Since the Wright brothers' first powered plane flight on 17 December 1903 - the historic event will be reenacted on Wednesday on the North Carolina beach of Kitty Hawk - aviation experienced its most dramatic progress after the 1950s.

But space exploration these past 46 years has been limited to orbital activities due to exorbitant costs and propulsion techniques that have barely improved since the first rocket was launched.

The National Aeronautics and Space Administration (NASA), shaken by the loss of the Columbia in February, wants to replace the fleet of space shuttles in the next 10 years with two orbital spacecrafts: one for carrying astronauts, another to ferry cargo.

The concept is not new, however, and several US lawmakers are critical of what they see as lack of vision in the US space agency.

If despite their financial difficulties the Russians have been able to provide a minimum service to the International Space Station after the Columbia tragedy by means of the Soyuz space craft, the Chinese also harbour major space ambitions for the 21st century.

This year marked China's first successful manned flight into orbit, and the nation has plans to send teams up to the Moon.

Space programme

In the United States, a number of lawmakers have been calling for relaunching the space programme, which has been under intense White House scrutiny since the Columbia accident.

The US and other countries are
planning ambitious space
programmes

At the centenary celebration of the first Wright brothers' flight on 17 December, President George Bush may announce his new space policy, including the possible resumption of flights to the Moon.

"We are wandering around and around in circles at the edge of this new ocean, going nowhere and doing nothing of importance," complained Space Frontier Foundation founder Rick Tumlinson in an October 2003 appearance before Congress.

The association of space enthusiasts, one of NASA's most vehement critics, has been pushing for a resumption of Moon flights, as well as manned flights to Mars and interstellar space.

NASA, on its part, six months ago launched a research programme on nuclear powered space travel that aims to shorten the length of the voyage itself and open new horizons to astronauts.

Private space travel

In the meantime, however, space travel is out of reach for normal people, a situation that private investors hope to remedy in the near future by staging a race for the development of a light vehicle that can reach the edge of space and return to Earth as planes do.

About 20 international teams, galvanised by a $10 million prize from the X-Prize Foundation, are currently trying to develop a reusable vehicle that would be able to ferry three people to an altitude of 100km.

From basic planes like this, the
world is today thinking of crafts to
ply between Earth and space

Under foundation rules, the vehicle should be capable of making the journey twice in two weeks.

An announcement on the development is expected in the next few months.

By 2050, other researchers, including David Smitherman of NASA's Marshall Space Centre, are working on the Space Elevator concept for space travel: a ribbon-like structure that would extend from Earth up to geo-stationary Earth orbit (GEO).

"The entire structure orbits the Earth in sync with the Earth rotation maintaining a stationary position over its base attachment at the Equator," Smitherman explained.

The cable used might potentially be made of a carbon nanotube material "that exhibits strengths 100 times stronger than steel".

"Such a structure would be used as a mass transportation system in the latter part of the 21st century for transporting people, payloads, gases and power between Earth and space," he added.