City Labs’ Tiny Nuclear-Battery-Powered Satellite Aims To Set A Precedent

As you get up to leave the movie theater, you might notice at the end of the dark hallway an exit sign dimly glowing red. Do not be alarmed, but the sign might be radioactive.

For decades, some movie theaters, office buildings, schools and the like have lit their exit signs using tritium, a gaseous radioactive isotope of hydrogen. As tritium decays, it emits low-energy beta particles that excite a phosphor coating, causing it to glow. Such signs can shine for more than 10 years—and that steady flow of energy intrigues the space industry.

• Government interest in nuclear batteries is growing

• The company is working with AFWerx on a tritium-powered ion engine for small satellites

City Lab, a Miami-based company specializing in space nuclear micropower, launched its first satellite into space in July carrying a tritium-based nuclear battery. NASA has launched nuclear-battery-powered spacecraft for many years—including the plutonium-238 dioxide-powered Voyager 1 and Voyager 2 deep-space probes in 1977—but City Labs says it is the first commercial entity to launch a nuclear battery.

The company’s Betavoltaic Orbital High-Reliability (BOHR) demonstration satellite—a tribute to the famous quantum physicist Niels Bohr—used an FAA pathway for nuclear launch approval that was outlined in 2019 in National Security Presidential Memorandum-20, City Labs says.

Interest in nuclear batteries is growing as NASA and the U.S. Defense Department look for new ways to generate electricity and heat on deep space missions as well as in situations where shadows might prevent solar panels from generating enough energy, such as during the lunar night or behind another spacecraft.

The BOHR is tiny. As a 1U cubesat, it measures 10 X 10 X 10 cm (4 X 4 X 4 in.). The amount of tritium the small satellite carries is also minute.

“An exit sign has about 10-20 curies, depending on the model that you buy,” Peter Cabauy, cofounder and CEO of City Labs, tells Aviation Week. “We had roughly two exit signs’ worth.”

The company’s NanoTritium betavoltaic batteries generate electricity when beta particles from decaying tritium hit a semiconductor. The product generates only nanowatts to microwatts of electricity, but City Labs says that is enough to power electronics that might require only a trickle of power, such as a temperature sensor or inertial measurement unit.

The betavoltaic batteries could be useful when the BOHR’s solar panels cannot supply enough electricity. Cabauy says the technology could also ensure certain critical electronics maintain power, including memory chips during a space launch or communications security electronics that need to maintain encryption keys.

The NanoTritium product is engineered into a solid form as metal hydrides and can be integrated into solid-state materials. That allows it to be compact or have a variety of form factors, City Labs says. Tritium has a 12.3-year half-life, allowing for more than 20 years of “predictable power,” the company says.

Although the BOHR satellite is a small proof of concept, City Labs has bigger plans for its tritium technology.

In partnership with the U.S. Air Force’s AFWerx innovation unit, the company is in the early phases of developing a tritium-powered ion engine that could be used on cubesats for station-keeping, flying in a coordinated cluster or even pushing through the thicker atmosphere of very low Earth orbit. A laboratory demonstration is expected within about a year, Cabauy says.

The tritium-based technology can also be adapted to generate heat to warm landers, rovers or other Moon-based sensors so they can survive the frigid, two-week lunar night. For example, on a vehicle the size of Firefly Aerospace’s Blue Ghost 2—a lunar lander planned to launch late this year to the far side of the Moon—Cabauy estimates 60 kg (132 lb.) of batteries will be carried to power a radio telescope to operate during the lunar night, during which temperatures can drop to -280F.

“We can replace the 60 kg of batteries with a quarter to a half a kilogram of tritium metal heat source,” Cabauy says. “That’ll provide the heat not just for that lunar night, but it’ll provide it for decades.”