Space radiation could force a manned mission to Mars to take less than four years

An international team of scientists calculated that a manned mission to Mars would only last up to four years if they wanted to keep astronauts' health from being threatened by long-term exposure to cosmic radiation. Planning a manned mission to Mars will be one of the most daunting challenges ever attempted at space exploration. Every aspect of such a multi-year adventure can have a complex impact on other factors, creating a constant tug-of-war as scientists and engineers seek compromises to meet mission requirements.

In addition to the types of engines, crew sizes, diets, and countless other juggling matters, manned fire detection programs also need to take into account ubiquitous radiation hazards. Once left from the protective shield of Earth's atmosphere and its magnetic field, astronauts were at the mercy of cosmic rays from the sun and large galaxies, so the question was, how to minimize this threat?

According to recent research, including researchers from UCLA, the Massachusetts Institute of Technology, the Skolkovo Institute of Science and Technology, and the GFZ potsdam, the key to protecting astronauts traveling to the Red Planet is the issue of time and shielding materials.

The important point is that cosmic radiation is not constant. It varies according to what appears to be the same as the activity of the Sun, which in fact is a variable star with a primary period of 11 years, during which its activity periodically increases and decreases.

Cosmic rays from the Solar System have two sources. One is the Sun, which spews out solar-powered particles (SEP), which tend to be lighter and less energetic than galactic cosmic rays (GCRs), followed by supernovae, black holes, quasars, and similar high-energy events. These GCR rays are usually made up of very heavy particles that fly at speeds and energies that are only barely close to the most powerful particle accelerators on Earth, and can cause considerable damage to biological tissue over time.

The good news is that the sun can act as a temporary shield against GCR. When the Sun is most active, the solar wind becomes very strong enough to block GCR, meaning astronauts will be primarily exposed to less energetic SEP, which is more of a reduced amount of background radiation.

According to the study's calculations, since GCR activity is lowest within 6 to 12 months after maximum solar activity, Mars missions lasting less than two years will easily correspond to a more suitable space climate. However, a mission lasting more than four years will expose the crew to dangerous radiation levels before returning to Earth, which puts an upper limit on mission duration.

One of the reasons for this restriction is the nature of the radiation hazard. The most serious dangers will come from GCRs because they have a lot of energy, and shielding materials themselves become a problem when researchers take models of human organs and set them behind different shields. There are many different ways to shield astronauts, including plates of heavy metal, water tanks, or low-density polymers. The problem is that a shield large enough to provide direct protection not only creates weight problems for the spacecraft, but also emits secondary radiation when cosmic rays split the atoms in the shield.

"This study shows that while space radiation imposes strict limits on the weight and launch time of spacecraft, and it presents technical difficulties for humans' Mars missions, such missions are feasible," said Yuri Shprits, a UCLA research geophysicist.