WEB EXCLUSIVE

Expert Forum With Brad Edwards

Thursday, September 23, 2004
RELATED TAGS: SPACE FLIGHT

In our July cover story, “Going Up,” contributing editor Brad Lemley explored maverick aerospace engineer Brad Edwards's wild plans to build an elevator into space. The idea caught the imagination of our readers, who had many questions. Edwards, contributor to several space elevator organizations and president of Carbon Designs, a developer of high-strength materials, has graciously answered a selection.

Full name: David O. Scaer

E-mail: vergerdecedres@yahoo.fr

Location: Roanoke, Virginia

Question: How thoroughly I enjoyed the article on the space elevator [“Going Up,” July]! The sheer whimsy of it, plus the notion that it just might work, combined to make for a great read. One of the places I got stuck on was how all the energies of the various elevator components get managed. If it takes a big rocket to get a spool of ribbon into geosynchronous orbit in the first place, would it not take similar energies to unwind it back toward Earth (and still more energy to unreel a counterweight away from Earth)? Wouldn’t the dangling end of a 22,300-mile-long ribbon have to be deorbited with a big booster just to get it to approach Earth again?

Edwards: From geosynchronous orbit the ribbon would be pulled down by gravity, and the counterweight would be moved upward by an electric propulsion system and the outward acceleration due to Earth’s rotation. No large boosters would be required. The end of the ribbon descending to Earth would need to be slowed, which would be done by brakes on the spacecraft. We should also remember that the energies required here are very manageable when spread out over a week or so. Boosters are large and impressive largely because they are inefficient.

Full name: Jim Chamberlain

E-mail: jfchamberlain@earthlink.net

Location: Thousand Oaks, California

Question: The story about the space elevator only discusses the strength of the cord used to fabricate it. Nowhere does Brad Lemley address the matter of tangential velocity. At Earth’s surface the velocity at the equator is approximately 1,048 miles per hour, and at the top of his elevator the cord would need to have a velocity of about 17,280 mph. Any object traveling up the cord must have its tangential velocity steadily increased to remain geostationary, and the cord could not provide that energy. If you got off the elevator at the space station, you would simply fall right back to Earth without the necessary orbital speed necessary at the 240-mile altitude of the station.

Edwards: The orbital velocity is supplied by the ribbon as the climber ascends. This is easily accomplished if the ribbon bends very slightly (less than a degree). It is true that if you ascended the ribbon to only 240 miles up you would fall back down to Earth if you let go. If you ascend to 25,000 kilometers, you would fall into an elliptical orbit, with its lowest altitude being that of the station. If you ascend it to geosynchronous orbit, however, you would be in orbit when you stepped off. If you ascend even further, you would have enough velocity to escape Earth’s clutches and travel to the moon or to Mars.

Full name: William H. Shallenberger, PE Ret.

E-mail: billshall@juno.com

Location: Oxnard, California

Question: What an interesting article and a fascinating concept. Here is one of my concerns: As Earth rotates, the gravitational forces of the sun and moon cause tidal movements in the oceans. These waves are restricted by the continents and by friction on the seafloor. What effect would these forces have on the space elevator? Would the outer end of the ribbon wave back and forth? In doing so would it be straight, as if hinged from the Earth end, or would it assume some other shape?

Edwards: The gravitational forces of the sun and the moon can move the elevator within a 24-hour period. The frequency of the elevator is 7 hours, so the interaction is poor, and little more than a small deflection would occur. Any such oscillations can also be canceled by an opposite movement of the anchor station.

Full name: Tommy Person

E-mail: tperson@midsouth.rr.com

Location: Memphis, Tennessee

Question: “Going Up” was fascinating. The idea is so simple (if the carbon nanotubes can be mass produced) that it’s brilliant. However, a couple of things are still unresolved in my head. First, why do the space shuttle and other rockets have to reach bone-jarring velocities to get into orbit but the elevator could lollygag along at only 125 miles per hour to go higher than any rocket? Also, would there not be a problem with this ribbon becoming a massive electrical conductor as it spun through the magnetosphere traveling at Earth’s rotational velocity?

Edwards: Since the climber is hanging on a ribbon, it can travel at any speed and can even stop without penalty. Rockets do not have this luxury. A rocket must continue to produce thrust to ascend or maintain its altitude. The faster it ascends, the more efficient it is. Rockets are just barely efficient enough to make orbit; if they were only slightly slower, they wouldn’t make it. The ribbon is conducting, but since the magnetosphere and the ribbon are rotating together, little current is produced. There is some current produced by the ribbon passing through the interplanetary magnetic field, but this is also minimal.

Full name: Julian Kane

E-mail: MURIELKANE@aol.com

Location: Great Neck, New York

Question: Brad Lemley writes that Brad Edwards’s concept of space elevators, moving along fantastically strong nanotube ribbons, could make space voyages as simple and safe as using planes, trains, and cars to travel on Earth, by eliminating the use of huge, dangerous rockets to escape the strong pull of gravity close to Earth. However, an impediment that must be overcome before this bold and innovative plan can succeed involves the conservation of angular momentum. A mass ascending a fixed cable from the 1,140-mile-per-hour, 15-degree-per-hour eastward-rotating equator surface is continually increasing its angular inertia. Therefore, wouldn’t its angular (as well as linear) velocity decrease as it traveled up, farther away from Earth’s surface and its spin axis? Wouldn’t the rising mass continually drift to the west and cause the taut nanotube tether-cable to bend and pull an attached geosynchronously orbiting space platform closer to Earth at increasing velocities until it struck Earth in a spectacular crash?

Edwards: Actually, as the climber ascends, its angular velocity will increase linearly with the distance from Earth’s center. This angular velocity is provided by the ribbon, and yes, the ribbon is slowed slightly by the climber as it ascends. The amount the ribbon is bent is a function of the rate of ascent and the relative masses of the climber , the ribbon, and the counterweight. Since the ascent is relatively slow (taking a week to get to geosynchronous orbit), and the climber’s mass is only 1.5 percent that of the ribbon and the counterweight, the ribbon will be deflected a small fraction of a degree at most. The angular momentum of the ribbon and the counterweight is restored by Earth’s rotation. This has all been modeled carefully, so there is no need to fear a “spectacular crash.”

Full name: William Carpenter

E-mail: Billswmc@aol.com

Age:14

Location: Kennett Square, Pennsylvania

Question: If you were to put a space elevator into orbit, wouldn’t it slow the rotation of the Earth ever so slightly? It seems very similar to a person spinning on a stool. When a person spins with his legs tight to his chest, he spins faster, and when he stretches out his legs, his rate of rotation slows. His mass doesn’t increase or decrease during the spinning, but the placement of the mass changes, and so does the rate of rotation. If we follow this line of thought, is it possible that a space station attached to Earth via a carbon cable (as described in the article) would slow the Earth’s rate of rotation because it would be like Earth sticking out its “legs”?

Edwards: Yes, the space elevator would slow Earth’s rotation. However, we must look at the amount it will slow Earth itself. If we were to launch the maximum from 100 space elevators for 1,000 years, it would lengthen Earth’s day by about 100 nanoseconds, or by a second in a billion years.

Full name: Jesse Newman

E-mail: newmaj@rpi.edu

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.

Name: Allen

E-mail: allenev@verizon.net

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

E-mail: rfeyerharm@yahoo.com

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

E-mail: wasmtn51@aol.com

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

E-mail: leighestevens@comcast.net

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

E-mail: Shane.M.Wilson@BHPBilliton.com

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

E-mail: EMJavelina@aol.com

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

E-mail: keener.bill@epa.gov

Age: 52

Gender: male

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

E-mail: williamgwood@cox.net

Age: 37

Gender: male

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.

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