Mission – Mars: Physicists Calculated Optimal Window of Opportunity and Thickness of Shielding against Cosmic Radiation

A team of researchers identified a window of opportunities for manned space flights to Mars. According to the developed models, the most favorable and safe period for astronauts will be the 2030s.

Researchers from Russia (Skolkovo Institute of Science and Technology, Moscow), USA (University of California and Massachusetts Institute of Technology) and Germany (Helmholtz Center Potsdam (GFZ) and University of Potsdam) led by Yurii Shprits and Dr. Mikhailo Dobynde modeled mission options of space weather, which took into account the factor of space weather, i.e. solar and galactic radiation, so as the exposure of the spacecraft crew to be as small as possible.

Cosmic radiation is the most important challenge to long-term space missions, because a spacecraft can be equipped with protective shielding only up to a certain limit, when it becomes too heavy, and its launch is economically unprofitable. The team decided they needed to adapt to space weather rather than resist.                                    

A flight to Mars at the current level of technologies will take about nine months. During the journey, the spacecraft and its crew will be exposed to radiation of two types: energy particles of solar origin (mainly protons) and galactic cosmic rays (84% of protons, 14% of positively charged alpha particles, 2% of negatively charged electrons). It is quite difficult to protect against them, because they move with high energy and penetrate deeper into materials or even through them.

The picture on the left illustrates 100 protons hitting the spacecraft with 10 g/cm2 aluminum shielding with energy of 100 megaelectronvolts. On the right, there are only 10 protons coming in, but with 10 times more energy. The blue lines indicate primary protons, with the resulting secondary particles shown in red (neutrons), yellow (gamma rays), and cyan (electrons). The green dots indicate particle-matter interactions. Image: Dr. Mykhailo Dobynde/Scoltech

Every 11 years, the sun exhibits a maximum in its activity emitting the most radiation. The model of the international team of physicists proposes to fly to Mars during this period of the greatest solar activity: after all, the flux of solar radiation actually reflects more harmful galactic rays.

Researchers modeled two levels of radiation inside the spacecraft, taking into account 28 kinds of hazardous particles of galactic origin and 10 emitted by the sun during solar flares. Scientists relied on the measurements of particles of solar origin from 1998 to 2012 and on an empirical model of galactic cosmic rays, which depends on the solar cycle.

A sphere with an inner diameter of 2 m simulated the spacecraft in the model. Aluminum of various thicknesses was used as a protective shielding. A sphere with a diameter of 35 cm filled with water served as a model of the human body. Scientists calculated the exposure dose that the human body accumulates during the flight to Mars under different conditions. They also analyzed different depths of penetration into the body to distinguish skin sensitivity, hematopoiesis and other organs.

“Today, most space agencies assume that the total exposure dose for astronauts during their life should not exceed 1 Sv,” says Yurii Shprits. “New calculations show that this limit can be met if the spacecraft has optimal shielding, the flight starts during the peak solar activity and the total flight time does not exceed 3.8 years.”

“We have identified the optimal combination of spacecraft shielding and the launch date which enables the longest flight duration. Our calculations show that the best time to start a manned flight to Mars and back is during the decaying phase of solar activity. If the average shielding is 10 cm of aluminum, the mission could last up to four years without exceeding the allowed radiation risk limit. Since the next solar max is coming up fairly soon — somewhere around 2025 — Mars might just have to wait until the mid-2030s,” commented the study’s first author, Dr. Mikhailo Dobynde of Skoltech.

The study results indicate that shielding material density of 30 g/cm2 is the most optimal: a denser material leads to an intensification of particle scattering that forms the so-called secondary particles, which can increase exposure inside the spacecraft. If the shielding density is less than 30 g/cm2, then a critical exposure dose can be received even during shorter flights.                                                                          

The authors continue to study the effectiveness of various shielding materials and radiation environments on the surface of Mars and the Moon.

According to: German Research Centre for Geosciences, EurasiaReview