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Radioisotope generators − inside the ‘nuclear batteries’ that power faraway spacecraft

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Last Updated on May 1, 2025 by Daily News Staff

Radioisotope
Voyager 1, shown in this illustration, has operated for decades thanks to a radioisotope power system.
NASA via AP

Benjamin Roulston, Clarkson University

Powering spacecraft with solar energy may not seem like a challenge, given how intense the Sun’s light can feel on Earth. Spacecraft near the Earth use large solar panels to harness the Sun for the electricity needed to run their communications systems and science instruments.

However, the farther into space you go, the weaker the Sun’s light becomes and the less useful it is for powering systems with solar panels. Even in the inner solar system, spacecraft such as lunar or Mars rovers need alternative power sources.

As an astrophysicist and professor of physics, I teach a senior-level aerospace engineering course on the space environment. One of the key lessons I emphasize to my students is just how unforgiving space can be. In this extreme environment where spacecraft must withstand intense solar flares, radiation and temperature swings from hundreds of degrees below zero to hundreds of degrees above zero, engineers have developed innovative solutions to power some of the most remote and isolated space missions.

So how do engineers power missions in the outer reaches of our solar system and beyond? The solution is technology developed in the 1960s based on scientific principles discovered two centuries ago: radioisotope thermoelectric generators, or RTGs.

RTGs are essentially nuclear-powered batteries. But unlike the AAA batteries in your TV remote, RTGs can provide power for decades while hundreds of millions to billions of miles from Earth.

Nuclear power

Radioisotope thermoelectric generators do not rely on chemical reactions like the batteries in your phone. Instead, they rely on the radioactive decay of elements to produce heat and eventually electricity. While this concept sounds similar to that of a nuclear power plant, RTGs work on a different principle.

Most RTGs are built using plutonium-238 as their source of energy, which is not usable for nuclear power plants since it does not sustain fission reactions. Instead, plutonium-238 is an unstable element that will undergo radioactive decay.

Radioactive decay, or nuclear decay, happens when an unstable atomic nucleus spontaneously and randomly emits particles and energy to reach a more stable configuration. This process often causes the element to change into another element, since the nucleus can lose protons.

A graphic showing a larger atom losing a particle made of two protons and two neutrons and transforming into a smaller atom.
Plutonium-238 decays into uranium-234 and emits an alpha particle, made of two protons and two neutrons.
NASA

When plutonium-238 decays, it emits alpha particles, which consist of two protons and two neutrons. When the plutonium-238, which starts with 94 protons, releases an alpha particle, it loses two protons and turns into uranium-234, which has 92 protons.

These alpha particles interact with and transfer energy into the material surrounding the plutonium, which heats up that material. The radioactive decay of plutonium-238 releases enough energy that it can glow red from its own heat, and it is this powerful heat that is the energy source to power an RTG.

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A circular metal container with a glowing cylinder inside.
The nuclear heat source for the Mars Curiosity rover is encased in a graphite shell. The fuel glows red hot because of the radioactive decay of plutonium-238.
Idaho National Laboratory, CC BY

Heat as power

Radioisotope thermoelectric generators can turn heat into electricity using a principle called the Seebeck effect, discovered by German scientist Thomas Seebeck in 1821. As an added benefit, the heat from some types of RTGs can help keep electronics and the other components of a deep-space mission warm and working well.

In its basic form, the Seebeck effect describes how two wires of different conducting materials joined in a loop produce a current in that loop when exposed to a temperature difference.

[youtube https://www.youtube.com/watch?v=l-Puj0uyCAg?wmode=transparent&start=0]
The Seeback effect is the principle behind RTGs.

Devices that use this principle are called thermoelectric couples, or thermocouples. These thermocouples allow RTGs to produce electricity from the difference in temperature created by the heat of plutonium-238 decay and the frigid cold of space.

Radioisotope thermoelectric generator design

In a basic radioisotope thermoelectric generator, you have a container of plutonium-238, stored in the form of plutonium-dioxide, often in a solid ceramic state that provides extra safety in the event of an accident. The plutonium material is surrounded by a protective layer of foil insulation to which a large array of thermocouples is attached. The whole assembly is inside a protective aluminum casing.

A piece of machinery, which looks like a metal cylinder with fan-like structures outside it.
An RTG has decaying material in its core, which generates heat that it converts to electricity.
U.S. Department of Energy

The interior of the RTG and one side of the thermocouples is kept hot – close to 1,000 degrees Fahrenheit (538 degrees Celsius) – while the outside of the RTG and the other side of the thermocouples are exposed to space. This outside, space-facing layer can be as cold as a few hundred degrees Fahrenheit below zero.

This strong temperature difference allows an RTG to turn the heat from radioactive decay into electricity. That electricity powers all kinds of spacecraft, from communications systems to science instruments to rovers on Mars, including five current NASA missions.

But don’t get too excited about buying an RTG for your house. With the current technology, they can produce only a few hundred watts of power. That may be enough to power a standard laptop, but not enough to play video games with a powerful GPU.

For deep-space missions, however, those couple hundred watts are more than enough.

The real benefit of RTGs is their ability to provide predictable, consistent power. The radioactive decay of plutonium is constant – every second of every day for decades. Over the course of about 90 years, only half the plutonium in an RTG will have decayed away. An RTG requires no moving parts to generate electricity, which makes them much less likely to break down or stop working.

Additionally, they have an excellent safety record, and they’re designed to survive their normal use and also be safe in the event of an accident.

RTGs in action

RTGs have been key to the success of many of NASA’s solar system and deep-space missions. The Mars Curiosity and Perseverance rovers and the New Horizons spacecraft that visited Pluto in 2015 have all used RTGs. New Horizons is traveling out of the solar system, where its RTGs will provide power where solar panels could not.

However, no missions capture the power of RTGs quite like the Voyager missions. NASA launched the twin spacecraft Voyager 1 and Voyager 2 in 1977 to take a tour of the outer solar system and then journey beyond it.

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A diagram of a Voyager probe, with its parts labeled and a cylinder broken into three parts coming off its side labeled 'RTGs'.
The RTGs on the Voyager probes have allowed the spacecraft to stay powered up while they collect data.
NASA/JPL-Caltech

Each craft was equipped with three RTGs, providing a total of 470 watts of power at launch. It has been almost 50 years since the launch of the Voyager probes, and both are still active science missions, collecting and sending data back to Earth.

Voyager 1 and Voyager 2 are about 15.5 billion miles and 13 billion miles (nearly 25 billion kilometers and 21 billion kilometers) from the Earth, respectively, making them the most distant human-made objects ever. Even at these extreme distances, their RTGs are still providing them consistent power.

These spacecraft are a testament to the ingenuity of the engineers who first designed RTGs in the early 1960s.

Benjamin Roulston, Assistant Professor of Physics, Clarkson University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Science

October Meteor Showers Give Phoenix Skywatchers a Reason to Look Up

Phoenix skywatchers have several chances to catch October’s meteor showers. Here’s when to watch the Taurids and Orionids—and how moonlight affects the view.

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Last Updated on October 10, 2026 by Daily News Staff

PHOENIX — October is bringing several opportunities to spot shooting stars over the Valley, with the Draconids reaching their October 8–9 peak and more meteor activity ahead.

The Draconids remain active through October 10, although viewers should expect a light display as the peak passes. Under favorable conditions, the shower typically produces only a handful of meteors per hour. timeanddate.com

Illustration of Orionid meteor shower above Arizona mountains and saguaro cacti, with a sky chart labeling Orion, Betelgeuse, and the shower’s radiant.
An illustrated view of the Orionid meteor shower above the Arizona desert. The shower peaks October 21–22, 2026.

Next, the Southern Taurids have an annual activity peak around October 14. Known for occasional bright fireballs, the shower continues into November. The stronger Orionids peak on the night of October 21 into the morning of October 22, typically producing 10–20 meteors per hour under dark skies. A bright Moon will interfere with this year’s display. American Meteor Society

Phoenix Meteor Showers October 2026: When to Watch

The Orionids originate from debris left by Halley’s Comet. For Phoenix viewers, the best opportunity will be after moonset and before dawn, weather permitting. City lights will further reduce the number visible. amsmeteors.org

NASA recommends finding a viewing area away from streetlights, allowing about 30 minutes for eyes to adjust, and watching a broad stretch of sky. No telescope is needed—just a comfortable chair and patience. NASA Science

ECurious about what’s happening above us? Explore more space stories and science explainers in The Knowledge at STM Daily News.xplore more space, science and everyday

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unknown

Did Jackie Gleason See Aliens? Inside the Strange Nixon–UFO Legend

Jackie Gleason reportedly told his wife that President Richard Nixon arranged for him to view preserved extraterrestrial bodies at a Florida Air Force base. Here is what we know—and why the remarkable story remains unverified.

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The beloved comedian reportedly told his wife that President Richard Nixon arranged for him to view preserved extraterrestrial bodies at a Florida Air Force base. Decades later, the extraordinary story remains fascinating—but unverified.

Jackie Gleason and Richard Nixon portrayed against a mysterious nighttime military-base setting
Jackie Gleason’s alleged encounter with preserved alien bodies remains one of Hollywood’s strangest UFO legends.

Jackie Gleason is remembered as “The Great One,” the larger-than-life entertainer who turned bus driver Ralph Kramden into one of television’s most enduring characters on The Honeymooners. Away from the cameras, however, Gleason had another consuming interest: UFOs, psychic phenomena and the possibility of extraterrestrial life.

That interest eventually became the foundation of one of the strangest stories ever associated with an American president and a Hollywood celebrity. According to Gleason’s second wife, Beverly McKittrick, her husband came home late one night in 1973 and claimed that President Richard Nixon had helped him see the preserved bodies of extraterrestrial beings at Homestead Air Force Base in Florida.

Did Jackie Gleason really see aliens?

The honest answer is that we do not know. The allegation is remarkable, but the available evidence never rises above an uncorroborated story attributed to Gleason years after the supposed event.

Gleason’s fascination with UFOs was real

There is little question that Gleason took the UFO subject seriously. He reportedly assembled a substantial personal library devoted to UFOs, the paranormal and related mysteries. His unusual circular home in New York—often nicknamed “The Mothership”—only strengthened his public association with flying saucers, although its distinctive architecture is not evidence of an extraterrestrial encounter.

Gleason also had a genuine social connection with Nixon. The two men shared an interest in golf and spent time together in Florida. That documented friendship is the factual starting point from which the more sensational story grew.

The alleged trip to Homestead Air Force Base

McKittrick said that Gleason returned to their Florida home at about 11:30 one evening looking disturbed. According to her account, he told her that Nixon had arrived without the usual presidential entourage and taken him to Homestead Air Force Base, south of Miami.

Once there, Gleason allegedly entered a secured building where he saw small humanoid bodies preserved inside glass-topped containers. Published versions differ over the number of bodies and some physical details, but they generally describe child-sized beings with oversized heads.

Importantly, McKittrick did not claim to have accompanied the men or witnessed anything at the base. Her account was based entirely on what she said Gleason told her after returning home.

The story became public in 1983, years after the alleged visit and after the couple had divorced. It circulated widely through tabloid reporting, UFO publications and later books, gradually becoming part of UFO folklore.

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Why the story remains unverified

No authenticated photograph, visitor record, military document or firsthand statement from Nixon has emerged to confirm the alleged trip. Gleason also never provided investigators with a signed affidavit describing the experience.

UFO researcher Larry Bryant reportedly sought records from Homestead and tried to obtain a statement from Gleason, but those efforts produced no confirming documentation. Gleason’s refusal to address the account publicly has sometimes been portrayed as suspicious, but silence is not proof that an event occurred.

There is another important complication: McKittrick later expressed uncertainty about her former husband’s story.

During telephone interviews conducted by researcher Kenny Young in 2003, she stood by her recollection that Gleason told her he had seen “dead aliens.” She also acknowledged that, as the years passed, she wondered whether he might have invented the explanation because he had been out late. She declined to appear on camera and said the story should be authenticated first.

Her later comments do not establish that the account was false, but they considerably weaken any attempt to treat it as verified history.

Could a president have slipped away unnoticed?

Some versions of the legend emphasize that Nixon supposedly drove to Gleason’s house alone and then entered a military installation without his Secret Service detail. Presidents have occasionally sought privacy or slipped away from tightly managed schedules, but a secret nighttime excursion of this nature would have involved serious security and logistical obstacles.

The claim becomes even more difficult to accept when we consider what Nixon allegedly revealed. If the United States possessed extraterrestrial bodies, granting a comedian personal access to them would have represented an extraordinary breach of national security—with no apparent official purpose and no surviving documentation.

None of that makes the episode logically impossible. It does, however, mean that the story requires exceptionally strong evidence. That evidence has never appeared.

A compelling legend, not a confirmed encounter

The Jackie Gleason story endures because it combines three irresistible ingredients: a famous comedian fascinated by UFOs, a secretive American president and a nighttime visit to a military base containing an alleged government secret.

What can be established is that Gleason was deeply interested in UFOs, knew Nixon and was said by his former wife to have made an extraordinary claim. What cannot be established is that Nixon took him to Homestead Air Force Base or that preserved extraterrestrial bodies were ever stored there.

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So, did Jackie Gleason see aliens?

Perhaps he believed that he did—or perhaps he simply told an unforgettable story. Until corroborating evidence emerges, the alleged encounter belongs in the intriguing borderland between celebrity history and American UFO mythology.

Sources and further reading

Step into The Unknown, where STM Daily News explores the strange phenomena, unexplained encounters and enduring mysteries that continue to challenge what we think we know. From UFO sightings and paranormal events to historical mysteries and unusual scientific discoveries, we examine the stories, evidence and competing explanations—without losing our sense of wonder. https://stmdailynews.com/science/unknown/

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health and wellness

Lactose intolerance is actually the human norm – but racism, the US government and business interests have made it into a condition

Lactose intolerance is the global human norm, but Western dietary standards, government policies and commercial interests helped frame it as a medical deficiency.

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Close-up of spilled glass bottle of milk. Lactose intolerance is actually the human norm
The majority of the world is unable to process the lactose in milk without uncomfortable symptoms. Olga Miltsova/iStock via Getty Images Plus

Hilary Smith, University of Denver

Lactose intolerance makes drinking milk or eating ice cream a literal pain. For some people, eating a dairy treat can lead to bloating, nausea and diarrhea. You might’ve experienced its effects yourself. If so, you may think of lactose intolerance as a defect rather than the norm.

But did you know that most people in the world today are lactose intolerant – and that the condition itself was invented in the 1960s?

“Surely you mean discovered, not invented,” I hear you saying. I don’t. As a historian who has traced the origins of nutrition-science ideas, I have chosen the word “invented” on purpose.

Inventing lactose intolerance

Variations in people’s ability to digest lactose first came to scientists’ attention after American dairy producers found a way to rid themselves of a postwar milk surplus. To offload what they couldn’t sell, they looked to the government to intervene. And it did, buying the excess and embedding it in school lunches and other places with publicly funded meals.

Suddenly, many people who had not habitually drunk milk were consuming it regularly, including not only some Americans but also people overseas. Part of that same milk surplus found its way into school lunches in places such as Japan and Taiwan in the 1950s as the American government began to sell milk to allies during the Cold War.

Black and white photo of children in uniform eating lunch at their desks
Longshou Elementary School students in Taiwan in 1964 eat an American aid lunch for the first time. National Archives of Taiwan, CC BY-NC-SA

Many of the groups drinking milk regularly for the first time did not like it. In fact, it made them feel sick. Intrigued, scientists set up experiments to figure out why. In a 1966 study comparing how Black and white people incarcerated in Baltimore metabolized lactose, researchers found that Black participants had lower levels of lactase – the enzyme that breaks down lactose – in their guts.

To the white scientists conducting this study, the trouble that the Black prisoners had digesting milk looked like an “inborn error of metabolism.” They assumed that the normal human state was lactose tolerance and that the lactose intolerant had inherited a genetic mutation.

It was only after years more work with research participants of many races that experts realized that, as one National Institutes of Health official put it in 1981, “lactose intolerance is a normal physiological condition, shared by every adult animal except for certain ethnic and racial groups in man.” People of northern European descent, it turned out, were the weird ones. It was their ancestors who had passed down a genetic mutation – one that made them able to digest milk after infancy.

In short, what scientists discovered in the 1960s was that different bodies process milk differently. What they invented was the idea that lactose intolerance is a defect. Accepting that framing would mean nearly two-thirds of the human population – the estimated prevalence of lactose intolerance worldwide – is defective.

Instead of acknowledging that dairy-free diets can be healthy, people innovated ways to overcome this supposed disability so everyone could consume more.

Statue of cow dressed as Superman in an advertising display, two people working in the background
Milk is advertised in China as essential to health, even though most of the population is lactose intolerant. Ng Han Guan/AP Photo

Nutritional imperialism

Lactose intolerance is one example of what I call nutritional imperialism: a way of thinking that treats white diets as the norm and everyone else’s as an aberration.

Nutritional imperialism was common in the 20th century, when scientists thought that not only milk-rich but also meat-heavy diets were best; they considered diets outside of the United States and Europe too vegetarian. Some also argued that wheat flour, not rice, ought to be the universal staple.

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The same bias applied to bodies. Besides faulty lactose digestion, nonwhite bodies were accused of other failures, too, such as aldehyde dehydrogenase deficiency, an inability to digest alcohol quickly. The less technical term for this may be more familiar: Asian flush.

Such differences might have been thought of as variety, just another way of being human. Instead, each became a deficiency.

Many people today have inherited and perpetuated this way of thinking without knowing it, including those who are deemed deficient by it. In 1959, the director of Japan’s nutrition bureau declared that “rice-eating peoples” such as the Japanese were “resigned and passive” and could correct this by imitating Western diets and switching to wheat.

Grocery store aisle filled with various brands of milk
Milk is ubiquitous in grocery stores in China. Shwangtianyuan/Wikimedia Commons, CC BY-SA

Today, the most prominent scientist promoting the idea that Asian flush is a disease is a geneticist of Taiwanese descent who started a research consortium to study “the most common human enzymopathy in the world.”

The Chinese Nutrition Society placed a tall glass of milk next to its 2022 Food Guide Plate – never mind estimates that the vast majority of Han Chinese, the largest ethnic group in China and worldwide, are lactose intolerant.

Turning sickness back into difference

Science that pathologizes difference helps racism persist.

In recent years, white supremacists have embraced the concept of lactose intolerance as a distinguishing debility of nonwhite people. Social media users have copied and pasted a map of the geographic distribution of lactose tolerance originally published in the scientific journal Nature into racist chat threads on the online discussion forum 4chan.

In 2017, internet trolls disrupted an anti-racist art installation with neo-Nazi chants and messily downed jugs of milk to accentuate their white identity.

Turning a lactose-digestion difference into a deficiency has done more to reinforce narratives of racial hierarchy than to improve public health. So here’s a suggestion: If you enjoy eating dairy, keep doing it; if you don’t, don’t – and know that there is nothing wrong with you.

Hilary Smith, Professor of History, University of Denver

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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