Amazon founder Jeff Bezos joins fellow billionaires using their resources to open a new frontier in space exploration. They include:

•Tesla Motors founder Elon Musk's California-based SpaceX company is vying with Boeing to become the first private firm to fly astronauts to the International Space Station for Nasa some time in 2017.

•Next year, SpaceX is expected to send an uncrewed version of the company's Dragon capsule to the space station atop the company's Falcon 9 rocket. Mr Musk has said that his company could land humans on Mars in the next 10 or 12 years.

•Microsoft co-founder Paul Allen's Vulcan Aerospace plans an air pad in the sky to speed up deliveries from Earth at a lower cost than existing technologies allow.

•Vulcan will use a huge Strato carrier aircraft to launch spacecraft and probes into orbit.

•Virgin Group chief executive Richard Branson's Virgin Galactic rocket will be air-launched from under a carrier aircraft, similar to the firm's proposed tourist space plane. The company aims to offer suborbital flights into space to paying customers in the next few years.

•Virgin announced this month that it is beefing up its rocket power to allow the company to fly much larger payloads, with the aim of launching small satellites.

AGENCE FRANCE-PRESSE, REUTERS