Predicting The
Radiation Risk To ESA's Astronauts
(13 February 2008) European scientists have developed the most accurate method yet for predicting the doses of radiation that astronauts will receive aboard the orbiting European laboratory module, Columbus, attached to the ISS this week.
ESA astronaut Christer Fuglesang during the second spacewalk of the STS-116 mission to the International Space Station. Fuglesang stands on a platform at the end of the Station's robotic arm, Canadarm2, during operations to relocate two CETA carts. (courtesy: NASA)
The new software package accurately
simulates the physics of radiation particles passing through spacecraft walls
and human bodies. Such techniques will be essential to use for calculating the
radiation doses received by astronauts on future voyages to the Moon and
Mars.
To predict accurately the radiation risk faced by astronauts,
scientists and engineers must tackle three separate problems: How much
radiation is hitting the space vehicle? How much of that radiation is blocked
by the available shielding? What are the biological effects of the radiation on
the astronauts?
ESA astronaut Christer Fuglesang during the second spacewalk of Space Shuttle mission STS-116. Fuglesang stands on a platform on the end of the Station's robotic arm, Canadarm2, during operations to move two CETA carts on the truss - the Station's girder-like backbone structure. (courtesy: NASA)
This project, funded by ESA's General
Studies Programme and the Swedish National Space Board, mostly concentrates on
the second of those questions. It was initiated by Christer Fuglesang of ESA's
European Astronaut Corps.
During a stay onboard the ISS in December
2006, he experienced firsthand the effects of space radiation. "You see flashes
when you close your eyes as a result of interactions with your eye," he
says.
The frequency of these flashes depends on where the ISS is in its
orbit and the level of solar activity. There was a solar storm whilst Fuglesang
was in space. "That night we were told to sleep in the more shielded sections
of the station," he says.
The ESA simulation is called Dose Estimation
by Simulation of the International Space Station (ISS) Radiation Environment
(DESIRE). "The project was designed to provide a European capability in
accurately predicting radiation doses onboard Columbus," says Petteri Nieminen,
ESA's Technical Officer on the study.
The first step was to build a
programme that would accurately simulate the physics of radiation passing into
a spacecraft and then through a human body. To do this, Tore Ersmark of the
Royal Institute of Technology (KTH), Stockholm, Sweden worked with several
existing software packages. These included a software toolkit known as Geant4,
which simulates the propagation of radiation particles. Geant4 has been
successfully used in disciplines such as space physics, medical physics and
high-energy physics, and is developed by a large international collaboration
involving ESA, CERN, and many other institutes and universities.
One of
the lengthiest aspects of the work was that Ersmark had to build from scratch a
computer model of the International Space Station itself. The configuration and
orientation of the ISS are crucial parameters in defining the amount of matter
that radiation passes through.
The Columbus module, launched into space
by NASA's Space Shuttle on 7 February, is the most ambitious and sophisticated
contribution to human spaceflight that Europe has yet made. It is equipped with
radiation monitors to test the DESIRE predictions. "We are really pleased with
the results from DESIRE and look forward to comparing them to the actual
measurements," says Petteri.
Inside Columbus, during quiet solar times,
the radiation levels are expected to be low. "Although they are several hundred
times greater than the background radiation level here in Sweden, that is still
not dangerous," says Ersmark.
Beyond Columbus, the DESIRE tool can be
developed into a European software package that can be used to predict the
radiation risks for other manned space flight missions, both close to Earth and
beyond the protection of our planet's magnetic field.
A significant geomagnetic storm impacted the Earth beginning early Thursday afternoon around 1:00 p.m. Eastern time, 14 December 2006, according to forecasters at the NOAA Space Environment Center in Boulder, Colo. Impacts from events like this can cause problems with High Frequency communications, satellite operations and induce currents in power grids. (courtesy: SOHO/EIT (ESA & NASA))
The radiation environment close to Earth
consists of three main components: Particles trapped in the Earth's magnetic
field; particles that arrive from deep space called Galactic Cosmic Rays (GCRs)
and particles expelled from the Sun during solar eruptions. These components
all vary with time, mainly due to the unpredictable activity of the Sun, which
influences the Earth's magnetic field. In turn, the Earth's field determines
the extent of the trapped particles and how well Earth is shielded from
incoming GCRs.
Beyond Earth's magnetic field, spacecraft and their
occupants will be exposed to the full force of the GCRs and the solar
eruptions. Missions to the Moon and Mars will venture into this harsher and
unpredictable radiation environment for periods of many month or even
years.
During the Apollo missions of the 1960s-70s, the astronauts were
simply lucky not to have been in space during a major solar eruption that would
have flooded their spacecraft with deadly radiation. Essentially, they took
risks and got away with it. For the kind of long-duration journeys being talked
about today, a far more robust system of predicting radiation doses is
required.
"The main uncertainties in these calculations are our
knowledge of the space radiation environment beyond the Earth's magnetic field,
and the biological response to radiation," says Ersmark.
To provide the
environmental information ESA is flying a standard radiation monitor on a
number of its spacecraft, including Proba-1, Integral, Rosetta, GIOVE-B,
Herschel and Planck. Known as the Standard Radiation Environment Monitor
(SREM), it measures high-energy radiation particles. It was developed and
manufactured by Oerlikon Space in co-operation with Paul Scherrer Institute,
under a development contract from ESA.
Developing the appropriate
strategies and countermeasures to deal with the interplanetary radiation hazard
is essential. At present it is one of the most difficult challenges to our
exploration the wider solar system. Thanks to DESIRE, Europeans have taken a
step towards being able to test future space vehicle designs to find those that
offer the most protection.
(source: ESA)
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