Final answer:
Astronauts do not need to worry about the cosmic microwave background radiation while in space. They are more at risk from solar flares and space junk, which can expose them to high-levels of radiation and damage spacecraft electronics, especially during long-term missions like a journey to Mars.
Step-by-step explanation:
Astronauts in space face various dangers, but one of the major challenges they need not worry about is the cosmic microwave background radiation because it is not harmful to them. Instead, more pressing concerns include solar flares and the risk of collisions with space junk. Solar flares can expose astronauts and spacecraft to intense radiation and charged particles which can ionize atoms in Earth's upper atmosphere. The result can be a buildup of static charge on spacecraft surfaces, which can damage electronics upon discharge. Additionally, the solar wind is deflected by Earth's magnetic field, but astronauts outside this protective zone can be directly exposed to these charged particles, posing a significant risk to their health, especially over prolonged missions. Reducing astronauts' exposure to high-energy solar radiation is a crucial consideration for missions such as human exploration of Mars.