By Jason Palmer
Science and Technology reporter, BBC News
Kilo for kilo, space elevator payloads would cost much less than rockets
The prospects for the space elevator have been shaken up with a simple prototype using a broomstick.
Age-Raymond Riise of the European Space Agency demonstrated the device at a space elevator conference in December.
The project could see a 100,000km long tether anchored to the Earth as a "lift into space" for cheaper space missions.
While the approach could solve one of the idea's great technical hurdles, many issues remain, according to conference attendees.
First mooted by Russian scientist Konstantin Tsiolkovsky in 1895, the space elevator idea has captured imaginations as what would be the greatest space mission ever conceived.
The idea rests on balancing a number of forces; imagine fixing a short length of string to a football and spinning it - the string flies outward and remains taut.
Keeping an object moving in an orbit requires a centripetal force, directed Earthward. The object is inclined to move in a straight line, however, resulting in the so-called centrifugal force that acts against the centripetal force, keeping the string - or the space elevator cable - taut.
By making use of a space elevator cable or tether whose centre of mass is at geostationary orbit - tracking a fixed point on the Earth's surface - gravity provides the centripetal force that keeps the tether taut, providing a means to propel people and cargo into space.
A long-standing critical issue is how to power the "climber" that would ascend the cable into space. Prevailing ideas include delivering microwave or laser power to the climber beamed from the Earth's surface, or even from orbiting solar power collectors.
In December the private firm Eurospaceward hosted the Second International Conference on Space Elevator and Tether Design in Luxembourg to discuss such schemes.
But European Space Agency ground station engineer Mr Riise provided a markedly more simple idea.
He proposed sending power mechanically - effectively by providing a carefully timed jerk of the cable at its base.
Space elevator climber demo
To demonstrate, he employed a broomstick to represent the cable held in tension, and an electric sander to provide a rhythmic vibration to the bottom of the stick.
Around the broomstick's circumference he tied three brushes representing the climber with their bristles pointing downwards - meaning it took slightly more force to lower the brush assembly than to raise it.
The vibration from the sander allowed the assembly to slide upward along the broomstick as it moved slightly downward, but grip it as it moved slightly upward. The net effect: the assembly rose against gravity straight to the top of the stick.
The prototype's approach would make for a bumpy ride in practice, but Mr Riise believes the rhythmic tugging on the cable could be smoothed out.
"It would be possible to make a suspension system that completely decouples the cabin where the passengers are," he told BBC News. "For them it would be a linear movement with very little disturbance."
While the novel idea could greatly simplify the provision of climbing power to the space elevator, a number of considerable technical challenges remain, namely in the makeup of the cable on which the climber ascends.
The idea might first see use in skyscrapers here on Earth
Such a cable, at least 36,000km long and strained in the middle with all its weight, is no easy thing to produce. While next-generation materials, namely carbon nanotubes, could provide the enormous strength-to-weight ratio that would be required, debate rages on about how or even if cables of that scale and strength could be manufactured.
But the stakes are high; payloads could be sent via space elevator much more cheaply than by rocket.
Besides cheaper space missions and space tourism, the space elevator would allow the development of space-based energy solutions that would be otherwise prohibitively expensive.
"From my point of view, the space elevator project is important because it enables a far more directly useful project - installation of large space solar power satellites around the Earth to provide continuous, cheap, CO2-neutral, environmentally friendly energy," said Benoit Michel of the Catholic University of Leuven, who attended the conference.
"I firmly believe that the next century will have a large space-based industry and that industry will be the main energy provider for the whole mankind," he added.
Mr Riise said that he has been approached by commercial lift companies, who are researching new ideas for lifts in superscrapers. The simplicity of the approach makes it attractive when compared to other nascent ideas for powering lifts, such as compressed air.
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