The idea of a space elevator that lifts people and cargo from Earth into the big, black beyond has been a dream of mankind for more than a century.
News that Thoth Technology, a Canadian firm, recently patented a 20-kilometre space tower has reignited interest in what has long been considered a far-fetched concept.
Aeronautics experts say that while Thoth's concept is intriguing, it's a small step rather than a giant leap towards the goal of travelling into space using something other than a conventional rocket.
A space elevator "is still rather an academic idea, rather than something we're going to start building next week," says Ted Semon, president emeritus of the California-based International Space Elevator Consortium.
Like a cable car
For decades, there has been an abiding desire to develop a so-called space elevator as a transportation system for vehicles and satellites to save the exorbitant costs associated with launching a rocket into space.
The classic conception of a space elevator is a giant cable tethered to the Earth's surface near the equator, with a counterweight out in space beyond geostationary orbit (approximately 36,000 kilometres up).
The scientific rationale is that the combination of gravity (stronger on the lower end) and centrifugal force (stronger on the upper end) would ensure that the tether would remain tense and straight over a single position on Earth.
What Pembroke, Ont.-based Thoth Technology is proposing is an inflatable tower that could carry a space elevator to a height of around 20 kilometres, and theoretically to 200 kilometres, into low Earth orbit.
The structure, which Thoth had previously patented in the U.K., would be made of stacked rings of Kevlar cells inflated with hydrogen or helium.
An elevator could theoretically climb up the tower carrying all manner of cargo, from spacecraft to satellites, possibly even moneyed tourists looking for an otherworldly view.
More of a platform
According to Caroline Roberts, president and CEO of Thoth Technology, the company hopes to build a 1.5-km-high prototype within five years.
Brendan Quine, the inventor behind the patent, unveiled a seven-metre scale model in 2009 at Toronto's York University, where he is an associate professor.
While Thoth's concept is intriguing, it's not really a space elevator in the traditional sense, says Ron Turner, senior science advisor to the NASA Innovative Advanced Concepts program and a distinguished analyst at U.S. research institute ANSER.
He says it falls short of the classic conception of a giant shaft that reaches hundreds of thousands of kilometres into space. And once you get to the top of Thoth's proposed platform, you still need to use a conventional rocket to get into orbit, he says.
"In the grand scheme of human progression out into space, it doesn't have the same appeal as the full-blown space elevator," says Turner.
The idea of a gleaming metal beanstalk rising up to the stars was first envisioned by Russian scientist Konstantin Tsiolkovsky back in 1895, after seeing the Eiffel Tower in Paris.
But it was eventually abandoned as a mere "thought experiment," in the words of the late science-fiction writer Arthur C. Clarke.
In 1960, a Russian engineer named Yuri Artsutanov determined that the idea may not be so outlandish after all, provided you had a material that was strong enough to support the tension between a base station on Earth and a counterweight in space.
Around this time, a U.S. engineer named Jerome Pearson had a similar idea, but he went further, calculating the material and tensile strength necessary to make it a reality.
In the early 2000s, physicist Bradley Edwards brought the idea closer to the mainstream after publishing papers that suggested carbon nanotubes may have the tensile strength necessary to support such a colossally tall structure.
If the world is to ever witness the manufacture of a space elevator, ISEC's Semon says engineers need to solve two problems: Ensuring the tensile strength of the cable and finding a way to power the elevator wirelessly.
Theoretically strong enough
In the past decade, NASA has held a number of Centennial Challenges that have attracted proposals to help realize this vertiginous dream.
In 2009, a team from the Seattle-based firm LaserMotive won the Space Elevator Power-Beaming Challenge Games — and $900,000 — after their laser-powered robot climbed a 900-metre cable suspended from a helicopter in under 7 1/2 minutes.
While innovations such as these are heartening, engineers are still a long way from making the space elevator a reality, says Semon.
Scientists have created three or four materials that are theoretically strong enough to support such a structure, Semon says, including carbon nanotubes and boron nitride nanotubes. But "the material to make a real space elevator has not been developed yet in quantities large enough to build a space elevator," he says.
While tensile strength is an abiding issue, Turner says an even bigger hurdle may be dealing with orbital debris, commonly known as "space junk," which refers to the shards of equipment from satellites and space vehicles that orbit the earth.
Turner says that even if someone were able to build a space elevator, a sizeable piece of space junk could "fatally sever" it.
"My personal bias is that the debris problem will continue to be a fatal flaw to the elevator concept," says Turner.
"Before I would invest any of my money in this project, I would need somebody to convince me that they really, really thought that they could surmount the orbital debris problem."
With files from Emily Chung