Cosmic weather researchers in the United States have published such an estimate: in the future manned exploration of Mars, "the most appropriate period for spacecraft to depart from Earth is the period of maximum solar activity and activity, plus round-trip voyages and missions, preferably within 4 years." Solar activity during extreme periods releases many high-energy particles, so astronauts' radiation exposure increases, and this is why artificial satellites malfunction. Why is it suitable for manned exploration of Mars during the most active period when the sun, which should be very dangerous? This is because active solar activity can deflect dangerous galactic radiation, reducing the radiation dose for astronauts.
NASA has made manned exploration of Mars a future target after restarting lunar manned exploration. Unlike Earth, which is protected by the atmosphere and magnetosphere, astronauts will be exposed to radiation "cosmic rays" from the universe during their journey to Mars, which takes about 9 months. How to control the radiation dose is a major issue in Mars exploration.
Cosmic rays are roughly divided into "solar high-energy particles (SEP)" released by solar activity and "galactic cosmic rays (GCR)" flying from outside the solar system. SEP increases or decreases between active and stable periods of solar activity that repeat in 11-year cycles. During the most active "maximum period", sudden activities such as solar flares are prone to occur, and the amount of SEP will increase. Astronauts staying on the International Space Station have repeatedly dodged to thicker shades when solar flares occur.
GCR, on the other hand, emits a large amount of radiation and is prone to colliding with atmospheric nuclei inside cosmic ray walls or cosmic rays, producing newly generated secondary cosmic rays.
If you only consider SEP, it seems that it is safer to sail to Mars during periods of weakening solar activity. But cosmic weather researchers at California State University, Los Angeles, estimated the effective dose received during the round-trip voyage and mission to Mars. At present, Japan, Russia and other space agencies have set the limit value of the lifetime effective dose of astronauts as 1 siever. Since the effective dose criteria for the envisaged Mars exploration mission have not yet been determined, researchers at UCLA ran simulations with a ceiling of 1 sievert.
The simulated spacecraft is set up with an aluminum plate separated by water and an astronaut inside. Based on data from 1997 to 2014, the relationship between solar activity and the amount of GCR rays in planetary space close to Earth was calculated, and if the amount of GCR rays decreased after the maximum period of solar activity, if astronauts had a thick enough shield to protect them from sunlight, the total amount of cosmic rays they received could be reduced. This is said to be because solar activity transfers GCR particles during extreme periods, making it difficult to reach the spacecraft. In addition, the maximum period of travel to and from Mars and missions within the range of 1 Siever is 3.8 years.
Based on simulations, the best departure year to study the shortest round-trip voyage between Earth and Mars and coinciding with the maximum solar maximum is said to be 2030 or 2050.
Because the degree of solar activity varies depending on the sun's cycle, it is difficult to predict future activity. In addition, if materials other than aluminum are used on the spacecraft's protection, its shielding performance may also be improved, so the simulation results cannot immediately determine the "time limit" for mars manned exploration.
The solar high-energy particles emitted by the active sun not only increase the astronauts, but also increase the radiation dose of the aircraft on the earth, and can lead to the misoperation and malfunction of the computer on the satellite, and the error of gps satellite position information is expanded, which has a great impact on life on the ground. During the solar maximum period, when SEP is frequent and in danger, the idea of using the phenomenon of reduced galactic radiation for Mars manned exploration can be considered a bold method of "attacking poison with poison".
It is said that there is a difference of 6 to 12 months between the period of high solar activity and the period of GCR weakening, and it may be difficult to determine the departure time of the Mars manned exploration using this method. Regardless of its feasibility, if the topic of "minimizing the radiation dose of manned exploration on Mars" is set, it seems that it is impossible to simply say that "the maximum solar activity period of the increase in the solar high-energy particles is not the best choice". The technology to transfer galactic radiation with a magnetic shield of the size that a spacecraft can carry is also under discussion, and it may be necessary to eliminate assumptions and "put all the options on the table" to solve these problems.