Suppose that U.S. intelligence finds indisputable evidence that a major terrorist leader is dining right now in a remote farmhouse in central Asia. Say also that local political sensitivities prohibit calling in bombers for an air strike and that the meal is unlikely to last the two hours it would take a Tomahawk cruise missile to reach the site from its maximum range. How to respond?
Pentagon weapons procurers hope to have an answer in an advanced turbine engine that can shrink a cruise missile's "time on target" to "tens of minutes." Such a system might catch the hypothetical terrorist chief before dessert.
The problems posed by highly mobile targets became clear during the first Iraq war, when allied forces had difficulty tracking and hitting truck-mounted Scud-missile launchers. Other armed forces, including Russia's and China's, have supersonic cruise missiles that are powered by ramjets. Unlike a turbine engine, a ramjet does not rely on turbine wheels to compress air for rapid fuel combustion—it simply gulps oncoming air as it travels at high velocity. But these ramjets burn more fuel, have shorter ranges and cannot easily change speeds (be throttled) like the turbine engines in cruise missiles can. In addition, existing long-range supersonic missiles need booster rockets to propel them to speed.
The U.S. Office of Naval Research instead opted to work with Lockheed Martin's Advanced Development Programs (" Skunk Works" ) and Rolls-Royce's Liberty-Works to build a gas turbine-powered cruise missile that can achieve Mach 3 or more. (Much above Mach 3—in excess of 3,675
kilometers an hour at sea level—rising turbine temperatures start to damage key components.) Called the Revolutionary Approach to Time-Critical Long-Range Strike program, RATTLRS may yield a cruise missile with much greater operational flexibility and effectiveness than its ramjet-powered predecessors, says Lockheed Martin program manager Craig Johnston.
The new long-range strike weapon would be able to tailor its flight configuration to its mission, he explains. For instance, after
launch from an aircraft, surface ship or submarine, a RATTLRS-type missile could loiter near a target until the time for attack was right. Or it might extend its range by cruising to its objective at fuel-efficient low supersonic velocities and then dispense lethal submunitions precisely across a battlefield at subsonic speeds. In a bunker-buster penetra-tor role, the missile could accelerate to multiMach speeds during its final approach.
A full-size mock-up of the 20-foot-long RATTLRS missile closely resembles the engine nacelle of Lockheed's now retired SR-71 Blackbird spy plane, particularly its moving air-inlet spike and its severely swept wings. Johnston acknowledges that "RAT-TLRS has a lot of heritage from the SR-71," which could exceed Mach 3. When shifted forward or back, the innovative spike would alter the engine's intake geometry so it could absorb the shock waves in the oncoming supersonic airflow and thus slow it to usable, subsonic velocities. Depending on the Mach number, the air would either be vented away or injected into the Blackbird's engine.
Unseen in the 21-inch-diameter mock-up, however, is the real key to RATTLRS, news
Should the RATTLRS project prove successful, the U.S. Department of Defense will most likely try to extend its top speed to Mach 4 by installing an afterburnerlike system called a ramburner. (This system, which creates extra thrust by shooting fuel into a hot jet nozzle, propelled the SR-71 Blackbird to a world speed mark for piloted aircraft.) This type of engine could then provide initial propulsion for hypersonic aircraft and even orbital boosters powered by supersonic combustion ramjets (scramjets), which cannot fly slower than Mach 4. Hence, says U.S. Office of Naval Research program manager Lawrence Ash, RATTLRS would also "demonstrate a class of technologies that would enable space access."
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the highly compact and fuel-efficient YJ102R turbofan engine, which produces six times the specific thrust (pounds of thrust per pound of ingested air) of the SR-71's engine, says LibertyWorks program director Bob Duge. Although the details are classified, Duge attributes most of the engine's performance to its high operating temperature, which requires an "advanced thermal management" system to keep critical parts relatively cool. The burner and the hot turbine blades are made of special temperature-resistant alloys with myriad tiny cooling air passages cast into them.
Johnston says that the U.S. Navy plans to test-fly a prototype missile by the end of 2007 and hopes that a RATTLRS-based missile could be deployed by 2015.
TO FIGHT GLOBAL WARMING, KISS THE RED-EYE GOOD-BYE BY CHRISTINA REED
Air travelers have more to hate about red-eye flights, where sleep is as ephemeral and satisfying as a bag of pretzels for dinner. Those overnight trips contribute more to atmospheric warming than daytime jetting.
Scientists have long known that airplane condensation trails act to both cool and heat the atmosphere. Formed by jet engines' hot exhaust, contrails act as thin cloud barriers that not only reflect sunlight but also prevent the earth's heat from escaping into space. During the day, the effect of blocked incoming radiation tends to outweigh that of trapped heat, thereby cooling the atmosphere. Indeed, after the events of 9/11 grounded all commercial U.S. flights for three days, daytime temperatures across the country rose slightly, whereas nighttime temperatures dropped. This evidence supported the hypothesis that contrails reduce the temperature range by cooling the atmosphere during the day and heating it at night.
Thus, the timing of the flights is critical, but so is the atmosphere itself. Nicola Stuber of the University of Reading in England and her colleagues collected data from weather balloons over a region in southeastern England that lies within the North Atlantic flight corridor. Her team reported in the June 15 Nature that even though fewer jets fly during the winter months, the season's higher humidity makes these flights twice as likely to create contrails. The team also
found that flying between 6 P.M. and 6 A.M. contributed between 60 and 80 percent of the climate warming that originated from contrails, even though these flights represent a quarter of the total air traffic.
Atmospheric scientist David Travis of the University of Wisconsin-Whitewater, who reported the 9/11-related contrail findings, agrees with the British researchers that a reduction in nighttime flights is needed. He adds that contrails "are currently a regional-scale problem but could eventually become a global-scale problem as air traffic continues to expand and increase." Scientists are only beginning to study the contribution of jet exhaust to global warming, but so far, like red eyes, contrails don't look so good.
Christina Reed flies frequently out of Seattle.
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