Galileo (spacecraft)

The Galileo spacecraft was launched on October 18, 1989 by NASA to study Jupiter and its moons. Your name, the probe after the Italian inventor and scientist Galileo Galilei.


Prior to this mission, the planet Jupiter extended period of time has never been continuously observed by a spacecraft. Although four spacecraft were previously flown past him ( Pioneer 10 and 11 and Voyager 1 and 2), but they could during their flyby each provide only brief snapshots. That should change with Galileo. It should be permanently circling an orbiter around Jupiter to observe both the planet itself as well as its moons.

Prior to the arrival of a daughter probe should be decoupled, which penetrate into Jupiter's atmosphere and should provide various data on temperature, pressure, wind speed and chemical composition. The flyby spacecraft should spark as a relay station, the information to Earth.


After initial planning of 1977 Galileo should start as early as January 1981. Various delays after the initial launch vehicle Space Shuttle, by funding uncertainties, and finally the Challenger disaster led to several years of delay and changes of the probe and the trajectory. Originally was to be lifted into space with the canceled mission STS -61- G in May 1986 Galileo. On October 18, 1989, but was finally ready. The space shuttle Atlantis brought Galileo mission STS -34 into earth orbit, where it was exposed. To exit the Earth's orbit was the solid IUS upper stage mounted on Galileo, which served as a driving stage for heavy satellites and space probes in other space shuttle mission. Galileo led before they took their journey to Jupiter, with three swing-by maneuvers to get through the attractions of the planets Venus and Earth swing. In February 1990, Galileo flew past in 16,000 km distance to Venus, in early December of the same year she passed the Earth for the first time, and again two years later. Meanwhile, they could send spectacular images both from Venus and from the earth to the ground station.

On the way to Jupiter, Galileo passed the asteroid Gaspra in 1991 only 1600 km distance and Ida in 1993, with detailed images of the heavenly bodies emerged. For the latter, the first time an asteroid moon was discovered. The 1-2 km large chunk was named Dactyl.

Shoemaker- Levy -9 impact

One year later, was able to observe a dramatic event Galileo. The comet Shoemaker- Levy 9 crashed into the still 238 million kilometers distant Jupiter. Despite the distance Galileo was able to capture unique images of the direct lightning strikes that took place on the far side. On the Earth itself one could observe only the effects after the planet had rotated further. Had Galileo not been sent due to the Challenger disaster with only three years late to Jupiter, the probe would have to track the comet hit at close range in the Jupiter orbit.


As mid-April 1991, the ground station radioed the command to deploy the 4.80 m parabolic antenna, this could be opened only partially. Thus, the possibility of data transmission with more than 130 kbit / s was no longer given. They tried the unfolding thousands of times, but to no avail. The probe was then reprogrammed so that the received data has been cached on both the host computer and on a tape drive, and then radioed in portions of the much weaker circular antenna to Earth. However, since this allowed a very low transmission rate, the probe new software, including algorithms for data compression sent. This could be provided, notwithstanding the failure of the parabolic antenna still a significant amount of scientific data. Also, there were other problems: The Umspulmechanismus of magnetic tapes got stuck more often, but could always be made ​​to run the tape.

Beginning of the research

In 82 million km Distance to Jupiter broke up in July 1995, the daughter of the probe from the mother ship. On 7 December 1995 their journey was over. With a speed of 170,000 km / h, daughter probe plunged into Jupiter's atmosphere at an angle of about 9 °. Within two minutes, the speed was slowed down to 3000 km / h, the maximum delay of the probe was 230 g. The material of the heat shield was almost completely removed, in the shock wave temperatures up to 16,000 ° C occurred. In around 40 km altitude at 0.35 bar pressure, the parachute opened.

Jupiter is a gas planet. Density and pressure of the atmosphere to increase with increasing depth. Once the pressure reaches the so-called critical point of the atmosphere gases, a distinction between gas and liquid is not physically possible. So thus, there is no clearly identifiable lower boundary of the atmosphere of Jupiter. In analogy to the Earth is defined instead the zero level as that point at which a pressure of one bar is reached. At the equator, this level is about 72,000 km from the planet center.

The heat shield was jettisoned and the measurements started. At a depth of 50 km below the zero level wind speeds could be measured in excess of 500 km / h. This hoist occurred not only horizontally, but there was also strongest katabatic winds and turbulence in the vertical. And, although the probe in a "fair weather area " in which the nephelometer (fog diameter) clear weather registered, went down.

The radio contact was lost about an hour after admission from a depth of 160 km. In the final seconds of the probe registered a pressure of 22 bar and a temperature of 152 ° C.

Meanwhile, the flyby spacecraft directed a 50- minute main engine burn in an elliptical orbit Jupiter. The jupiter next point ( Perijovum ) amounted to 185,000 km and the farthest ( Apojovum ) 19.3 million kilometers. The Apojovum was flown in March 1996, and a 24 -minute re- ignition engine, the Perijovum was raised to 786,000 km, because you wanted to avoid that the probe would be jeopardized by the outgoing radiation from Io. The other rounds were conducted in each different tracks to observe the moons of Jupiter better.

Exploration of the moons; Burn up in Jupiter in 2003

After the failure of the main antenna originally planned permanent observation of Jupiter weather had to be abandoned. This was taken by the Hubble Space Telescope, and only as deemed particularly interesting cloud formations also observed by Galileo.

The main task of the probe was instead the observation of the four Galilean moons. It hints to a water ocean beneath the icy crust of Europa were delivered and monitored for zones of liquid water in coats of Ganymede and Callisto and the volcanoes on Io. Both Io is constantly being kneaded by the tidal forces of Jupiter and the largest moon in our solar system, Ganymede, have an iron core, Ganymede, surprisingly, a strong magnetic field.

The part mission at Jupiter was originally planned for 23 months until December 1997, but was extended three times, as devices and drive were still functional and could expect good results. Focus of the first two mission extensions was there the moon Europa, while they dared two flybys of Io in the interior, dominated by dangerous radiation Jupiter System Mission in the last part. As Cassini -Huygens on its way to Saturn used the Jupiter for a swing-by accelerating the end of 2000, get interesting parallel measurements.

On September 21, 2003 Galileo was steered into Jupiter's atmosphere and burned up there, because the probe later no longer would have been steered because of fuel shortages and failures of the electronics due to the resultant of Jupiter during the last years of high radiation dose. There was a danger that Galileo could pounce on the moon Europa and contaminate it with terrestrial bacteria. This would have hampered future missions for the exploration of traces of life on Jupiter 's moons.


  • Orbiter with takeoff weight of 2,233 kg and a length of 5.3 m
  • A total of 18 scientific instruments (15 from the USA, three from Germany ) for the study of UV radiation, magnetic fields and electrically charged particles
  • Camera system with 20 - to 1000 -fold higher resolution than previous missions, Voyager 1 and 2


  • First direct measurement of Jupiter's atmosphere
  • Detection of liquid salt water below the surface of the three moons of Jupiter, Europa, Ganymede and Callisto
  • Strong evidence of volcanic activity on Io, which are 100 times stronger than on Earth
  • First flyby of an asteroid ( (951) Gaspra on October 29, 1991)
  • Measurement of a magnetic field on Ganymede