Engineers reportedly have come up with a fix for the Cassini mission to Saturn so the spacecraft now is aimed to pass a bit further from the planet's moon Titan and delay a mini-probe's drop there to compensate for an error that would have cost a lot of data.
The change, which also adds another swing past swampy Titan for the Huygens probe, was required to overcome a failure to account for the Doppler effect on the probe's communications equipment. If uncorrrected, the error would have left Cassini unable to receive much data during the smaller probe's three-hour, data-grabbing mission.
The Doppler effect changes the perceived frequency or tone of a radio signal as it speeds toward or away from an observer.
Cassini now will drop the Huygens probe in February 2005, three months later than initially planned, during the spacecraft's third orbit of Saturn rather than its first, according to the Associated Press.
The larger craft also will pass much more tentatively than initially planned past Titan -- 40,300 miles -- while Huygens descends. Cassini was to fly within 750 miles of Titan while the probe parachuted through Titan's nitrogen atmosphere.
Scientists with the European Space Agency (ESA), which contributed Huygens to the NASA/ESA mission, discovered the error last year, saying the Doppler effect would wreck efforts to accurately receive signals sent from the probe to the mother ship.
By distancing Cassini from Titan, and hence the probe, during the drop, the mother ship will appear to move away from the probe at a slower rate. At the close pass, Cassini would have sped past Titan at more than 12,000 mph while receiving radio transmissions from the probe.
Cassini was launched in 1997 and is set to enter Saturn's orbit on July 1, 2004. When released, the Huygens probe should study Titan's clouds and atmosphere during a suicide plunge to the surface, after which it is expected to operate no longer than 30 minutes.
Titan intrigues scientists as its carbon-rich atmosphere and surface could resemble early conditions for life at Earth.
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