Galileo was an American robotic space probe that studied the planet Jupiter and its moons, as well as the asteroids Gaspra and Ida.

Galileo arrived at Jupiter on December 7, 1995, after gravitational assist flybys of Venus and Earth, and became the first spacecraft to orbit an outer planet.

NASA's Ames Research Center managed the atmospheric probe, which was built by Hughes Aircraft Company.

[6] NASA's Scientific Advisory Group (SAG) for Outer Solar System Missions considered the requirements for Jupiter orbiters and atmospheric probes.

It noted that the technology to build a heat shield for an atmospheric probe did not yet exist, and facilities to test one under the conditions found on Jupiter would not be available until 1980.

[7] NASA management designated the Jet Propulsion Laboratory (JPL) as the lead center for the Jupiter Orbiter Probe (JOP) project.

[9] An important decision made at this time was to use a Mariner program spacecraft like that used for Voyager for the Jupiter orbiter, rather than a Pioneer.

Pioneer was stabilized by spinning the spacecraft at 60 rpm, which gave a 360-degree view of the surroundings, and did not require an attitude control system.

By contrast, Mariner had an attitude control system with three gyroscopes and two sets of six nitrogen jet thrusters.

His 1610 discovery of what is now known as the Galilean moons orbiting Jupiter was important evidence of the Copernican model of the solar system.

NASA's Ames Research Center managed the atmospheric probe, which was built by Hughes Aircraft Company.

[14] On December 19, 1985, it departed the JPL in Pasadena, California, on the first leg of its journey, a road trip to the Kennedy Space Center in Florida.

[18] RTGs were necessary for deep space probes because they had to fly distances from the Sun that made the use of solar energy impractical.

string) was composed of the same functional elements, consisting of multiplexers (MUX), high-level modules (HLM), low-level modules (LLM), power converters (PC), bulk memory (BUM), data management subsystem bulk memory (DBUM), timing chains (TC), phase locked loops (PLL), Golay coders (GC), hardware command decoders (HCD) and critical controllers (CRC).

This 8-bit microprocessor was the first low-power CMOS processor chip, similar to the 6502 that was being built into the Apple II desktop computer at that time.

The BUMs and DBUMs provided storage for sequences and contain various buffers for telemetry data and interbus communication.

The propulsion subsystem was developed and built by Messerschmitt-Bölkow-Blohm and provided by West Germany, the major international partner in Project Galileo.

This provided a reliable and long-lasting source of electricity unaffected by the cold environment and high-radiation fields in the Jovian system.

[33] The modules were designed to survive a range of potential accidents: launch vehicle explosion or fire, re-entry into the atmosphere followed by land or water impact, and post-impact situations.

An outer covering of graphite provided protection against the structural, thermal, and eroding environments of a potential re-entry into Earth's atmosphere.

[34] Scientific instruments to measure fields and particles were mounted on the spinning section of the spacecraft, together with the main antenna, power supply, the propulsion module and most of Galileo's computers and control electronics.

It also carried the Heavy Ion Counter, an engineering experiment to assess the potentially hazardous charged particle environments the spacecraft flew through, and an extreme ultraviolet detector associated with the UV spectrometer on the scan platform.

[2] The despun section's instruments included the camera system; the near infrared mapping spectrometer to make multi-spectral images for atmospheric and moon surface chemical analysis; the ultraviolet spectrometer to study gases; and the photopolarimeter-radiometer to measure radiant and reflected energy.

The camera system was designed to obtain images of Jupiter's satellites at resolutions 20 to 1,000 times better than Voyager's best, because Galileo flew closer to the planet and its inner moons, and because the more modern CCD sensor in Galileo's camera was more sensitive and had a broader color detection band than the vidicons of Voyager.

Light then passed through an exit slit into photomultiplier tubes that produced pulses of electrons, which were counted and the results sent to Earth.

As Galileo rotated, EUV observed a narrow ribbon of space perpendicular to the spin axis.

A 100 mm (4 in) aperture reflecting telescope collected light and directed it to a series of filters, and, from there, measurements were performed by the detectors of the PPR.

[46][47] The HIC was, in effect, a repackaged and updated version of some parts of the flight spare of the Voyager cosmic-ray system.

One set was located at the end of the magnetometer boom and, in that position, was about 11 m (36 ft) from the spin axis of the spacecraft.

[54][55] The atmospheric probe was built by Hughes Aircraft Company's Space and Communications Group at its El Segundo, California plant.