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How do we protect the astronauts from space radiation?
A number of parameters affect astronaut exposure to radiation. In general, these parameters include the mission location (e.g., LEOLow Earth Orbit,
cis-lunar space, lunar surface), the radiation environment at the mission location (e.g., nominal conditions, energetic particle enhancements), and protective shielding (e.g., structure and material
of the spacecraft or spacesuit). SRAGSpace Radiation Analysis Group considers all of these parameters to ensure that radiation
exposure received by astronauts remains below established safety limits.
Providing Radiological Support During Missions
For LEOLow Earth Orbit missions such as the ISSInternational Space Station,
SRAGSpace Radiation Analysis Group SEOSpace Environment Officers support
operations in Mission Control 4 hours each weekday during nominal space weather conditions. For missions outside of LEOLow Earth Orbit
such as Artemis, this support will be 24 hours daily. During EVAExtra-Vehicular Activitys and contingency conditions,
SRAGSpace Radiation Analysis Group SEOSpace Environment Officers support Mission
Control continuously regardless of the mission.
SRAGSpace Radiation Analysis Group SEOSpace Environment Officers work closely
with NOAANational Oceanic and Atmospheric Administration/SWPCSpace Weather Prediction Center
forecasters. SWPCSpace Weather Prediction Center uses real-time data, model results, and their expertise to provide
SRAGSpace Radiation Analysis Group SEOSpace Environment Officers with forecasts of
the near-future space weather conditions. SRAGSpace Radiation Analysis Group
SEOSpace Environment Officers use these forecasts along with telemetry from
SRAGSpace Radiation Analysis Group's radiation detectors onboard mission spacecraft, space weather conditions, model results, and their
own expertise to determine if there will be an impact to operations.
During contingency conditions (i.e., energetic particle enhancements), SRAGSpace Radiation Analysis Group SEOSpace Environment Officers
verify that the ALARAAs Low As Reasonably Achievable principle is maintained and provide recommendations to the Flight Surgeon in order to mitigate
radiation exposure to crew. Such recommendations include having crew avoid lower shielded areas of the spacecraft, build a shelter if necessary (such as in the Orion spacecraft
(link to video: here)),
shelter in higher shielded areas of the spacecraft, delay an EVAExtra-Vehicular Activity, or return from an ongoing EVAExtra-Vehicular Activity.
The RADRadiation Assessment Detector, currently deployed in the ISSInternational Space Station
US Laboratory module, contains two detector subsystems: the CPDCharged Particle Detector and the
FNDFast Neutron Detector. The CPDCharged Particle Detector
is a particle telescope consisting of planar silicon diodes and scintillators capable of identifying protons and helium of from 10-100 MeVMega Electron Volt,
heavier ions of higher energies, and neutrons and gamma rays from 5-100 MeVMega Electron Volt. The
CPDCharged Particle Detector can measure the LETLinear Energy Transfer spectrum in
silicon for charged particles in a ±30 degree field of view from 0.1-1000 keV/micron. The FNDFast Neutron Detector consists of a boron-loaded
plastic scintillator; its signal-processing logic uses the capture-gating method which allows for measurements of neutrons from 0.5-10
MeVMega Electron Volt, which are abundant in shielded environments in space and can cause more damage to health than other particles.
RADRadiation Assessment Detector has two main roles. First, it acts as an alarm for crew when the detected dose rate exceeds a level
where crew may need to shelter. This alarm capability is especially important if communication is ever lost between the crew and the Flight Control Team. Second,
RADRadiation Assessment Detector acts as a reference for trending crew exposure during the course of their mission. Based on this reference,
SRAGSpace Radiation Analysis Group can effectively communicate how much additional radiation exposure crew may receive from
EVAExtra-Vehicular Activitys.
REMRadiation Environment Monitors and HERAHybrid Electronic Radiation Assessor both
utilize the CERNEuropean Council for Nuclear Research Timepix technology to detect ionizing radiation passing through the sensor layer of the
detector. The pixelated detector collects charge carriers generated as a result of energy deposition within the silicon sensor material. The charge is collected within each pixel and digitized
before readout using a time-over-threshold method. Calibrations are applied to convert the measured values into energy deposited by the ionizing radiation.
The Timepix-based detectors use an acquisition approach similar to a camera, collecting snapshots of the energy deposited during the collection time, resulting in a map of location and energy deposition
values. Using this pixel-frame data, the dose rates can be calculated for each acquisition frame. In addition, the frame times can be modified in real-time, allowing longer or shorter time segments to be
captured. This, in turn, allows tuning of the frame acquisition rates to take data at a cadence that minimizes track overlaps and allows for analysis of individual pixel clusters. With well-separated,
individual clusters for each ionizing radiation track, additional information such as LETLinear Energy Transfer and basic particle classification
(photon, electron, proton, heavy ion) can be calculated as well.
Both REMRadiation Environment Monitor and HERAHybrid Electronic Radiation Assessor are
currently operational on the ISSInternational Space Station. The REMRadiation Environment Monitor
units are deployed across station to provide active radiation area monitoring in 6 different modules. The active aspect (time-resolved) allows ground teams to separate impacts from different components of
the space radiation environment. Timestamps for each measurement associates the data with an ISSInternational Space Station orbital location and
allows generation of dose rate maps for the ISSInternational Space Station orbit. Deployed in different locations within the
ISSInternational Space Station, the REMRadiation Environment Monitor units also reveal
information on the impact of the different amounts of mass-shielding for each location. The AHOSSArtemis HERA on Space Station payload, along
with its predecessor ISSInternational Space Station HERAHybrid Electronic Radiation Assessor,
demonstrate the HERAHybrid Electronic Radiation Assessor system readiness for use in the space environment and allow ground teams and scientists to
gain experience with the hardware before use of the hardware aboard crewed Artemis EM-2 missions and beyond (and uncrewed EM-1 mission for
ISSInternational Space Station HERAHybrid Electronic Radiation Assessor).
Radiation Detectors: Crew Active Dosimeters
Starting in 2020, SRAGSpace Radiation Analysis Group began collecting time-resolved dosimetry for individual crew members with the introduction
of the Crew Active Dosimeters for missions to the ISSInternational Space Station. In contrast to passive dosimetry that only provides the
cumulative mission dose upon return, Crew Active Dosimeters continuously measure and log each astronaut's radiation exposure throughout the mission.
In the approximate size of two AA batteries, the Crew Active Dosimeters houses multiple radiation sensors, a microcontroller, Bluetooth® communication, and an e-paper display - all powered by
coin-cell batteries. Dose is measured using Direct Ion Storage™ technology whereby radiation interactions deplete a fixed-charged placed on a floating gate of a transistor. Radiation interacting
in a small nitrogen-filled volume around the transistor slowly neutralizes the gate charge inducing a change to its electrical characteristics. By periodically measuring the transistors, the
Crew Active Dosimeter correlates electrical changes to an absorbed dose through a relationship obtained during ground calibrations. The dose readings are timestamped and transmitted via
Bluetooth®
to laptops aboard the ISSInternational Space Station as crew members conduct their duties enabling seamless downlink to
SRAGSpace Radiation Analysis Group. Meanwhile, the always-on display provides the astronaut with their total mission dose and the recently
measured dose rate at a glance.
Crew Active Dosimeter
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To support mission planning, SRAGSpace Radiation Analysis Group maintains an extensive set of tools for estimating the exposure received by
crew during LEOLow Earth Orbit missions. The suite of tools includes time-resolved models of the Earth's magnetic field, maps of radiation
fluxes trapped in the magnetosphere, and trajectory translator/propagator algorithms. Space environment conditions (e.g., interplanetary proton flux, status of the electron belts, geomagnetic
field conditions) are integrated with mission parameters (e.g., altitude and inclination of the spacecraft, location and timing of
EVAExtra-Vehicular Activitys) in order to project crew exposure.
ARRTAcute Radiation Risks Tool is an operational tool that uses direct measurements from onboard dosimeters to project organ doses and
likelihood of ARSAcute Radiation Syndrome symptoms during times of increased radiation exposure. The modeling of acute biological responses
to SEPSolar Energetic Particle event exposure in ARRTAcute Radiation Risks Tool is
based on two sets of neurovascular models (for nausea and vomiting, and for fatigue and weakness, respectively) and four sets of hematopoietic models (for describing the dynamics of lymphocytes,
granulocytes, leukocytes, and platelets in the peripheral blood after exposure).
ARRTAcute Radiation Risks Tool was specifically designed for the Orion MPCVMulti-Purpose Crew Vehicle
- the interplanetary spacecraft intended to carry a crew of four astronauts to destinations beyond LEOLow Earth Orbit. In the Orion
MPCVMulti-Purpose Crew Vehicle, the HERAHybrid Electronic Radiation Assessor unit will
provide onboard dosimetry for ARRTAcute Radiation Risks Tool. Since crew will not have the protection of Earth's magnetic field while
outside LEOLow Earth Orbit, the projection of acute biological responses from
ARRTAcute Radiation Risks Tool will provide SRAGSpace Radiation Analysis Group
console operators with critical information they need for passing recommendations to the Flight Control Team.
SRAGSpace Radiation Analysis Group's ability to predict and assess space radiation to
ISSInternational Space Station crew is supplemented by state-of-the-art CADComputer Aided Design
ray tracing and physics-based radiation transport tools. These tools allow SRAGSpace Radiation Analysis Group to make accurate predictions of the
type and intensity of radiation that might penetrate the ISSInternational Space Station. This information is used along with radiation measuring
instrumentation and dosimetry to compute astronaut career dose.
This extensive workflow also allows SRAGSpace Radiation Analysis Group to analyze
CADComputer Aided Design models of current and future crewed vehicles designed to go beyond
LEOLow Earth Orbit. SRAGSpace Radiation Analysis Group works closely with
commercial developers to compute the shielding capabilities of crewed exploratory vehicles under the Artemis program, such as the Orion
MPCVMulti-Purpose Crew Vehicle (below), the future Gateway spacecraft, and the Human Landing System. These tools allow
SRAGSpace Radiation Analysis Group to ensure that crewed vehicles can be configured to provide safe shelter for astronauts even in the
event of an unexpected, intense SEPSolar Energetic Particle event.
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