Podcast Summary: New Books Network — Interview with James Welsh et al., "Weathering Space" (American Scientist 114:1, 2026)

Date: December 31, 2025
Host: Gregory McNiff
Guest: Dr. James Welsh (co-author)

Episode Overview

This episode centers on Dr. James Welsh’s recent article, “Weathering Space: Efficient Routes and Good Luck Will Not Be Enough to Protect Humans from the Deadly Radiation They Will Face When Venturing Beyond the Earth-Moon System,” from American Scientist (Jan/Feb 2026). Welsh, a leading expert in radiation oncology and space radiation biology, explores the threats of ionizing radiation to future human deep space missions—especially journeys to Mars and beyond. Together with host Gregory McNiff, he breaks down the physics, biology, history, and potential countermeasures related to space radiation, highlighting the invisible yet severe risks posed to astronauts.

Key Discussion Points and Insights

1. Origins and Motivation for the Article

• Dr. Welsh's Background and Interests (03:17)

  • Deep interest developed over a decade, culminating in a comprehensive textbook written during the pandemic.
  • The article offers a more accessible summary, co-authored with Andy Karam and Robert Peter Gale.

  “During the pandemic, I had an opportunity to write an entire textbook on the subject ... but my colleagues ... got sidetracked ... so I wound up writing the whole book myself. ... I thought it would be fun to contribute a less intense, shorter version ... for American Scientist.”
  — Dr. James Welsh (03:17)

2. Early Space Missions and Earth's Natural Protection

• Radiation Hazards in Early Exploration (05:26)

  • Initial missions (Mercury, Apollo, International Space Station) benefited from Earth's atmosphere and magnetosphere, which shielded against dangerous space radiation.
  • Ionizing radiation as an underappreciated hazard in the early days.

  “The atmosphere and the magnetosphere will protect astronauts ... Once you get beyond both ... you're at the mercy of unmitigated radiation from above.”
  — Dr. Welsh (05:26)

3. Understanding Space Radiation

• Ionizing Radiation: Definition & Dangers (07:21)

  • Ionizing radiation is energetic enough to remove electrons from atoms and molecules, causing biological harm.
  • Not all radiation is ionizing—danger lies specifically in high-energy particles.

• Linear Energy Transfer (LET) and Biological Impact (08:34)

  • LET measures ionizations per unit length; high-LET radiation is more biologically damaging, sometimes contrary to intuition about higher energy being deadlier.

  “It’s a little counterintuitive ... The higher the LET, the higher the biological impact.”
  — Dr. Welsh (08:34)

4. Primary & Secondary Cosmic Rays

• Sources and Effects (09:54)

  • Primary cosmic rays originate from the Sun or beyond the solar system; secondary cosmic rays form when primaries interact with Earth's atmosphere.
  • Muons, secondary particles, can reach the Earth’s surface due to relativistic time dilation.

  “Muons prove that the special theory of relativity is the real thing ... Muons are perhaps the primary example of secondary cosmic rays that affect us here at sea level.”
  — Dr. Welsh (11:53)

5. Relative Biological Effectiveness (RBE)

• RBE Explained (14:28)
  • RBE quantifies biological damage: it’s not fixed, and higher energy does not necessarily mean more harm (lower LET often means lower RBE).
  • Counterintuitive relationships are central to understanding space radiation risks.

6. NASA's Early Strategies and Van Allen Belts

• Minimizing Exposure (17:10)

  • Discovery of the Van Allen belts led NASA to route Apollo missions to minimize time spent passing through them.
  • Electronics and equipment need to be 'hardened' against radiation, often tested at cancer therapy proton/neutron centers.

  “Space travel missions aimed to avoid those Van Allen belts ... going to the moon aimed to minimize the extent that astronauts would be traveling through ...”
  — Dr. Welsh (17:10)

7. The Near-Miss of August 1972

• Solar Storm Hazard (19:34)

  • Powerful solar storm nearly coincided with Apollo flights; had astronauts been in transit, they could have been fatally irradiated.

  “If the astronauts were up there and exposed to the unmitigated full fury of that radiation, it could have led to a dose that might have been fatal.”
  — Dr. Welsh (19:34)

8. Why Mars Missions are Particularly Risky

• Longer Exposure, Higher Cumulative Dose (21:57)

  • Mars is farther than the Moon, resulting in months (not days) of deep space exposure; the Martian atmosphere helps slightly but offers limited protection.

  “If it takes a year or 18 months to get there and back, there's a lot of radiation exposure en route.”
  — Dr. Welsh (21:57)

9. Sources of Space Radiation

• The Sun: Solar Wind, Flares, SEPs (26:32)

  • Solar wind is constant but relatively mild; flares and coronal mass ejections (CMEs) cause dangerous solar energetic particle events (SEPs).

• Solar Maximum vs. Minimum (28:01)

  • Paradox: Solar maximum brings more solar activity but ironically reduces galactic cosmic ray influx, as solar wind 'blows away' incoming GCRs.

  “Ironically, it is during solar max that radiation exposure to astronauts is lower ... the solar wind will be blowing hotter and counteracting the incoming galactic cosmic ray radiation.”
  — Dr. Welsh (28:01)

• Galactic Cosmic Rays (30:40)

  • Origins are still not fully understood; suspected products of supernovae, hypernovae, kilonovae, possibly the formation of black holes.
  • These include heavy atomic nuclei traveling at enormous energies, thus extremely damaging and hard to shield against.

  “Galactic cosmic rays ... are products of supernova explosions many light years away ... The energies are absolutely astounding ... highly and densely ionizing and very biologically effective.”
  — Dr. Welsh (30:40)

10. Acute Radiation Syndrome and Medical Treatment

• Acute Syndrome (36:44)

  • High, whole-body doses can cause potentially fatal acute radiation syndrome: involves gastrointestinal, blood-forming (hematopoietic), and CNS/cardiovascular subsystems.
  • Earth-based treatments (e.g., bone marrow transplant) are not currently possible during deep space missions.

  “... may be salvageable by intense medical efforts ... blood transfusions ... might require a bone marrow transplant ... currently beyond anything that could be even imagined in a spacecraft today.”
  — Dr. Welsh (38:00)

11. Challenges of Shielding in Space

• Weight and Effectiveness (39:42)

  • For the cosmic ray energies encountered in space, practical shielding must be much thicker and heavier than feasible for current spacecraft design.
  • Magnetic or electromagnetic shielding is a proposed avenue, but currently not realized.

  “If you’ve ever been to a radiation oncology center ... the walls are about a meter thick ... This starts to become impractical in terms of creating spacecraft ...”
  — Dr. Welsh (39:42)

12. Possible Mitigation Strategies

• Layered (Multicomponent) Shields (41:41)

  • Proposes combining different materials to address secondary radiation generated when primary cosmic rays hit shields.
  • Example: Dense outer layers (lead/tungsten) for charged particles, high-hydrogen content (paraffin) for neutrons, multiple layers for cascading protection.

• Electromagnetic Deflection

  • Theoretically, spacecraft could generate magnetic fields to divert charged particle trajectories.

• Biological Innovations: Radiotrophic Fungi (41:41)

  • Inspired by fungi surviving in Chernobyl, speculates about the potential use of melanin-rich fungi (“radiosynthesis”) as a living radiation shield—though this is very speculative.

  “...a fungus garden that would be so thick that it serves as shielding, and it’s growing on its own because of the radiation ... and if we’re lucky, it tastes good, and you can just grab a little bit, saute it up and have ... mushroom stew.”
  — Dr. Welsh (41:41)

Select Notable Quotes (with Timestamps)

• On Lucky Breaks in Apollo Missions:
  “The Apollo astronauts were very fortunate to not be en route to the moon in August 1972 because they could have suffered dire consequences.”
  — Dr. Welsh (19:34)

• On Space Radiation Paradoxes:
  “High energy does not necessarily mean high RBE or high biological effectiveness ... This is a little bit counterintuitive but ... as that energy is increased ... it actually goes down because the distance between ionizing events increases.”
  — Dr. Welsh (14:28)

• On Earth’s Protection:
  “Once you get beyond both the atmosphere and the magnetosphere, you’re at the mercy of unmitigated radiation from above. And there’s a lot of radiation that is out there that was not appreciated early on.”
  — Dr. Welsh (05:26)

• On Galactic Cosmic Rays:
  “Nobody does know about it for a fact ... The energies are absolutely astounding ... highly and densely ionizing and very biologically effective.”
  — Dr. Welsh (30:40)

• On Future Solutions:
  “...certain fungi may actually be using the radiation as a source of energy, just like plants use light from the sun in photosynthesis. Is it possible that some fungi are using radiation as a source of energy for radiosynthesis?”
  — Dr. Welsh (41:41)

Timestamps for Key Segments

• 03:10 — Motivation for Writing “Weathering Space”
• 05:26 — Protection by the Magnetosphere and Early Missions
• 07:21 — Explanation of Ionizing Radiation
• 08:34 — Linear Energy Transfer (LET)
• 09:54 — Primary vs. Secondary Cosmic Rays
• 11:53 — Muons and Special Relativity
• 14:28 — Relative Biological Effectiveness (RBE)
• 17:10 — Van Allen Belts, NASA Planning
• 19:34 — The 1972 Solar Storm Near-Miss
• 21:57 — Why Mars So Much More Dangerous than Moon
• 23:45 — Shielding Electronics and Hardening Equipment
• 26:32 — Types of Solar Radiation
• 28:01 — Solar Maximum vs. Minimum Radiation Exposure
• 30:40 — Origins and Dangers of Galactic Cosmic Rays
• 36:44 — Acute Radiation Syndrome
• 38:00 — Limits of Earth-Style Medical Care in Space
• 39:42 — Shielding Challenges for Spacecraft
• 41:41 — Emerging Ideas: Multilayered Shields & Radiotrophic Fungi

Episode Tone and Style

James Welsh blends scientific rigor with approachable explanations and a sense of awe for deep space phenomena. The conversation remains informative, with Dr. Welsh using illustrative analogies and a touch of humor, especially when speculating on the possibility of future mushroom “stew” harvests in space.

Conclusion

The episode distills why deep space radiation remains humanity's most daunting and least visible obstacle to sustainable interplanetary travel—and why luck, like that enjoyed by the Apollo crews, is not a sufficient plan. Dr. Welsh makes clear that massive engineering, biomedical, and even speculative biological innovations will be essential to "weathering space" as humans push their horizons beyond the Earth-Moon system.