New Power Source for Spaceships Could Make CubeSats a Common Sight in the Solar System

Radioisotope Thermoradiative Cell Power Generator concept 6 photos
Photo: NASA/Stephen Polly
Radioisotope Thermoradiative Cell Power Generator conceptMulti-Mission Radioisotope Thermoelectric GeneratorMulti-Mission Radioisotope Thermoelectric GeneratorMulti-Mission Radioisotope Thermoelectric GeneratorMulti-Mission Radioisotope Thermoelectric Generator
It’s been several years now since NASA started the Innovative Advanced Concepts program. NIAC for short, it’s an effort to publicly recognize the merits of people’s ideas when it comes to the tools we need for space exploration, but also to support them in their early stages through various grants.
We’ve been covering these NIAC grants for a while now here, on autoevolution, and on more than one occasion, we were blown away by how imaginative some people are and how revolutionary some of the projects they propose. Kind of like the Radioisotope Thermoradiative Cell Power Generator we’re here to discuss now.

You all know by now how space exploration works. Someone here on Earth points something at a celestial target, launches it, and voila, instant space science. It seems pretty simple, straightforward and, most importantly, the best we can do. Turns out, we could do a lot more to advance our goals.

Our current probes, spaceships, and whatnot are relatively simple devices, generally sent into the great unknown with a unique mission in mind: study this, impact that, or land there. Only recently have we begun sending companion hardware alongside the main spacecraft, not only to observe the leader of the mission, but also to perform additional science. Yet like all our other endeavors in space, this approach has limits, too, imposed by access to power, mostly. Let me explain.

Say you send a mission to the outer reaches of the Solar System, but you have multiple goals and targets there. You’ll have the main spacecraft, tasked with looking at what’s what, and a series of other smaller, accompanying machines with their own specific missions.

Multi\-Mission Radioisotope Thermoelectric Generator
Photo: NASA
Both the main and secondary spacecraft will probably be equipped with solar panels for power, but the outer solar system is so far from the Sun that you can’t always rely on those. When it comes to the main spacecraft, you could easily solve the issue with a generator the likes of the MMRTG, for instance.

MMRTG stands for multi-mission radioisotope thermoelectric generator, and it’s what powers the Perseverance rover now on location on Mars, for instance. It is used to convert heat generated by the natural decay of a radioisotope fuel (in this case, plutonium-238) into electricity, by means of solid-state thermocouples.

Seen by its makers not like a nuclear reactor, but more like a nuclear battery, the MMRTG generates 110 watts of power in the Perseverance. That is about as much as a light bulb, but more than enough to keep the rover’s systems up and running. It can keep them so for many years, even if the output is expected to drop as time passes (down to 72 watts after 17 years, as per NASA).

That makes the MMRTG quite the suitable solution for such applications, but there’s one catch: it’s quite large and cannot be used to power much smaller spacecraft. Just to give you an idea, the MMRTG on the Perseverance is 25 inches (64 cm) in diameter, 26 inches (66 cm) tall, and weighs about 94 pounds (45 kg).

Multi\-Mission Radioisotope Thermoelectric Generator
Photo: NASA/Department of Energy
And this is why researcher Stephen Polly from the Rochester Institute of Technology in Rochester, New York, came up with the idea of the Radioisotope Thermoradiative Cell Power Generator, one of the 14 projects NASA recognized through NIAC at the beginning of this year.

Described as a “revolutionary power source for missions to the outer planets,” this thing, too, is powered by the heat generated by a radioisotope, but uses thermoradiative and photovoltaic cells to turn that into electricity.

According to the researcher, this approach could allow for “an order of magnitude increase in mass-specific power” and “three orders of magnitude decrease in volume” when compared to the MMRTG, effectively making it suitable for deployment in secondary spacecraft that could be sent along with a primary one in the depths of Sol.

The idea is still in its early stages, and Polly says he’ll now use the NASA funds (unclear how much of the total $175,000 NIAC money went to him) to study the creation of such a system, with a focus on system size, weight, and power.

Multi\-Mission Radioisotope Thermoelectric Generator
Photo: NASA
Once that is out of the way, a concept study will be conducted, with the general idea being that a Radioisotope Thermoradiative Cell Power Generator could be fitted into a CubeSat (a spacecraft made of cubes no more than 10 cm/3.9 inches in size and weighing just 4.4 pounds/3 kg). The CubeSat could be sent, for instance, on a mission to Uranus, accompanying a main spacecraft and acting as an information relay for various atmospheric probes, for instance.

This approach reminded us of another NIAC idea from back in 2021, when another scientist talked about probe-launching spacecraft that could be sent to Uranus.

That one was called Sustained CubeSat Activity Through Transmitted Electromagnetic Radiation (SCATTER) and called for the probes to be powered not by solar panels or batteries, but by electromagnetic radiation beamed to them by the parent spacecraft.

We have no clue what happened to SCATTER since last year, and there’s a big chance the idea we discussed in the lines above could follow the same path. After all, NASA has always warned that even if it likes something and invests in it, NIAC ideas “are not considered and may never become NASA missions.”
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Editor's note: Gallery shows the Multi-Mission Radioisotope Thermoelectric Generator.

About the author: Daniel Patrascu
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Daniel loves writing (or so he claims), and he uses this skill to offer readers a "behind the scenes" look at the automotive industry. He also enjoys talking about space exploration and robots, because in his view the only way forward for humanity is away from this planet, in metal bodies.
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