Had NASA decided to launch an extra mission between Apollo 16 and 17, its astronauts would’ve been killed by an acute overdose of radiation caused by a solar radiation storm courtesy of a solar flare.
In extreme circumstances, you wouldn’t even have to be in space to suffer the consequences of increased energetic particle activity caused by a nasty solar flare – passengers on commercial airlines would receive a unhealthy dose of radiation too. During this extreme solar weather, satellites can be rendered useless and high frequency communications would stop working near the polar caps.
Geomagnetic storms are potentially more deadly, however.
Disturbances in the Earth’s magnetic field caused by the Sun’s solar wind have been enough to wreak havoc with power systems across the world. In 1989 an electromagnetic storm wiped most of Quebec off the power grid for nine hours. In fact, the effects were so strong auroras (the visible effects of particles interacting with the Earth’s magnetic field) could be seen as far south as Texas.
There’s also the thought of micrometeor showers. Space rain is actually made of tiny particles of rock and metal travelling at tens of miles per second. Micrometeoroids are remnants of the creation of the solar system and millions of them bombard the Earth from space everyday.
The most common forms of space weather include solar wind, raining micrometeoroids and geomagnetic storms.
Micrometeoroids – These are only called micrometeorites once they’ve fallen to Earth. They can potentially destroy satellites and other space-based technology, though rarely make their way to Earth.
Solar radiation storms – Caused by solar flares rushing at the Earth, solar radiation storms could potentially kill an astronaut stone dead and even severely harm unfortunate airline passengers.
Geomagnetic storms – Ever-changing solar winds create geomagnetic storms, which could completely overload power systems and cause devastating country-wide blackouts.