The Sun throws lots of high speed protons around. Especially during its sudden and short intensive "events". Much of that is blocked by Earth's magnetosphere and atmosphere. But astronauts work outside some of those natural shields. Could a Sun event actually have disabled and killed an Apollo crew during flight? Or did their spacecrafts have sufficient radiation protection.

I'm not interested in shortened lifetime or other statistical cancer incidents here. But instead of whether there was a real risk of acute radiation sickness disabling the crew and becoming a serious risk to the mission. If they'd had bad luck with the space weather.

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    $\begingroup$ All your answers are in this document: hq.nasa.gov/alsj/tnD7080RadProtect.pdfhttps://www.hq.nasa.gov/…. My understanding is that they protected the astronauts from radiation by (apart from using regular shielding) simply doing everything as quick as they could. They thus limited the radiation exposure. $\endgroup$ Jun 11, 2015 at 12:49
  • $\begingroup$ @VedantChandra Your link doesn't work for me, maybe you could repost it? And is your conclusion that the Apollo program really just gambled for good space weather, and would've failed if the Sun had had a bad day at the wrong time. $\endgroup$
    – LocalFluff
    Jun 11, 2015 at 13:03
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    $\begingroup$ hq.nasa.gov/alsj/tnD7080RadProtect.pdf $\endgroup$ Jun 11, 2015 at 13:04
  • $\begingroup$ Cheers, I messed up my link @Rikki. I don't have an answer to your question about random events like flares, that's why I haven't posted an answer. $\endgroup$ Jun 11, 2015 at 13:20
  • $\begingroup$ Plot of the book "Space" by James Michener: Apollo 18 takes a major solar flare hit. They even made a TV mini series about it. I recall, I had chickenpox when it was on TV. $\endgroup$
    – geoffc
    Jun 11, 2015 at 13:46

6 Answers 6


There were plans in place to deal with a large scale CME. These storms would not have been instantly deadly, but could have caused a serious case of acute radiation syndrome. The plan was if such an event happened was to get home ASAP, and treat the ARS on Earth. There is an article from NASA talking a bit about this.

If there was a storm threatening, they would have stayed as much "Indoors" as possible. If still in the CM, even a particularly large storm would have only caused a dose around 35 rem inside, although it would have been as much as 400 rem outside the spacecraft! That was the storm that happened in 1972, in the middle of the Apollo program and one of the worst storms ever recorded. The absolute worst case, had there been a large enough storm when astronauts were on the surface they would have immediately aborted an EVA, got back to the CM ASAP, and headed home, where they could be treated as possible.

ARS can be deadly, but the symptoms rarely appear in the first few days. They would have had enough time to make it back home to seek treatment, and probably lived. It was theoretically possible they could have died, but not that likely, given the contingencies in place.


Every Apollo mission sent to the moon was a roll on the dice praying like hell that a major solar flare wouldn't be sending an ejection Earthside. This is why NASA didn't raise that much of a fuss when the last 3 missions were canceled.

As demonstrated in the movie "Space" the Lunar Module would have provided no protection whatsoever. The Command Module would have been able to put a good deal of mass in the way, but anyone outside or on the lunar surface would been killed.

Long term missions that venture outside the Van Allen Belts will have to deal with this hazard.

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    $\begingroup$ A lot of speculation here. Do you have any sources to back up the claim that "this is why NASA didn't raise that much of a fuss when the last 3 missions were canceled"? $\endgroup$
    – Bassinator
    Nov 8, 2018 at 1:00

Yes, they could have been killed if a solar flare had erupted. My 1st-year university essay which I wrote in 2009 as a 64 year old mature student, refuting the dilly claims of the 2001 made-for-television documentary, "Conspiracy Theory: Did we land on the moon?", cites a reference revealing this. Unfortunately that website I referenced no longer exists.

I have read other serious sources which reveal how fatal a strong solar flare could be, but naturally didn't keep their details because "I already had a reference".

However you can read my essay which cites the information, at: https://stanhoodnz.weebly.com/essay-1-apollo.html The university gave me an A+ for it, so I guess you can trust my research of the time.

And anyway, even the idiots who made that conspiracy theory doco support the belief that a strong solar flare can be fatal. They claimed in the doco that the Apollo 16 trip was a lie because the astronauts would have been "fried" by the strongest solar flare of the century which happened while Apollo 16 was in space.

Er, yes and no. The solar flare really did happen and it really was the strongest in the century, but it happened in August 1972, months after Apollo 16 was finished and months before Apollo 17 in December that year.


Part of the plan was to time the missions for a time period when the sun was not expected to be active. Secondary plan was to point the Service Module, getting as much mass between the astronauts and the Sun as possible. But likely would have died.

Orion is being designed to have an area where they can hang out, in such a case, where the mass of the vehicle best protects them. (That is, not an area that will protect them, but best protects them. As best can be done. Best is to avoid it entirely).


CME or Coronal Mass Ejections were a huge question, still are and NASA was very concerned about them as well as our first trip out side the Van Allen belt which protect the earth from CME. We still are concerned about CME and actually sent the crew of the ISS to safe areas in the last year because SOHO picked up on a huge one.

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    $\begingroup$ Welcome to Space Exploration SkipBerne. This is a good beginning, but it is still pretty short and vague, and lacks links to supporting material. Can you expand on it? $\endgroup$
    – kim holder
    Jun 11, 2015 at 17:03

According to Wikipedia, "Whole body doses of more than 1,000 rad are almost invariably fatal" "A dose of 100 to 200 rad delivered to the entire body in less than a day may cause acute radiation syndrome (ARS), but is usually not fatal"


According to Apollo 11 Lunar Surface Journal, https://history.nasa.gov/alsj/a11/a11.posteva.html

Apollo 11 crew received 0.18 rad through the whole mission. Apollo 14, for comparison, received "an average dose of 1.14 rad, in part because their trajectory took them closer to the center of the Belts than any of the other crews"

Comparing the above figures the answer is no, the crew couldn't have been killed by normal solar radiation.

Partial reason for this is because the path of their outbound and inbound trajectories was above the center of Van Allen belts, where radiation is at its maximum. See the related question and answer here: Did the Apollo missions fly "over the top" of the Van Allen radiation belts?

Regarding solar flares and coronal mass ejection - any answer would be a speculation.


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