The Radiation Environment in Space Sources of Radiation in Space ? Galactic Cosmic Rays ? The Sun ? The Solar Wind ? Coronal Mass Ejections Radiation in Space NASA research programs for The International Space Station Mission to Mars ? Understand the biological effects ? Design adequate shielding Galactic Cosmic Rays Source unknown Isotropic Fluence constant over time Image removed. Figure 2.1 in [SSB-Crew Hazards]. Commission on Physical Sciences, Mathematics, and Applications, Space Studies Board (SSB). Radiation Hazards to Crews of Interplanetary Missions: Biological Issues and Research Strategies. Washington DC: National Academies Press, 1996. See http://books.nap.edu/books/0309056985/html/14.html#page_bottom. Galactic Cosmic Rays Broad energy distribution Peak at about 1 GeV/nucleon Image removed. Figure 2.1 in [SSB-Crew Hazards]. See http://books.nap.edu/books/0309056985/html/15.html#page_top. Galactic Cosmic Rays Attenuation in the upper atmosphere Image removed. Radiation from the Sun Source: NASA. “Living in the Atmosphere of the Sun.” [updated 20 Jan 2000, cited 29 March 2004.] http://www-istp.gsfc.nasa.gov/exhibit/main.html Radiation from the Sun The solar wind deforms the Earth’s magnetic field lines Image removed. Radiation from the Sun Sunspots Observed for centuries Occur in an 11 year cycle Source: NASA Goddard Space Flight Center . [updated 30 March 01, cited 29 March 2004.] http://www.gsfc.nasa.gov/gsfc/spacesci/solarexp/sunspot.htm Radiation from the Sun Image removed. During maximum sunspot activity, there is an increased likelihood of solar flares and coronal mass ejections. Radiation from the Sun Solar flares Associated with production of high energy particles, mostly protons. Potentially lethal doses Source: NASA. “Our Magnificent Sun.” [cited 29 March 2004] http://cossc.gsfc.nasa.gov/images/epo/gallery/solar/ 1996 photo from Skylab Violent Space Weather High Energy Coronal Mass Ejections produce “shocks” ? Highest energy particles reach Earth in 10 – 100 min ? Particle fluence increases by many orders of magnitude ? Astronauts directly exposed risk lethal radiation doses ? Spacecraft design must include “storm shelters” ? A network of satellites and ground stations monitor the sun for signs of SPEs Violent Space Weather Coronal mass ejection, or solar particle event Image removed. Figure 4.1 in [SSB-Space Station]. Commission on Physical Sciences, Mathematics, and Applications, Space Studies Board (SSB). Radiation and the International Space Station: Recommendations to Reduce Risk. Washington DC: National Academies Press, 2000. See http://books.nap.edu/books/0309068851/html/40.html#page_middle. The van Allen Radiation Belts Inner Belt mostly protons E ~ 10 MeV Outer Belt mostly electrons E up to 10 MeV “Horns” dip in at the poles Image removed. Figure 1.1 in [SSB-Space Station]. See http://books.nap.edu/books/0309068851/html/8.html#page_top. The van Allen Radiation Belts Image removed. The van Allen Radiation Belts ? Degrade satellite components ? Background noise in detectors ? Errors in digital circuits ? Electrostatic charge-up in insulators ? Present a threat to astronauts ?Apollo missions: largest dose component was from travel through the van Allen radiation belts The van Allen Radiation Belts NASA limits the time spent in high- dose regions of the inner radiation belt. Image removed. The South Atlantic Anomaly Image removed. Figure 1.2 in [SSB-Space Station]. See http://books.nap.edu/books/0309068851/html/9.html#pagetop. The Aurora Image removed. Energetic charged particles entering the upper atmosphere (~ 70 miles up) ionize neutral gas molecules. Source: NASA. “Space Science Photos: Prior to 1997 [cited 29 March 2004] http://www.gsfc.nasa.gov/indepth/photos_spaceearly.html The International Space Station Radiation exposure: ? Radiation Belts ? GCR ? SPEs Image removed. Figure 1.4 in [SSB-Space Station]. See http://books.nap.edu/books/0309068851/html/13.html#page_bottom. The International Space Station ISS orbit enters higher dose region at high latitudes Image removed. The International Space Station Image removed. Figure 1.5 in [SSB-Space Station]. See http://books.nap.edu/books/0309068851/html/14.html#page_top. Radiation in Space Image removed. Figure 2.4 in [SSB-Crew Hazards]. See http://books.nap.edu/books/0309056985/html/17.html#page_middle. Biological Effects NASA has invested much research effort into the biological effects of the radiations in space. Protons: RBE close to 1 Biological effects fairly well known GCRs: Fluence is low Biological effects are poorly understood May represent the greatest risk Galactic Cosmic Rays Fluence rate, outside the earths magnetic field ? 4 protons/cm 2 /sec ? 0.4 helium ions/cm 2 /sec ? 0.04 HZE particles/cm 2 /sec For a 100 μm 2 nucleus, every cell nucleus in the body would be hit by: ? a proton once every 3 days ? a helium ion once every month ? an HZE particle once per year NASA’s Dilemma Image removed. Shielding Image removed. Figure 1.3 in [SSB-Space Station]. See http://books.nap.edu/books/0309068851/html/10.html#page_top. The risk to astronauts Astronauts inside a spacecraft are shielded The risk is to astronauts outside the spacecraft, or on the surface of the Moon or Mars Image removed. Figure 2.3 in [SSB-Crew Hazards]. See http://books.nap.edu/books/0309056985/html/16.html#pagetop. Early Biological Effects of Radiation Radiation Sickness ? Occurs within a few hours ? Nausea, vomiting ? Doses: > 1 Sv in less than 1 day Acute Radiation Syndrome ? Occurs within 2-4 weeks ? Bone marrow suppression doses: 1.5-2.0 Sv ? Lethal doses (whole-body) 10% at 3 Sv; 90% at 4 Sv (with no countermeasures Skin ? Erythema (reddening) occurs at about 6 Gy ? 15-20 Gy will cause moist desquamation Hair loss ? At doses of ~ 6 Gy or higher Early effects are unlikely unless an astronaut is exposed while in a non- shielded environment. Late Biological Effects of Radiation Cancer CNS damage Cataracts: threshold 1.5-2 Gy low-LET (protons similar to low-LET, data in primates) Late effects are the major concern following exposure to radiation during spaceflights Damage to the CNS HZE effects in the CNS Premature aging? Experiments underway in rats Image removed. Figure 2.7 in [SSB-Crew Hazards]. See http://books.nap.edu/books/0309056985/html/25.html#page_top. Shielding Source: NASA. “Cosmic Rays.” [updated 25 Nov 2001, cited 29 March 2004] http://www-istp.gsfc.nasa.gov/Education/wcosray.html Track structure of a cosmic ray collision in a nuclear emulsion. Image removed. Shielding GCRs present the greatest shielding problem Image removed. Shielding of GCRs Shielding …can make matters worse! Image removed. Figure 2.5 in [SSB-Crew Hazards]. See http://books.nap.edu/books/0309056985/html/17.html#page_middle. Shielding of GCRs Image removed. Figure 3.1 in [SSB-Crew Hazards]. See http://books.nap.edu/books/0309056985/html/37.html#page_top. Mission to Mars Shielding for SPEs must be part of the design Images removed. “Mars TransHab vehicle concept” Mission to Mars Characteristics of the inflatable wall and pantry shielding Mission to Mars Slides with images removed. “Mars TransHab vehicle” Exposure limits for Astronauts NCRP (1989) Limits for organ dose equivalents (Sv) for low earth orbit exposures Blood Forming Organs Skin Lens of the eye Career 1-4 6 4 Annual 0.5 3 2 30 days 0.25 1.5 1 [Average annual background dose to general population is 0.0036 Sv (360 mrem).] Mission to Mars Summary of dose equivalent (cSv) estimates for TransHab inflatable concept Exposures to Astronauts Whole-body dose equivalent (mSv) measured by shuttle passive dosimetry in low-inclination orbits. [Annual background is ~3.6 mSv] Exposures to Astronauts Apollo: 5-12 days 160-1140 mrad 0.01 Sv Skylab: 20-90 d 1.6-7.7 rad 0.08 Sv Shuttle: 3.2 cGy 0.003 Sv/d (highest, Hubble repair) MIR (144 – 468 uGy/day) 0.0005 Sv/d ISS (~0.5 – 2.5 mGy/day 0.0025 Sv/d Mars mission bone marrow 60-130 cSv* *Exceeds the LEO limit for bone marrow of 50 cSv/y Average annual background dose 0.0036 Sv Summary The radiation risks to astronauts are real. NASA is currently investing in radiation biology experiments using high energy Fe ions. [High dose rate as opposed to the low dose rate in space.] The biological effects of GCRs are still largely unknown.