December 10, 2001
As if going to Saturn wasn't hard enough, deciding what science to collect once in orbit around the giant planet is a logistic maze.
Launched in 1997, the international mission Cassini-Huygens will take almost seven years to reach the planet famed for those amazing rings that puzzled generations of astronomers. To save fuel and to travel the huge distance, more than 3 billion kilometers so far, the spacecraft used a technique called gravity assist. It looped around Venus twice, then flew past Earth and finally around Jupiter. The slingshot boost from these passes will deliver the Cassini orbiter and its probe, Huygens, to Saturn in July 2004. The probe will later descend to Titan, the biggest of some 30 known moons orbiting Saturn.
The Huygens probe will provide information on Titan, which has an atmosphere that extends about 1,000 kilometers (620 miles) from the surface. Because of its distance from the Sun, its surface is frozen and its temperatures are extremely low. Compared to Earth, Titan receives only one percent of the Sun's light.
Choosing what data to collect with the spacecraft's many instruments once at Saturn is keeping scientists busy these days, as they are planning a minute-by-minute timetable for the four-year mission. The challenge is caused by the abundance of interesting science targets along the planned 74 orbits around Saturn, and the wealth of instruments onboard the spacecraft.
"There is a lot of intriguing science with Titan, the most Earth-like world out there, and we want to know a lot more about Saturn," says Dr. Kevin Baines, a planetary scientist at JPL involved with the science timetable. "The rings are sitting there, shining away. They are mysterious and we are going to look at those and also the icy satellites."
Logistic issues complicate the planning task.
One matter is downloading the information collected by the data recorder on board. Once it is full, the spacecraft must turn toward Earth and begin downloading the data. Because of the great distance, the signal takes about an hour and 15 minutes to reach the Deep Space Network's antennas. Downloading the data takes up to 9 hours. When Cassini is collecting data, scientists have to make hard choices on which instrument to use. In order to save money, Cassini's instruments are all fastened in fixed positions and cannot be pointed independently of another.
"We have all these mutually exclusive desires," explains Baines. "We have different targets and when we get to a particular target there are a lot of different things we want to do. All the scientists involved must collaborate with each other."
Eager to decode the many mysteries of Saturn and its moons, scientists are painstakingly examining each of the 74 planned orbits around the planet, trying to include as many unique and relevant observations as possible, without compromising each other's instruments and goals.
The complicating factor is that of the 265 scientists involved with the mission, only 125 live in the U.S. This translates in teleconferences across 12 time zones, with scientists in Hawaii getting up early while their colleagues in Europe are putting their kids to bed. Through tons of emails, web charts and conference calls, scientists from 16 countries have 30 months to come up with an integrated time chart that will provide the best plan to gather as much information as possible about the sixth planet from the Sun, the second largest in our solar system.