To: Valueman who wrote (5455 ) 3/11/1999 6:57:00 PM From: djane Respond to of 10852
2/99 Scientific American on new launch vehicles [excerpt only] The Way to Go in Space To go farther into space, humans will first have to figure out how to get there cheaply and more efficiently. Ideas are not in short supply by Tim Beardsley, staff writer ........... SUBTOPICS: After the Gold Rush Buck Rogers Rides Again Beyond Earth Beam Me Up SIDEBARS: Air-Breathing Engines by Charles R. McClinton Space Tethers by Robert L. Forward and Robert P. Hoyt Highways of Light by Leik N. Myrabo Light Sails by Henry M. Harris Compact Nuclear Rockets by James R. Powell Reaching for the Stars by Stephanie D. Leifer ILLUSTRATIONS: Spacecraft Design Roton Vehicle Ion Engine FURTHER READING RELATED LINKS The year 1996 marked a milestone in the history of space transportation. According to a study led by the accounting firm KPMG Peat Marwick, that was when worldwide commercial revenues in space for the first time surpassed governments' spending on space, totaling some $77 billion. Growth continues. Some 150 commercial, civil and military payloads were lofted into orbit in 1997, including 75 commercial payloads, a threefold increase over the number the year before. And the number of payloads reaching orbit in 1998 was set to come close to the 1997 total, according to analyst Jonathan McDowell of Harvard University. Market surveys indicate that commercial launches will multiply for the next several years at least: one estimate holds that 1,200 telecommunications satellites will be completed between 1998 and 2007. In short, a space gold rush is now under way that will leave last century's episode in California in the dust. Space enthusiasts look to the day when ordinary people, as well as professional astronauts and members of Congress, can leave Earth behind and head for a space station resort, or maybe a base on the moon or Mars. The Space Transportation Association, an industry lobbying group, recently created a division devoted to promoting space tourism, which it sees as a viable way to spur economic development beyond Earth. The great stumbling block in this road to the stars, however, is the sheer difficulty of getting anywhere in space. Merely achieving orbit is an expensive and risky proposition. Current space propulsion technologies make it a stretch to send probes to distant destinations within the solar system. Spacecraft have to follow multiyear, indirect trajectories that loop around several planets in order to gain velocity from gravity assists. Then the craft lack the energy to come back. Sending spacecraft to other solar systems would take many centuries. Fortunately, engineers have no shortage of inventive plans for new propulsion systems that might someday expand human presence, literally or figuratively, beyond this planet. Some are radical refinements of current rocket or jet technologies. Others harness nuclear energies or would ride on powerful laser beams. Even the equivalents of “space elevators” for hoisting cargoes into orbit are on the drawing board. “Reach low orbit and you're halfway to anywhere in the Solar System,” science-fiction author Robert A. Heinlein memorably wrote. And virtually all analysts agree that inexpensive access to low-Earth orbit is a vital first step, because most scenarios for expanding humankind's reach depend on the orbital assembly of massive spacecraft or other equipment, involving multiple launches. The need for better launch systems is already immediate, driven by private- and public-sector demand. Most commercial payloads are destined either for the now crowded geostationary orbit, where satellites jostle for elbow room 36,000 kilometers (22,300 miles) above the equator, or for low-Earth orbit, just a few hundred kilometers up. Low-Earth orbit is rapidly becoming a space enterprise zone, because satellites that close can transmit signals to desktop or even handheld receivers. Scientific payloads are also taking off in a big way. More than 50 major observatories and explorations to other solar system bodies will lift off within the next decade. The rate of such launches is sure to grow as the National Aeronautics and Space Administration puts into practice its new emphasis on faster, better, cheaper craft: science missions now being developed cost a third of what a typical early-1990s mission did. Furthermore, over its expected 15-year lifetime the International Space Station will need dozens of deliveries of crew, fuel and other cargo, in addition to its 43 planned assembly flights. Scores of Earth-observing spacecraft will also zoom out of the atmosphere in coming years, ranging from secret spy satellites to weather satellites to high-tech platforms monitoring global change. The pressing demand for launches has even prompted Boeing's commercial space division to team up with RSC-Energia in Moscow and Kvaerner Maritime in Oslo to refurbish an oil rig and create a 34,000-ton displacement semisubmersible launch platform that will be towed to orbitally favorable launch sites. More at sciam.com