1. Radiation Biophysics and Human Spaceflight Dr. John M. Jurist Adjunct Professor of Space Studies, Odegard School of Aerospace Sciences, and Adjunct Professor of Biophysics and Aviation, Rocky Mountain College Note: This material was used in formal biophysics, human factors, and aerospace medicine and physiology classes as well as in various seminars at the above institutions, and is not to be reused without attribution

2. Radiation Exposure Sources and characteristics Radiation Biophysics and Human Spaceflight2

3. Radiation Exposure Sources of exposure: On board fluid level sensors Cosmic photons (includes gamma bursts) Cosmic particulate radiation Solar photons Solar particulate radiation (includes flares) Trapped particulate radiation belts (Van Allen) Terrestrial background Radiation Biophysics and Human Spaceflight3

4. Radiation Exposure Primary issues for external sources: Radiation exposures vary widely with location relative to Earth or other bodies Radiation of solar origin varies with multi-year solar cycle – periodic solar storms cause intense radiation bursts Radiation of extrasolar or galactic origin consists of relatively steady background component punctuated by intense random bursts of particulate and photon radiation Radiation Biophysics and Human Spaceflight4

5. Radiation Exposure Primary issues for external sources – cont: Location of occupants within spacecraft and construction of spacecraft influence quality and magnitude of radiation to which occupants are exposed Biological response to radiation exposure varies widely with nature of radiation and exposure rate Cumulative effect of multiple exposures not purely additive – depends at least partly on intervals between exposures Radiation Biophysics and Human Spaceflight5

6. Radiation Exposure Primary issues for external sources – cont: Biological response variable and depends on gender, age and health Biological effects of low doses are poorly characterized since responses are confounded by other unknown variables No agreement on threshold dose below which exposure is harmless or whether response is dose-related down to infinitesimally small exposures High exposure responses depend on availability and quality of medical care for managing complications Radiation Biophysics and Human Spaceflight6

7. Radiation Exposure 2 types of ionizing radiation: Electromagnetic (photons – gamma rays or X-rays) Particulate Radiation Biophysics and Human Spaceflight7

8. Radiation Exposure Photons: X-rays are created in extranuclear events such as decelerating or accelerating charged particles and gamma rays are created in nuclear events Otherwise, they are same – packets of short wavelength electromagnetic radiation Radiation Biophysics and Human Spaceflight8

9. Radiation Exposure Particulate: Neutral particles – such as neutrons Charged particles: Alpha particles (ionized helium nuclei) Protons (ionized hydrogen nuclei) Beta particles (electrons) or their anti- counterparts Other ionized nuclei Radiation Biophysics and Human Spaceflight9

10. Radiation Exposure Particulate Cosmic Ray Spectrum: Radiation Biophysics and Human Spaceflight10 Composite energy spectrum for particulate cosmic rays [Microcosm, SME 2011]

11. Radiation Exposure High end particulate event was so-called Oh My God particle October 15, 1991 over Dugway Proving Ground (Utah) (repeatedly confirmed since then): Particle had a kinetic energy of about 3*10 20 eV or 50 Joules (60 MPH baseball for comparison) Believed to be proton traveling within 1 part in 10 24 of the speed of light (3*10 8 m/sec) Radiation Biophysics and Human Spaceflight11

12. Radiation Exposure Solar photons in X-ray region occur as part of blackbody emission spectrum of hot solar gases Photons are short wavelength tail of regular solar spectrum that humans see in visible light Solar flares can also emit X-rays at flux that can exceed 1 mw/m 2 at Earth's orbit Solar particulate emissions include the solar wind (mostly conductive plasma) and coronal mass ejection events Emissions associated with ionizing radiation Radiation Biophysics and Human Spaceflight12

13. Radiation Exposure Radiation Biophysics and Human Spaceflight13 Typical time history of a solar flare or coronal mass ejection event for X-rays and high and low energy protons as observed on Earth The vertical axis is in relative units of intensity with 10 0 corresponding to baseline values [Microcosm, SME 2011]

14. Radiation Exposure Units and their evolution Radiation Biophysics and Human Spaceflight14

15. Radiation Exposure Units used in radiobiology of historic interest since recent rationalization to SI units Evolution of units followed logical but potentially confusing progression Early unit of radiation exposure was Roentgen (R) Defined as the amount of ~100 kilo-electron volt (kV) energy X-rays that would produce 1 ESU of ionization per cm 3 of dry air at 1 atm and 0 o C This is ~258 microColumbs (μC) per kg of dry air Radiation Biophysics and Human Spaceflight15

16. Radiation Exposure Dry air and tissue ionize differently when exposed to same amount of radiation Radiation absorbed dose (rad) was defined as amount of 100 kV X-rays resulting in 100 ergs of absorbed energy per gram of material For dry air under standard conditions, 1.0 R is equivalent to 0.876 rad Equivalency is defined as f factor and varies with material Radiation Biophysics and Human Spaceflight16

17. Radiation Exposure Biological systems differ in response to different types of radiation Relative Biological Effectiveness (RBE) was defined as ratio of standard X-ray dose to actual dose of radiation to which system was exposed and which would produce same biological response 50 rads of some type of radiation with an RBE of 2.0 would produce same biological damage as 100 rads of standard X-rays Radiation Biophysics and Human Spaceflight17

18. Radiation Exposure Roentgen Equivalent Man (rem) was defined as product of RBE and dose in rads Rem is indication of biological damage with acute radiation exposure When units were rationalized, RBE was defined as Q, the quality factor Radiation Biophysics and Human Spaceflight18

19. Radiation Exposure Energy/MassBioeffect 100 rad times Q(RBE) 100 Rem 1 Gray (Gy)times Q 1 Sievert (Sv) Relation between modern SI units and older units – 1 Gy = 100 Rads Radiation Biophysics and Human Spaceflight19

20. Radiation Exposure Radiation SpeciesRBE or Q Alpha particles (helium nuclei) 20 Beta particles (electrons) 1 High energy protons (hydrogen nuclei) 10 X-rays (photons) 1 Gamma rays (photons) 1 Neutrons (unknown energy) – conservative 10 Radiation Biophysics and Human Spaceflight20

21. Radiation Exposure Radiation Biophysics and Human Spaceflight21

22. Radiation Exposure Short term acute whole body exposure (Rems): 10-50Minor blood changes 50-1005-10% nausea (1 day), blood, survivable 100-2001/4-1/2 nausea (1 day), blood, GI, survivable 200-350Most nausea (1 day), blood, GI, 5-50% die 350-550 450 LD 50 Most nausea, blood, GI, 50-90% die 550-750Nausea (hours), blood, GI, almost all die 750-1,000Nausea (hours), blood, GI, fatal (2-4 weeks) 1,000-2,000Nausea (hours), fatal (2 weeks) 4,500Incapacitation (hrs), fatal (1 week) Radiation Biophysics and Human Spaceflight22

23. Radiation Exposure Radiation biological effects and biophysics Radiation Biophysics and Human Spaceflight23

24. Radiation Exposure Low to moderate acute (prompt) doses damage rapidly dividing cells in blood-forming tissues, skin, and gastrointestinal tract: Decreased white cell blood counts (impaired ability to combat infection) Erythema (reddening), blistering, or destruction of skin depending on dose Radiation Biophysics and Human Spaceflight24

25. Radiation Exposure Low to moderate acute (prompt) doses: Destruction of gastrointestinal system lining (nausea, diarrhea, and secondary infection) Long term effects from damage to genetic and other cellular systems Carcinogenesis although mechanisms and immune system role unclear Radiation Biophysics and Human Spaceflight25

26. Radiation Exposure Treatment and effects: Extrinsic radiation exposure treatment involves medical management of complications as appropriate Success depends in part on quality and quantity of available medical care Isolation makes treatment during deep spaceflight problematic Radiation Biophysics and Human Spaceflight26

27. Radiation Exposure Treatment and effects: Subsequent radiation injuries not treated with maximum effectiveness as result of isolation Radiation effects studied in humans exposed to radiation accidentally, for medical diagnostic or therapeutic procedures, and as result of nuclear weapons In addition, many animal experiments have been conducted Radiation Biophysics and Human Spaceflight27

28. Radiation Exposure Chronic low dose effects: Example: Typical total dose for treating breast cancer is 3,000 to 3,500 rads split into 30 daily doses If administered as single dose, it would destroy the skin overlying the breast and most likely be fatal Skin effects of split dose administration usually limited to erythema or reddening and easily managed Not clear if repair mechanisms result in threshold dose under which no radiation damage incurred Radiation Biophysics and Human Spaceflight28

29. Radiation Exposure Chronic exposure examples Radiation Biophysics and Human Spaceflight29

30. Radiation Exposure Polar airline flight 0.10-0.23 mSv per day 2 view chest X-ray 0.06-0.25 mSv Bone scan 0.15 mSv Chest CT 0.3-30 mSv (typical 10 mSv) Billings MT background 1.2 mSv per year (quiet sun) Typical US background 2.4 mSv per year Typical US medical average 0.6 mSv per year Radiation Biophysics and Human Spaceflight30

31. Radiation Exposure Radiation Biophysics and Human Spaceflight31

32. Radiation Exposure Estimated HTO suborbital flight: Upper limit 0.0053 mSv per flight Compare: Polar airline flight 0.10-0.23 mSv per day Radiation Biophysics and Human Spaceflight32

33. Radiation Exposure Orbital and beyond: 0.6-0.9 mGy/day (Skylab) 0.2-1.3 mGy/day (Apollo landing missions) ~0.06 mGy/day (STS) 0.049-1.642 mGy/day (STS-2, STS-31) 0.053 mGy/day 0.146 mSv/day galactic cosmic 0.042 mGy/day 0.077 mSv/day trapped belt Radiation Biophysics and Human Spaceflight33

34. Radiation Exposure Approximate Dose (mSv/day) Source Average RBE 0.146 Galactic cosmic 2.75 0.077 Van Allen belt1.83 trapped radiation in LEO Radiation Biophysics and Human Spaceflight34

35. Radiation Exposure Shielding factors Radiation Biophysics and Human Spaceflight35

36. Radiation Exposure Altitude effect result of shielding action of atmosphere on incoming solar and galactic radiation In terms of incoming cosmic radiation, atmosphere at sea level equivalent to ~ 5 meters water or ~ 1 meter lead Radiation Biophysics and Human Spaceflight36

37. Radiation Exposure Beam hardening phenomenon: Softer (longer wavelength) photons generally absorbed more efficiently by matter than harder photons Effective beam spectrum progressively hardens with absorption depth although intensity decreases Compton scattering is also an issue – causes fogging of conventional X-ray images Radiation Biophysics and Human Spaceflight37

38. Radiation Exposure In LEO, shielding effect of Earth's atmosphere lost, but shielding by geomagnetic field retained although dependent on orbital inclination Earth’s magnetic field deflects charged particles & reduces effective doses experienced at lower latitudes Contributes to latitude effect on radiation background Radiation Biophysics and Human Spaceflight38

39. Radiation Exposure Geometric shielding effect lost during space flight beyond LEO: Comes from Earth subtending large part of sky as seen from LEO Shields incoming galactic & solar radiation to extent that flight beyond LEO but in vicinity of Earth's orbit results in roughly twice cosmic radiation exposure compared to LEO Same shielding effect would occur near Moon or Mars, but not in transit Radiation Biophysics and Human Spaceflight39

40. Radiation Exposure Protective ModalityAluminum Equivalent (g/cm 2 ) Atmosphere of Earth 1,020 Atmosphere of Mars 22 International Space Station 10 Space Shuttle (STS) 10 Apollo space suit 0.1 Radiation Biophysics and Human Spaceflight40

41. Radiation Exposure Space flight: Moon & Mars both have essentially no magnetic fields Mars field on order of one 800 th strength of Earth's field Vertically directed cosmic radiation at surface of Mars about 46 times as intense as on surface of Earth Radiation Biophysics and Human Spaceflight41

42. Radiation Exposure Dose standards (1994): For reference, 2 view chest X-ray 0.06-0.25 mSv Public limit 1 mSv per year NASA classifies astronauts as radiation workers Worker whole body 50 mSv or 0.05 Sv per year Worker organ limit 0.5 Sv per vear Worker organ limit 0.25 Sv per month Historical trend to reduce limits: Compare 1994 to 2000 limits Radiation Biophysics and Human Spaceflight42

43. Radiation Exposure Career limits for radiation workers (1994): Blood-Forming Organs Limit atLensSkinMaleFemale Age 254.0 Sv6.0 Sv1.5 Sv1.0 Sv Age 354.0 Sv6.0 Sv2.5 Sv1.75 Sv Age 454.0 Sv6.0 Sv3.2 Sv2.5 Sv Age 554.0 Sv6.0 Sv4.0 Sv3.0 Sv Historical trend to reduce limits: Compare 1994 to 2000 limits Radiation Biophysics and Human Spaceflight43

44. Radiation Exposure Radiation carcinogenesis: 0.5/10 6 /mSv/yearBreast 0.4/10 6 /mSv/yearThyroid 0.3/10 6 /mSv/yearLung 7-17/10 6 /mSv/yearAll cancers 100 mSv/10 5 800 deaths added to 20,000 w/o radiation (4% increment/10 rads) Radiation Biophysics and Human Spaceflight44

45. Radiation Exposure Is radiation a show-stopper for a trip to Mars? Radiation Biophysics and Human Spaceflight45

46. Radiation Exposure Trip segments for dosimetry: Transit Van Allen belts (departure) Free space baseline (departure) Solar flares (CMEs) and galactic pulses Mars stay (ignore for free return) Habitat & Rover Suit Free space baseline (return) Solar flares (CMEs) and galactic pulses Transit Van Allen belts (return) Radiation Biophysics and Human Spaceflight46

47. Radiation Exposure Minimum energy transfer roughly 9 months each way Assume STS-like free space galactic radiation exposure of 0.146 mSv/day (doubled due to loss of Earth’s geometric shielding) 270 days times 0.146 mSv/day = 39.4 mSv for 1 way News Flash – New data 1.8 mSv/day (12 times above estimate) – Zeitlin et al., Science 340:1084-1084, 2013 MSL data: 253 days times 1.8 mSv/day = 455.4 mSv for 1 way, 911 mSv for 506 day free return round trip Radiation Biophysics and Human Spaceflight47

48. Radiation Exposure 2000 standards more stringent than prior standards – Committee on the Evaluation of Radiation Shielding for Space Exploration: Managing Space Radiation Risk in the New Era of Space Exploration, National Research Council, National Academies Press, Washington, DC, 2008 MSL data: 253 days times 1.8 mSv/day = 455.4 mSv for 1 way, 911 mSv for 506 day free return round trip New Standards for 3% Added Risk of Exposure Induced Death (REID, 95% confidence, assumes baseline solar and galactic activity) Radiation Biophysics and Human Spaceflight48

49. Radiation Exposure Career Limit for 1 yr mission and 3% REID (mSv) Age (yrs)MaleFemale 30 620 470 35 720 550 40 800 620 45 950 750 501150 920 5514701120 MSL data: 253 days times 1.8 mSv/day = 455.4 mSv for 1 way, 911 mSv for 506 day free return round trip with no CMEs Radiation Biophysics and Human Spaceflight49

50. Trip segments: Transit Van Allen belts (departure)depends on trajectory Free space baseline (departure)1.8 mSv/day times 253 days Solar flares (CMEs) and galactic pulsesprobabilistic (see slide 13) Mars stay (ignore for free return) Habitat & Rover~ 0.4 mSv/day * Suit0.6-15 mSv/day ** Free space baseline (return)1.8 mSv/day times 253 days Solar flares (CMEs) and galactic pulsesprobabilistic (see slide 13) Transit Van Allen belts (return)depends on trajectory * Estimated average between solar maximum and minimum ** Depends on suit construction, posture, and particulate mix Radiation Exposure Radiation Biophysics and Human Spaceflight50

51. Radiation Exposure Is it legal? Compare to career limits (3 Sv old, 1.12 Sv new for 55 yr old female) Issues of informed consent and regulatory waiver Boost cancer death risk 1.7% for baseline trip to Mars with old dosage data – multiply old doses by 12 for new risk calculation Boost cancer death risk 25% for continuous 0.146 mSv/day Flares and Mars orbit time, surface time additional Radiation issues become significant Radiation Biophysics and Human Spaceflight51

52. Radiation Exposure The conundrums: Are long term space missions legal? Informed consent vs. legal limitations Conceive and raise children on Mars? Conceive and raise children in space habitats? Remember planets shield by geometry Large variability in exposure (flares) Large variability in response Radiation Biophysics and Human Spaceflight52

53. Radiation Exposure Orbital (and beyond) human factors status Radiation Biophysics and Human Spaceflight53

54. NewSpace awaremess is dismal: Assumption that it is accomplished and can be ignored Lack of appreciation of risks Wishful thinking and denial trumps reality Aging normative population undefined Minimal gravity level is undefined Radiation issues become significant Working is microgravity is hard Radiation Exposure Radiation Biophysics and Human Spaceflight54

55. Why? Culture shock (engineering vs. biomedical): Engineers look for limiting parameters Engineers design to limiting parameters Engineers minimize variables Human responses vary enormously Human responses probabilistic Human responses – many variables Human responses poorly characterized Never say never in medicine Radiation Exposure Radiation Biophysics and Human Spaceflight55

56. Medical issues related to living in space and going to Mars: Outside assistance is impossible or very difficult Life support degradation – toxin accumulation Acute urinary retention – renal lithiasis Cardiac event Microgravity and radiation issues Cancer (Antarctica example – isolation and treatment) Drug shelf life (accelerated degradation with radiation) Medical/surgical infrastructure – how much is enough? Radiation Exposure Radiation Biophysics and Human Spaceflight56

57. Opportunities Many unknowns: What we don’t know can hurt us or provide opportunities for play/research: Microgravity – musculoskeletal, cardiovascular, reproductive, and immune systems; embryogenesis, fetal development; aging; optimization Radiation – shielding (mass, electrostatic, or magnetic), abatement (pharmaceutical, antioxidants, modification of humans – genetic engineering) Radiation and microgravity synergisms Long term exposure to different gas mixes vs. standard air Other – Moon/Mars dust and urban/rural pollution effects Radiation Biophysics and Human Spaceflight57