Full name: Jesse Newman
Location: Staten Island, New York
Question: As an undergraduate student in materials engineering, I was delighted to read the article about the space elevator. At first glance it seems laughable, but as I read on I was intrigued and hopeful about the prospect of such a technological feat. A few considerations still bug me: If the space elevator ribbon will need to be 50 percent carbon nanotubes, a substantial amount of carbon will be required for both the polymer matrix phase and the nanotubes themselves. At 26 pounds per mile, and for a ribbon that’s eight times the diameter of Earth, we’re talking about 1.6 billion pounds total, more than 50 percent of which will be carbon. Can Earth’s geosphere supply that amount without substantial environmental effects?
Edwards: At 26 pounds per mile and 62,000 miles, this would be 1.6 million pounds or 800 tons, or roughly 800 small trees.
Location: Larchmont, New York
Question: The article said that Brad Edwards has batted away many if not all possible objections to the space elevator, so I was wondering what provisions he has to deal with the radiation belts. For instance, in the nearby Van Allen belts there is intense ionizing radiation on the order of 10 million electron volts or more. Although it might be possible to shield the ascent vehicles, the main ribbon would be constantly exposed. Would the ribbon not be susceptible to gradual weakening from this exposure? In the far radiation belts there is intense electron energy. Is it possible to use the elevator to tap into the belts as a source of electrical energy, either for the elevator itself or to supply grid power on the ground?
Edwards: The carbon nanotube–composite matrix is extremely radiation resistant and can survive the radiation belts for roughly 1,000 years. The coupling between the ribbon and the radiation belt is very weak, so little energy can be produced by this method.
Full name: Robert Feyerharm
Location: Columbia, Missouri
Question: I have a few questions regarding the excellent ”Going Up” article. Would it be feasible to build an “elevatorless” space elevator? That is, to lift cargos into orbit using the laser alone, without using an elevator as a track? Why exactly is the elevator tower a necessary part of the elevator if the lasers are doing all the lifting?
Edwards: The lasers supply power, but they do not actually push the climber. The laser is converted to electricity and is used in motors that pull the climber up the ribbon. To push a substantial mass using a laser would require an extremely large laser and would probably melt anything used for the vehicle.
Full name: Wesley Schalamon
Question: In 1964, I along with Dr. Roger Bacon figured out how to make high-performance carbon fibers from a rayon precursor (working for Union Carbide Corp., Carbon Products Division), which later led to the product named Thornel. I would like to draw your attention to the graphite whiskers that Dr. Bacon produced in 1958. Their structure seemed exactly like the scrolled chicken-wire-mesh structure of carbon nanotubes, except they were longer. Why not build on Dr. Bacon’s work and make the whiskers into a practical length rather than trying to make nanotubes into a thread? I remember seeing Dr. Bacon’s whiskers, and they could be easily seen with the naked eye. The whiskers were grown in a graphite boule under high temperature, and I believe a technique could be developed to grow them continuously.
Edwards: The graphite whiskers are much weaker than carbon nanotubes and would be much more difficult to use for the space elevator. The nanotubes are also now being produced in comparably long segments.
Full name: Leigh Stevens
Question: I am interested in a number of things not mentioned in the article. What happens if a natural phenomenon like a meteor or a human crashes into the ribbon? What would be the consequences? The equivalent of repaving/filling pot holes in a road will need to be done. What are the anticipated maintenance costs? Eventually, a particular ribbon will come to the end of its ability to be safely operated. How would we safely decommission/eliminate the ribbon?
Edwards: Any ribbon that is severed would pass from Earth orbit into space or burn up in Earth’s atmosphere. Repair has been planned with the climbers, although we expect that little of this will be required except in special cases. To decommission a ribbon, we would likely release it into space or pull it up along another ribbon.
Full name: Shane M. Wilson
Location: Port Hedland, Australia
Question: “Going Up” was fascinating, but the first elevator wouldn’t need a ribbon supporting 13-ton climbers traveling at 125 miles per hour. Climbers the size of shopping carts, traveling at 10 miles per hour, would still revolutionize the use of space. The carts could transport consumables and equipment to a space station inhabited by assembly workers sent into orbit by conventional rocketry. At the station, satellites could be assembled from parts sent up by the elevator. Also, the global warming problem could be solved if we used the elevator to deploy sunlight-reflecting foil in orbit. Each year we could increase the quantity of foil to maintain the current climate. The fossil-fuel industry could save the world by funding the elevator.
Edwards: This is true to an extent. The ribbon needs to be a certain size to have a long life, so there really is a lower limit.
Full name: Emmett McGill
Location: Satellite Beach, Florida
Question: I fully support research into the space elevator, although the timetable seems a bit optimistic. In the interim, I believe a currently achievable method of access to space should be developed. It involves a maglev [magnetically levitated] system up the side of a high mountain range such as the Andes. Northern Chile would seem the best choice as it is close to the equator and in a politically stable country. This system would eliminate solid rocket boosters (which Wernher von Braun said should never be used to transport humans), would place the spacecraft in a controllable flight condition when exiting the maglev, and would alleviate the need to accelerate vast amounts of chemical fuel. In addition, the technology would have vast applications for earthbound uses, such as an adjunct to the interstate highway system.
Edwards: The magnet railguns have been conceived for some time, but the challenges (velocity required, length, cryogenics, launch forces) in completing them are easily comparable to the space elevator.
Full name: Bill Keener
Location: San Francisco, California
Question: I read the article on the space elevator with great interest. Mr. Edwards, does your design allow the cable to be temporarily detached from the earthbound platform so that it could be lifted out of the way of storms? While the equatorial Pacific Ocean is relatively calm, the possibility of high winds and electrical storms still exist.
Edwards: Detaching the lower end of the elevator is conceivable but challenging. The ribbon is designed to survive winds well above any that may occur at this anchor location.
Full name: William Wood
Location: Las Vegas, Nevada
Question: If you were to ride a space elevator, how would your sensation of gravity change as you went up? At the bottom, you’d presumably feel normal gravity, correct? At the top, would you essentially be in free fall around Earth? How would the transition appear to you? Would you feel increasingly weightless the higher you went?
Edwards: Initially, the gravity would slowly decrease at a few percentage points per hour and continue to get slower until, about seven days into the trip, you would feel no gravity at all.