Study on the Survivability and Adaptation of Humans to ......Final Presentation ESTEC, 30 May 2001...

ESTEC, 30 May 2001Final Presentation

3100-1

HUMEX WP 3100

Study on the Survivability and Adaptation of Humans to Long-Duration Interplanetary and Planetary

Environments

WP 3100 Limiting Factors

for Human Health and Performance:Space Radiation

R. Facius, DLR, Cologne


3100-2

HUMEX WP 3100

Determinants of Radiation Hazards in Manned Space Flight

PRIMARY SPACERADIATIONSOURCES

RADIATIONTRANSPORT

THROUGHSHIELDING

SECONDARYRADIATION FIELD

INTERNALRADIATION Field

Parameters

SPACE FLIGHTENVIRONMENT

COUNTER-MEASURES

RADIATIONHEALTHEFFECTS

IN MANNEDSPACE FLIGHTBIOLOGICAL

RESPONSE


3100-3

HUMEX WP 3100

Determinants of Radiation Hazards in Manned Space Flight

GalacticHeavyIons

SolarParticleRadiation

.SPE

.solar wind

TrappedRadiation

Electro-magnetic

Electrons,M uons

Protons

Neutrons

HeavyIons(HZE-Particles)

ChargeSpectra

EnergySpectra

LinearEnergyTransfer(LET-)Spectra

Dose.physical,.effective

Micro Gravity

.direct/cellular interactions..metabolism..repair

.indirect effects

..immune system,..hormonal/..metabolic/..fluid shifts

ClosedEnvironment

Physical/PsychicalStress

Early Effects

.early mortality

..hematopoetic death

.early morbidity

..prodromal syndrom...fatigue,...aneurexia,...nausea,...diarrhea,...vomiting..erythema

.performance decrement

Late Effects.cancer..incidence,..mortality.cataracts,.hereditary

Avoidance.mission planning. - operation.shielding (shelter)

Surveillance.forecasting.dosimetry..physical..biological

Prophylaxis.drugs,.crew selection,.induced radiation resistance (adaptive response)

Therapy.drugs

PlanetaryMagneticFields

MassShielding

.external masses

.body self- shielding

PRIMARYSPACE

RADIATIONSOURCES

RADIATIONTRANSPORT

THROUGHSHIELDING

SECONDARYRADIATION

FIELD

INTERNALRADIATION

FIELDPARAMETERS

SPACE FLIGHTENVIRONMENT

COUNTER-MEASURES

RADIATIONHEALTH EFFECTS

IN MANBIOLOGICALRESPONSE

Dose/FluenceResponseFunctions

BiologicalWeighting-,(Quality-)Factors

Single(HZE-)ParticleEffects


3100-4

HUMEX WP 3100

External Radiation Sources: Temporal Dose Rate Profile

Acute component:3 protons (mainly) and ‘heavy’ ions from Solar Particle Events, SPE3 ‘moderate’ energies â mass shielding effective 3 time of occurrence, particle composition, energies and intensities unpredictableý early - potentially lethal - radiation injuries Chronic component:3 Galactic Cosmic Rays, GCR ( ions H - Fe )3 high energies â mass shielding ineffective3 particle composition, energies and intensities and temporal variation sufficiently well known/predictableý late mortality from radiogenic cancer


3100-5

HUMEX WP 3100

External Radiation Sources: Galactic Heavy Ions (HZE particles)

Galactic Cosmic Rays, GCR:3 steady and isotropic fluxes in interstellar space3 fully ionised ions

≈ 87% H, 12% He, 1% heavy ions up to Fe ( U )3 energies up to 1000 GeV/n (and beyond) 3 ion fluxes attenuated by solar wind at energies

below ≈ 50 GeV/n3 peak fluxes at 1AU, free space during quiet sun:

H ≈ 2*105 ions / ( year & cell-nucleus )Fe ...≈ 60 ions / ( year & cell-nucleus )

3 peak fluxes during maximum solar activity lower -by factors of about 5 to 7 ( H ) - than during quiet sun

3 total fluxes lower by about a factor of 4

3 fluxes increase with larger distance from the sun


3100-6

HUMEX WP 3100

External Radiation Sources: Solar Particle Events

3 SPE frequencies roughly evenly distributed between years 2 to 11 of solar cycle

3 large or giant ‘killer flares’ (>1010 H/cm2 >10MeV) usually occur around maximum solar activity

3 individual event duration from about half a dayto a few days

3 rise time to peak fluxes from 2 hours to half aday

3 short term forecasting of occurrence of individual events moderately successful

3 forecasting of event ‘severity’ – fluences, charge- and energy spectra and temporal profile impossible

3 probabilistic long term modelling improving, mainly due to increase of observational data base


3100-7

HUMEX WP 3100

External Radiation Sources: Worst case SPE3 SPE from Feb. 23rd 1956 produced the by far largest neutron ground event ever

3 time profile, charge and energy spectrum characterise a radiobiological ‘severe’ event

3 SPE from Sept. 29th, 1989 matches closely Feb. 1956 SPE ( time profile, charge and energy spectrum )

3 Sep. 1989 ground event 10X smaller than Feb. 1956 ground event

è an ‘artificial’ SPE with 10x the flux of the Sept. 29th 1989 SPE constitutes the presently best approximation to a worst case SPE

3 event frequency 2.2 *10-2 a-1

= 1! event per 46 years

95% (binomial) confidence limits: 1-in-8 to 1-in-1818 years

h

E / MeV/n


3100-8

HUMEX WP 3100

Radiation Transport through Mass Shielding: Shielding Distributions

3 body self shielding protects blood forming organs, BFO with ≈15 Al cm-2 equivalent tissue; median value for skin is about 3 to 4 g cm-2..

30.3, 1, 5, and 10 g cm-2 typical for spacesuit, pressurised vehicle, equipment room (Space Lab) or prospected ‘radiation shelter’ respectively

3 ≈ 50 (outbound) and 40 (inbound) g cm-2

necessary to meet LEO limits for worst case exposure during Mars mission

3 complete, realistic mass distribution functions of vehicles and habitats required for realistic predictions of mission exposures.

3 efficacy of mass shielding against galactic radiation is poor compared to SPE particles due to dose build-up from secondary radiation

3 optimal ‘material’ for attenuation of heavy ion doses is Hydrogen since build-up is minimised.


3100-9

HUMEX WP 3100

Whole Body/Organ Exposure: Biologically Effective Dose, H

3 Linear Energy Transfer, LET, is taken as unifying physical parameter for radiation weighting/ quality factor Q(L) of ionising radiation of any quality

3 biologically effective, equivalent dose H for any mixture of ionising radiation:

H = ∫ Q(L)*D(L) *dL = c*∫ Q(L)*(-L*δΦ(L)/δ L) * dLL : Linear Energy Transfer

D(L): distribution in dose of LΦ(L): integral distribution in fluence of L

3 Q(L) with respect to cancer mortality is expert committee decision

3 measured/calculated LET spectra in an organ are considered sufficient to determine biologically effective, equivalent organ dose of any radiation field


3100-10

HUMEX WP 3100

Whole Body/Organ Exposure: Chronic Galactic Radiation Doses

Reference Scenario Galactic Cosmic Ray BFO Equivalent Doses / Sv

Reference homogeneous Al shield thickness

Solar Mission 1 g cm-2 5 g cm-2 10 g cm-2

Activity ‘pressure vessel’ ‘equipment room’ ‘radiation shelter’

Moon 190d 0.195 0.177 0.161Minimum Mars 450d 0.828 0.754 0.687

Mars 947d 0.993 0.918 0.852

Moon 190d 0.074 0.070 0.066Maximum Mars 450d 0.317 0.299 0.280

Mars 947d 0.420 0.383 0.364

NCRP (NASA) organ dose limits in Sv for Low Earth Orbitmissions (age and gender averages)

skin lens BFO#

career limits 6.0 4.0 T §

annual limits 3.0 2.0 0.5030 day limits 1.5 1.0 0.25

#: Blood Forming Organs §: male: T / cSv ≈ (age/a - 30)*7.5 + 200, female: T / cSv ≈ (age/a - 38)*7.5 + 200

3Mars mission around solar max reduces GCR dose by a factor of ≈ 2.5

310X heavier shield spares at most 15% to 20%

3lunar missions never collide with LEO BFO limits for cancer mortality

3career limits for life time lunar ‘colonists’ no serious constraint

3Mars mission during solar max comply with LEO constraints even in lighter shielded habitat

3Mars missions during solar min infringe BFO limits even in a heavier shielded habitat

3limits for early effects in the skin or the ocular lens will not be touched in any of the scenarios


3100-11

HUMEX WP 3100

Whole Body/Organ Exposure: Acute, Worst Case SPE Doses

'Worst$ case' SPE radiation exposures in Sv

Space suit (0.3)# Pressure vessel (1) Radiation shelter (10)

Skin Lens BFO Skin Lens BFO Skin Lens BFO

free space295. 81.3 4.21 64.4 35.5 3.52 2.62 2.43 1.26

lunar surface147. 40.6 2.11 32.2 17.8 1.76 1.31 1.22 0.63

Martian surface0.45 0.44 0.32 0.44 0.42 0.31 0.33 0.32 0.25

$: 1956 February 23rd event ≈10X flux of 1989 September 29th event., #: g cm-2 Al

NCRP (NASA) organ dose limits in Sv for Low Earth Orbitmissions (age and gender averages)

skin lens BFO#

career limits 6.0 4.0 T §

annual limits 3.0 2.0 0.5030 day limits 1.5 1.0 0.25

#: Blood Forming Organs §: male: T / cSv ≈ (age/a - 30)*7.5 + 200, female: T / cSv ≈ (age/a - 38)*7.5 + 200

3

3planetary/lunar surfaces halve SPE dose3only on Mars, event doses in shelter will comply with 30 day exposure limits3SPE doses in space suits or normal pressure vessels constitute severe radiation accidents 3even behind 5 g cm-2 shielding of an equipment room, worst case event doses are sufficiently high to provoke symptoms of early radiation injury è mission design/planning must ensure that shelters of sufficient thickness are accessible in time to escape the bulk dose of such an event, in particular during solar min missions


3100-12

HUMEX WP 3100

Effects from whole Body/Organ Exposure: Late Effects, Cancer Mortality

Average Excess Relative Risk(all cancers)

ERR = 4 *10-2 Sv-1

Conditions for Dose-Effect Curve on Late Cancer Mortality$

exposureparameters

A-bomb Exposure Space Exposure

dose rate,duration

instantaneous/acute,seconds

GCR: chronic/protracted,months – years; SPE:acute, hours-days

radiationquality

low LET gamma rays most complex mixture ofdisparate radiationqualities conceivable

bodydistribution

essentiallyhomogeneous

depending on externalshielding, inner organslargely homogeneous

exposedpopulation

common age-,gender- health status-distribution

selected for physical/psychic prowess, age,and health

environmentalconditions

normal terrestrial microgravity, confinedecological system,artificial/technicalcomponents dominating

§: Data Base: atomic bomb survivor epidemiology


3100-13

HUMEX WP 3100

Effects from ACUTE whole Body/Organ Exposure: Early Radiation Injury

Conditions for Dose-Effect Curves for Early Radiation Sequelae$

from SPE Exposures#

exposureparameters

Accidental/TherapeuticExposure

Space Exposure

dose rate,duration

instantaneous/acute,protracted, seconds toweeks

SPE: acute, hours-days

radiationquality

low LET gamma raysand electrons, alphaparticles, neutrons

most complex mixture ofdisparate radiationqualities conceivable

bodydistribution

in accidents usuallyhomogeneous, selectedorgans only in therapy

strongly inhomogeneousdue to body self-shielding

exposedpopulations

healthy workers orailing patients

selected for physical/psychic prowess, age, andhealth

environmentalconditions

workplace or hospital microgravity, confinedecological system,artificial/technicalcomponents dominating

§: Data Base: radiation accidents, therapeutic exposures#: GCR probably below threshold


3100-14

HUMEX WP 3100

Effects from ACUTE whole Body/Organ Exposure: Performance

Performance contours: tank commander

4 Data base for dose and time dependent performance decrements: 1- dose response functions for early radiation sequelae after

instantaneous, whole body exposure (nuclear battlefield)2- dose dependent temporal profiles of symptom severity3- questionnaires filled in by military personnel of various

assignments

4 Performance decreases indirectly due to symptoms of acute radiation sequelae ( fatigue, nausea, vomiting, diarrhea, cateracts, erythema

4 Performance decrement profiles are task dependent

4 Distribution of symptoms after SPE exposure is significantly different than that after homogeneous whole body exposures

è If SPE exposures above threshold ( 0.2 ... 0.7 Gy for prodromal syndrom symptoms, 1 ... 2 Gy for lens opacification, 2 to 5 Gy for skin erythema ) cannot strictly be excluded by mission design, a re-evaluation will be necessary

4 Integrated Performance Modelling may provide advanced tools for solving this task


3100-15

HUMEX WP 3100

Interactions between Space Environmental Factors and Radiation

psychic stress

microgravity

4 response to radiation of most ‘high level’ physiological systems has been investigated in mammals

4 their response in many cases is coupled directly, in most cases at least indirectly to related systems.

4 some of them are directly affected by stress factors of space flight, e.g., microgravity or even psychic stress

è pathways exist, along which space flight environment could modify expression of radiation effects


3100-16

HUMEX WP 3100

Interactions between Space Environmental Factors and Radiation

4 most major physiological systems have to adapt to microgravity

4 many systems settle to a new equilibrium 0-g set-point different from the 1-g set-point

4 in particular, cellular oxidative stress is enhanced during weightlessness

4 reactive oxygen/radical species are important intermediate substances which transmit/transform physical radiation damage into biological damage

4 most cellular mechanisms - including repair mechanisms - are under endocrine control

è until the opposite can be demonstrated, the expression of final radiobiological endpoints is likely to be altered under long term microgravity


3100-17

HUMEX WP 3100

Countermeasures ⇒ Minimisation of Radiation Health Effects

3develop risk criterium appropriate for exploratory LONG term Missions3integrate risks assessment of radiation hazards in a risk analysis3reduce uncertainties for exposure estimates3reduce uncertainties for dose effect relations (late & early)

3 optimise shielding design ( material & thickness ) 3 optimise mission design

å durationå timeline relative to solar activity cycleå guarantied shelter accessibility

3 advance forecasting capabilities for solar particle events3 monitor and document

å exposure historyå health status

1. Improve advance risk assessment

2. Minimise Radiation Exposure

3. Maximise Radiation Resistance

3 select genetically resistant individuals3 modify dose response curve of ‘normal’ crew members

å attenuate early effects by prior and post medicationå mitigate late effects by prophylactic nutrition


3100-18

HUMEX WP 3100

Research/Development : For Improved Risk Assessment - 1

¶ Elaborate Approach for Integrating Radiation Risk Assessment into Total Mission Risk Analysis

3 contrive the expectation value for Healthy Lifetime Lost (HLL) as safety design criterium

· Improve Exposure Estimates for Given Mission Scenarios

3 establish distribution function for radiation dose received from SPE for given mission scenario3 establish dependence of cosmic ray fluxes on solar distance for interplanetary missions3improve/validate radiation transport codes

å integrate secondary neutron contribution from thick shields into equivalent dose estimateså verify computed doses with dose measurements

3 in human phantoms and model shields exposed toå accelerated heavy ionså in situ space radiation (ISS)


3100-19

HUMEX WP 3100

Research/Development : For Improved Risk Assessment - 2

¸ Improve Reliability of Radiation Dose Response Estimates

3 establish dose response function for early radiation sequelae from acute SPE exposure3 determine time profile of critical performance decrement as function of SPE dose

å re-analyse response to specific distribution of acute SPE radiation symptoms3 establish probability for excess late cancer mortality / morbidity

as function of mission dose and ageå in tissue culture and small animal experiments at relevant doses

(Biostack/microbeam experiments)

¹ Check Aptitude of Terrestrial Dose Response Functions for Space Environment/Radiation

3 lifetime studies of small animal populations under exposure to space radiation on ISS (and lunar habitats)

å launch feasibility study on suitable test animals and population sizes4 supervise long term space crews’ health for their entire lifetime to estimate

upper bounds of risk


3100-20

HUMEX WP 3100

Research/Development : For Minimisation of Radiation Exposure -1

Ê Optimise Shielding Design

3 establish minimum mandatory shelter volume, mainly from psychological constraints3 minimise necessary shield weight

å study availability of consumables and (irrecoverable) wastes for shielding purposeså maximise fraction of low atomic number materials (ideally hydrogen)

3 trade off between structural constraints and radiation build up

Ë Optimise Mission Design

3 minimise mission duration subject to mission objectiveå maximise speed of interplanetary transfer by advanced propulsion techniques

3 chose timeline relative to solar activity cycle to minimise probability for killer SPEs

3 minimise access time to radiation shelter in case of SPEå limit distance from or increase transport velocity to stationary shelter during high solar activity

å provide mobile shelters

å provide equipment/material for fast in situ shelter construction


3100-21

HUMEX WP 3100

Research/Development : For Minimisation of Radiation Exposure -2

¸ Advance Solar Flare Forecasting Capabilities

3 maximise advance alert timeå advance our grasp of stellar/solar physical mechanisms of SPE development

å enlarge quantity and quality of solar observations to improve probabilistic modellingå increase observational coverage of the solar surface

¹ Monitor and Document Radiation Exposure

3 for operational as well as for curative purposes

å record physical characteristics of ambient radiation field as comprehensive as feasible (charge and energy spectra instead of equivalent dose)

å advance biological test systems for in situ on line monitoring of

biologically weighted radiation doseså supervise immunological, oxidative and karyotypic status of crew members

during and after missions

3 adapt and advance terrestrial assays to applicability in microgravity space


3100-22

HUMEX WP 3100

Research/Development : For Maximisation of Radiation Resistance

¶ Select Resistant Individuals

3 study inter-individual variation of radiation resistance

å of mammalian/human cells in vitro/in vivo

3 with respect to survival/apoptosis, mutations, transformation, cancerogenesis

3 explore the genome of individuals with elevated resistance

for genetic markers associated with that phenotype

3 screen genome of applicants for genetic markers known to be associated with elevated susceptibility to early or late radiation injuries

· Modify Dose Response Functions of ‘Normal’ Crew Members

3 attenuate early effects by prior and post irradiation medication

å screen common on-board medication for therapeutic efficacy against early radiation sequelae

å evaluate applicability of known radioprotective drugs for side effects

tolerable in accidental SPE overexposures

3 suppress late effects by prophylactic nutrition

å improve assays for appraisal of oxidative status of tissues

å ascertain efficacy of established anti-oxidant nutrients in HEF studies

Study on the Survivability and Adaptation of Humans to ......Final Presentation ESTEC, 30 May 2001...

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