This Week in Space 170

Powering spacecraft, especially out in the dark, cold outer solar system, is a huge challenge. There are limits to how large solar panels can be, and they are not very efficient in the weak sunlight beyond Mars. For decades, choice flagship NASA missions have used RTGs--radioisotope thermoelectric generators--to fill this need. From the experiments on the Apollo missions to the Viking Mars landers, Galileo to Jupiter, Cassini to Saturn, and the twin Voyagers, RTGs have provided decades of power for space exploration. From Plutonium to Americium, nuclear elements provide years and years of heat that can be converted into electricity. Dr. Rob O'Brien is the Director of the Center for Space Nuclear Research for the Universities Space Research Association and has specialized in RTGs for decades. It's a fascinating dive into atomic space batteries!   

Headlines

• The End of the Universe is Nigh (in 33 Billion Years): New dark matter discoveries suggest an earlier end to the universe, leading to a humorous discussion about bucket list items.
• August 2nd "Solar Eclipse": Rumors of an August 2nd, 2025, total solar eclipse are false; the next one on that date is in 2027 that won't darken the entire world, but will be the longest one of the century.
• Mother Earth 2.0 (L98-59f): Discussion of exoplanet L98-59f, 35 light-years away, and its potential habitability despite orbiting a red dwarf with a 23-day year.
• NASA Budget Concerns: Senate and House pushback against proposed cuts to NASA's 2026 science mission budget is discussed, with calls to preserve vital research.
• Mass Exodus at NASA: Senior NASA staff, including scientists and engineers, are reportedly leaving due to budget cuts, raising concerns about future capabilities.

Main Topic - Dr. Robert O'Brien & RTGs (Radioisotope Thermoelectric Generators)

• Understanding RTGs: Dr. O'Brien explains RTGs convert heat from radioactive decay into electricity using the Seebeck effect.
• Early Use of RTGs in Space: The first US public RTG demonstration was on President Eisenhower's desk, and the first space use was the US Navy's Transit 4A satellite in 1961.
• RTGs on Mars and Deep Space Missions: RTGs power Mars landers and rovers (Viking, Curiosity, Perseverance), and deep space missions like Voyager, Galileo, and Cassini, providing long-term power in harsh environments.
• Fission Reactors vs. RTGs: RTGs suit small systems and backup power, while fission reactors are better for high-power needs of human expeditions.
• Plutonium-238 Production Challenges: The scarcity of plutonium-238 is due to its production requiring nuclear reactors and past moratoriums on reprocessing.
• Americium-241 as an Alternative: Americium-241, abundant in spent fuel and now accessible due to lifted moratoriums on reprocessing, is a viable alternative for powering missions despite lower energy density.
• Americium in Smoke Detectors and Safety: Americium's safe use in smoke detectors is highlighted, while acknowledging the hazards of working with nuclear materials.
• Public Perception and RTG Safety: Discussion covers historical atomic energy perceptions, from early toys to environmental concerns, emphasizing rigorous engineering and safety measures like ablative and impact-resistant casings for RTGs.
• Recovery of Spent RTGs: The Department of Energy's mission to recover radioactive sources is highlighted, alongside potential future service missions for retrieving or restarting graveyard-based space assets.
• DARPA's Nuclear Thermal Propulsion Program: The cancellation of DARPA's Draco program was a program management decision, not a technical one, and Dr. O'Brien emphasizes the need for continued investment in nuclear thermal propulsion for national security.
• Global Competition in Space Nuclear Power: The episode concludes with a strong call for the US to invest in nuclear power and propulsion  for space, citing growing international cooperation from Russia and China.

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• Tech: How Mariner 4 Changed Space Exploration 60 Years Ago
• Transcripts: This Week in Space 170 Transcript

Links

• Astronomers calculate that the universe will die in 33 billion years — much sooner than we thought
• No, the whole world won't go dark on Aug. 2 — but a once-in-a-century eclipse is coming
• This 'super-Earth' exoplanet 35 light-years away might have what it takes to support life
• Universities Space Research Association Appoints Robert O’Brien Director, Center for Space Nuclear Research
• Radioisotope thermoelectric generator - Wikipedia
• Pioneer 10
• Viking 1 & 2
• Americium