Jump to content

After 60 Years, Nuclear Power for Spaceflight is Still Tried and True


Recommended Posts

  • Publishers
Posted
5 Min Read

After 60 Years, Nuclear Power for Spaceflight is Still Tried and True

Engineers in cleanroom suits insert a cylindrical device into a spacecraft.
Workers install one of three Radioisotope Thermoelectric Generators (RTGs) on the Cassini spacecraft. More ›
Credits:
NASA

Editor’s Note: Originally published on June 21, 2021.

Six decades after the launch of the first nuclear-powered space mission, Transit IV-A, NASA is embarking on a bold future of human exploration and scientific discovery. This future builds on a proud history of safely launching and operating nuclear-powered missions in space.

“Nuclear power has opened the solar system to exploration, allowing us to observe and understand dark, distant planetary bodies that would otherwise be unreachable. And we’re just getting started,” said Dr. Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate. “Future nuclear power and propulsion systems will help revolutionize our understanding of the solar system and beyond and play a crucial role in enabling long-term human missions to the Moon and Mars.”

Space nuclear power to explore the deepest, dustiest, darkest, and most distant regions of our solar system and beyond.
NASA

From Humble Beginnings: Nuclear Power Spawns an Age of Scientific Discovery

On June 29, 1961, the John’s Hopkins University Applied Physics Laboratory launched the Transit IV-A Spacecraft. It was a U.S. Navy navigational satellite with a SNAP-3B radioisotope powered generator producing 2.7 watts of electrical power — about enough to light an LED bulb. Transit IV-A broke an APL mission-duration record and confirmed the Earth’s equator is elliptical. It also set the stage for ground-breaking missions that have extended humanity’s reach across the solar system.

Since 1961, NASA has flown more than 25 missions carrying a nuclear power system through a successful partnership with the Department of Energy (DOE), which provides the power systems and plutonium-238 fuel.

“The department and our national laboratory partners are honored to play a role in powering NASA’s space exploration activities,” said Tracey Bishop, deputy assistant secretary in DOE’s Office of Nuclear Energy. “Radioisotope Power Systems are a natural extension of our core mission to create technological solutions that meet the complex energy needs of space research, exploration, and innovation.”

There are only two practical ways to provide long-term electrical power in space: the light of the sun or heat from a nuclear source.

We couldn’t do the mission without it. No other technology exists to power a mission this far away from the Sun, even today.

Alan Stern

Alan Stern

Principal Investigator, NASA’s New Horizons Mission to Pluto and Beyond

“As missions move farther away from the Sun to dark, dusty, and harsh environments, like Jupiter, Pluto, and Titan, they become impossible or extremely limited without nuclear power,” said Leonard Dudzinski, chief technologist for NASA’s Planetary Science Division and program executive for Radioisotope Power.

That’s where Radioisotope Power Systems, or RPS, come in. They are a category of power systems that convert heat generated by the decay of plutonium-238 fuel into electricity.

“These systems are reliable and efficient,” said June Zakrajsek, manager for NASA’s Radioisotope Power Systems Program office at Glenn Research Center in Cleveland. “They operate continuously over long-duration space missions regardless of sunlight, temperature, charged particle radiation, or surface conditions like thick clouds or dust. They’ve allowed us to explore from the Sun to Pluto and beyond.”

RPS powered the Apollo Lunar Surface Experiment Package. They’ve sustained Voyager 1 and 2 since 1977, and they kept Cassini-Huygens’ instruments warm as it explored frigid Saturn and its moon Titan.

Today, a Multi-Mission Thermoelectric Generator (MMRTG) powers the Perseverance rover, which is captivating the nation as it searches for signs of ancient life on Mars, and a single RTG is sustaining New Horizons as it ventures on its way out of the solar system 15 years after its launch.

“The RTG was and still is crucial to New Horizons,” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute. “We couldn’t do the mission without it. No other technology exists to power a mission this far away from the Sun, even today.”

Two men work on a grand piano-sized spacecraft wrapped in a gold insulating blanket. A large cylinder, a radioisotope thermoelectric generator, sticks out of the side.
New Horizons carries seven scientific instruments and a radioisotope thermoelectric generator. The spacecraft weighs 1,060 pounds.
NASA/JHUAPL

Great Things to Come: Science and Human Exploration

Dragonfly, which is set to launch in 2028, is the next mission with plans to use an MMRTG. Part of NASA’s New Frontiers program, Dragonfly is an octocopter designed to explore and collect samples on Saturn’s largest moon, Titan, an ocean world with a dense, hazy atmosphere.

“RPS is really an enabling technology,” said APL’s Zibi Turtle, principal investigator for the upcoming Dragonfly mission. “Early missions like Voyager, Galileo, and Cassini that relied on RPS have completely changed our understanding and given us a geography of the distant solar system…Cassini gave us our first close-up look at the surface of Titan.”

According to Turtle, the MMRTG serves two purposes on Dragonfly: power output to charge the lander’s battery and waste heat to keep its instruments and electronics warm.

“Flight is a very high-power activity. We’ll use a battery for flight and science activities and recharge the battery using the MMRTG,” said Turtle. “The waste heat from the power system is a key aspect of our thermal design. The surface of Titan is very cold, but we can keep the interior of the lander warm and cozy using the heat from the MMRTG.”

As the scientific community continues to benefit from RPS, NASA’s Space Technology Mission Directorate is investing in new technology using reactors and low-enriched uranium fuel to enable a robust human presence on the Moon and eventually human missions to Mars.

Astronauts will need plentiful and continuous power to survive the long lunar nights and explore the dark craters on the Moon’s South Pole. A fission surface power system could provide enough juice to power robust operations. NASA is leading an effort, working with the DOE and industry to design a fission power system for a future lunar demonstration that will pave the way for base camps on the Moon and Mars.

NASA has also thought about viable ways to reduce the time it takes to travel to Mars, including nuclear propulsion systems.

As NASA advances its bold vision of exploration and scientific discovery in space, it benefits from 60 years of the safe use of nuclear power during spaceflight. Sixty years of enlightenment that all started with a little satellite called Transit IV-A.

News Media Contact
Jan Wittry
NASA’s Glenn Research Center

View the full article

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Similar Topics

    • By NASA
      CSA (Canadian Space Agency) astronaut Jeremy Hansen, alongside NASA astronauts Victor Glover, Reid Wiseman, and Christina Koch, will launch on the Artemis II mission early next year. The crew will participate in human research studies to provide insights about how the body performs in deep space as part of this mission. Credit: (NASA/James Blair) A sweeping collection of astronaut health studies planned for NASA’s Artemis II mission around the Moon will soon provide agency researchers with a glimpse into how deep space travel influences the human body, mind, and behavior.
      During an approximately 10-day mission set to launch in 2026, NASA astronauts Reid Wiseman, Victor Glover, and Christina Koch, and CSA (Canadian Space Agency) astronaut Jeremy Hansen will collect and store their saliva, don wrist monitors that track movement and sleep, and offer other essential data for NASA’s Human Research Program and other agency science teams. 
      “The findings are expected to provide vital insights for future missions to destinations beyond low Earth orbit, including Mars,” said Laurie Abadie, an aerospace engineer for the program at NASA’s Johnson Space Center in Houston, who strategizes about how to carry out studies on Artemis missions. “The lessons we learn from this crew will help us to more safely accomplish deep space missions and research,” she said.
      One study on the Artemis II mission, titled Immune Biomarkers, will explore how the immune system reacts to spaceflight. Another study, ARCHeR (Artemis Research for Crew Health and Readiness), will evaluate how crew members perform individually and as a team throughout the mission, including how easily they can move around within the confined space of their Orion spacecraft. Astronauts also will collect a standardized set of measurements spanning multiple physiological systems to provide a comprehensive snapshot of how spaceflight affects the human body as part of a third study called Artemis II Standard Measures. What’s more, radiation sensors placed inside the Orion capsule cells will collect additional information about radiation shielding functionality and organ-on-a-chip devices containing astronaut cells will study how deep space travel affects humans at a cellular level.
      “Artemis missions present unique opportunities, and challenges, for scientific research,” said Steven Platts, chief scientist for human research at NASA Johnson.
      Platts explained the mission will need to protect against challenges including exposure to higher radiation levels than on the International Space Station, since the crew will be farther from Earth.
      “Together, these studies will allow scientists to better understand how the immune system performs in deep space, teach us more about astronauts’ overall well-being ahead of a Mars mission, and help scientists develop ways to ensure the health and success of crew members,” he said.
      Another challenge is the relatively small quarters. The habitable volume inside Orion is about the size of a studio apartment, whereas the space station is larger than a six-bedroom house with six sleeping quarters, two bathrooms, a gym, and a 360-degree view bay window. That limitation affects everything from exercise equipment selection to how to store saliva samples.
      Previous research has shown that spaceflight missions can weaken the immune system, reactivate dormant viruses in astronauts, and put the health of the crew at risk. Saliva samples from space-based missions have enabled scientists to assess various viruses, hormones, and proteins that reveal how well the immune system works throughout the mission.
      But refrigeration to store such samples will not be an option on this mission due to limited space. Instead, for the Immune Biomarkers study, crew members will supply liquid saliva on Earth and dry saliva samples in space and on Earth to assess changes over time. The dry sample process involves blotting saliva onto special paper that’s stored in pocket-sized booklets.
      “We store the samples in dry conditions before rehydrating and reconstituting them,” said Brian Crucian, an immunologist with NASA Johnson who’s leading the study. After landing, those samples will be analyzed by agency researchers.
      For the ARCHeR study, participating crew members will wear movement and sleep monitors, called actigraphy devices, before, during, and after the mission. The monitors will enable crew members and flight controllers in mission control to study real-time health and behavioral information for crew safety, and help scientists study how crew members’ sleep and activity patterns affect overall health and performance. Other data related to cognition, behavior, and team dynamics will also be gathered before and after the mission.
      “Artemis missions will be the farthest NASA astronauts have ventured into space since the Apollo era,” said Suzanne Bell, a NASA psychologist based at Johnson who is leading the investigation. “The study will help clarify key mission challenges, how astronauts work as a team and with mission control, and the usability of the new space vehicle system.” 
      Another human research study, Artemis II Standard Measures, will involve collecting survey and biological data before, during, and after the Artemis II mission, though blood collection will only occur before and after the mission. Collecting dry saliva samples, conducting psychological assessments, and testing head, eye, and body movements will also be part of the work. In addition, tasks will include exiting a capsule and conducting simulated moonwalk activities in a pressurized spacesuit shortly after return to Earth to investigate how quickly astronauts recover their sense of balance following a mission.
      Crew members will provide data for these Artemis II health studies beginning about six months before the mission and extending for about a month after they return to Earth.
      NASA also plans to use the Artemis II mission to help scientists characterize the radiation environment in deep space. Several CubeSats, shoe-box sized satellites that will be deployed into high-Earth orbit during Orion’s transit to the Moon, will probe the near-Earth and deep space radiation environment. Data gathered by these CubeSats will help scientists understand how best to shield crew and equipment from harmful space radiation at various distances from Earth.
      Crew members will also keep dosimeters in their pockets that measure radiation exposure in real time. Two additional radiation-sensing technologies will also be affixed to the inside of the Orion spacecraft. One type of device will monitor the radiation environment at different shielding locations and alert crew if they need to seek shelter, such as during a solar storm. A separate collection of four radiation monitors, enabled through a partnership with the German Space Agency DLR, will be placed at various points around the cabin by the crew after launch to gather further information.
      Other technologies also positioned inside the spacecraft will gather information about the potential biological effects of the deep space radiation environment. These will include devices called organ chips that house human cells derived from the Artemis II astronauts, through a project called AVATAR (A Virtual Astronaut Tissue Analog Response). After the Artemis II lands, scientists will analyze how these organ chips responded to deep space radiation and microgravity on a cellular level.
      Together, the insights from all the human research science collected through this mission will help keep future crews safe as humanity extends missions to the Moon and ventures onward to Mars.
      ____
      NASA’s Human Research Program
      NASA’s Human Research Program pursues methods and technologies to support safe, productive human space travel. Through science conducted in laboratories, ground-based analogs, commercial missions, the International Space Station and Artemis missions, the program scrutinizes how spaceflight affects human bodies and behaviors. Such research drives the program’s quest to innovate ways that keep astronauts healthy and mission ready as human space exploration expands to the Moon, Mars, and beyond.
      Explore More
      9 min read Artemis II Crew Both Subjects and Scientists in NASA Deep Space Research
      Article 20 hours ago 5 min read NASA’s Northrop Grumman CRS-23 Infographics & Hardware
      Article 20 hours ago 4 min read NASA Uses Colorado Mountains for Simulated Artemis Moon Landing Course
      Article 2 days ago Keep Exploring Discover More Topics From NASA
      Living in Space
      Artemis
      Human Research Program
      Space Station Research and Technology
      View the full article
    • By Space Force
      The U.S. Space Force honored Ed Mornston, associate deputy chief of Space Operations for Intelligence, for his 50 years of combined military and civilian service.

      View the full article
    • By NASA
      Space changes you. It strengthens some muscles, weakens others, shifts fluids within your body, and realigns your sense of balance. NASA’s Human Research Program works to understand—and sometimes even counter—those changes so astronauts can thrive on future deep space missions.  
      NASA astronaut Loral O’Hara pedals on the Cycle Ergometer Vibration Isolation System (CEVIS) inside the International Space Station’s Destiny laboratory module.NASA Astronauts aboard the International Space Station work out roughly two hours a day to protect bone density, muscle strength and the cardiovascular system, but the longer they are in microgravity, the harder it can be for the brain and body to readapt to gravity’s pull. After months in orbit, returning astronauts often describe Earth as heavy, loud, and strangely still. Some reacclimate within days, while other astronauts take longer to fully recover.
      Adjusting to Gravity  
      NASA’s SpaceX Crew-7 astronaut Jasmin Moghbeli after landing in the Gulf of America on March 12, 2024, completing 197 days in space.NASA/Joel Kowsky The crew of NASA’s SpaceX Crew-7 mission— NASA astronaut Jasmin Moghbeli, ESA (European Space Agency) astronaut Andreas Mogensen, JAXA (Japan Aerospace Exploration Agency) astronaut Satoshi Furukawa, and Roscosmos cosmonaut Konstantin Borisov—landed in March 2024 after nearly 200 days in space. One of the first tests volunteer crew members completed was walking with their eyes open and then closed.  
      “With eyes closed, it was almost impossible to walk in a straight line,” Mogensen said. In space, vision is the primary way astronauts orient themselves, but back on Earth, the brain must relearn how to use inner-ear balance signals. Moghbeli joked her first attempt at the exercise looked like “a nice tap dance.”   
      “I felt very wobbly for the first two days,” Moghbeli said. “My neck was very tired from holding up my head.” She added that, overall, her body readapted to gravity quickly.  
      Astronauts each recover on their own timetable and may encounter different challenges. Mogensen said his coordination took time to return. Furukawa noted that he could not look down without feeling nauseated. “Day by day, I recovered and got more stable,” he said. 
      NASA astronaut Loral O’Hara after landing in a remote area near the town of Zhezkazgan, Kazakhstan, on April 6, 2024.NASA/Bill Ingalls NASA astronaut Loral O’Hara returned in April 2024 after 204 days in space. She said she felt almost completely back to normal a week after returning to Earth. O’Hara added that her prior experience as an ocean engineer gave her insight into space missions. “Having those small teams in the field working with a team somewhere else back on shore with more resources is a good analog for the space station and all the missions we’re hoping to do in the future,” she said. 
      NASA astronaut Nichole Ayers, who flew her first space mission with NASA’s SpaceX Crew-10, noted that the brain quickly adapts to weightlessness by tuning out the vestibular system, which controls balance. “Then, within days of being back on Earth, it remembers again—it’s amazing how fast the body readjusts,” she said. 
      Expedition 69 NASA astronaut Frank Rubio outside the Soyuz MS-23 spacecraft after landing near the town of Zhezkazgan, Kazakhstan, on Sept. 27, 2023. NASA/Bill Ingalls When NASA astronaut Frank Rubio landed in Kazakhstan in September 2023, he had just completed a record 371-day mission—the longest single U.S. spaceflight.  
      Rubio said his body adjusted to gravity right away, though his feet and lower back were sore after more than a year without weight on them. Thanks to consistent workouts, Rubio said he felt mostly recovered within a couple of weeks.  
      Mentally, extending his mission from six months to a year was a challenge. “It was a mixed emotional roller coaster,” he said, but regular video calls with family kept him grounded. “It was almost overwhelming how much love and support we received.” 
      Crew-8 astronauts Matt Dominick, Jeanette Epps, Michael Barratt, and cosmonaut Alexander Grebenkin splashed down in October 2024 after 235 days on station. Dominick found sitting on hard surfaces uncomfortable at first. Epps felt the heaviness of Earth immediately. “You have to move and exercise every day, regardless of how exhausted you feel,” she said.  
      Barratt, veteran astronaut and board certified in internal and aerospace medicine, explained that recovery differs for each crew member, and that every return teaches NASA something new. 
      Still a Challenge, Even for Space Veterans  
      NASA astronaut Suni Williams is helped out of a SpaceX Dragon spacecraft aboard the SpaceX recovery ship after splashing down off the coast of Tallahassee, Florida, March 18, 2025. NASA/Keegan Barber Veteran NASA astronauts Suni Williams and Butch Wilmore returned from a nine-month mission with Crew-9 in early 2025. Despite her extensive spaceflight experience, Williams said re-adapting to gravity can still be tough. “The weight and heaviness of things is surprising,” she said. Like others, she pushed herself to move daily to regain strength and balance.  
      NASA astronaut Don Pettit arrives at Ellington Field in Houston on April 20, 2025, after returning to Earth aboard the Soyuz MS-25 spacecraft. NASA/Robert Markowitz NASA astronaut Don Pettit, also a veteran flyer, came home in April 2025 after 220 days on the space station. At 70 years old, he is NASA’s oldest active astronaut—but experience did not make gravity gentler.  During landing, he says he was kept busy, “emptying the contents of my stomach onto the steppes of Kazakhstan.” Microgravity had eased the aches in his joints and muscles, but Earth’s pull brought them back all at once.  
      Pettit said his recovery felt similar to earlier missions. “I still feel like a little kid inside,” he said. The hardest part, he explained, isn’t regaining strength in big muscle groups, but retraining the small, often-overlooked muscles unused in space. “It’s a learning process to get used to gravity again.”  
      Recovery happens day by day—with help from exercise, support systems, and a little humor. No matter how long an astronaut is in space, every journey back to Earth is unique. 
      The Human Research Program help scientists understand how spaceflight environments affect astronaut health and performance and informs strategies to keep crews healthy for future missions to the Moon, Mars, and beyond. The program studies astronauts before, during, and after spaceflight to learn how the human body adapts to living and working in space. It also collects data through Earth-based analog missions that can help keep astronauts safer for future space exploration.  
      To learn more about how microgravity affects the human body and develop new ways to help astronauts stay healthy, for example, its scientists conduct bedrest studies – asking dozens of volunteers to spend 60 days in bed with their heads tilted down at a specific angle.  Lying in this position tricks the body into responding as it would if the body was in space which allows scientists to trial interventions to hopefully counter some of microgravity’s effects.  Such studies, through led by NASA, occur at the German Aerospace Center’s Cologne campus at a facility called :envihab – a combination of “environment” and “habitat.”  
      Additional Earth-based insights come from the Crew Health and Performance Exploration Analog (CHAPEA) and the Human Exploration Research Analog (HERA) at NASA’s Johnson Space Center in Houston. Both analogs recreate the remote conditions and scenarios of deep space exploration here on Earth with volunteer crews who agree to live and work in the isolation of ground-based habitats and endure challenges like delayed communication that simulates the type of interactions that will occur during deep space journeys to and from Mars. Findings from these ground-based missions and others will help NASA refine its future interventions, strategies, and protocols for astronauts in space. 
      NASA and its partners have supported humans continuously living and working in space since November 2000. After nearly 25 years of continuous human presence, the space station remains the sole space-based proving ground for training and research for deep space missions, enabling NASA’s Artemis campaign, lunar exploration, and future Mars missions. 
      Explore More
      7 min read A Few Things Artemis Will Teach Us About Living and Working on the Moon
      Article 6 years ago 3 min read Inside NASA’s New Orion Mission Evaluation Room for Artemis II 
      Article 2 weeks ago 12 min read 15 Ways the International Space Station Benefits Humanity Back on Earth
      Article 3 years ago
      View the full article
    • By European Space Agency
      Estonia marked its 10th anniversary in the European Space Agency alongside the plenary session of the European Interparliamentary Space Conference on 4 September.  
      View the full article
    • By NASA
      Patricia White is a contracting officer at NASA’s Stennis Space Center, where she contributes to NASA’s Artemis program that will send astronauts to the Moon to prepare for future human exploration of Mars. NASA/Danny Nowlin When NASA’s Artemis II mission launches in 2026, it will inspire the world through discovery in a new Golden Age of innovation and exploration.
      It will be another inspiring NASA moment Patricia White can add to her growing list.
      White supports the Artemis program to send astronauts to the Moon to prepare for future human exploration of Mars as a contracting officer at NASA’s Stennis Space Center near Bay St. Louis, Mississippi.
      White takes special pride in the test operations contract she helped draft. The contract provides support to the Fred Haise Test Stand, which tests the RS-25 engines that will help power NASA’s SLS (Space Launch System) rocket on Artemis missions.
      “I was awestruck the first time I witnessed an engine test,” White said. “I remember how small I felt in comparison to this big and fascinating world, and I wondered what that engine would see that I would never be able to see.”
      Four RS-25 engines tested at NASA Stennis will help launch Artemis II with four astronauts to venture around the Moon. As the first crewed Artemis mission, it will represent another milestone for the nation’s human space exploration effort.
      From Interstate Signs to NASA Career
      White describes NASA Stennis as a hidden gem. Growing up in nearby Slidell, Louisiana, she had driven by the interstate signs pointing toward NASA Stennis her entire life.
      When she heard about a job opportunity at the center, she immediately applied. Initially hired as a contractor with only a high school diploma in February 2008, White found her motivation among NASA’s ranks.
      “I work with very inspiring people, and it only took one person to say, ‘You should go to college’ to give me the courage to go so late in life,” she said.
      Hard But Worth It
      White began college classes in her 40s and finished at 50. She balanced a marriage, full-time job, academic studies, and household responsibilities. When she started her educational journey, her children were either toddlers or newborns. They were growing up as she stayed in school for nine years while meeting life’s challenges.
      “It was hard, but it was so worth it,” she said. “I love my job and what I do, and even though it is crazy busy, I look forward to working at NASA every single day.”
      She joined NASA officially in 2013, going from contractor to civil servant.
      Setting an Example
      White’s proudest work moment came when she brought home the NASA Early Career Achievement award and medal. It served as a tangible symbol of her success she could share with her family.
      “It was a long road from being hired as an intern, and we all made extraordinary sacrifices,” she said. “I wanted to share it with them and set a good example for my children.”
      As Artemis II prepares to carry humans back to lunar orbit for the first time in over 50 years, White takes pride knowing her work helps power humanity’s return to deep space exploration. Her work is proof that sometimes the most important journeys begin right in one’s own backyard.
      Learn More About Careers at NASA Stennis Explore More
      4 min read NASA Stennis Provides Ideal Setting for Range Operations
      Article 1 week ago 10 min read NASA’s Stennis Space Center Employees Receive NASA Honor Awards
      Article 3 weeks ago 6 min read A Defining Era: NASA Stennis and Space Shuttle Main Engine Testing
      Article 4 months ago View the full article
  • Check out these Videos

×
×
  • Create New...