The plane has been circling the Earth for the past nine months as a test for the next generation of space vehicles

It looks like a miniature space shuttle, complete with solar panels for power and a cargo bay to carry satellites or scientific experiments into orbit. But unlike the venerable Discovery, Endeavour or Atlantis, the US Air Force's X-37B space plane comes without one crucial element: human astronauts.

The space plane has been circling the Earth for the past nine months and will land some time this week at the Vandenberg Air Force Base in California. Officially known as the Orbital Test Vehicle, it has been flying as a technology testbed for the next generation of space vehicles.

The X-37 project was started by Nasa in the late 1990s as a way of getting into space more cheaply and was adopted by the military a few years later. The first flight was designed to test equipment, sensors and materials in a space environment, with a view to using these in future space-based technologies.

Exact details of the mission, including costs, have been classified by the military, though amateur astronomers have watched the orbits of the X-37B as it has travelled around the Earth since its launch in April.

According to Space.com, the first mission will emphasise the testing of "technologies necessary for long duration reusable space vehicles with autonomous re-entry and landing capabilities". The plane is designed for low-Earth orbits, similar to the civilian space shuttle.

The space plane is around 9 metres long and has a wingspan of 4.5m, compared to the 37m-long and 23.8m-wingspan space shuttle. It can orbit at similar speeds of up to 17,500mph. But, unlike its iconic cousin, the X-37B is designed to stay in space for months at a time before landing, by itself, on a runway. The plane's landing this week will be the US space programme's first attempt at an autonomous re-entry from orbit.

Roger Handberg of the political science department at the University of Central Florida in Orlando told Space.com that the X-37B was a natural extension of the US military's forays into unmanned aerial vehicles, which are increasingly being used in warzones for reconnaissance or to drop bombs. "From the perspective of international observers – especially in space-aspiring states such as China, the X-37B programme just reinforces their view that the US is pushing to gain first mover advantage in rapid response including possible weaponisation of space using this vehicle or a derivative."

The USAF plans to fly another X-37B in the spring.