Deployed Magnetic Shielding for Long Duration Spaceflight

Transcription

1 Deployed Magnetic Shielding for Long Duration Spaceflight Darin Knaus, Ph.D. Creare Inc., Hanover, NH Copyright 2005 MTG xx xx xxxx / #### 1

2 Creare Overview Founded 1961 by a group of Dartmouth researchers Owned by a partnership of engineers ~100 employees Multiple spin off companies Primary business areas Cryogenics Biomedical Fluid Dynamics, Heat Transfer Advanced Manufacturing Sensors and Controls Software and Data Systems MTG xx xx xxxx / #### 2

3 Spaceflight Research at Creare Bioastronautics Cryocoolers Power generation Radiation Shielding Urinary calcium monitoring ISS hearing assessment DCS risk for EVA MTG xx xx xxxx / #### 3

4 DISCLAIMER This is a controversial topic Human have never traveled beyond LEO for long durations All shielding concepts are merely concepts The validity of any approach depends on: NASA s mission is moving target For a recent discussions see Mission profile Spacecraft architecture Operational constraints Acceptable risk Eugene Parker, Shielding Space, Scientific American, March 2006 Jay Buckey, Next Stop Mars, The Scientist, 19(6):20, March 2005 MTG xx xx xxxx / #### 4

5 Roadmap The radiation environment in space presents significant risks that must be addresses in order to enable long duration space travel Current technology cannot solve the radiation problem for some missions Active shielding is a radical approach that could potentially solve the radiation problem Radiation environment on Earth and in space Radiation risk Current technology: passive shielding Active shielding approaches MTG xx xx xxxx / #### 5

6 Radiation Dose Units The SI unit for absorbed dose is the Gray (Gy) SI unit for dose equivalent is the Sievert (Sv) Dose Equivalent (Sv) = Q*N*Absorbed Dose (Gy) Purely physical unit describing energy deposition to matter 1 Gy = 100 rad Weighted unit used to estimate tissue damage 1 Sv = 100 rem Quality factor: Q Reflects the relative damage caused by different particles Electron Q = 1, Alpha particle Q = 20 Tissue factor: N Reflects relative sensitivity of different tissues to radiation Most sensitive tissues reproductive, colon, bone marrow MTG xx xx xxxx / #### 6

7 Radiation on Earth Radiation Dose (msv) Background from Space 2.4 Total Background 5.0 Chest CT Radiation Worker We enjoy shielding from the Earth s atmosphere and magnetic field Particles originating in space muons, neutrons and electrons (low Q) MTG xx xx xxxx / #### 7

8 Radiation Environment in Space Radiation Belts Solar Particles Galactic Cosmic Radiation Only a concern in orbit Solution: mission planning High flux, high energy protons Passive shielding effective Solution: early warning + shelter Low flux, high energy nuclei HZE GCR most damaging Passive shielding ineffective Solution:??? MTG xx xx xxxx / #### 8

9 Radiation Risk for Spaceflight Dose limits for space travel are based on risk Primary risk considered is carcinogenesis 3% increased lifetime cancer mortality typically used Radiation limits for LEO, Male (35) Most experience is for LEO HZE GCR present unique risks 500 msv/year, 1,000 msv/career Earth s magnetic field shields GCR Difficult to establish Q Non cancerous risks Non repairable cells: CNS MTG xx xx xxxx / #### 9

10 Passive shield thickness typically expressed in units g/cm2 Low molecular weight materials more effective for GCR than high Typical hull thickness 1 cm Al (2.7 g/cm2) Significant shielding unsatisfactory for typical Mars mission profiles Cucinotta et al., Managing Lunar and Mars Mission Radiation Risks, NASA/TP Mars surface mission Aluminum shielding Spallation Radiation Limits GCR Performance 2500 GCR Solar 2000 Radiation Dose (msv) Passive Shielding g/cm2 20 g/cm2 Hydrogen shielding reduces dose by ~50% MTG xx xx xxxx / #### 10

11 Passive Shield Analysis: CEV Current CEV plan is for 5 m diameter capsule, based on Apollo capsule At 20 g/cm2, shield mass approaches shuttle launch capability (~30,000 kg) Larger spacecraft will be required for Martian missions 20 g/cm2 is not adequate Increasing thickness has limited effect on GCR dose MTG xx xx xxxx / #### 11

12 Active Shielding Deflect particles using electric or magnetic fields Plasma and electrostatic approaches require large voltages (order kv) that make them generally impractical Superconducting technology enables magnetic approaches Two magnetic strategies: Confined Deployed Superconducting technology MTG xx xx xxxx / #### 12

13 Confined Magnetic Shield Analysis Field confined via torus, concentric spheres, cancellation Equation of motion for particle in magnetic field F = q (v x B) Larmor Radius Consider HZE GCR particle rl (m) = 3.33 R (GV) / B (T) Rigidity = Momentum / Charge 1 GeV/nucleon Fe nucleus R = 3.65 GV rl = 1.2 B = 10 T MRI magnet ~5 T MTG xx xx xxxx / #### 13

14 Issues with Confined Approach Habitability issues close to large magnetic field Interference with communications Interference with on board electronics Constraints on spacecraft architecture Quench risk Energy proportional to B2, order GJ for confined approach Alpha Magnetic Spectrometer 0.8 T, LTSC magnet for ISS MTG xx xx xxxx / #### 14

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16 Overview of Deployed Approach Spatial dimension is large, so that small bending radii can still miss spacecraft B is not constant such that Larmor analysis does not apply Störmer studied the polar auroras Störmer defined characteristic dimension protected by the field of a magnetic dipole rst (M/R)1/2 For current loop, M = NIA N I rcoil2 M = Magnetic Moment of Dipole MTG xx xx xxxx / #### 16

17 Störmer Analysis Consider 1 GeV/nucleon Fe nucleus (R = 3.65 GV) rst = 5 m Assumes 120 A HTS wire (commercially available) B value is for loop axis Mass calculation based on HTS wire only rcoil (m) I N (turns) B B m (kg) MA 1,750, T 130 kg 560, MA 17, mt 130 G 56,000 1, ka µt 130 mg 5,600 10, A 2 13 pt 0.13 mg 650 MTG xx xx xxxx / #### 17

18 Advantages of Deployed Approach Benefits Challenges No spallation radiation Rigidity cutoff can theoretically be set anywhere Minimal energy requirement Reasonable mass requirement for large shield Storage/deployment/retraction of coil HTS cooling Redundancy Structural/control issues for maneuvers, external disturbances (spacecraft only) MTG xx xx xxxx / #### 18

19 Cooling Overcoming Challenges HTS temperatures currently ~70 K Selective emitter coatings have been proposed Orientation dependent Active cooling strategies Inflatable structures Deployment NASA Tethered Satellite System 250 m, then jammed Shield stored on spool for launch Deployment in LEO B induces hoop stress to aid deployment MTG xx xx xxxx / #### 19

20 Solar Magnetic Sails Zubrin primary champion Interaction of solar wind and magnetic field imparts acceleration on spacecraft Acceleration is very small (order mm/s2) but is continuous 10 mm/s2 over 6 days results in final velocity of 18,000 km/hr (5g rocket over 100 sec) Cosmos 1 (non magnetic) Private launch 2005 Russian submarine! Launch failure MTG xx xx xxxx / #### 20

21 Lunar Surface Applications GCR dose for lunar surface 50% of deep space In a habitat, astronauts can be well protected by creating large thickness regolith barriers During EVA/surface exploration, astronauts will be exposed Applications include large area shielding and shielding rover vehicles MTG xx xx xxxx / #### 21

22 Selected References Buckey, J.C., Radiation Hazards: Establishing a Safe Level, Space Physiology, Oxford University Press, New York, in press Cocks, F.H., A Deployable High Temperature Superconducting Coil (DHTSC): A Novel Concept for Producing Magnetic Shields Against Both Solar Flare and Galactic Radiation During Manned Interplanetary Missions, J. British Interplanetary Soc., Vol. 44, 1991, pp Cocks, J.C., Watkins, S.A., Cocks, F.H., Sussingham, C., Applications for Deployed High Temperature Superconducting Coils in Spacecraft Engineering: A Review and Analysis, J. British Interplanetary Soc., Vol. 50, 1997, pp Curtis, S.B., Vazquez, M.E., Wilson, J.W., Atwell, W., Kim, M., Capala, J., Cosmic Ray Hit Frequencies in Critical Sites in the Central Nervous System, Advanced Space Research, Vol. 22 No. 2, 1998, pp Hilinski, E.J., Cocks, F.H., Deployed High Temperature Superconducting Coil Magnetic Shield, J. Spacecraft, Vol. 31, No. 2, 1993, pp Landis, G.A., Magnetic Radiation Shielding: An Idea Whose Time Has Returned? Space Manufacturing 8: Energy and Materials from Space, AIAA, 1991, pp Letaw, J.R., Silberberg, R., Tsao, C.H., Radiation Hazards on Space Mission Outside the Magntosphere, Adv. Space Res., Vol. 9, No. 10, 1989, pp Levy, R.H., Radiation Shielding of Space Vehicles by Means of Superconducting Coils, ARS Journal, Nov 1961, pp Masur, L.J., Kellers, J., Li, F., Fleshler, S., Podtburg, E.R., Industrial High Temperature Superconductors: Perspectives and Milestones, IEEE Trans. Applied Superconductivity, Vol. 12, No. 1, Mar 2002, pp Simonsen, L.C., Nealy, J.E., Radiation Protection for Human Missions to the Moon and Mars, NASA Technical Paper 3079, Feb Simonsen, L.C., Nealy, J.E., Townsend, L.W., Wilson, J.W., Space Radiation Shielding for a Martian Habitat, SAE Technical Paper , 20th Intersociety Conference on Environmental Systems, Williamsburg, VA, July 912, Sussingham, J.C., Watkins, S.A., Cocks, F.H., Forty Years of Development of Active Systems for Radiation Protection of Spacecraft, J. Astronautical Sciences, Vol. 47, No. 34, JulyDec 1999, pp Townsend, L.W., HZE Particle Shielding Using Confined Magnetic Fields, J. Spacecraft, Vol. 20, No. 6, 1983, pp Townsend, L.W., Nealy, J.E., Wilson, J.W., Large Solar Flare Radiation Shielding Requirements for Manned Interplanetary Missions, J. Spacecraft, Vol. 26, No. 2, 1989, pp Townsend, L.W., Wilson, J.W., Shinn, J.L., Nealy, J.E., Simonsen, L.C., Radiation Protection Effectiveness of a Proposed Magnetic Shielding Concept for Manned Mars Missions, SAE Technical Paper Series , 20th Intersociety Conference on Environmental Systems, Williamsburg, VA, July 912, Townsend, L.W., Overview of Active Methods for Shielding Spacecraft from Energetic Space Radiation, Physica Medica, Vol. 17, Sup. 1, 2001, pp Townsed, L.W., Fry, R.J.M., Radiation Protection Guidance for Activities in Low Earth Orbit, Advanced Space Research, Vol. 30, No. 4, 2002, pp MTG xx xx xxxx / #### 22