Dosimetry for Interplanetary Missions: The Geant4 REMSIM Application

1. Moon habitat www.ge.infn.it/geant4/space/remsim guatelli@ge.infn.it Dosimetry for Interplanetary Missions:the Geant4 REMSIM applicationS. Guatelli1, P. Nieminen2, M.G. Pia1 IEEE NSS, October 2004, Rome, Italy Talk by S. Guatelli 1. INFN Genova, Italy, 2. European Space Agency, ESTEC, The Netherlands

2. A project in the European AURORA programme for the robotic and human exploration of the Solar System Mars, theMoon and the asteroids as the most likely targets The radiation hazard to crew is critical to the feasibility of interplanetary manned missions To protect the crew: shieldingmust be designed, the environment must be anticipated and monitored, a warning system must be put in place Vision • First quantitative evaluation of the effects of space radiation environment on astronauts • in vehicle concepts for interplanetary missions • in planetary surface habitats Scope of the Geant4 REMSIM simulation

3. Modeling the interplanetary space radiation Modeling the vehicle concepts and surface habitats Modeling the physics interactions Results First quantitative dosimetry in vehicle and surface habitats Outline

4. The adoption of a rigorous software process guarantees reliability Essential for mission critical software application Iterative and incremental approach First study to evaluate the conceptual possible solution The Rational Unified Process (RUP) has been adopted as process framework Sound industrial standard Equivalent to ISO 15504, level 3 at least Software process

5. Model of the radiation environment according to current standards Geant4 based simulation for radiation effects Dosimetric analysis in a phantom Vehicle concepts • Simplified geometrical configurations Surface habitats Essentialcharacteristics for dosimetric studies kept Electromagnetic physics + hadronic physics Strategy • Physics processes

6. Selected space radiation components: Galactic Cosmic rays Protons, α particles and heavy ions (C -12, O -16, Si - 28, Fe - 52) Solar Particle Events Protons and α particles Space radiation environment Worst case assumption for a conservative evaluation Envelope of CREME96 October 1989 and August 1972 spectra GCR: p, α, heavy ions SPE particles: p and α At 1 AU At 1 AU Envelope of CREME96 1977 and CREME86 1975 solar minimum spectra

7. New and alternative vehicle design with respect to hard shell Habitat: inflatable Habitation Module(K.J. Kennedy, NASA JSC, AIAA 2002-6105) composed by a hard central core and an inflatable exterior shell transportation module to Mars waiting on orbit around Mars transport back to Earth SIH (Simplified Inflatable Habitat) is a multilayer consisting of: • MLI: external thermal protection blanket - Betacloth and Mylar • Meteoroid and debris protection - Nextel (bullet proof material) and open cell foam • Structural layer - Kevlar • Rebundant bladder Polyethylene, polyacrylate, EVOH, kevlar, nomex Materials and thicknesses of the SIH by: V. Guarnieri, C. Lobascio, P. Parodi, R. Rampini – ALENIA SPAZIO,Torino, Italy The Geant4 geometry model retains the essential characteristics of the vehicle concept relevant for a dosimetric study Vehicle concepts

8. Example: surface habitat on the Moon Cavity in the Moon soil + covering heap Surface Habitats Moon soil Engineering model by V. Guarnieri, C. Lobascio, P. Parodi, R. Rampini – ALENIA SPAZIO,Torino, Italy The Geant4 model retains the essential characteristics of the vehicle concept relevant for a dosimetric study

9. Hadronic Physics for protons and α as incident particles • Set of Geant4 hadronic models covering the energy range of interest • For protons two alternative approaches: Bertini and Binary Cascade in the intermediate energy range • Precompound and nuclear deexcitation at low energy • Quark Gluon String Models at high energy Physics processes • E.M. Physics • Geant4 Low Energy Package for p, α, ions and their secondaries • Geant4 Standard Package for positrons • Validation of the Geant4 e.m. physics processes with respect to protocol data • See: • N42-1 Validation of Geant4 Electromagnetic Physics Versus Protocol Data

10. SIH + no shielding SIH + 10. cm water / polyethylene shielding SIH + 5. cm water / polyethylene shielding 2.15 and 4. cm thick aluminum structure (conventional engineering design) vacuum air GCR p GCR p SIH + 5. cm water / polyethylene 2.15 cm al 4. cm al GCR particles SIH + 5 cm water SIH +10. cm water / polyethylene SIH +10. cm water shielding Phantom: water box Energy deposit (MeV) with respect to the depth in the phantom (cm) Multilayer - SIH Dosimetric analysis of SIH vehicle concept Configurations SIH Geant4 model The energy deposit is calculated for all the GCR components (p, α, C - 12, O - 16, Si - 28, Fe - 52 ions)

11. SIH + no shielding Preliminary ! GCR (all ion components) p 4. cm Al SIH + 10. cm water O - 16 C - 12 α 2.15 cm Al SIH + 5. cm water e.m. physics e.m. + hadronic physics – bertini c. e.m. + hadronic physics – binary c. Fe - 52 Si - 28 cm Dosimetric analysis of SIH vehicle concept Preliminary ! Calculation of the equivalent dose (mSv/day) with respect to the depth in the phantom (cm) Total equivalent dose in the phantom (mSv/day) with respect to the thickness of the shielding • Thicker layer of shielding limit the exposure of the astronaut to the GCR • Water and polyethylene have the equivalent shielding behaviour • The hadronic contribution to the dose calculation is relevant

12. vacuum Shelter air vacuum SPE energy deposit (MeV) in the phantom with respect to the depth (cm) SIH + 10 cm water SPE energy > 300 MeV SPE p Phantom Multilayer (28 layers) SPE α GCR and SPE particles SIH SPE shelter model • When SPE particles are detected by a warning system, the crew moves into the shelter Total equivalent dose in the phantom given by GCR: • 4.98 mSv/day – e.m. physics • 7.83 mSv/day – e.m. + hadronic physics – bertini c. • 7.41 mSv/day – e.m. + hadronic physics – binary c. Preliminary ! Shelter Geant4 model Geant4 model

13. Worst case (no roof) Add a log on top with variable height x 0.5 m 1.m vacuum Moon soil 1.5 m 2.m 2.5 m 3. m SPE p – no roof x GCR and SPE beam SPE α– no roof SPE p – 3.m thick roof SPE α – 3 m thick roof e.m. physics e.m. + hadronic physics – bertini c. e.m. + hadronic physics – binary c. Dosimetry in surface habitats Total equivalent dose (mSv/day) in the phantom with respect to the roof thickness (m) Preliminary ! Phantom x = roof thickness - can vary between 0. m and 3. m Energy deposit (MeV) given by SPE with respect to the depth in the phantom (cm) SPE with energy > 300 MeV

14. A first quantitative study has been performed in a set of vehicle and surface habitats Simple geometrical configurations representing the essential features of vehicle concepts moon surface habitats An innovative concept of Inflatable Habitat offers similar radioprotection behaviour as a conventional aluminum structure with significant engineering advantages Water and polyethylene have equivalent shielding effects Water shelter is effective in shielding dangerous SPE A surface habitat built out of local material looks a possible solution thickness to be optimised Preliminary dosimetric analysis to be further refined Conclusions

15. Thank you !