Page "Galileo (spacecraft)" Paragraph 44

Each GPHS-RTG, mounted on a 5-meter long boom, carried 7. 8 kilograms ( 17. 2 lb ) of < sup > 238 </ sup > Pu.

Each RTG contained 18 separate heat source modules, and each module encased four pellets of plutonium dioxide, a ceramic material resistant to fracturing.

The modules were designed to survive a range of hypothetical 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 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 arrived at Jupiter.