A survey of Radiation Hazards & Shields for Space Craft & Habitats

Transcription

1 A survey of Radiation Hazards & Shields for Space Craft & Habitats By Philip Erner Presented at Institute for Nuclear Theory s Summer School on Nuclear & Particle Astrophysics, University of Washington, Seattle, 10 July 2009

2 Acknowledgements INT Summer School on Nuclear & Particle Astrophysics organizers and participants U.-Albany physics research advisers Drs. Jesse Ernst, Kevin Knuth and Eric Woods

3 GCR is the greatest expected threat to long-term human presence beyond earth s magnetosphere -Semkova

4 Units Dose = energy deposited per gram of material traversed Acute exposure: Absolute dose rad = 100 erg/g gray (abbrev. Gy; photo above left) = 1 J/kg = 100 rad Chronic exposure rem = effect of 100 rad of x-rays sievert (abbrev. Sv; photo above right) = 100 rem Equivalent dose = Dose x generic weight factor for each body tissue Summed over all radiation types > integrated over the whole body OR Effective dose equivalent = dose x specific weight factor for each body tissue Integrated over each organ > sum of all organs

5 Abbreviations Orbits LEO: low-earth orbit, km Geo: Geostationary orbit, earth rotational period, about 38,000 km EVA: extra-vehicular activity Particle types/events SPE: solar energetic particle event CME: coronal mass ejection GCR: galactic cosmic radiation ERB: Earth s trapped radiation (Van Allen) belts Other particle properties HZE: high charge and energy LIS: local interstellar spectrum Radiation effects LET: linear energy transfer

6 A simple summary Particle type/event Locations Max flux, (m 2 sr sec) -1 Energy, log(mev) LET or Dose, Gy Quality Factor Optimal Shield Protons ERB, CME, GCR 0-3,, Neutrons Electrons ERB Inner: 1 Outer: Heavy Nuclei GCR 1-12, 3 max Gamma photons Interstellar flight EVA Solar flare 150 mm Al

7 Types of radiation ERB - Trapped protons & electrons - Depends on inclination and altitude near Earth -2 bands -worst for Earth escape GCR -protons & heavier nuclei SPEs - Flares & CME - High flux of particles & photons Albedo - Secondaries from GCR & atmosphere - Low threat

8 Rules of thumb Penetration Z 2 Radiation dose (velocity) 3 Maintenance: redundancy better than EVA repair Prevention: chronic harder than acute Solar cycle is ~11 years. At solar minimum, GCR is enhanced. At solar maximum, CMEs are acute hazards.

9 National Council on Radiation Protection & Measurements (NCRP) Recommendation for relative biological effectiveness numbers Particle Type RBE 1 to 5 MeV neutrons to 50 MeV neutrons 3.5 Heavy ions 2.5 Protons > 2 MeV 1.5 Reference: Tripathi

10 Dose experiments LIULIN (several generations): radiation in atmosphere and space Human Phantom Cosmic Ray Experiments Advanced Composition Explorer (ACE), ? - L1 Earth-Sun Alpha Magnetic Spectrometer (AMS) -ISS -2 nd generation launch 2010 July 29 Geostationary Operational Environmental Satellite (GOES) - Weather Interplanetary Monitoring Platform (IMP), 1960s-2000s - Various missions - Several Earth radii

11 Principal Problems Leaving the Terrestrial shield: outside Earth s magnetosphere, charged particles are not deflected; unknown effects of human exposure, long-term or acute, to cosmic radiation beyond Earth s magnetosphere Unpredictable Solar Particle Events: Late warning; characteristics variable Weight: Heavy shield cannot be launched from Earth

12 What s safe? NCRP to NASA: < 3% lifetime cancer increase Wolfson: 4 Sv in a relatively short period kills half of the people exposed. Conservative: 5 rem/life, 0.1 rem/year Perhaps 200 rem/several years Permissive: 0.5 rem/year Perhaps 500 rem/life

13 Hazards to Humans & Domestic Animals (& Space Craft) Laika, 1st Earth-orbiting passenger

14 LEO ISS from Space Shuttle Atlantis, Background: 1 rem/day -Van Allen Belts: South Atlantic Anomaly -Solar flare: 100s-1000s rem / several hours -Inclination: stronger field; avoid SAA -Altitude: closer to Van Allen

15 Van Allen Belts

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17 Trans-lunar passengers FORE! Alan Shepard Outside magnetosphere Lunar albedo Through Van Allen belt One week

18 Aluminum: NASA standard space craft shield Secondary radiation Differential shield of the space craft

19 Options for Space craft Shield Electric-magnetic -1 GV - + attracts - -neutrons Material: Light weight, total and by Z -Liquid hydrogen / Water -Polyethylene

20 She turned me into a newt! What s so bad about neutrons?

21 Bundled Bricks, Folded Fibers: Reinforced Polyethylene - Blocks / fragments more radiation - Half the weight of aluminum - Bonus: Deflects micrometeorites Study by Raj Kaul, Marshall Center

22 Dosimeter: radiation detector Active: heavy, powered, time included Passive: lightweight; unpowered; no time

23 Record events 1859, Carrington 1956 February 1972 August, between Apollo 16 and Apollo September-October, aboard Mir 2000 July 14, Bastille Day CME 2001

24 Zubrin s Interplanetary Proposals Mars Direct - Launch: conjunction Jovian moons - Callisto OK; Ganymede with heavy shielding - Io, Europa impossible

25 Interstellar Overdose 10 x speed = 1000 x rads! Gamma Photons, Lethal Protons at 0.01c: 50 kev/particle = 1 rad/s in top mm - skin-safe at 0.1c: 5 MeV/particle = rad/s - spacesuit/plastic OK

26 SUMMARY Particle -Type -Location -Energy Hazard -Equipment -Biology Shield -Material -Reliability

27 References Benton, E. R., and Benton, E. V. Space radiation dosimetry in low-earth orbit and beyond. Nuclear Instruments and Methods In Physics Research B. 184 (2001), p Gaisser, T. K., and Stanev, T., eds. Cosmic Rays, PDG,(2008), ch. 24. Hannah, E. C. Radiation Protection for Space Colonies. JBIS,(1977), p Kline, R. L. Habitat Requirement, Design and Options. In: Human Factors of Outer Space Production, AAAS Symposia (1980), p Mauldin, John H. Prospects for Interstellar Travel. Science and Technology, vol.80 (1992). MSC, Environmental Factors Involved and the Choice of Lunar Landing Sites, NASA Project AWP No. 1100, (22 Nov. 1963), p Pinsky, L., NASA s interest in Cosmic Ray as a radiation hazard to a human presence in space. In: Il Nuovo Cimento, Vol. 120B, N.6-8, (2005), p Semkova, J., et. al. Experiment for Radiation Dose Measurements in a Human Phantom IEEE (2005). In: RAST conference proceedings. Townsend, L. W. Implications of the Space Radiation Environment for Human Exploration in Deep Space. In: Radiation Protection Dosimetry, Vol. 115, No. 1-4, (2005), p Tripathi A., Nealy, J., Mars Radiation Risk Assessment & Shielding Design, IEEE. In: IEEEAC paper #1291, V4, (23 Nov. 2007). Wolfson, R. Energy, Environment & Climate. W.W. Norton (2008), p Zubrin, Robert. The Case for Mars. (1996) p Zubrin, Robert. Entering Space. New York : Penguin Putnam (1999), p Edit: 14 Jan Access: June 2009.