Galileo was designed to collect scientific information on Jupiter and its moons. Unfortunately, its high-gain antenna, shaped like an umbrella, failed to open properly, while the probe’s tape recorder became jammed.
Galileo ultimately succeeded in its mission despite these setbacks by studying Jupiter’s four large moons and two main-belt asteroids, discovering that Ida has its own small moon named Dactyl.
Its mission
Galileo made an extraordinary series of discoveries while orbiting Jupiter. One major finding was confirmation that Europa, one of Jupiter’s four large moons, contains either liquid water or frozen sediment beneath its surface. Furthermore, Io was revealed as having widespread volcanic activity.
Galileo was named in honor of Galileo Galilei, an Italian astronomer renowned for developing a revolutionary telescope which revolutionized planetary science. Galileo became the first spacecraft capable of conducting comprehensive studies of Jupiter with both an orbiter and descent probe.
NASA’s Jet Propulsion Laboratory in Pasadena, Calif. designed and constructed this orbiter. Featuring two radioisotope thermoelectric generators to convert radioisotope decay heat to electrical power for its descent probe; equipped with 11 scientific instruments including cameras for taking pictures of Jupiter’s clouds, rings, satellites and atmosphere as well as spectrometers that measured sunlight intensity and gaseous composition; transmission capabilities were made available until its fall into Jupiter’s atmosphere, which concluded on Sunday Sept 21 2003.
Its design
Galileo relied on two radioisotope thermoelectric generators that converted heat from radioactive decay into electricity – similar engines were also employed on Viking, Voyager, Ulysses and Cassini missions to distant planets and Saturn respectively.
Galileo engineers faced an immense design challenge in protecting it from Jupiter’s powerful radiation. To do this, they employed multiple shielding methods as well as an orbit that made use of gravity assists from planets to minimize Galileo’s exposure.
Galileo made significant scientific strides despite these hurdles, meeting many of its original goals. It discovered two new asteroids and observed Comet Shoemaker-Levy 9 as it collided with Jupiter; performed detailed studies of its moons, atmosphere and magnetic field; as well as returning data at a reduced rate due to recorder upgrades developed at NASA’s Jet Propulsion Laboratory.
Its launch
After General Dynamics Centaur booster cancellation and threats to shut down NASA’s Jet Propulsion Laboratory, Galileo mission slipped further into the late ’80s. Engineers devised a flight path using gravity assists from Jupiter to get Galileo into Jupiter orbit, changed hardware as necessary and devised ways of compressing data in order for more telemetry data transmission back.
Galileo satellite was equipped with a dual-spin attitude stabilization system. A rotating section, known as the rotor, rotated at three revolutions per minute while another component called the stator kept Galileo stable in space. The rotor held science instruments that measured fields and particles while its counterpart held spacecraft engineering subsystems as well as its primary antenna.
Galileo discovered during its two-year tour of Jupiter the presence of active volcanoes on Io and hinted that liquid oceans may lie hidden under Europa’s icy crust. Additionally, Galileo offered unique insight into the collision of comet Shoemaker-Levy 9 with Jupiter in July 1994.
Its first orbit
Galileo had originally planned to travel directly towards Jupiter from its launch from a payload bay of a space shuttle in 1985, but following the Challenger accident of 1986, US spacecraft launch policy changed drastically and Galileo’s Centaur upper stage was replaced with an inertial upper stage with less power, leading to a much longer, circuitous path to Jupiter than had originally anticipated.
The spacecraft employed Itek Advanced Technology Airborne Computers (ATACs) designed on radiation-hardened 2901s for navigation and avionic system control. Furthermore, HAL/S programming language designed for the Space Shuttle program was utilized to write flight software specifically tailored for this mission.
One of the mission’s key discoveries was that of Gaspra’s own moon, Dactyl. This astounding discovery occurred during Ida’s flyby in August 1993 and marks a historic achievement – scientists named Dactyl after their discovery!