Magnetic "deflector shields" could one day guard astronauts against dangerous space radiation, if experiments now underway pay off. (w/pic)
A radiation shield that mimics the deflection properties of the Earth’s magnetic field could one day protect astronauts on long missions. An imaginative view – not to scale – shows a spacecraft protected from solar activity by such a shield (Illustration Ruth Bamford et al/Rutherford Appleton Laboratory)
Exposure to energetic charged particles could put astronauts on lengthy missions at increased risk of cancer and even cognitive problems (see Future mars astronauts have radiation on their minds). The particles come from the solar wind and also from supernovae and still-unidentified sources outside the solar system.
The Earth’s magnetic field protects spacecraft in low-Earth orbits, such as the space shuttle and International Space Station, from such particles. But astronauts journeying to Mars or living on the Moon would benefit from no such protection.
Now, US and European plans for long-term missions to the Moon and Mars have sparked renewed interest in the problem of radiation shielding.
One group at the University of Washington in Seattle, US, has just completed a round of experiments investigating one possible approach, using a bubble of charged particles, or plasma, as a deflector shield (see Plasma bubble could protect astronauts on Mars trip).
Now, a second team has begun deflector shield experiments of their own. The team, led by Ruth Bamford of the Rutherford Appleton Laboratory in the UK, hopes to eventually fly a test satellite surrounded by a cloud of plasma in space.
The concept is based on the fact that plasma clouds have strong magnetic and electric fields that can in principle deflect charged particles.
The group has begun testing a simple magnetic field generator that consists of loops of wire with electric current running through them.
Within a few months, they plan to use it to trap a cloud of plasma and test its ability to deflect particles inside a vacuum chamber about 2 metres long. By the end of 2007, they hope to test it in a chamber about twice as large, using higher speed particles.
Eventually they hope to attract funding for a demonstrator mission that uses wires around a spacecraft to generate a magnetic field that can contain a plasma cloud. "Hopefully we’ll be able to fly a test mission in the next, say, 10 to 15 years," says team member Robert Bingham of Rutherford Appleton Lab.
It would not be the first time a satellite had released a plasma cloud in space. In 1984, one of three satellites in a mission called the Active Magnetospheric Particle Tracer Explorer (AMPTE), which was designed to study the basic physics of plasmas, produced a plasma cloud thousands of kilometres across.
The cloud protected the satellites from the solar wind, but the mission had no way of containing the plasma, so it simply drifted away after a while, leaving the satellites unprotected.
Some researchers say the deflector shield concept shows early promise. John Slough, who leads the University of Washington group, says its NASA-funded feasibility study showed they were able to deflect charged particles with a plasma bubble and a wire mesh measuring a few centimetres across. "The question is, can you do it on a larger scale," Slough says.
But Frank Cucinotta, NASA’s chief radiation health officer at the agency’s Johnson Space Center in Houston, Texas, US, says there are drawbacks to such ‘active shielding’ methods compared to simply using extra layers of material to block out the dangerous particles.
For example, if something breaks in the device generating a plasma shield, the whole shield could disappear, whereas material shielding has no moving parts to break down.
He says materials like polyethylene could provide effective shielding, at least against particles from the Sun. As for cosmic rays from outside the solar system, he says there is a lot of uncertainty in how big the health risk really is. "We will not be able to understand how poorly or efficiently shielding works until more biological knowledge is obtained," he said.
Bamford is presenting the work this week at the Royal Astronomical Society’s National Astronomy Meeting in Preston, UK.
Via New Scientist