These images were obtained by NASA's Galileo spacecraft."
Scientific instruments to measure fields and particles were mounted on the spinning section of the spacecraft, together with the main , power supply, the propulsion module and most of the Galileo computers and control electronics. The sixteen instruments, weighing 118 kg altogether, included sensors mounted on an 11 m boom to minimize interference from the spacecraft; a instrument for detecting low energy charged particles and a plasma wave detector to study waves generated by the particles; a high energy particle detector; and a detector of cosmic and Jovian . It also carried the Heavy Ion Counter, an engineering experiment added to assess the potentially hazardous charged particle environments the spacecraft flew through, and an added Extreme detector associated with the UV spectrometer on the scan platform.
A city-sized impact crater was viewed by NASA's Galileo spacecraft."
For reasons which are not currently known, and in all likelihood will never be known with certainty, Galileo's failed to fully deploy after its first flyby of Earth. Investigators speculate that during the time that Galileo spent in storage after the Challenger disaster, the evaporated, or the system was otherwise damaged. Engineers tried thermal cycling the antenna, rotating the spacecraft up to its maximum spin rate of 10.5 rpm, and "hammering" the antenna deployment motors - turning them on and off repeatedly - over 13,000 times; all attempts failed to open the high-gain antenna. Fortunately Galileo had an additional that was capable of transmitting information back to Earth, though since it transmitted a signal , the low-gain antenna's was significantly less than the high-gain antenna's would have been; the high-gain antenna was to have transmitted at 134 kilobits per second whereas the low-gain antenna was only intended to transmit at about 8 to 16 bits per second. Galileo's low-gain antenna transmitted with a power of about 15 to 20 watts, which, by the time it reached Earth, and had been collected by one of the large aperture (70 m) DSN antennas, had a total power of about -170 dBm or 10 zeptowatts (10 × 10−21 watts). Through implementation of sophisticated data compression techniques, arraying of several antennas and sensitivity upgrades of receivers used to listen to Galileo's signal, data throughput was increased to a maximum of 160 bits per second. The data collected on Jupiter and its moons was stored in the on board , and transmitted back to Earth during the long portion of the probe's orbit using the low-gain antenna. At the same time, measurements were made of Jupiter's magnetosphere and transmitted back to Earth. The reduction in available bandwidth reduced the total amount of data transmitted throughout the mission to about 30 and reduced the number of pictures that were transmitted significantly; in all, only around 14,000 images were returned.
Ganymede at lower left, Callisto at lower right, Io on upper left, and Europa on upper right in a combined biew from NASA's Galileo and Voyager spacecraft.">
Galileo spacecraft - Solar System
As the launch of Galileo neared, anti-nuclear groups, concerned over what they perceived as an unacceptable risk to the public's safety from Galileos RTGs, sought a court injunction prohibiting Galileos launch. RTGs had been used for years in planetary exploration without mishap: the 8/9, launched by the U.S. , had 7% more plutonium on board than Galileo, and the two each carried 80% as much plutonium as Galileo did. However, activists remembered the messy crash of the Soviet Union's nuclear-powered satellite in Canada in 1978, and the 1986 had raised public awareness of the possibility of explosive spacecraft failures. Also, no RTGs had ever been made to swing past the Earth at close range and high speed, as Galileos Venus-Earth-Earth Gravity Assist trajectory required it to do. This created a novel mission failure modality that might plausibly have entailed total dispersal of Galileos plutonium in the Earth's atmosphere. Scientist , for example, a strong supporter of the Galileo mission, said in 1989 that "there is nothing absurd about either side of this argument."
Galileo Spacecraft Flight Path - The Planets Today
A broad, umbrella-shaped plume of gas and dust has been spotted above Prometheus by NASA's Voyager and Galileo spacecraft every time the viewing conditions have been favorable.">
Galileo Spacecraft « Cosmology & Space Research
were not a practical solution for Galileo's power needs at Jupiter's distance from the Sun (it would have needed a minimum of 65 square metres (700 ft²) of solar panels); as for batteries, they would have been prohibitively massive. The solution adopted consisted of two (RTGs). The RTGs powered the spacecraft through the radioactive decay of -238. The heat emitted by this decay was converted into electricity for the spacecraft through the solid-state . This provided a reliable and long-lasting source of electricity unaffected by the cold space environment and high radiation fields such as those encountered in Jupiter's magnetosphere.