What is the X-37B plane up to this time? (Image: US Air Force Photo/Michael Stonecypher)

There it goes again. The mysterious X-37B plane is preparing to head into space for its fourth trip. But now, for the first time, we have a clue about what’s happening inside.

The X-37B, built by Boeing, is a miniature, uncrewed version of NASA’s retired space shuttle. It flew for the first time in 2010, and its most recent mission ended in October after 674 days. Throughout, US officials have remained tight-lipped about the space plane’s exact purpose.

Earlier this month, NASA revealed that on this trip the plane will carry nearly 100 small samples of different materials, including polymers, coatings and composites.


The idea is to see how the materials fare when exposed to a space environment for more than 200 days, perhaps giving an indication of how long the X-37B’s latest voyage will last – although it has previously flown missions lasting almost 2 years.

In addition, the plane will test a new type of fuel-efficient thruster that relies on electrically charged propellant. The thruster could prove useful in future for manoeuvring satellites that need to make minor orbital corrections.

Plans are for the plane to take off from Cape Canaveral Air Force Station in Florida on Wednesday. It’s not clear when the plane will return; previous missions have landed at the Vandenberg Air Force Base in California.