Cassini Team Pushes for 7-Year Extended Mission at Saturn

SAN FRANCISCO - As NASA scientists continue to report startling discoveries made during the Cassini spacecraft's initial tour of Saturn, a plan is being drafted that would extend the mission through 2017.

Funding for the Cassini program is scheduled to end Sept. 30, 2010. However, the spacecraft remains in good shape and could continue to return valuable data for years to come, scientists say, provided NASA approves the necessary funding to extend Cassini's tour. Mission officials are preparing to present their case for a seven-year extension to NASA headquarters next month.

"The things that is magic about seven more years is that Saturn will reach its northern hemisphere's summer solstice," said Robert Mitchell, Cassini program manager at the Jet Propulsion Laboratory in Pasadena, Calif. "When we arrived in June 2004, it was a little ways past the southern hemisphere's summer solstice. If we could go seven more years, we would see nearly half of Saturn's orbit."

By monitoring Saturn during half of its 29-year trip around the sun, scientists hope to study the effect of seasonal changes on Saturn, its rings, and its moons Titan and Enceladus. Saturn's orbit is tilted 27 degrees relative to its equator. Just as it does on Earth, that tilt creates distinct seasons for different areas of the planet.

If the Cassini mission continues beyond 2010, scientists want to observe seasonal changes around Titan's lakes of methane and Enceladus' south pole where vents spew ice crystals and water vapor, according to Carolyn Porco, Cassini imaging team leader for the Space Science Institute in Boulder, Colo.

"Cassini has taken up residence in this magnificent planetary system," Porco said. "We've discovered a tremendous amount. We want to stay and observe for as long as possible."

The current NASA budget includes approximately $80 million a year for Cassini's operations and science. That money pays for an engineering team to operate the 12- instrument spacecraft, a navigation team to keep it on course and 125 U.S. scientists associated with the program. In addition, 130 European scientists participate in Cassini research.

The Cassini-Huygens mission was developed cooperatively by NASA, the European Space Agency and the Italian Space Agency. NASA funding does not pay the salaries of the foreign scientists, but their work adds to the overall cost of the mission because Cassini teams design flights and instrument plans to cover their targets of investigation, Mitchell said.

Any Cassini mission that extends beyond 2010 would include fewer scientific investigations and operate at a much lower cost than the current program. Initially, program officials hoped to plan an extended mission that would cost $40 million per year, or half the current funding level. "We concluded that wasn't quite enough to operate the spacecraft, keep it on track and conduct worthwhile science," Mitchell said.

As a result, proposals for the extended mission will include a range of funding levels with information on the scientific investigations that could be performed at each level. "There is no single mission laid out," Mitchell said. "We are looking at options."

Cassini scientists are scheduled to gather in late January at the Jet Propulsion Laboratory to select the tour trajectories they would like the spacecraft to follow if the mission is extended beyond 2010. Those plans will be presented to NASA headquarters for review in mid-February, Mitchell said.

In addition to citing the scientific goals that could be attained by extending Cassini's orbit of Saturn, the report to NASA headquarters will provide a detailed description of the health of the spacecraft, which was launched in 1997. Overall, the spacecraft appears to be healthy. Some engineering subsystems show signs of wear and tear, but the spacecraft operations team has developed a set of rules designed to treat those subsystems carefully, Mitchell said.

Cassini uses two types of fuel, hydrazine, which is used for small navigation maneuvers, and a standard bipropellant for larger maneuvers. While there is ample hydrazine to continue the mission through 2017, the Cassini navigation team has to be more conservative with its bipropellant. "We will design future tours knowing how much propellant is available for velocity change," Mitchell said.

Recent tours throughout the Saturn system have presented intriguing findings, such as evidence of what appear to be cryovolcanoes spewing extremely cold liquid into the atmosphere of Titan. Scientists also presented high-resolution images at the American Geophysical Union meeting in San Francisco in December showing distinct changes over time in the appearance of the south pole of Enceladus. Those changes may indicate tectonic movement on Enceladus similar to the tectonic activity found on Earth.

• Video - Cassini at Saturn: Four Years of Discovery
• Vote Now! Cassini's Greatest Hits: Images of Saturn
• Special Report: Cassini's Mission to Saturn