Humans venturing beyond Earth orbit deeper into space face increased exposure to cosmic radiation, so ESA has teamed with Germany's GSI particle accelerator to test potential shielding for astronauts, including Moon and Mars soil.
ESA's two-year project is assessing the most promising materials for shielding future astronauts going to the Moon, the asteroids or Mars.
"We are working with the only facility in Europe capable of simulating the high-energy heavy atomic nuclei found in galactic cosmic radiation - the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany," explained Alessandra Menicucci, overseeing the project. "We assessed materials including aluminium, water, polyethylene plastic, multilayer structures and simulated Moon and Mars material - the latter on the basis these will be accessible to planetary expeditions.
"We have also confirmed a new type of hydrogen storage material holds particular promise." Space is awash with charged particles, meaning that astronauts are officially classed as radiation workers. The International Space Station orbits within Earth's magnetic field, safeguarding its occupants from the bulk of space radiation. To venture further out, dedicated shielding will be required.
Space radiation comes from the Sun - in the form of intense but short-lived 'solar particle events' - as well as galactic cosmic radiation originating beyond our Solar System: atomic nuclei produced by dying stars, their passage sped by magnetic fields as they cross the galaxy.
"Solar particle events are made up of protons that can be shielded quite simply," added Alessandra. "The real challenge for deep-space missions is galactic cosmic radiation, which cannot be shielded completely because of its very high energy, although the exposure level decreases with increased solar activity. Most are small prot ons or helium nuclei, but about 1% are larger, the size of an iron atom or more - known as 'high-ionising high energy particles' or HZE for short. Radiation shielding can be counter-intuitive because denser and thicker does not always mean better.
HZEs striking metal shields can produce showers of secondary particles that might be even more harmful. And as shield thickness increases, overall the energy loss of ionising radiation rises to a peak then declines rapidly.
"In general, the lighter a material's atomic nuclei the better the protection," notes Alessandra. Water and polyethylene performed better than aluminium for instance, and new hydrogen-rich materials developed by UK company Cella Energy tested better still. Cella Energy originally developed its patent-pending materials for storing hydrogen fuel but is currently investigating their radiation resistance.
ROSSINI for space radiation protection testing
Formally known as ROSSINI - Radiation Shielding by ISRU (In-Situ Resource Utilisation) and/or Innovative Materials for EVA, Vehicle and Habitat - the project also involves complex 'Monte Carlo' simulations to get a statistical overview of radiation effects.
One key resource is the Geant4 toolkit to simulate particles striking matter, developed through a CERN-led international collaboration and also employed on CERN's Large Hadron Collider. "Simulation results are then compared against test data - an essential stage because this is such a complex field with many unknowns, especially in terms of human biology," Alessandra says. "Our completed research will then be available in the planning of manned missions."
GSI also provided access to its US counterpart, NASA's Space Radiation Laboratory at Brookhaven in New York, where the first round of testing was recently performed. ROSSINI is being managed for ESA by Thales Alenia Space Italy, with GSI performing testing and data analysis and Swiss company SpaceIT working on simulations.
ESA's cooperation with GSI extends beyond ROSSINI: the Agency will be a major user of its new Facility for Antiproton and Ion Research particle accelerator. When complete, FAIR will give experimental access to an even higher range of particle energies.