Explosions, Education and e-Commerce

Space Cowboy
Tester to thank for new data from Titan
The Cassini-Huygens Saturn mission, a cooperative project of NASA and the European Space Agency (ESA), is providing unparalleled information about Saturn and its moons. The Huygens probe through the atmospheric veil of Titan, Saturn’s largest moon, has been one of the more successful elements of the mission. Yet, if not for one intrepid engineer doing some diligent testing, that part of the mission might have been a bust.

Boris Smeds, a twenty-six-year veteran of the ESA, discovered in 2000 that Cassini’s receiver, intended to relay information from the Huygens probe to Earth, was at risk of scrambling the data beyond recognition. Initially confronted by doubters and bureaucracy, Smeds eventually was able to implement a test program sufficient to prove the existence of the communications problems, thereby saving the mission from embarrassment and failure.

Both the Cassini orbiter and the Huygens lander had undergone extensive testing on the ground, separately and together. But a test that would have simulated the exact signals and conditions experienced during flight was scrapped for budget reasons. Luckily ESA’s grounds operations manager suggested running some tests during Cassini’s long travels between planets. Enter Smeds, who designed a test to send a signal from Earth toward Cassini that would mimic a radio transmission from Huygens during its landing—accounting for all atmospheric and Doppler variations. Though fairly easy to implement once designed, Smeds had to push to get approval to run his more thorough mimicry test rather than a straight carriersignal-only test. Good thing. By mimicking variations due to Doppler shift, Smeds found a serious problem with the data reception. In effect, the Doppler shift was pushing the signal out of synch with the timing scheme used to recover data from the carrier. The result would have been disastrous.

Armed with Smeds’ information, the Cassini team designed a response plan that centered on reducing the Doppler shift to keep the data signal within the range of the receiver. By changing Cassini’s trajectory, the radio waves were emitted perpendicular to Huygens’ direction of motion and, therefore, were neither stretched nor compressed.

So, as scientists continue to study and learn from the information sent back from Titan, we can credit a thorough and well-designed test for making it all possible. —NASA.gov; Cassini-Huygens mission diary; IEEE Spectrum online

Technology FYI
A Bang-Up Job
Ultrafast supercomputer to simulate full nuclear explosion
Sometime this summer an aging nuclear bomb will explode just east of San Francisco—onscreen in a massively detailed computer simulation, that is. In perhaps the greatest effort yet in supercomputing, a machine doing 360 trillion calculations per second will simulate a nuclear explosion in three dimensions.

The BlueGene/L supercomputer consists of sixteen modules, each loaded with massive computing power. The first version of Blue/Gene, built by IBM, became operational in mid-December at ninety trillion calculations per second. Housed in a room nearly half the size of a football field, the ramped-up version for this simulation should be completed next month.

Still, even at a speed of 360 trillion calculations per second, the simulation may take two to four months to complete.

The US has about 10,000 nuclear warheads as a deterrent against attack. The government stopped real nuclear tests in 1992. Scientists hope to use this simulation to make sure that nuclear weapons dating back decades haven’t developed fatal flaws. —Computerworld.com; CNN.com

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