The HAMLET team became the first group of researchers to determine the actual radiation exposure for bodily organs inside and outside the International Space Station, “where astronauts are exposed to radiation doses 100 times higher than those on Earth,” says HAMLET project manager, Thomas Berger of the German Aerospace Center (DLR) in Cologne.

The HAMLET team constructed a dummy of human bones and polyurethane (a plastic-like polymer) to replicate the upper body and help measure the radiation dose absorbed by individual organs. Berger says that “more than 6,000 detectors were implanted to determine how deep radiation penetrates the dummy and how much is absorbed by each ‘organ’”.

To obtain actual measurements, the dummy was shuttled to the International Space Station. There, it was fastened to the outside of the station for 18 months to measure the exposure astronauts can expect when conducting space walks. The dummy was also placed inside various sections of the station for more than three years.

In space, astronauts are only protected by a spacecraft – and during potential walks on the surface of other planets, only by a spacesuit. “These radiation exposures could be life threatening,” says Berger. “Up until now, no astronaut has been known to develop cancer due to space travel,” adds Berger. “But the longer they are up there, or if they want to go to Mars, they could approach the limit for what is considered safe. If they go over the limit, they may not fly again.”

“The main thing we learned during the project is that if we want to calculate the risks, we need data for each organ,” says Berger. The data collected by the HAMLET team and the new technique developed can now be used to estimate the health risks of long-term space travel, including manned missions to Mars.

All astronauts wear external sensors to measure their overall radiation exposure. What has not been known, however, is the dose absorbed by individual organs. According to Berger, certain organs are more sensitive than others, so it is critical to know the specific radiation doses absorbed by the lungs, thyroid, liver, kidney, skin and so on.

“The technique is expected to be used to monitor the health risk of German astronaut Alexander Gerst, who is scheduled to fly to the International Space Station in May 2014 for a six-month mission,” advances Berger.

HAMLET project was part of MATROSHKA, a broader initiative by the European Space Agency to assess the radiation risks of prolonged space travel.

Radiation is ubiquitous in the universe. Life on Earth, however, is protected by its atmosphere and magnetic field. Without the benefit of these shields, astronauts can spend only a limited time in space. In terms of radiation exposure, five days in space is equal to one year on Earth.