Space Radiation Health Operations: From LEO to Beyond

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Space Radiation Health Operations From LEO to
Beyond A Steve Johnson1, William Murtagh2, Tom
Lin1 and Mark D. Weyland3 1Lockheed Martin, NASA
Space Radiation Analysis Group, Johnson Space
Center 2 Space Environment Center NOAA 3 NASA
Space Radiation Analysis Group, Johnson Space
Center
Space Radiation Health Operations From LEO to
Beyond A Steve Johnson1, William Murtagh2, Tom
Lin1 and Mark D. Weyland3 1 Lockheed Martin,
NASA Space Radiation Analysis Group, Johnson
Space Center 2 Space Environment Center NOAA 3
NASA Space Radiation Analysis Group, Johnson
Space Center
SOHO (ESA NASA)
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• Energetic Solar Particle Event
• Flux of the 100 MeV protons exceed 1 pfu
• Both 100 and 10 MeV protons elevated
• These are the well known Large events
• Prompt SEP effect onset minutes to an hour
• Usually 100 MeV protons peak w/in first 12
  hours
• Usually 10 MeV protons peak about a day later
  w/CME shock arrival (ESP)
• Difficult to predict and rapid onset Major
  operational challenge
• Internal and External Hazard

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• Low Energy Solar Particle Event
• Flux of the 10 MeV protons exceed 10 pfu
• For purposes of this discussion these events will
  be defined as 10 MeV only events
• Generally delayed CME Arrival
• 10 MeV peak fluxes usually 2 magnitudes lower
  than during Energetic SPEs
• Due to delay in arrival, these events are easier
  to address operationally
• Visual verification and radio signatures reliable
  indicators of inbound event
• Cannot assess magnitude but advanced warning
  facilitates EVA Rescheduling
• This class of events will not be addressed here
• Primarily an EVA Hazard

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Solar Particle Event Flux of the 10 MeV
protons exceed 10 pfu Primarily an EVA Hazard
Energetic Solar Particle Event Flux of the 100
MeV protons exceed 1 pfu Generally prompt SEP
effect Internal and External Hazard Current
Operational Recall 24 hr coverage
X-RAYS
Protons
GOES Data, NOAA SEC
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100 MeV events since beginning of ISS Events
requiring continuous Operations Coverage
SPE 1 pfu _at_ 100 MeV
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100 MeV Events Solar Cycle 23 All Cycle 23 Events
that meet Operational Coverage Criteria
SPE 1 pfu _at_ 100 MeV
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Oct 28
29 Oct 03
28 Oct 03
4 Nov 01
8 Nov 00
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Part 1
ISS EVA Mission Rules Part I
Risk from additional radiation exposures compared
to the risk incurred by going EVA is low enough
to support continuing an EVA already in
progress Replanning will be more aggressive,
including accepting future timeline impacts.
Delay the EVA up to 14 days to allow the
increased radiation environment to subside and/or
delayed or accelerated by 1-2 revs to precess out
of the enhanced radiation areas The risk from
this level of radiation exposure/risk compared to
the risk incurred by going EVA is low enough to
support continuing an EVA already in progress.
Consider delaying the EVA up to 2 days or
delaying or accelerating egress 1-2 revs. An EVA
in progress will continue. Consider not adding
unscheduled items to existing timeline. Delay
EVA up to 14 days if still possible to accomplish
mission objectives, or delay or accelerate egress
1-2 revs. An EVA in progress will continue.
Consider expediting tasks not required for
primary mission objectives.
For predicted exposure less than 0.5 rad above
the mission projected exposure Predicted crew
exposure greater than 0.5 rad above the mission
projected exposure at the end of the EVA
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ISS EVA Mission Rules Part II
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Apollo Mission Rules Part I
Mission Phase
Comment
Rule
Condition
Major Solar Flare has been Predicted
All
Continue Mission
Major Solar Flare has Occurred
Unconfirmed Particle Event Has Occurred
All
Continue Mission
Confirmed Particle event and SPAN or real-time
analyses indicated the MOD will be exceeded
during the Mission
Prelaunch
Hold until data analysis indicates that the MOD
will not be exceeded
Earth Parking
Continue Mission. If data analysis indicates that
the MOD will be exceeded by a significant amount
before mission completion, trans-Lunar injection
is no-go
Trans-Lunar injection is no-go only if firm
computation before go/no-go indicates more than
the MOD
All Other Phases
Continue Mission. Consideration will be given to
early (or extended) trans-Earth injection and
inhibiting crew transfer to the Lunar module
Continue Mission. Consideration will be given to
early (or extended) trans-Earth injection and
inhibiting crew transfer to the Lunar module
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Apollo Mission Rules Part II
Mission Phase
Comment
Rule
Condition
Continue Mission. Consideration should be given
to entering in the next best preferred target
point if the total dose can be reduced
significantly without increasing the total risk
to the crew
Crew should begin personal dosimeter and
radiation survey meter read-outs. A projection of
greater than the MOD is not required for crew
read-outs
Confirmed particle event and spacecraft telemetry
personal dosimeter read-out projections indicate
the MOD will be exceeded during the mission
Trans-Lunar Coast
Hatch down attitude may be used to reduce the
total dose
Continue mission. Consider extending lunar orbit
stay time if the total dose to the crew would be
reduced significantly by lunar shielding
Lunar Orbit
If a particle event is confirmed, the crew will
transfer from the lunar module to the command
module
Consider reducing the lunar stay time or EVA if
the total dose to the crew can be reduced
significantly without increasing the total risk
to the crew
Lunar Stay
Comparison of command and Service Module and
Lunar surface personal radiation dosimeters is
advised
All Other Phases
Continue Mission
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Comparison of Apollo / ISS exposure limits.
Currently there are no Official
Lunar/Exploration Mission Limits It is suspected
that the short term limits may remain very similar
MOD Maximum Operational Dose NAS National
Academy of Science
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Examine the effectiveness of the following
mission rule Assuming local alarm notification
to EVA astronauts, Terminate Lunar EVA and return
to habitat when 100 MeV protons exceed 1 pfu
(energetic SEP definition)
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• Lunar EVA Scenarios
• 100 MeV events for Solar Cycle 23
• Estimate skin and BFO doses
• Lunar EVA Scenario assumptions
• EVAs limited to 8 hours total
• Early Lunar Scenario / No pressurized rovers
• Exploration profiles suggest a max rover time of
  3 hours
• Rover failure 5 hour exposure (Requires
  another rover to meet returning crew before
  consumables run out
• Walking EVA worst case is 4 hours, but
  probably less

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• Evaluation Tools
• Transport code PDOSE
• Straight ahead approximation
• No secondaries
• No Dose Equivalent
• Skin and BFO shields (Computer Anatomical Man)
• Lunar 2 Pi shielding
• Directional effects not considered
• Suit Shielding 0.5 g/cm2
• No neutron secondary source from regolith
• Approximate Qave 2 for Dose Equivalent

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100 MeV events With Highest Dose Rises Cycle 23
SPE 1 pfu _at_ 100 MeV
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BFO Dose Equivalent vs Rise of SEP
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Skin Dose Equivalent vs Rise of SEP
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Skin Dose Equivalent vs Rise of SEP
LEO Skin limit 150 cSV
Highest dose for time interval
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BFO Dose Equivalent vs Rise of SEP
LEO BFO limit 25 cSV
Highest dose for time interval
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• Summary
• The proposed operational rule to return to lunar
  base when 100 MeV protons exceed 1 pfu appears
  to enable emergency response.
• Calculations suggest that Lunar EVAs may not
  violate Exposure Limits on their own
• 5 hour Skin Dose Equivalent 1/3 of the 30 Day
  Skin limit
• 5 hour BFO Dose Equivalent 2/5 of the 30 Day
  BFO limit
• No one event is limiting for skin and BFO during
  the whole 8 hour EVA interval. The Nov 2000
  event is the limiting event for the scenario
  critical times of 3 to 5 hours

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• Some Closing Operational Thoughts
• However, this assessment does not include
  additional exposure for the remainder of the
  event
• A reasonable worst case exposure profile might
  consist of
• An EVA in progress at event initiation
• Remainder of event in habitation volume
• Integrated scenarios must be evaluated Match
  EVA return times with available shelter
  capability
• Future forecasting improvements will be valuable
  to increase exposure dose management,
• Especially if rapid onset events can be reliably
  predicted.
• Conversely, reliable negative forecasts, an
  event is highly unlikely to occur, may be just a
  valuable

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SOHO (ESA NASA)
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Split events