June 30, 2004: Cassini Spacecraft Arrives at Saturn
The Cassini spacecraft was built by NASA's Jet Propulsion Laboratory (JPL) and the Italian Space Agency (ASI) and is one of the largest, heaviest, and most complex interplanetary spacecraft ever built.
The Cassini orbiter alone weighs 2,125 kg (4,685 lbs), and when Huygens, the launch vehicle, and 3,267 kg (7,203 lbs) of propellants are added, it brings the total weight up to 5,712 kg (12,593 lbs). More than half of that weight is liquid propellent, which is needed because Saturn is so far away. Cassini is more than 6.7 m (22 ft) tall and over 4 m (13.1 ft) wide.
Throughout its voyage, Cassini is guided by onboard computers that determine the spacecraft's position and sensors that recognize reference stars as well as the sun. The spacecraft is directed by sequences, programs of detailed computer instructions stored on the spacecraft, for the majority of its journey. Any large changes to the orbiter's trajectory are powered by one of Cassini's two identical main engines.
Cassini receives its electrical power from radioisotope thermoelectric generators (RTGs). The RTGs contain plutonium dioxide, which decays radioactively. This heat is converted into electrical energy, which is in turn used to produce power. Using RTGs is a very reliable source of power and very durable - there are no moving parts which could break off during the long journey to Saturn.
Since Cassini travels through both very hot and cold temperatures, the spacecraft had to be properly equipped to deal with extreme temperatures. To protect Cassini from too much heat, the spacecraft uses its high-gain antenna to shield itself and the probe, and it is also coated with special paints that reflect and radiate the Sun's energy when it was built. To protect Cassini from the frigid cold, the orbiter is wrapped in thermal blankets to heat it.
Cassini communicates with Earth using 3 separate antennas: 1 high-gain antenna (which is 4 m or 13.1 ft in height) and 2 low-gain antennas. It relays data in the form of radio signals at the speed of light, but since Saturn is 8.6 to 10.6 Astronomical Units away from Earth (depending on its orbit position), it takes 68 - 84 minutes for the data to travel to Earth!
Visit the Cassini homepage
Read about Cassini's 12 instruments by clicking here
Artwork courtesy of the Cassini Website
