How the INL is changing space with $100 million power generators that last decades

EDITOR’S NOTE: EastIdahoNews.com is working with Idaho National Laboratory to celebrate its 75th anniversary. Each month, we’ll highlight the history, achievements and trials of the U.S. Department of Energy’s desert site. We’ll explore the INL’s influence on eastern Idaho and its impact on local people.

IDAHO FALLS — When Stephen Johnson, Ph.D., tells most people what he does for a living, they’re usually surprised – especially when they learn what’s happening in the desert west of Idaho Falls.

Johnson is the director of the Space Nuclear Power and Isotope Technologies Division at the Idaho National Laboratory’s Materials and Fuels Complex.

In other words, “I’m part of a group that provides small power systems for NASA applications,” Johnson explains. “I’d say most people that come in here have no idea that this work is done here.”

It all happens inside a highly secure building, where cell phones, smart watches, Wi-Fi, and anything that transmits a signal are strictly prohibited.

Johnson took EastIdahoNews.com on a rare tour inside the building where Radioisotope Thermoelectric Generators, or RTGs, are constructed. Each RTG costs around $100 million and takes years to complete.

“Typically, they go for deep space missions – missions that are orbiting Saturn, Jupiter, flying by Pluto, going into the Kuiper Belt, which is the asteroid belt around our solar system,” Johnson says. “They will go down to the surface of Mars and will go explore the various moons.”

Since the 1960s, RTGs produced at INL have supported over 24 missions to space, including Apollo 12, 14, 15, 16 and 17.

Constructing the RTG

Before the power generators arrive in Idaho, they’re at Oak Ridge and Los Alamos National Laboratories, where the components and heat sources are produced.

“We’re the last step in a chain of events of the Department of Energy labs. We integrate pieces and parts from all the labs and from private industry in order to take heat sources made of Plutonium 238, harness that heat, and put it into a converter system that will supply power for NASA missions,” Johnson says.

The materials arrive at INL from Los Alamos in heavy-duty stainless steel containers that are welded shut. Inside are heat sources that are put into module assembly glove boxes which are used to make the RTGs.

This process takes about six weeks to complete. Once the generator is ready, it is moved into the inert atmospheric assembly chamber, where controllers use robotic arms to place radioisotope heat sources inside the RTGs.

“When we’re actually doing operations, the chamber is filled with about one foot of water. Water is a very effective neutron shield, so it protects the people,” Johnson explains.

Testing the RTG

The last generator finished at INL was in 2019 for the 2020 Mars Perseverance Rover. They take around four months to build and undergo a series of tests to make sure they’ll work.

Inside one room, loud equipment simulates vibration and shock similar to what occurs on a spacecraft launch pad.

“We have an armature that will move up and down at a fairly high frequency – about 20-2,000 hertz is our testing profile with up to 30,000 pounds of force,” says Craig Dees, the Radioisotope Power Supply Group lead engineer. “We’ll test the Z axis, and the shaker head will move up and down. As we reorient the shaker to attach to the slip table, we’ll do the X and Y shake on a slip table.”

Johnson describes the room as essentially “one big woofer.” The walls are covered with sound-deadening foam, and workers wear hearing protection.

“This is the one piece of equipment that could physically damage the generator if we twist the knob a little bit too hard,” Johnson says.

After vibration testing, scientists measure the generator’s magnetic field to ensure it won’t interfere with the delicate instruments on the spacecraft.

A magnetic field in space is an invisible area surrounding objects like planets and stars where moving charged particles create a force that can influence the movement of other charged particles.

“If you’re on a rover, you’re going to have instrumentation nearby. You’re pretty interested in making certain the magnetic fields don’t screw up your instruments, or else you have a really fast mission to Mars and zero data,” Johnson says.

The final step in the process is to place the RTG inside a large chamber where more rigorous testing is done. A forklift loads the unit to a rail system inside the chamber that has electrical and gas connections.

“Once we have good signals and good feedback from the chamber in terms of temperatures and pressures, we’ll shut the door, and we’ll actually evacuate all the gas out of the chamber similar to space,” says engineer Jaymon Birch.

If all the tests pass, the RTG is ready to go. It’s loaded into a specialized shipping container before being placed in a truck for a cross-country trip to the launch pad at Cape Canaveral Space Force Station in Florida.

“It needs to be down there about 4-6 months prior to launch. It takes about four days to get down there from here,” Johnson says. “As a valuable piece of US property, it is escorted with lots of armed men.”

The future of RTGs

Because the RTGs are so unique, scientific, and expensive, nothing was spared when the facility at MFC was built. The walls are 12-inch poured concrete, and the roof is six-inch concrete. There are no windows, and the garage door can stand up to 88 mph winds.

“This building is overbuilt so that we could have a basic seismic event here. Other buildings on site might fall down. This one won’t. It may lose power, but it won’t fall down. That’s to safeguard the RTG,” Johnson explains.

Those RTGs are often called space batteries, but Johnson says that is technically incorrect.

“I call it a power system. It does not get recharged. It works all the time. It has a half-life, meaning it decays half of the material in 88 years. So when you’ve got 88 years and still have half your power left, that’s a pretty flat power curve. It’s very suitable for doing long-term missions,” Johnson says.

Space missions that have been happening for decades are partially the result of what has been happening at INL. Lab officials hope research and engineering will continue supporting these space missions for years.

Watch our video tour of the facility in the video player above.