Resumo de Galileo's Spacecraft - http://en.wikipedia.org/wiki/Galileo

The Jet Propulsion Laboratory built the Galileo spacecraft and managed the Galileo mission for NASA. Germany supplied the propulsion module. NASA's Ames Research Center managed the probe, which was built by Hughes Aircraft Company.
At launch, the orbiter and probe together had a mass of 2,564 kilograms (5,653 pounds) and was seven metres tall. One section of the spacecraft rotated at 3 rpm, keeping Galileo stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments. The other section of the spacecraft held steady for cameras and the four instruments that had to point accurately while Galileo was flying through space. This was the job of the attitude control system (see below). In addition to computer programs which directly operated the spacecraft and were periodically transmitted to it, back on the ground the mission operations team used software containing 650,000 lines of programming code in the orbit sequence design process; 1,615,000 lines in the telemetry interpretation; and 550,000 lines of code in navigation.
The spacecraft was controlled by a RCA 1802 Cosmic microprocessor CPU, clocked at about 1.6 MHz, and fabricated on sapphire (Silicon on Sapphire) which is a radiation- and static-hardened version, ideal for spacecraft operation. This microprocessor was the first low-power CMOS processor chip, quite on a par with the old 8-bit 6502 that was being built into the Apple II desktop at that time. Galileo's attitude control system software was written in the HAL/S programming language, also used in the Space Shuttle program. The 1802 CPU had previously been used onboard the Voyager and Viking spacecraft.The Propulsion Subsystem consisted of a 400 N main engine and twelve 10 N thrusters together with propellant, storage and pressurizing tanks, and associated plumbing. The fuel for the system was 925 kg of monomethyl hydrazine and nitrogen tetroxide. Two separate tanks held another 7 kg of helium pressurant. The Propulsion Subsystem was developed and built by Daimler Benz Aero Space AG (DASA) (formerly Messerschmitt?Bolkow?Blohm) and provided by Germany, the major international partner in Project Galileo [Solar panels 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 consists in two radioisotope thermoelectric generators (RTGs). The RTGs powered the spacecraft through the radioactive decay of plutonium-238, which has a half-life of 87.8 years. This decay emits heat, which is converted into electricity for the spacecraft through the solid-state Seebeck effect. This provided a reliable, long-lasting source of electricity, insensitive to the chilling cold of space and virtually invulnerable to high radiation fields such as those encountered in Jupiter's magnetosphere.Each RTG, mounted on a 5-metre long boom, carried 7.8 kilograms (17.2 lb) of 238Pu [2]. Each RTG contained 18 separate heat source modules, and each module encased four pellets of plutonium dioxide, a ceramic material which is resistant to fracturing. The modules were designed to survive a range of postulated 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. Additional graphite components provided impact protection, while iridium cladding of the actual fuel cells provided post-impact containment. The RTGs produced about 570 watts at launch. The power output initially decreased at the rate of 0.6 watts per month and was 493 watts when Galileo finally arrived at Jupiter.
As the launch of Galileo neared, anti-nuclear groups, concerned over what they perceived as an ueptable risk to the public safety from Galileo's RTGs, sought a court injunction prohibiting Galileo's launch. In fact, RTGs had been safely used for years before in planetary exploration. The Lincoln Experimental Satellites 8/9, launched by the U.S. Department of Defense, had 7% more plutonium on board than did Galileo, and the two Voyager spacecraft each carried 80% as much plutonium as Galileo did.
After the Challenger accident, a study considered additional shielding and eventually rejected it, in part because such a design significantly increased the overall risk of mission failure and only shifted the other risks around (for example, if a failure on orbit had occurred, additional shielding would have significantly increased the consequences of a ground impact) [Scientific instruments to measure fields and particles, together with the main antenna, the power supply, the propulsion module, most of the galileo computers and control electronics, were mounted on the spinning section. The sixteen instruments, weighing 118 kg altogether, included magnetometer sensors, mounted on an 11 m boom to minimize interference from the spacecraft; a plasma instrument 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 dust. 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 Ultraviolet detector associated with the UV spectrometer on the scan platform.

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