Seattle: Microsoft Corp. co-founder Paul Allen is planning to build a spaceship that could replace the Space Shuttle and put paying passengers into orbit this decade.

Lifelong space enthusiast Allen is hoping to launch unmanned rockets from a massive flying carrier plane to put government and commercial satellites into space and eventually evolve to human space missions.

Microsoft co-founder Paul Allen looks across at a model of a giant airplane and spaceship he plans on building, during a news conference about the plane on 13 December 2011, in Seattle. AP

Its wingspan will be about 385ft (117 metres), bigger than a football field and 70% longer than the wings of a Boeing 747.

The rocket itself will be made by private space company SpaceX, created by Elon Musk, the billionaire co-founder of PayPal. The rocket and carrier will be integrated by aviation and missile specialists Dynetics. The first test flight is targeted for 2015 with the first commercial flight the year after.

“I have long dreamed about taking the next big step in private space flight," said Allen. “To offer a flexible, orbital space delivery system."

The new company to manage the project, called Stratolaunch Systems, has the slogan “Any orbit. Any time."

Allen, the sole funding source for development, did not say how much he would spend on the project, but indicated it would be $200 million or more, an “order of magnitude" greater than the $20 million he spent backing the first privately funded, manned space flight in 2004.

Fifty-eight-year-old Allen— listed by Forbes magazine as the world’s 57th-richest person, with a fortune of $13.2 billion—is the latest in a line of tech billionaires with interests in the privatization of space travel. His space ambitions put him alongside Musk and founder Jeff Bezos, whose Blue Origin aims to put people into space at an affordable price, rather than the millions of dollars it has cost up to now. Richard Branson’s Virgin Galactic is also looking to transport passengers into sub-orbital space in the next two years, for about $200,000 a trip. It already has nearly 500 reservations.

Allen said he has long harboured space fantasies.

“I dreamed of becoming an astronaut," he said at the company’s launch at his offices in downtown Seattle. Poor eyesight ruined his dreams of becoming a pilot, but he said his ambitions for space travel never died.

Initially, Stratolaunch will aim to fly unmanned rockets to put mid-sized satellites into orbit, and perhaps fly cargo to the International Space Station, if permitted.

After that, Allen’s target is to fly paying customers into space, which he said had a massive potential market.