Tired of your ordinary earthly vacations? Some day soon you might be able to board a rocket and get a room with a view - of the whole planet - from a hotel in space.

At least, that is the sales pitch of several companies racing to become the first to host guests in orbit on purpose-built space stations.

"It sounds kind of crazy to us today because it is not a reality yet," said Frank Bunger, founder of U.S. aerospace firm Orion Span, one of the companies vying to take travellers out of this world.

"But that's the nature of these things, it sounds crazy until it is normal."

U.S. multimillionaire Dennis Tito became the world's first paying space tourist in 2001, travelling to the International Space Station (ISS) aboard a Russian Soyuz rocket for a reported $20 million. A few others have followed.