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David M. Klaus, Ph.D. Assistant Professor, Aerospace Engineering

ASEN 5335 Guest Lecture Radiation Effects on Astronauts. David M. Klaus, Ph.D. Assistant Professor, Aerospace Engineering Associate Director, BioServe Space Technologies. April 10, 2003. Challenges to Staying Alive in Space. Vacuum Temperature Extremes ~ -120 to +110°C in LEO

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David M. Klaus, Ph.D. Assistant Professor, Aerospace Engineering

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  1. ASEN 5335 Guest Lecture Radiation Effects on Astronauts David M. Klaus, Ph.D. Assistant Professor, Aerospace Engineering Associate Director, BioServe Space Technologies April 10, 2003

  2. Challenges to Staying Alive in Space Vacuum Temperature Extremes ~ -120 to +110°C in LEO Micrometeoroids Weightlessness Radiation - Electromagnetic and Particulate

  3. Electromagnetic (EM) Radiation • Characterized by l and C, high flux, low energy • - waves or streams of massless particles traveling in a wave-like fashion and each carrying energy (photons) • Decay at 1/x2 from the source • Primary source is the sun (solar wind) • Radio, light, X-rays, IR, extreme UV • Gamma () rays are most abundant and originate outside the solar system

  4. Particulate • Characterized by mass and n2, low in flux, high energy • HZE particles (cosmic sources)  High Mass and Energy (Z = atomic number, E = energy) • SEPs – Solar Energetic Particles, also SPEs Solar Particle Events • GCRs – Galactic Cosmic Radiation (neutrons, protons & nuclei) median velocity is ~0.95 C • Electrons, protons, neutrons and nuclei • Ranges from helium to uranium, with peak in abundance of iron • a - helium nuclei (solar and galactic)b - electrons (sun and van Allen belts) • ionizing radiation – dislodged electron, capable of producing charged atoms (ions) as passes through matter • UV is non-ionizing

  5. · Trapped Belt Radiation Van Allen Belts (inner 1-3x Earth Radii, outer 4.5-10x) - Verified by Explorer I (31 Jan 58) SAA – cusp in VA Belts -         90% of exposure in LEO occurs in the SAA region Solar Flares -         EM waves reach Earth in ~8.5 min -         Magnetic cloud (particulates) reaches Earth 2-3 days later -         Solar Max moderates GCRs but increases SEPs

  6. Units RAD = Radiation Absorbed Dose (amount of energy absorbed in the body by radiation) RBE – Relative Biological Effectiveness (varies dependent on type of radiation) Roentgen – basic unit for measuring amount of radiation exposure REM (Roentgen Equivalent, Man - measure of biological effect) REM = [dose, RAD] x RBE = ~1.3 RAD SI: Sievert (Sv) = 100 REM 1 RAD = absorption of 100 ergs/gm = 0.01 Gray (Gy) or 10 mGy (SI) 1 Gy = absorption of 1 J/kg mGy = 0.1 RAD

  7. Biological Risks • Primary biological risk from space radiation exposure is cancer • When radiation is absorbed in biological material, the energy is deposited along the tracks of radiation. • Neutrons and heavy ions produce much denser pattern of ionization causing more biological effects per unit of absorbed radiation dose. • Secondary concerns such as cataracts are beginning to receive more administrative attention

  8. Lethal Dosages of Radiation During violent solar events, the Sun can accelerate electrons and protons to almost the speed of light which gives them huge amounts of energy. Protons and electrons at these high energies can be very dangerous to living cells 1 sievert=1000 millisievert=100 REM

  9. Two major factors in the determination of radiation damages: (1) total dose over the life of a material, (2) dose rate, the rate at which energy is deposited. • Different materials have different susceptibilities to damage:

  10. Biological Effects Two general categories: somatic (exposed individual) and genetic (hereditary effects) Different types of radiation produce different amounts of damage HZE and low energy protons > electrons and high energy protons Higher rate of energy loss per length of track  Linear Energy Transfer (LET) Tissue effects = thermal, chemical, cellular and genetic Sensitivity proportional to complexity e.g. eyes > skin > bone Symptoms: nausea, vomiting, illness, death ~RADs required for inactivation/death ·        Molecules 107 ·        Viruses 105 ·        Bacteria 104-106 ·        Mammalian cells 100-104 ·        Mammals 320-540

  11. How Much is Too Much ??

  12. LD50 for humans = 320-540 RAD Sickness can occur at 25-30 RAD

  13. NRC Report (2000) • “ When the intensity of relativistic electrons is greatest, a single ill-timedEVA could deliver a radiation dose big enough to push an astronaut over the short-term limit for skin and eyes. “ • Recommendation 3c: A project should be initiated to develop a protocol for identifying the conditions that produce highly relativistic electron events based on the demonstrated good correlation between changes in solar wind conditions and the onset of such events. 1 sievert (Sv)=100 REM

  14. Ave exposure in the US: ~40 mREM / year (soil, rocks, wood, etc.) East coast ~20 mREM / year Rocky Mtn area ~90 mREM / year Cosmic Rays: add ~40 mREM / year (~160 mREM high in the Rocky Mtns) Food and water: add ~ 20-50 mREM / year NY to Paris flight: add ~4 mREM à ~ 100 mREM / year compared to ~65 – 195 mREM / typical shuttle flight

  15. Biological effects are cumulative Effects are acute (early) or chronic (late) tissue damage loss of fertility lens opacification cancer induction heritable effects Sunburn à melanoma Carcinogenic effects are of great concern Proliferating cells of renewing tissue & organs are most sensitive - bone marrow, lymph, intestine and reproductive organs Younger people and women are more susceptible to radiation damage in general - Youth have longer for potential damage to develop - Women have 2 radiation sensitive organs (breasts and ovaries) and longer expected life span than men

  16. PARTICLE ENERGIES OF CONCERN

  17. EVA • EVAs - additional radiation exposure concern • Lower shielding • Eye dose • Skin dose • 51.6 degrees, new concern for electron events • One area where there are no currently a good model. • 140 more EVAs are planned for ISS completion

  18. Legal and moral reasons require NASA limit astronaut radiation exposures • U.S. Occupational Safety and Health Administration officially classifies astronauts as “radiation workers” • Adherence to ALARA (As Low As Reasonably Achievable) is recognized throughout NASA’s manned space flight requirements documents • Radiation protection philosophy--any radiation exposure results in some risk • ISS astronaut exposures will be much higher than typical ground-based radiation worker • Astronaut legal dose limits (In BFO: 50 REM/yr and 30 REM/mo) are 10 times that allowed ground based radiation workers • Space radiation more damaging than radiation typically encountered by ground-based workers

  19. DOSE FACTORS • ISS originally planned at 28.5 degrees latitude, now at 51.6 • Dose received is a factor of: • Altitude • Attitude • Shielding • Solar Cycle • Time in orbit

  20. RADIATION MONITORING SYSTEM

  21. Current Research Summaries

  22. The three EVARM radiation badges, which are less than 8 centimeters long and 3 centimeters wide, are small enough to fit comfortably into pockets placed inside TCUs. The badges use tiny MOSFET chips to read radiation dose. [NASA/JSC] EVA Radiation Monitoring Experiment on ISS The purpose of EVARM is to carry out flight experiments to characterize the radiation doses experienced by astronauts during extravehicular activity (EVA). These measurements will include doses to skin, eye, and blood-forming organs and will be carried out using a relatively new type of electronic radiation dosimeter, the Metal Oxide Semiconductor Field Effect Transistor (MOSFET). http://spaceresearch.nasa.gov/research_projects/ros/evarm.html

  23. Bonner Ball Neutron Detector (BBND) Radiation exposure—and the subsequent physiological damage—is one of the primary hazards faced by long-duration space crews. Because neutrons do not carry a charge, they are able to deeply penetrate the body, potentially damaging blood-forming organs. In low Earth orbits, the contribution of the neutron component is estimated to be about 20 percent of the total radiation. Characterization of this radiation environment will help scientists develop safety measures to protect space crews. BBND Detector Unit opened to show interior structure. A metal counter sits inside a white sphere of polyethylene plastic. [NASA/JSC] http://spaceresearch.nasa.gov/research_projects/ros/bbnd.html

  24. BBND (BONNER BALL NEUTRON DETECTOR) • solar-neutron (from the Sun.), albedo-neutron (produced by collision of high energy proton and gas particle in atmosphere), and local-neutron (produced by collision of high energy proton and spacecraft material) http://sees.tksc.nasda.go.jp/English/WhatsSEES/bbnd.html

  25. Dosimetric Mapping (DOSMAP) In order to better understand the internal environment of the ISS, this experiment will map the radiation levels throughout the Station and in the immediate vicinity of each crew member. The measurements will be taken using Thermo Luminescent Dosimeters (TLDs). The resulting data will help determine the best radiation shielding locations on board the Station, providing the crew with the best possible protection during unusually high levels of radiation due to solar flares or other cosmic phenomena. http://spaceresearch.nasa.gov/research_projects/ros/dosmap.html

  26. Phantom Torso (TORSO) Currently, both experimental and operational methods for assessing radiation levels are limited to the measurement of surface (skin) levels. Internal level estimations can only be done by calculations using the radiation environment model and the appropriate radiation transport models. They do not account for the diffusion or redirection of particles as a result of other surfaces, namely the spacecraft walls, interior air, or human skin, and do not include the production of secondary particles within the spacecraft and the human body. Fred the Phantom Torso is an anatomical model of a torso and head containing more than 300 radiation sensors. [NASA/JSC] http://spaceresearch.nasa.gov/research_projects/ros/ptorso.html

  27. Countermeasures Distance from local source (decays at 1/x2) Timing of exposure (when radiation is least intense) e.g. no scheduled EVAs over SAA Shielding (but secondary effects…) evaluation of effectiveness is complex and depends on actual composition of the impacting radiation Pharmaceutical treatment Shielding stops or alters the trajectory of high energy particles before the reach humans In general, the more dense a material, the more effective it is as shielding Protection against non-ionizing radiation is relatively simple, but ionizing sources create secondary and tertiary particles, some of which produce gamma rays Low (equatorial) orbits are considerably less hazardous than polar orbits

  28. CONCLUSIONS • Of all the risks encountered by astronauts during space flight, cancer induction from radiation exposure is one of the few that persists after landing • During construction of the ISS, there is a relatively large probability that EVAs will coincide with a radiation enhancement in the belts • Issues for Mars Mission include: monitor and forecast, storm shelter, effects on humans, evaluation of risk, pharmaceutical intervention and/or shielding • Liquid Hydrogen likely best shielding candidate

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