The space elevator: going up? (part 1)
The first space elevator
The HighLift Systems NIAC study included a design for building the first space elevator that Edwards and Westling described in detail in their book. An initial deployer spacecraft, weighing about 80 tons, would be placed in low Earth orbit using several expendable rocket launches and assembled there, possibly with the assistance of a shuttle crew. The deployer would then use an electric propulsion system to gradually climb to GEO. Once there, it would begin unspooling the initial ribbon, 20 centimeters wide on average but only one micron thick, down towards the Earth. The deployer spacecraft would also drift above GEO to keep the center of mass of the system in GEO. The full length of the ribbon would be 100,000 kilometers, with the deployer spacecraft serving as a counterweight on the far end.
Once the initial ribbon was in place and anchored on the Earth’s surface, it can support payloads of about one ton. That is too small to be of use by itself, but it is enough to support the mass of “climbers”, vehicles that would crawl up the cable, adding additional ribbons to increase the elevator’s capacity. After about two years and over 200 climber missions, the ribbon would be large enough to support 20 tons. The space elevator could then be used to transport payloads into space: a climber weighing seven tons could carry 13 tons of payload into GEO in about a week. Smaller payloads could be carried to other orbits, such as LEO and MEO, because these spacecraft would need additional propulsion systems to reach those orbits.
To keep the climbers simple and lightweight, they would not carry their power systems with them. Instead, they would rely on beamed power, using a 350-kilowatt free-electron laser located on the Earth’s surface. The laser would target an array of gallium arsenide cells on the underside of the climber, which would convert the laser light into electricity to power the climber’s motors. The same laser would also beam power to the initial deployer spacecraft to power its electric propulsion system.
The HighLift Systems proposal called for anchoring the ribbon on the Earth in the eastern Pacific along the Equator. The location has relatively calm, clear skies, reducing atmospheric loads on the ribbon as well as permitting the laser to beam power to the climbers (because clouds would block the laser, multiple beaming stations would likely be needed in any case.) The anchor itself would be a mobile platform akin to the Odyssey mobile launch platform used by Sea Launch. The mobility of the platform would also allow it to shift the ribbon itself to avoid satellites and debris.
The NAIC study estimated that the technical cost—excluding legal, regulatory, and related issues—of building the first space elevator would be about $7 billion. (A second elevator could be built using the first for only about $2 billion more.) Speaking in Washington earlier this year, Edwards estimated the total cost of the elevator to be about $10 billion, and would be operational in 15 years. Once in place the elevator would cost about $1 million a day to operate. With efficient use of the elevator, it would be possible to launch enough payloads to bring the payload cost down to about $220 a kilogram—the mythical $100/pound benchmark widely quoted as the key breakpoint for enabling expanded commercial use of space.
Hazards and challenges
After this simple description, a space elevator might simple relatively straightforward, if not simple, to build and operate. However, such a structure would face a number of hazards if ever built. An extensive chapter in the Edwards and Westling book covers these hazards, including lightning, wind loading, meteoroids, satellites, orbital debris, atomic oxygen, electromagnetic fields, radiation damage, and oscillations. These hazards can be mitigated in a number of ways. For example, the study locates the anchor in the eastern Pacific in part because of its relatively calm winds and very low incidence of lightning. A mobile anchor can allow it to dodge larger spacecraft, while redundancy built into the ribbon would allow it to weather the impacts of smaller objects and micrometeoroids while maintaining its overall integrity. Coatings could also be applied to the ribbon to protect it from the corrosive effects of atomic oxygen. No hazard they addressed appeared in any way to be a showstopper.
A bigger near-term challenge is developing the technology needed for the elevator itself. While carbon nanotubes have shown considerable promise, they are created today in relatively small quantities. Composite fibers containing carbon nanotubes are today about as strong as steel, but still are far short of the strength needed for the elevator. Edwards acknowledged earlier this year that development of carbon nanotube fibers was the biggest technical issue facing the space elevator, with no alternatives on the horizon should development fall short. “That is the hurdle,” he said.
The space elevator also faces other technical hurdles. The laser needed for beaming power to the deployer spacecraft and climbers doesn’t exist yet, although one California company, Bennett Optical Research, has developed plans for such a laser. The magnetoplasmadynamic (MPD) engine the deployer spacecraft would use to climb from LEO to GEO is also confined to the laboratory at the present time. An alternative using chemical propulsion is available, but it would roughly double the mass of the spacecraft and reduce the amount of ribbon it could carry in half.
The NIAC space elevator study by HighLift Systems was completed in January 2003. Since then the two principals behind HighLift, Edwards and Michael Laine, have moved in different directions to continue work on the concept. In March, Edwards moved to West Virginia to take a position as director of research at the Institute for Scientific Research (ISR), a research and development corporation that works closely with NASA and other federal agencies. Edwards and a number of other ISR employees are working on various aspects of the elevator concept, and seeking NASA support to continue their work.
Laine, meanwhile, has founded a new company, Liftport, based in Washington state, to commercially develop a space elevator. The company’s business plan has evolved in recent months to become a group of affiliated companies, one attempting to develop and commercialize carbon nanotube technologies, another to provide public outreach and education services, and a third to provide venture funding for other companies developing space technology. All are tied together to commercially develop a space elevator within 15 years (the site features a countdown to its planned inauguration of its space elevator: April 12, 2018.)
There is a perception within the small community of researchers studying the space elevator that the concept is gaining momentum. That perception is not unwarranted: in June the elevator won an endorsement from the National Space Society, who called it a “potential breakthrough development” that could “dramatically change our concept of space transportation.” The emphasis should be on potential: there are still major technical challenges the project faces, not to mention legal, regulatory, and funding issues that could even dwarf the technical ones. Now more than ever, though, the space elevator may be primed to make the leap from the pages of science fiction to the hard reality of science fact.