This article is part of a series covering Idaho National Laboratory (INL). Scroll visited different projects from INL, and this publication covers radioisotope power systems located west of Idaho Falls.

Tucked away in the Central Idaho desert, INL’s laboratories are akin to a space station on another planet. With the help of nuclear scientists, INL is assisting NASA space missions by supplying radioisotope thermoelectric generators (RTGs) and helping take the country to other frontiers.

Mario Miguel interviews Steve Johnson of Idaho National Laboratory.

Mario Miguel interviews Steve Johnson of Idaho National Laboratory. Photo credit: Gabriela Fletcher

How INL helps NASA

INL is NASA’s only supplier of radioisotope thermoelectric generators (RTGs) which make enough energy to last decades. These nuclear-power systems are the batteries that make deep space exploration with satellites and rovers possible.

RTGs turn the heat emitted from the radioactive decay of plutonium-238 directly into electricity. It then uses the excess heat to keep the spacecraft warm amid the cold temperatures in space and on other planets. The latest models produce 100 watts of electricity and are expected to last at least a decade in harsh environments.

INL will prepare the RTG for NASA’s Dragonfly mission, which will launch a drone named Dragonfly in 2026 for Titan, Saturn’s icy moon.This moon contains organic compounds and water similar to Earth and could provide insights into how life developed on our planet.

A rendering of the Dragonfly done that will launch in 2026.

A rendering of the Dragonfly done that will launch in 2026.

The development and improvement of RTGs have opened new possibilities for space exploration. From our moon to the far reaches of the solar system, the generators assembled in the Idaho desert are bringing the mysteries of the universe closer to home.

Previous space missions

INL’s Space Nuclear Power and Isotope Technologies Division has contributed to several space missions over the last twenty years by fueling and testing RTGs. RTGs fueled and tested at INL power the Pluto New Horizons probe, the Mars Science Laboratory Curiosity Rover and the Perseverance Mars Rover.

Display of space and nuclear power at the INL Materials and Fuels Complex.

Display of space and nuclear power technology at the INL Space Power museum. Photo credit: Gabriela Fletcher

Pluto New Horizons launched in 2006. It carried a spare RTG from the Cassini probe, which was the first spacecraft to orbit Saturn. The RTG reached Pluto in 2015, and it was the first spacecraft to explore the planet up close.

The Curiosity and Perseverance rovers, both powered by RTGs, landed on Mars in 2012 and 2021 respectively. Each rover is searching the Red Planet for signs of ancient life by collecting rock samples. The rovers are still on Mars, so I changed it to “searching”

How are RTGs fueled and tested?

Unfueled RTG is tested for integrity before experts place it into a glove box where they insert the plutonium-238 in several clads. The plutonium-238 comes from Los Alamos National Laboratory.

The four-fueled clads are placed into one graphite container called the General Purpose Heat Source. The fueling process takes four to six weeks.

Models of generators used in providing power to various NASA space exploration missions.

Models of generators used in providing power to various NASA space exploration missions. Photo credit: Gabriela Fletcher

Once the RTG is functional, experts test the generator’s ability to withstand harsh conditions through four simulations.

The first test simply measures the RTG’s electrical output and radiation field. For the second test, the scientists place the RTG onto a vibrating machine that mimics the shaking the generator will experience during liftoff.

Every ounce matters on a space flight, so in the third test, INL measures the RTG’s mass and center of gravity. For the final test, they place the RTG inside a thermal vacuum chamber to see how it would handle the pressure of outer space.