Flight plans changed to salvage Titan mission

A drawing of the Cassini satellite dropping the Huygens probe

By Richard Stenger
CNN

(CNN) -- International scientists have approved a strategy to ensure that an unexpected telecommunications glitch does not prevent a probe from sending data as it drops into the atmosphere of Saturn's largest moon.

The Cassini-Huygens mission left Earth in 1997 and should arrive in the Saturn system in late 2004. It consists of a NASA orbiter, Cassini, and a European Space Agency probe, Huygens, which will beam back information during a suicide plunge to the surface of Titan.

Last autumn, mission scientists realized that a design flaw would skewer transmissions between the spacecraft during Huygens' descent. The new strategy, adopted Friday by U.S. and European mission managers after six months of study, changes the flight plans to maximize the data return.

MESSAGE BOARD Space exploration

The revised descent date is January 12, 2005, seven weeks later than expected. The changed itinerary will position Cassini further away when Huygens parachutes to Titan, greatly improving the quality of the transmissions, said NASA and European Space Agency scientists.

"This recovery plan will allow us to meet all of the mission's scientific objectives," said Bob Mitchell, Cassini program manager at NASA's Jet Propulsion Laboratory in Pasadena, California.

Had Huygens flown as first expected, its antenna would not have compensated for the Doppler effect as it hurtled away from Cassini. The shift in radio frequency would have prevented the NASA mother ship from receiving most of the probe's data.

The changed itinerary will consume up to one-third of Cassini's reserve fuel supply.

Mission engineers will also send up software commands to Huygens to make the probe heat up before its deadly dive, which will improve the quality of the radio signal.

Shrouded in a thick orange haze, Titan has stirred the interest of astronomers since the Dutchman Christian Huygens discovered it in 1655.

The second largest moon and the only one with a thick atmosphere, Titan is enveloped by a dense hydrocarbon soup thought to resemble conditions on Earth in its infancy.

Huygens will drop for several hours before reaching the surface of Titan, studying its atmosphere on the way. Should it survive the impact, scientists hope it will continue to beam back data until its batteries fail or Cassini flies out of radio range.

In February 2005, Cassini will begin its prime, four-year mission, studying Saturn and its rings, moons and magnetic environment.