How Are Robots Powered In Space?

NASA’s newest Mars rover, Perseverance, powered off Earth recently, starting a 7 month voyage through deep space to Mars.

This robot is built to spend three years exploring the red planet’s surface, searching for clues of ancient alien microbes, saving Martian soil samples for future return to Earth, deploying the first-ever interplanetary helicopter, and creating the new way for human explorers with a range of different experiments.

A device called a multi-mission radioisotope thermoelectric generator, or MMRTG, is said to potentially power Perseverance for more than 14 years thanks to a special nuclear material called plutonium-238, or Pu-238. This material has powered NASA spacecraft for decades, including some for almost 50 years. 

Pu-238 is found as a byproduct of nuclear weapons manufacturing. Unlike plutonium-239 (which makes up the fissile cores of bombs), half of any chosen amount decays within 87 years.

On a spacecraft, Pu-238’s decay gives off warmth that helps protect fragile electronic systems. But above all, by wrapping Pu-238 with thermoelectric materials that convert heat to electricity, it forms a mind boggling long-lasting power source to power these spacecraft for decades. Physicist Glenn Seaborg discovered plutonium in 1940.

Only 20 years later, engineers used it to create nuclear batteries that powered spacecraft. In the 1960’s,  the US Navy took on an experimental plutonium-powered satellite program called TRANSIT to guide their submarines and missiles from space. The first satellite ever powered by plutonium, called Transit 4A  reached orbit on June 29, 1961.

In another space mission, Apollo 11 astronauts in July 1969 dropped off roughly 1.2 ounces of Pu-238 on the moon. This material lay in a piece of technology called the Apollo Lunar Radioisotopic Heater.

This clever device kept a seismic monitoring station warm during half-month-long lunar nights, when the surface temperatures dropped to -243 degrees Fahrenheit (-153 degrees Celsius).

Voyager 1 has been recorded to be 13.9 billion miles (22.4 billion kilometers) and counting, away from Earth making it the farthest man made object from Earth. Voyager 1 left the solar system and reached interstellar space between star systems, in August 2012.

Even though Voyager is so far away from Earth and it’s been operating for more than 40 years, they each have three Pu-238-filled nuclear batteries to allow the spacecraft to continue communicating with ground stations on Earth. NASA predicts each spacecraft to go fully offline by 2025.

The Future Of Power In Space

The future of power in space has extremely exciting prospects for long lasting power sources fit to fuel missions for huge, and potentially infinite amounts of time.

Dr George Williams of NASA states “As NASA plans to extend human presence across the solar system, including the Moon and Mars, it also seeks to shorten the time required to develop and apply transformative technologies that increase the nation’s capabilities in space, enable future missions and support a variety of commercial spaceflight activities”.

He adds that “NASA’s Solar Electric Propulsion (SEP) project is developing critical technologies to enable government and commercial customers to extend the length and capabilities of ambitious new exploration and science missions.

Advanced propulsion technologies such as SEP deliver the right mix of cost savings, safety and superior propulsive power to support a variety of next-generation journeys to destinations in deep space”.

“Energized by the electric power from on-board solar arrays, the electrically propelled system will use 10 times less propellant than a comparable, conventional chemical propulsion system, such as those used to propel the space shuttles to orbit.

Yet that reduced fuel mass will deliver robust propulsion capable of boosting robotic and crewed missions well beyond low-Earth orbit: sending exploration spacecraft to distant destinations, ferrying cargo to and from points of interest, laying the groundwork for future missions or resupplying those already underway”.

Could Microbes Be The Future Of Powering Space Exploration?

Jeremy Hsu, a science writer based in New York, whose work has appeared in the Scientific American, Discovery Magazine, BlackChannel and others, explains how microbes may be used to power spacecraft exploration in the future, “Today’s robotic space missions take careful steps to avoid carrying tiny bacterial life from Earth that could contaminate the surface of Mars or other planets.

That may all change if a NASA-funded effort can harness microbes as an almost endless power source for the next generation of robotic explorers”.

He adds that “Such microbial fuel cells could power space robots almost indefinitely, as long as their bacteria have the tiny amounts of food needed to stay alive and create electricity through their chemical reactions.

That would offer an alternative to space missions that rely upon either nuclear or solar power for their batteries — NASA’s Spirit Mars rover was officially declared dead last May after the Red Planet’s harsh winter deprived it of sunlight for its solar panels”.

“Whether you’re looking at satellites or planetary explorers, to have a power system that’s not reliant on the sun of the solar system, day or night cycles, and hazardous materials such as nuclear or other harsh chemicals, means you really open a lot of doors for expanding the duration of scientific missions,” said Gregory Scott, a space robotics engineer at the U.S. Naval Research Laboratory.

James Hsu adds that “The microbial fuel cells won’t power huge robots such as NASA’s car-size Curiosity rover in the near future, even if the experimental technology might eventually scale up to do so.

Instead, they would trickle small amounts of electricity that can slowly charge a battery until enough energy exists to power a scientific instrument or move a tiny robot.”

This process could potentially keep any space mission going for infinite amounts of time.

“Given the fact that they are living organisms, they have a really long shelf life,” Scott told InnovationNewsDaily. “The bacterial colony will live as long as you give it food — in our case, sugar — or one of the other biomass fuels we’re looking into. The colony will be able to survive pretty much indefinitely.”

Scott and his colleagues are hoping to create a prototype robot powered by microbes and weighing just over 2 pounds (1 kg) within the next 10 years. Their first year of funding comes from the NASA Innovative Advanced Concepts program.

Jeremy Hsu adds that “But shrinking microbial fuel cells — some prototypes weighing 35 pounds (16 kg) on the small side — down to something that fits on a 2-pound robot will take years of work.

The researchers must also figure out how to boost the small energy outputs of such microbial fuel cells even as they shrink the overall size and weight. Another challenge comes from making even lower-power electronics for the next generation of tiny space robots or rovers.

Such electronics must use very little or even no power in some periods to survive on the electricity supplied by microbial fuel cells”.

The researchers are also trying to figure out a simple, reliable way for their tiny robot or rover to move about. One of their primary ideas involves a spring-loaded ‘hopping system.’

Jeremy Hsu says that “Once a working prototype robot has been built, researchers would begin to consider the challenges of sending microbes on missions headed for deep space, asteroids or distant planets — including the question of protecting extraterrestrial surfaces from contamination.

Their current microbes consist of Geobacter sulfurreducens, a bacterium that does not require oxygen.”

“There are planetary protection concerns, as well as concerns about protecting the microbes themselves from radiation,” Scott said. “Sometime down the road we also have to consider whether the microbes we’re looking at are most effective for radiation environments or extreme temperatures.”

Final Thoughts

Although Pu-238 has been used to fuel robots in space for decades and has been very successful, a new theory involving microbes is now being studied by NASA in hopes to find a more sustainable way, but also a potentially infinite way, to power space exploration into the future and beyond. 

Gordon Watts