New Horizons conserved energy by taking naps on its 3 billion mile journey to Pluto but the spacecraft isn’t done yet and may have enough power for two more decades of exploration, according to NASA.

Traveling so far from the sun meant solar panels wouldn’t provide enough power. Instead, NASA went nuclear, equipping the piano-sized probe with a battery that converts radiation from decaying plutonium into electricity.

New Horizons loses about a few watts of power each year, according to NASA, but is estimated to have as much as 20 years left in its life expectancy.

Read the article “New Horizons: How Spacecraft Could Stay Powered for 20 More Years Beyond Pluto” on abcnews.go.com.