Free Astronomy Magazine September-October 2019

44 SEPTEMBER-OCTOBER 2019 ASTRONAUTICS higher than that absorbed in the same pe- riod on our planet. During the journey to Mars, assuming about 6 months long, as- tronauts could be exposed to at least 60% of the total radiation dose limit recom- mended by space agencies for their entire careers. Adding to the journey to Mars both the stay on the planet and the re- turn journey (almost 2 years in all), an as- tronaut would have the certainty of being exposed to enough radiation to probably cause serious or even lethal diseases. This problem could conceivably be solved by reinforcing the shielding of space- crafts, but this is not feasible, as current spacecrafts already possess shields at the limit of mass compatible with the power of the available carriers. Take, for exam- ple, NASA’s Orion, the most technologi- cally advanced spacecraft in existence today, currently at an advanced stage of testing and designed for both short mis- sions (nearby asteroids and the Moon) and journeys to Mars. In its case, the best solution adopted against particularly in- tense and unpredictable flows of high-en- ergy charged particles (typically of solar origin) is to protect the crew by using the W hen a high-energy particle hits the Earth’s atmosphere, it can produce a cascade of secondary particles of lower energy, as shown above. This phenomenon, called spallation, occurs in a similar way when a charged particle hits a spacecraft hull, generating a flow of intravehicular particles, whose potential effect on the astronauts’ bodies is almost unpredictable. [A. Chantelauze, S. Staffi, and L. Bret]