If you can make it into low-Earth orbit – about 160 kilometres up – then you are halfway to anywhere in the solar system. Sci-fi writer Robert Heinlein’s remark has become a mantra in the space community, mainly for its irony: despite leaps in rocket technology costing billions of dollars, those first 160 kilometres are still the hardest.
Now, with backing from NASA, a handful of entrepreneurs are going all out to crack the problem. Their solution is a device that is almost the complete opposite of the brute-force approach so long embodied by the crackling power of the rocket engine. They want to step into a small airtight box, push a button marked “spaceâ€, and ride an elevator all the way up a cable reaching far into the sky.
Even the most optimistic admit that a functional space elevator is still at least a decade away. Yet the idea has been gathering momentum since 1999 when a NASA study claimed that a space elevator was feasible. Earlier this year, US company LiftPort successfully unrolled a 1.6-kilometre-long carbon ribbon in the skies above Arizona, stretched it taut using helium-filled balloons and sent a robotic climber scrambling up part of its length (). The company aims to build a functioning space elevator by 2018.
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This October will see the second round of the Beam Power and Tether challenges, two competitions part-funded by NASA’s new Centennial Challenges programme. The first offers prize money to teams that can build devices capable of climbing up a ribbon cable 61 metres long. In the second, teams will have to build lightweight but extremely tough tethers. To date, two dozen teams, representing the US, Canada, Germany and Spain, have signed up – double the number of participants in last year’s first round.
In December, Washington-based company Tethers Unlimited will take another step in the space elevator race. MAST, the company’s Multi-Application Survivable Tether, is due for launch from the Baikonur Cosmodrome in Kazakhstan. Once in orbit, three small satellites will deploy a 1-kilometre-long tether woven from strands of Zylon, a high-strength Kevlar-like polymer. Then the satellites will move up and down the tether to monitor how it survives wear and tear out in space – vital information for anyone hoping to build a workable space elevator.
Even if this test succeeds, crucial questions remain. Can a lightweight cable ever be strong enough to stretch all the way into space? And even if it can, will it take an elevator into orbit any time soon?
Whatever the truth, NASA’s new philosophy of giving more money and time to small entrepreneurs with big ideas has helped push both space elevators and tether technology to the fore. Not before time: as a means of lifting things into orbit, rockets are close to their maximum efficiency, both in terms of technology and cost. To launch anything of significance into space costs between $30 million and $100 million, and that doesn’t include the cost of the satellite or spacecraft. These figures haven’t budged for years.
Those companies that have tried to bring launch costs down to Earth, like entrepreneur Elon Musk’s SpaceX, have met with serious setbacks. With NASA struggling to make President Bush’s return-to-the-moon plan a reality, the agency is thinking and spending more broadly in its search for cheaper, more efficient ways of getting into space.
While happy that NASA is finally bringing some funding to the space elevator idea, companies such as LiftPort and Tethers Unlimited have no intention of waiting for the space agency to come onboard. Bradley Edwards, entrepreneur and author of NASA’s 1999 concept study, believes that most of the research, prototyping and ultimately construction of space elevators will be done privately. “Financing is the key to progress on space elevators,†he says. “We don’t really see the space agencies playing a major role in the space elevator development, construction or operation.â€
This seemingly modern concept was first mooted by 19th-century Russian space visionary Konstantin Tsiolkovsky, who wondered why humans couldn’t place a “celestial castle†in space at the end of a spindly tower, to be reached by humans in an elevator running up and down the tower’s length. Tsiolkovsky proposed building his castle from the ground up, a Herculean feat even for today’s engineers.
It took another Russian scientist, Yuri Artsutanov, to suggest the idea from which all subsequent space elevator concepts have sprung. In a 1960 paper published by Pravda and titled “To the Cosmos by Electric Trainâ€, Artsutanov proposed that rather than building from the ground up, a cable could be deployed from a satellite downwards until it could be attached to a base station on the ground or onto a platform at sea.
To have any hope of success, the satellite would need to be placed in geostationary orbit – some 36,000 kilometres above sea level – so that the bottom of the cable would hang above a fixed point on the Earth’s equator and could be anchored safely to the ground. Artsutanov realised that by placing his satellite in this orbit, the net force on the cable dangling beneath the satellite would be downwards. To counterbalance this, and to prevent the whole thing falling to the ground, he reasoned that he could attach a massive object such as a small asteroid to the end of the cable and place it in a higher orbit, where it would act as a counterbalance. The result: the cable would be held taut through a combination of centrifugal force on the asteroid pulling it outward, and gravity pulling it downward.
“Once the cargo reaches the top it can be released into geostationary orbitâ€
Once in place, Artsutanov suggested that “trains†powered by an electric current running through the cable would carry material and people into orbit in much the same ways as an ordinary elevator. Once the cargo reached the top of the cable, it could simply be released into geostationary orbit. “The most complicated aspect,†Artsutanov wrote, “is probably the very beginning.†And so it has proved. Attempts to develop a workable prototype from Artsutanov’s idea have faltered largely due to requirements of mass and strength: the cable must be strong enough to withstand the incredible forces working to snap it, yet light enough to make its construction and maintenance practical.
The 1999 NASA concept paper envisioned a metre-wide ribbon 47,000 kilometres long and capable of carrying loads of up to 15 tonnes from Earth to orbit, the journey taking several days at a top speed of about 200 kilometres per hour. A working space elevator could therefore have a dramatic impact on the cost of hauling things into orbit: reducing costs from $22,000 per kilogram to perhaps less than $1.50 per kilo.
Such tantalising prospects prompted NASA to choose space elevators as a flagship competition in its Centennial Challenges programme, launched in 2005. It has not been easy going. Last October, 10 teams attempted to win a $50,000 prize for developing robotic climbers that might evolve into elevators to the stars. They had to meet very harsh criteria: the robots had to climb a 61-metre cable powered only by the light from a commercial searchlight shining upwards from the ground onto their photovoltaic cells. The team that carried the most weight to the highest point while maintaining an average speed of 1 metre per second would be the winner.
Alas, no team met the speed requirement, and the 12-metre height record, set by a team from the University of Saskatchewan in Saskatoon, Canada, fell far short of the programme’s ambitions. The four teams in the 2005 Tether Strength challenge also came away empty-handed. Again for a $50,000 prize, teams were required to build a tether lighter than 2 grams that could outperform a “house†tether made from commercially available materials by non-profit Spaceward Foundation, which is running both the beam and tether challenges for NASA. Depressingly, the house tether outperformed the best commercial effort, managing to carry 590 kilograms before snapping as opposed to 544 kilograms for a tether built by Centaurus Aerospace of Salt Lake City, Utah.
While such results might be seen as disappointing, many of last year’s participants will be back this year. A team from the University of British Columbia, which fared best in the Beam Power challenge, is aiming for that prize again and will also take on the Tether challenge. “We were awarded ‘Most Likely to Win in 2006’,†jokes engineering physics student Steve Jones, who is leading a team of 30 students in this year’s competition.
Jones says his team has learned from the 2005 competition. “It is difficult to accurately account for power losses in every stage,†Jones says of the Beam Power challenge. “But we gained a lot of valuable experience.â€
The combined purse for this year’s Beam Power and Tether challenges is $400,000. While more than the 2005 purse, NASA’s offering is unlikely to make a dent in what everyone agrees will ultimately be a multi-billion-dollar undertaking. “I don’t know what DuPont spent to develop Kevlar, but it was a hell of a lot more than the [Centennial Challenges] prize offered last year,†says Robert Hoyt, CEO of Tethers Unlimited.
Hoyt’s company is taking a different path altogether: it isn’t pursuing a space elevator. Instead, the company is developing a tether technology called MAST for spacecraft propulsion, where the idea is to drag a tether through Earth’s magnetic field and use the collected energy to power a spacecraft. Another plan is to take objects already placed in Earth orbit and send them to the moon using a rotating tether similar to a slingshot.
Those pursuing space elevators will find research by Tethers Unlimited useful, he says. “Many of the big challenges are essentially the same for space tethers and space elevators,†he says, noting that both require reliable climbers and power sources. Hoyt hopes the MAST tether will also make strides against another challenge facing space elevators: how to survive in the space environment. “Atomic oxygen, micrometeoroids and orbital debris, UV light and radiation all can cause degradation of materials in space,†Hoyt says. To that end, the MAST tether will be coated with a new polyarylene-based polymer that was found to resist oxidation in experiments on the International Space Station.
“Perhaps the biggest challenge is finding a material strong enough for the space elevator cableâ€
Perhaps the biggest challenge is finding a material strong enough for the elevator cable. A research paper published in May in the Journal of Physics: Condensed Matter (vol 18, p s1971) could dash the hopes of the carbon nanotube enthusiasts. According to Nicola Pugno of the Polytechnic of Turin, Italy, while carbon nanotubes are amazingly strong individually, manufacturing flaws will make them much weaker when ganged together on the scale required for a space elevator. Pugno says that if a nanotube lacks even one atom, its strength is reduced by 30 per cent. According to her statistical model, atomic-scale defects in the vast quantities of nanotubes that would be needed for a space elevator cable will, almost inevitably, reduce any elevator cable’s strength by at least 70 per cent.
The wrong stuff
Edwards admits that the carbon nanotubes being produced in volume, particularly in China, France and Japan, just aren’t right for space elevators. “Right now most of the carbon nanotubes produced are short and tangled,†he says, the kind of carbon nanotube useful for strengthening construction materials like concrete, for instance. “Optimally the nanotubes we need are long and aligned.†Edwards says about 600 tonnes of carbon nanotubes would be needed to construct an initial space elevator capable of carrying 15 tonnes of cargo.
Like Pugno, Hoyt isn’t optimistic about the evolution of carbon nanotubes as building blocks for space elevators, or for tether technology in general. “It would be foolish to say ‘never’,†Hoyt says. “However, it is clear that building a space elevator will require pushing our capabilities in nano-engineering and material processing to a level of perfection as yet unheard of.†Rather than “wait for unobtainiumâ€, Hoyt says that MAST uses a braided structure that is durable, light and ready to use now.
In addition to NASA funding, Tethers Unlimited has support from DARPA, the US Defense Advanced Research Projects Agency, and this could boost interest in space elevators in a different way. The company’s MXER (Momentum-Exchange tether propulsion) concept would use a tether to “throw†a satellite or spacecraft from one point to another, afterwards gathering energy from solar panels to regain any orbital altitude lost during the throw. MXER is still in early development, but if it makes it off the drawing board it will be extraordinary: a lightweight, high-strength tether up to 150 kilometres long.
Meanwhile, there are the 2006 Centennial Challenges. This year’s Beam Power and Tether competitions will occur during the first ever X Prize Cup event in New Mexico, which will also feature rocket plane races and other forward-looking space technology. While space elevator entrepreneurs would love someone to put up the $10 million award that spurred the original Ansari X Prize competition, Peter MacNeeley, another member of the University of British Columbia team, says that for most teams involved, money is not really the motivator. “With no rockets required, the cost of travel into space would be reduced by a thousandfold,†he says. “This would literally open the gate to the final frontier.â€
