchers have been tracking the space plane in orbit since its launch in 2017. Considering the fact that the aircraft is only the size of a van, it's a challenge to spot with the naked eye, but hobbyist observers have managed to find it with relative ease, and haven’t appeared to see these manoeuvres taking place.

Dutch astronomer Ralf Vandebergh has managed to photograph it twice. To take the images, Vandebergh had to wait until the space plane came above him in its orbit. The first time he tried to photograph it was on June 29, 2019, but conditions were less favourable and he had to take the picture from too far away to get a clear shot. The second time on July 2, the plane came directly above him and he was able to get a better shot.

This time he noticed that he had managed to capture an image looking directly into the open payload doors. “We look directly inside the payload bay and a quick photo-technical analysis can conclude that that space is filled mostly with white pixels [and is] thus reflecting a lot,” he says. “In other words: we could conclude that – at the moment of imaging – there probably were no large elements left in the payload bay.” This doesn’t mean that Vandebergh thinks the payload bay was empty, but rather that the objects were too small to see.

“There probably have been some satellites in the payload bay for carrying to orbit. Also, other things could have been deployed from the payload bay like solar arrays to feed the electrical power of the vehicle,” Vandebergh adds.

For now, exactly what the X-37B was doing for the past two years will remain a mystery. As far as we know, the findings could have huge implications for the future of surveillance, or it could simply be, as the Air Force like to focus on, a further test of reusable spacecraft technology.

Maria Mellor 

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