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.
