Space issue. (Letters).Advocates of a "space elevator A space elevator is a proposed megastructure designed to transport material from a celestial body's surface into space, first conceived by Konstantin Tsiolkovsky.[1] Many different types of space elevators have been suggested. " ("Ribbon to the Stars," SN: 10/5/02, p. 218) seem to have forgotten about angular momentum angular momentum: see momentum. angular momentum Property that describes the rotary inertia of a system in motion about an axis. It is a vector quantity, having both magnitude and direction. . When an elevator ascends the ribbon, it must be accelerated eastward because the Earth's rotation represents a larger eastward velocity the higher you go. The required eastward force on the ascending elevator would have to be provided by a corresponding westward force on the ribbon. Does Bradley Edwards have an answer to this? ROBERT H. BEEMAN, CORAL SPRINGS, FLA FLA Florida (old style) FLA Macromedia Flash (file extension) FLA Flash Files (file extension) FLA Fair Labor Association FLA Front Line Assembly . Bradley C. Edwards of the space-elevator design company Eureka Scientific in Berkeley, Calif., replies: "If you go through the math quantitatively, the angular momentum for the climbers requires a pound or so of force over the one-week travel time, and we do that easily with our many tons of material in the anchor and the counterweight coun·ter·weight n. 1. A weight used as a counterbalance. 2. A force or influence equally counteracting another. coun ." The greatest concern for the space elevator appears to be impacts. Has someone forgotten that each and every satellite in Earth orbit (except for those in an exact geosynchronous orbit) crosses the equator twice during each and every orbit? Unless that elevator is really good at dodging, one of these satellites is going to run into it. DAN PANKRATZ, HUNTINGTON BEACH, CALIF. Edwards replies: "We are good at dodging, and we will avoid the satellites. We are tracking them and will have days to weeks warning. We will move the anchor about a kilometer each day to avoid the debris." The last space shuttle--tether experiment, which unspooled about 12 miles of cable, generated thousands of volts of electrical potential and kilowatts of power, burned through the insulation of the cable, and generated a tremendous explosive arc of electricity, that snapped the tether tether to tie an animal up by the head or neck so that it can graze but not move away. See also barton tether. . Now imagine a 60,000-mile-long cable and its electrical-generating capacity and you begin to see the disastrous potential. JEFFREY WILSON, DEXTER, MICH v. i. 1. To lie hid; to skulk; to act, or carry one's self, sneakingly. . According to Edwards, the voltage builds up on tethers in space because they are traveling 11,000 mph relative to Earth's magnetic field Earth's magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the north pole (see Magnetic North Pole) and the other near the geographic south pole (see Magnetic South Pole). . The space ribbon would be stationary relative to Earth's magnetic field and thus the voltage produced is essentially zero. For more letters on "Ribbon to the Stars" go to http://www.sciencenews.org/ 20021005/bob9.asp. |
|
||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion