First European Workshop on Space Elevator Climber and Tether Design
Luxemburg, November 10-11, 2007 (published in Euroavia News - 4/2007)
In his 1979 book 'The Fountains of Paradise' famous sci-fi author Arthur C. Clarke described an efficient way for mankind to access outer space. He imagined a giant structure called the Space Elevator, rising from the ground and linking with a satellite in geostationary orbit (GEO) some 36.000 km above sea level. Its goal was to get cargo and people into space without having to use rockets, making it much more cost-effective and paving the path for human space exploration and, eventually, colonization.
Almost thirty years later, people from all over the world gather in Luxemburg for the First European Workshop on Space Elevator Climber and Tether Design. In the meantime, the world has changed. For a long time, the actual construction of a Space Elevator seemed far out, and wouldn't happen at least for another couple of centuries. However, technological advances are putting the highway to space in reach for the current generation. With some of the technology that is currently being developed at the worlds leading universities and research centres, we could be going up in just a couple of decades.
Actually, the Space Elevator concept is fairly straightforward: imagine swinging a yo-yo outwards. If it's strong enough, the string connecting your hand to the yo-yo stays stretched. That's basically why a long cable, connecting a base station near Earth's equator to an outer space counterweight, is stretched too. Once you have a tether like this, you can send elevator vehicles called 'climbers' up and down. This provides much more efficient space travel than has ever been possible with conventional chemical rockets (cf. Rockets vs. the Space Elevator). The cost to put a payload in Earth orbit would most likely come crashing down, opening up huge possibilities. To only name a few, huge space stations, big solar energy plants, telescopes, space hotels and interplanetary vehicles become feasible for the first time. In fact, emerging businesses are needed to pay for the initial investment of building the space elevator, estimated to be $15 billion by dr. Brad Edwards.
Conventional rocket technology is subject to the rocket equation. This means that the functional mass of a rocket can only be a small fraction of its total initial weight. The tanks, the motors and - more fundamentally - fuel, take the rest of the mass. It's the only current way of getting up into Earth orbit, and it's dirty. Basically, we're talking about an explosion. Although we've succeeded in fully controlling it, there always remains some small unpredictable part, and the few flaws that occur mostly turn out to be fatal. Actually, according to space historian Randy Liebermann, the reason most space agencies and companies still stick to chemical rockets is mainly because of the 'never change a winning thing'-habit, because we've had some experience with these things and we know they normally work.
Because the Space Elevator climbers can use Earth's rotation to reach orbital speed and because they don't take any fuel with them, they use far less energy to reach geostationary orbit. The needed energy can be beamed up wirelessly by using a powerful laser on the ground and advanced solar cells attached to the climbers. Comparing rockets with laser-powered electrical motors, the Space Elevator turns out to be far more controllable, more efficient and less polluting. But it's an entirely new concept, and as with most of these, big technological hurdles remain to be taken. And we'll need money of course, lots of it...
Well, what are we waiting for, you might ask. The answer is simple, really. As with all of these extreme engineering projects, it's not hard to spot major problems. The really big limiting factor is the strength of the cable connecting Earth to space. Being as long as 100.000 km, the needed tether has to be far stronger than anything ever built before to be able to support its own weight, together with that of the climbers. The tensile strength, with a safety factor of two, would have to be something like 130 GPa, whereas current materials as ZylonTM do not exceed 5.8 GPa. In the meantime, the needed material would have to be extremely light. This all seems quite impossible. But it probably isn't. Say hello to carbon nanotubes.
The second day of the Space Elevator conference in Luxemburg was all about these. Ever since 1991, these materials have been more and more promising. Being special carbon molecules just like graphite and diamond, they are amazingly strong and extremely lightweight at the same time. We learned all about them from prof. Shanov from the University of Cincinnati and dr. Motta from Cambridge University.
Carbon nanotubes nowadays can be grown to lengths of about 18 mm. These strands can then be made into a tether using advanced weaving techniques. Theoretically, a cable consisting of carbon nanotubes can be as strong as 300 GPa, more than enough for them to be used as Space Elevator tether material. Up until now, the bulk strength of laboratory-grown nanotubes did not surpass that of conventional fibres. Dr. Motta argued defects are to blame, yet was optimistic about solving this problem by tweaking the manufacturing process. Anyhow, carbon nanotubes have got an enormous potential in various domains, ranging from tiny biosensors to super-strong body armour or even lighter and stronger composites for airplanes.
The cable material is not the only issue the Space Elevator is facing. Going up there also means dealing with - amongst others - corrosion, meteorites, space debris and the Van Allen radiation belts. In his 1999 book 'The Space Elevator', dr. Brad Edwards sums up all of these and proposes a highly elaborated design of what an eventual Space Elevator might look like. It uses a 100.000 km tapered ribbon (a flat cable of varying width) with climbers that receive their energy from a strong laser on the ground. This design is now called the 'Reference Space Elevator'.
That didn't stop scientists from thinking outside the box, though. For example, a different system was proposed by prof. Michel Benoit during the conference, which included winding up the long cable to get the elevator cars into space easily. It could be a nice alternative, although it requires an even longer and stronger cable and tons of energy on the Earth, and - which is more of a problem - in space.
Back to reality now. Meet the Space Elevator Games! Think about how to design and construct a lightweight structure climbing a 100 meter ribbon at an average of 2 m/s, only using energy delivered to it wirelessly from the ground. That's exactly what up to twenty student teams from all over the world tried to do in October 2007, at the third edition of the Space Elevator Games in Salt Lake City. The games were started in 2005 to raise public awareness of the Space Elevator concept and to get students familiar with it. Back then, the goal was to climb a 50 m ribbon using a provided light source. Think of solar panels and some electrical motors attached to a lightweight construction. No one went up fast enough, so the NASA-provided prize money stayed in the purse for 2006.
For the second edition of the games, the teams had to bring their own power source. All kinds of systems appeared at the bottom of the ribbon: laser-based, using concentrated sunlight ('heliobeaming') or microwaves. Only a few of them made it up. One team came within two seconds of claiming the prize, the Canadian USST team from the University of Saskatchewan. The challenge in 2007: go twice as high and twice as fast. Again, USST came within seconds of taking home the purse, but didn't get to the top in time.
The goals of the upcoming 2008 edition are still unclear at the moment of writing. Possibly, the beam source (a powerful laser) will be supplied by the organization to allow for lower-budget teams. Co-organizer Ben Shelef told us Spaceward, the organizing foundation, is considering setting the height requirement to 1 km and replacing the flat ribbon by a round cable, suspended by a helium balloon. This should not discourage any Euroavia member from starting a team, though, as the prize money increases as well. For 2008, it will be $900.000 for the climber making it up fast enough.
Update: the goals for the 2008 are set and can be found at the Spaceward website. They indeed include a 1km high climb. The prize money is substantially higher, though: $2 million is offered for the team that makes it up there with an average speed of 5 m/s.
Next to this 'Power Beam' climber game, there also is a 'Strong Tether' competition. No less important, this game encourages researchers from all over the world to try and make that first real carbon nanotube cable. All they have to do to win the purse of, also, $900.000 is beat the 'house tether', made by the organizers. Required is a two meter long closed loop of rope that can withstand a force of more than 8.000 N and weighs less than 2 grams. Don't bother participating with a conventional fibre, normally only carbon nanotubes are able to outperform the house tether, because the organizers are allowed to use commercial products and their cable can be as 'heavy' as three grams.
Is the Space Elevator ever going to take part of our future? The question still remains, but technological successes over the past couple of years have made the project increasingly feasible. If carbon nanotubes can be used in all kinds of spin-off technologies, their cost could be drastically lowered, and private companies could use them to pay for part of the initial investment costs of building the elevator.
Still, huge as the possibilities of a future space elevator are, there have to be people that are interested in actually using it. As long as there is no promise of money, as long as there is no real market for going into space as cheap as possible, rockets will be our way into Earth orbit. When larger scale space tourism and space industry start getting real, the idea of a space elevator could do so too. That is entirely up to us. And off course, we'll need some rockets to put the first elevator into orbit. But after that, off we go. To Earth orbit, to the Moon, to Mars and beyond. Using our very own bridge to the stars.
by Joris Gillis and Simon Vanden Bussche
Interesting links:
- www.eurospaceward.org
- www.spaceelevator.com
- www.spaceelevatorblog.com
- www.spaceward.org
- BBC NEWS: Coming of age for future fibres: http://news.bbc.co.uk/2/hi/science/nature/7038702.stm
