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Faster Satellites That Travel Light

Developments to Watch


IN EARLY OCTOBER, HUGHES Electronics Corp. opened a new door to space by firing the first commercial xenon-ion propulsion system, dubbed XIPS, to correct the orbit of PanAmSat Corp.'s PAS-5 communications satellite. PAS-5 was launched in late August from Kazakhstan and now hovers over Brazil.

The xenon system will keep the satellite in position for decades by periodically squirting out charged particles, or ions. Before, this "stationkeeping" was done with small chemical thrusters. But xenon gas is inert, hence nonexplosive--yet produces highly energetic ions. They gush out at 62,900 mph, providing 10 times more thrust than current chemical reactions. As a result, the 1,400 pounds of fuel needed to keep a satellite in orbit is slashed by as much as 90%. That means more communications gear can be packed into a satellite, or that lighter "birds" can be launched with cheaper rockets.

For deep-space probes, ion engines could push spacecraft to speeds not possible with chemical thrusters--and trim months off interplanetary missions. The proof will come next summer, when NASA's Deep Space 1 probe will blast off. It will use a XIPS thruster and 100 pounds of xenon to gradually accelerate to 22,000 mph in space--fast enough to catch the comet West-Kohoutek-Ikemura and rendezvous with an asteroid named after Christa McAuliffe, the teacher who died in the 1986 Challenger explosion.EDITED BY OTIS PORTReturn to top


RUBBING YOUR FINGER OVER a textured surface is akin to tuning in an FM radio broadcast. How so? It seems the brain interprets signals from touch sensors in our fingers using principles remarkably like FM, according to Israeli researchers at the Weizmann Institute of Science and the Technion-Israel Institute of Technology.

In frequency modulation (FM) systems, sounds are encoded as variations in the frequency of a broadcast, and then receivers in the home translate those fluctuations into familiar sounds. Similarly, the brain may have its own "FM stations." Scientists have long known that certain brain cells oscillate at particular frequencies. But now they are finding that these oscillations are modulated by incoming sensory signals, according to a report in the Oct. 14 issue of Proceedings of the National Academy of Science. The Israeli scientists speculate that an FM-based technique could be the way the brain translates touch signals into perceptions of texture and temperature.

The discovery may enable scientists to crack the code used by the brain to decipher the streams of signals from touch sensors--and perhaps the other sensory organs as well. The researchers are now looking for signs of FM processing being used for visual signals, says team leader Ehud Ahissar of Weizmann's Neurobiology Dept. If the brain's inner workings can be fathomed and simulated, it would mark a breakthrough in areas such as artificial intelligence and robotics.EDITED BY OTIS PORTReturn to top


TO RELIEVE CYBERJAMS ON THE INTERNET, TELECOM carriers and service providers lay more optic fiber, beef up banks of modems, and install faster network switches. Yet delays continue. That's partly because most organizations store their Web sites and databases on just one computer "server." But Inktomi Corp. in San Mateo, Calif., creator of the HotBot search engine, has a fix that has nothing to do with fatter pipes or faster switches. Its Traffic Server will collect popular Web sites in huge repositories known as network caches.

What distinguishes these cache sites from the "mirror sites" already used by companies to alleviate home-page congestion? Each cache will contain broad swathes of the Internet, including information from many companies and Web sites. This massive amount of data--upwards of a trillion bytes--will be stored "intelligently," on the basis of how frequently it is requested. The caches will save money, asserts Inktomi Marketing Vice-President Dick Pierce, "because it's always cheaper to store a bit of data than to transport it."EDITED BY OTIS PORT Neil GrossReturn to top

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