How It Works

Unmanned spacecraft rely on radioisotope thermoelectric generators (RTGs) for the power they need for space exploration. RTGs use heat from plutonium to generate electricity. The craft use this electricity to run the computers that control their operation and collect and process the vast amounts of data, including images, that are sent back to Earth.

 

A typical RTG produces about 300 watts of electricity and will operate unattended for many years. Voyager 1, which was launched in 1977, is at the edge of the solar system. Although now more than 9 billion miles from the sun, Voyager 1 is still transmitting data. Voyager 2, also launched in 1977, is not far behind.

 

RTGs have powered 24 U.S. space missions reliably and safely. The missions include the Apollo Lunar Surface Experimental Packages, Pioneer 10 and 11, two Viking Mars craft, two Voyagers, and the Galileo, Ulysses, Cassini and New Horizons spacecraft. RTGs are essential for exploration in deep space, where spacecraft are too far from the sun to use solar power.

 

Galileo Spacecraft Mission
The Galileo spacecraft orbited Jupiter 35 times over a two-year period to better understand atmospheric science, including climate change on Earth. Galileo was the first craft to fly past an asteroid and the first to discover a moon of an asteroid. The Cassini spacecraft studied Saturn’s rings and some of the planet’s moons. Both craft relied on RTGs to gather data and record images of the planets.

 
New Horizons Spacecraft Mission

The New Horizons spacecraft, launched in 2006, is the latest NASA unmanned mission. The craft, bound for Pluto, will reach the dwarf planet in 2015. After studying Pluto and Charon, one of Pluto’s moons, the craft may view two newly discovered moons of Pluto. It then will fly on to explore the rocky, icy objects in the Kuiper Belt.