Many conspiracy theorists already believe this can happen.

London, Oct 11 A Boeing chief has suggested that the company’s mysterious unmanned space-plane, called X-37B, developed for the US Air Force, could be scaled up and modified to carry astronauts.

The company’s X-37B project chief Art Grantz revealed that at least two more versions of the 9-metre long space-plane are under investigation – one of which involves adding a crew to a much-enlarged version of the space drone, New Scientist reported.

If built, the new version would give the US back its ability to shuttle people to the International Space Station.

The X-37B is launched on an Atlas V rocket and has small thrusters that allow it to change its orbit at the whim of ground controllers.

According to Aviation Week, Grantz said that the next evolutionary step for the spacecraft is to have it deliver cargo – small stuff like gyros and pumps – to the ISS using the capacity of its current payload bay.

Then, he said, the machine will be scaled up from its 9-metre length to 14.3 metres, allowing even bigger payloads to be delivered to the station.

Success at this level would then pave the way for “a human-carrying derivative” capable of carrying “five to seven astronauts”, Grantz added.

Grantz suggested the possibility at Space 2011, an American Institute of Aeronautics and Astronautics conference in Long Beach, California, last week