# Radiation and windows for building of a great project in a low Earth orbit: reference request or exercise as a ficticious need to build it

I know about the existence of certain windows for which it is more suitable to launch a probe for the exploration of a cellestial body in our Solar System (see the Wikipedia Launch window). I wondered about a different problem.

In the past, if I refer well there was in the literature projects to build certain structures (you can to illustrate your answer with a generic example or with a specific one) in low orbits around of our planet Earth: for example a (great) spacecraft, telescope (we evoke a very big telescope) or a space elevator.

Question. I would like to know what is the more suitable period in terms of the expossition of radiation that is allowed for our workers, I mean an approximation of the date(s) of the more suitable periods, with a deadline for our project in next $$30$$ years (or few decades from your discussion) in which I evoke the fictious situation that we want/need (and we can in this thought experiment) to build a great construction project in a low orbit similar than the orbit of the International Space Station or other low orbit more suitable (see below again the requirement in the context of our ficticious project, since we want to minimize the radiation for our workers). Many thanks.

Thus you add an answer as a draft of computations or estimations for our generic project, you can to add all those variables that you need in your computations for our great project in order to get a more precise answer (if possible).

Important goal/assumption. While our workers have the possibility to save their bodies of radiation (this radiation in a wider meaning of ther word, but that I mean are the more probable conditions, I emphasize radiation exposure, that scientists should to expect in next few decades) eventually in shelters or those conventional protection means for the astronauts, we want to minimize this impact of radiation in their bodies and to know an approximation of when will be a suitable period/date for do a work of building of a great project in next few decades (for this thought experiment we evoke that the starting of activities for this ficticious project is at this year $$2020$$).

If my question is in the literature (or you know remarkable articles in this context), then please refer the literature answering my question as a reference request and I try to search and read the answer for my question from the literature.

• What I evoke as answer from professors or professional physicists are references, or a draft/essay where is added reasonings or computations (if possible) that are helpful and interesting for professional physicists in the purpose to adress my question. – user250478 Jun 3 at 18:02
• Many thanks for such excellent feedback, feel free to add all these paragraphs as an answer, I was asking what work can be done for my question and references or reasonings helpful for persons interested in this post @PM2Ring . If you or other person wants can to add in which approximate periods (in the $\approx$ thirty years that I've mentioned) can be the more suitable years to work from the begining of the project. – user250478 Jun 3 at 19:44

There's always dangerous radiation in space near Earth, but there are regions which are more dangerous, in particular, the Van Allen radiation belts. And there are events like solar flares and coronal mass ejections which increase the radiation temporarily. The Wikipedia article on space weather gives some details about this topic.

It's hard to make long-term predictions of space weather, but there are some long-term regularities due to the 11 year sunspot cycle. Also, the Sun rotates on its axis with a period of about 1 month (25 days at its equator, 34.4 days at its poles), so we can predict when a given group of sunspots will be facing the Earth.

It takes on average 3.5 days for the particles of a coronal mass ejection to reach Earth (although in extreme cases the particles can get here in less than a day). So for these events, astronauts have time to take shelter in radiation-hardened shelters, or to return to Earth.

So, unlike the launch window, which is easy to calculate using orbital mechanics, there is no simple "building window" which can be calculated, apart from the solar minimum that is caused by the sunspot cycle. And as Wikipedia says, "Their non-linear character makes predictions of solar activity very difficult". Long term prediction of space weather is difficult, like long term prediction of the weather on Earth.

honeste_vivere mentions in the comments that solar flares and CMEs can accelerate particles to relativistic speeds, which can reach Earth in under half an hour. These are called solar energetic particles or SEPs. These particles are especially dangerous because they have high energy, and because we don't get much warning time. Fortunately, only about about 1% of CMEs produce strong SEP events.

From Solar particle event:

Significant proton radiation exposure can be experienced by astronauts who are outside of the protective shield of the Earth's magnetosphere, such as an astronaut in-transit to, or located on the Moon. However, the effects can be minimized if astronauts are in a low-Earth orbit and remain confined to the most heavily shielded regions of their spacecraft. Proton radiation levels in low earth orbit increase with orbital inclination. Therefore, the closer a spacecraft approaches the polar regions, the greater the exposure to energetic proton radiation will be.

honeste_vivere also mentions the Forbush decrease, whereby the effects of CMEs actually protect us from energetic particles that originate outside the solar system:

A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following a coronal mass ejection (CME). It occurs due to the magnetic field of the plasma solar wind sweeping some of the galactic cosmic rays away from Earth.

• Many thanks I'm going to study your answer, that is excellent. I hope more feedback from your colleagues professionals/professors of this site. Sure that the post is very interesting for all. Many thanks for your generosity and patience. – user250478 Jun 3 at 19:55
• @user250478 This site focuses on physics, so we can answer questions about the physical causes of various space weather events. However, for details about space engineering and other practical matters regarding working in space, please see space.stackexchange.com – PM 2Ring Jun 3 at 20:01
• @PM2Ring - Just a few quick notes: The problematic particles from CMEs reach Earth in ~10-30 minutes and are called SEPs. The issue with solar minimum is that cosmic ray fluxes below ~1 GeV increase dramatically due to the decrease in CMEs. Since most flares and CMEs tend to have SEP peak energies well below 1 GeV, there is a difficult balance in risk between prolonged exposure to enhanced cosmic ray fluxes vs the possibility of short-term, transient exposures. – honeste_vivere Jun 4 at 15:00
• Thanks for that info, @honeste_vivere. I've updated my answer. But I don't understand why the decrease in CMEs during the solar minimum is associated with an increase in cosmic ray particles below 1 GeV. – PM 2Ring Jun 4 at 19:52
• @PM2Ring - Look up "Forbush decreases" which will return articles on how CMEs scatter cosmic rays mostly below ~1 GeV. – honeste_vivere Jun 4 at 21:19