Galileo was an unmanned spacecraft designed to study Jupiter and its moons which was launched on October 18, 1989. It was named in honor of Galileo Galilei who discover Jupiter's major moons in 1610. The craft's main object was to deploy a probe into Jupiter's atmosphere which would conduct tests on the interior of the planet. The probe was successfully deployed in December of 1995. Following its deployment the Galileo spacecraft went into orbit around Jupiter and began to explore its four largest moons as well as its surrounding magnetosphere. In order to conserve energy, Galileo took an six year looping journey that would allow the spacecraft to tap into the gravitational forces of both Venus and Earth to propel it toward Jupiter.
Scientist devised a way to keep Galileo stable while on its journey by having one section of the craft spinning (several times per minute) at all times. This may be easier to understand if you think of a football being thrown in a spiral. Galileo operates on much of the same principle. This spinning action keeps the object headed on a straight path and conserves energy. This section houses instruments that detect low-energy, high-energy, and potentially dangerous charges particles. This section also detects harmful cosmic and Jovian dust particles. Other scientific equipment includes an 11 m (26 ft.) boom with a magnetometer that measures planetary magnetic fields. It is mounted away from the body of the spacecraft to escape possible interference that Galileo might generate.
The stationary section of Galileo carries the instruments that need to be stabilized to operate correctly. This section includes:
- a high-resolution camera for taking photographs
- an ultraviolet spectrometer to analyze the chemistry of Jupiter's atmosphere
- an infrared mapping spectrometer which collects data that scientists use to create infrared maps
- a photo-polarimeter radiometer to measure radiant and reflected energy
- a dish antenna to track the probe and relay data to Earth as it enters Jupiter's atmosphere.
The entire Galileo spacecraft is power by the natural radioactive decay of plutonium 238 dioxide into electricity much like a mini nuclear power plant. The probe however is powered by a lithium-sulfur battery and contains many scientific instruments to collect data that will give scientists a full understanding of this gaseous giant.
During Galileo's flyby of Venus the spacecraft collected data to create infrared maps of its lower atmosphere, learn more about the planet's surface and atmosphere, and took photographs. All of which was sent back to Earth for analysis.
To this point Galileo's mission seemed to be going nearly flawless but soon it ran into problems. The spacecraft was unable to fully open the umbrella-like, high gain antenna so scientists were forced to transmit the data to Earth using the smaller antenna. The smaller antenna transmitted the data 100 times as slow as the larger one. But, scientists pressed on and figured out new ways to expedite the data transfer.
On its way to Jupiter, Galileo performed the first and second asteroid flybys when it observed Gaspra in October of 1991 and Ida in August of 1993. The spacecraft discovered the first asteroid moon which was later named Dactyl orbiting the asteroid Ida.
But the most spectacular footage recorded in July of 1994, just 18 months before Galileo reached Jupiter, was when more than 20 fragments of the Shoemaker-Levy comet plunged into the far side of Jupiter over a six day period.
The probe was released from the spacecraft on July, 13 1995 and headed toward its final destination of Jupiter's interior. It entered the atmosphere on December 7, 1995 and descended at a rate of almost 160,000 km/h (100,000 mph). Its parachute deployed as planned and it dropped its protective shield in order to collect data. What the probe observed during its 57 minute descent before being crushed by the pressure of Jupiter's dense core answered many scientists questions as well as bringing up a ton of new ones.
The Galileo spacecraft continues to observe the largest moons of Jupiter which include; Ganymede, Europa, Io, and Callisto. This is helping scientists to get a more complete understanding of what they are actually like. The spacecraft has survived longer than scientists first anticipated but its electronic components will eventually stop functioning from intense radiation. Currently the craft is being used to conduct an extensive study of Jupiter's moon Europa, where scientists believe vast oceans of water are present below its frozen surface.