Mars Radiation

[Yggdrasill]

I have started a YouTube channel and have made a video on Mars Radiation, and thought many here would find it interesting.



It would surprise me if I haven't made any errors, so if you spot any - let me know and I'll see if I can pin it in a comment on the video. I know there are a lot of knowledgeable people here, so hopefully no one completely destroys my video.

One issue I am aware of is that not all figures are fully consistent. The video uses estimates from a range of sources and the different sources have made different assumptions. But the big picture should be largely correct.

I decided to make the video because radiation is something I see generating a lot of uninformed discussion (not on this forum in particular), and hopefully it can over time become less uninformed.

[Slarty1080]

Interesting video - thanks. One point I would make is that there are a lot of unknowns about the effects of some types of space radiation such as heavy ions (Fe⁵⁶⁺) which although very low in numbers, appear to be very damaging. There are also some very complex interactions with some high energy particles creating secondary and tertiary particle cascades. So as things stand there are many unknowns about radiation effects on humans.

Perhaps not relevant, but another big issue is low gravity especially in terms of the longer term if and when colonisation is considered. We don't know to what extent the adverse effects of zero g will be mitigated by 0.38g and what effect it might have on pregnancy and developing children. It could be a show stopper.

[Robotbeat]

Interesting video - thanks. One point I would make is that there are a lot of unknowns about the effects of some types of space radiation such as heavy ions (Fe⁵⁶⁺) which although very low in numbers, appear to be very damaging. There are also some very complex interactions with some high energy particles creating secondary and tertiary particle cascades. So as things stand there are many unknowns about radiation effects on humans.

The idea these are unknown is inaccurate. The higher damage effects of heavy ions is already taken into account in any model of space radiation dose in use today. Same for secondary and tertiary radiation. Don’t mistake having larger error bars than we’d prefer with there being some big unknowns here (ie order of magnitude). This stuff is well-characterized, and the dosage effects assumptions are extremely conservative.

Perhaps not relevant, but another big issue is low gravity especially in terms of the longer term if and when colonisation is considered. We don't know to what extent the adverse effects of zero g will be mitigated by 0.38g and what effect it might have on pregnancy and developing children. It could be a show stopper.

No, it can’t, because we already know of methods to mitigate these problems, and future methods will necessarily be better.

[Yggdrasill]

Interesting video - thanks. One point I would make is that there are a lot of unknowns about the effects of some types of space radiation such as heavy ions (Fe⁵⁶⁺) which although very low in numbers, appear to be very damaging. There are also some very complex interactions with some high energy particles creating secondary and tertiary particle cascades. So as things stand there are many unknowns about radiation effects on humans.

The thing is that heavy ions are roughly as prevalent on the ISS as they are on Mars, so we have a pretty decent understanding of the damage they do. And the data thus far is very promising.

We don't know if the increased levels of these heavy ions during transit would be exponentially worse. The levels would be roughly twice as high. It's not impossible that it would be a problem, but at the same time, it could also be completely fine.

We should get more data about this when we start doing research on the lunar gateway. It should have mostly the same radiation environment as deep space.

Perhaps not relevant, but another big issue is low gravity especially in terms of the longer term if and when colonisation is considered. We don't know to what extent the adverse effects of zero g will be mitigated by 0.38g and what effect it might have on pregnancy and developing children. It could be a show stopper.

Yeah. Low gravity could be problematic. We have absolutely no idea what 0.38g does, so we must do more research on it before we have any idea to what extent it is an issue, or whether it is an issue at all. If it is a major issue, it's perhaps not completely a showstopper for Mars colonization, but it would make it much more difficult.

In my view, this is one of the biggest risks the first Mars crew would take. They absolutely would be guinea pigs, or maybe more accurately canaries.

[Robotbeat]

We actually do have “ideas” about what happens. People often use this idiom, and I think it’s a gross exaggeration. We’ve done lots of hypogravity simulation tests using off-loading, etc, plus interpolation hypothesis (of various curves) between zero gee and full gravity. Plus, we recently tested the long term effects of lunar gravity on mice on ISS, and the effects don’t seem to be too bad. Martian gravity would certainly be better.

[Yggdrasill]

We actually do have “ideas” about what happens. People often use this idiom, and I think it’s a gross exaggeration. We’ve done lots of hypogravity simulation tests using off-loading, etc, plus interpolation hypothesis (of various curves) between zero gee and full gravity. Plus, we recently tested the long term effects of lunar gravity on mice on ISS, and the effects don’t seem to be too bad. Martian gravity would certainly be better.

Assuming results from mice transfer to humans. And assuming results from lunar gravity transfers to martian gravity.

The logical thing is that the data is relevant, and can be extrapolated from, but without actually doing the research on the effects of the Martian environment on actual humans, we just don't know. It could be that some effects get better with lower gravity, and some effects get better with higher gravity, and exactly 0.38g is right in an area that is terrible for some reason.

We do have ideas. And it is reasonable to assume that Mars gravity should be okay for at least a short mission, to learn more about it, but there are some huge gaps in our actual knowledge.

[Slarty1080]

Perhaps not relevant, but another big issue is low gravity especially in terms of the longer term if and when colonisation is considered. We don't know to what extent the adverse effects of zero g will be mitigated by 0.38g and what effect it might have on pregnancy and developing children. It could be a show stopper.

No, it can’t, because we already know of methods to mitigate these problems, and future methods will necessarily be better.

Do you have any references to this research?

[Twark_Main]

It could be that some effects get better with lower gravity, and some effects get better with higher gravity, and exactly 0.38g is right in an area that is terrible for some reason.

While we're invoking bizarre special pleading arguments, it's also possible that there are alien ghosts on Mars who will be angered by our presence, and will pick us off one by one like in certain Hollywood movies. 

Perhaps not relevant, but another big issue is low gravity especially in terms of the longer term if and when colonisation is considered. We don't know to what extent the adverse effects of zero g will be mitigated by 0.38g and what effect it might have on pregnancy and developing children. It could be a show stopper.

No, it can’t, because we already know of methods to mitigate these problems, and future methods will necessarily be better.

Do you have any references to this research?

So just so we're clear, you're asking if we have any references to the fact that people will prefer any superior method that may come along, instead of preferring inferior methods? 

[Twark_Main]

At ~22 minutes in the video, you say that lava tubes suffer from stability issues, so one compromise is to put the colony at the base of the cliff.

The problem is that Mars cliffs also collapse, producing landslides... 

https://www.syfy.com/syfy-wire/heres-why-you-shouldnt-stand-at-the-base-of-a-martian-cliff-in-spring

https://skyandtelescope.org/astronomy-news/four-martian-landslides-caught-in-the-act/

[whitelancer64]

It could be that some effects get better with lower gravity, and some effects get better with higher gravity, and exactly 0.38g is right in an area that is terrible for some reason.

While we're invoking bizarre special pleading arguments, it's also possible that there are alien ghosts on Mars who will be angered by our presence, and will pick us off one by one like in certain Hollywood movies. 

That's not special pleading. We really don't know what level of gravity will mitigate the negative effects of zero g that we have spent the past few decades observing and researching. It could be that Mars gravity (0.37 g) will be sufficient to ameliorate these effects, or it might not. Maybe 0.5 g is the sweet spot. We don't know and we won't know for sure until we either build a rotating space station to study the long term effects of partial g, or we just go there.

Perhaps not relevant, but another big issue is low gravity especially in terms of the longer term if and when colonisation is considered. We don't know to what extent the adverse effects of zero g will be mitigated by 0.38g and what effect it might have on pregnancy and developing children. It could be a show stopper.

No, it can’t, because we already know of methods to mitigate these problems, and future methods will necessarily be better.

Do you have any references to this research?

So just so we're clear, you're asking if we have any references to the fact that people will prefer any superior method that may come along, instead of preferring inferior methods? 

It's obvious that Slarty is asking about the research implied in the statement "we already know of methods to mitigate these problems," which is partly true, we know that vigorous daily exercise and some medications do reduce some of the negative effects of zero g. But we are not able to mitigate all of them. We know nothing about how partial g might affect human pregnancy and childhood development. There have been some studies of mice in partial g (using the rodent habitat in a centrifuge on the ISS) that are promising, however, sometimes research in mice does not pan out when its applied to other animal or human studies.

[Yggdrasill]

At ~22 minutes in the video, you say that lava tubes suffer from stability issues, so one compromise is to put the colony at the base of the cliff.

The problem is that Mars cliffs also collapse, producing landslides... 

That did occur to me.

However, not all cliffs are prone to collapse, just like not all cliffs on earth are prone to collapse. In areas like Valles Marineris, there are a *lot* of cliffs to choose between, so being able to find a good spot with stable cliffs seems likely. And if all the cliffs are unstable, you can just ensure that the habitat is set up outside the expected landslide path, for a bit lower shielding effect, but still some shielding, if the cliffs are within view.

For lava tubes, you are much more at mercy of circumstance. With far fewer options, you may just have to settle for whatever option happens to be remotely close to the area you want to be.

[Yggdrasill]

I found this map of observed caves. https://www.mdpi.com/2072-4292/12/12/1970



As you can see, if you have a specific location in mind for a base, the nearest cave (that we are aware of) could be thousands of kilometers away.

And most of the caves on the map aren't ideal, as they are at a high altitude, making landings more costly (or reducing payload), providing less shielding, and making ISRU more complicated. Water ice is also thought to be most prevalent at lower altitude.

[Robotbeat]

It could be that some effects get better with lower gravity, and some effects get better with higher gravity, and exactly 0.38g is right in an area that is terrible for some reason.

While we're invoking bizarre special pleading arguments, it's also possible that there are alien ghosts on Mars who will be angered by our presence, and will pick us off one by one like in certain Hollywood movies. 

That's not special pleading. We really don't know what level of gravity will mitigate the negative effects of zero g that we have spent the past few decades observing and researching. It could be that Mars gravity (0.37 g) will be sufficient to ameliorate these effects, or it might not. Maybe 0.5 g is the sweet spot. We don't know and we won't know for sure until we either build a rotating space station to study the long term effects of partial g, or we just go there.

Perhaps not relevant, but another big issue is low gravity especially in terms of the longer term if and when colonisation is considered. We don't know to what extent the adverse effects of zero g will be mitigated by 0.38g and what effect it might have on pregnancy and developing children. It could be a show stopper.

No, it can’t, because we already know of methods to mitigate these problems, and future methods will necessarily be better.

Do you have any references to this research?

So just so we're clear, you're asking if we have any references to the fact that people will prefer any superior method that may come along, instead of preferring inferior methods? 

It's obvious that Slarty is asking about the research implied in the statement "we already know of methods to mitigate these problems," which is partly true, we know that vigorous daily exercise and some medications do reduce some of the negative effects of zero g. But we are not able to mitigate all of them. We know nothing about how partial g might affect human pregnancy and childhood development. There have been some studies of mice in partial g (using the rodent habitat in a centrifuge on the ISS) that are promising, however, sometimes research in mice does not pan out when its applied to other animal or human studies.

No. Rotating the whole building like a merry go round would totally mitigate any problems. That’s what tells us for certain this is not a showstopper. It’s probably not the best way, it would suck if this was necessary for kids or whatever but it would for sure work and wouldn’t even be that hard.

It’s extremely unlikely this would the the only possible mitigation. Complex life on Earth developed in the ocean, went to land, then in some cases went back to the land. Life is adaptable to large changes in effective gravity. (Buoyancy and other off-loading methods is not a PERFECT analogue to changes in gravity or zero-gravity, but we’re also not talking about zero gravity but just reduced gravity. Off-loading is considered a close enough analogue to publish peer reviewed studies, so it should not be completely dismissed.) Life, uh, finds a way. Humans, with the benefit of technology, most certainly will.

[Robotbeat]

I think that’s good enough to put the hypogravity temporarily to rest, we should focus on the actual topic of this thread, space radiation.

[whitelancer64]

It could be that some effects get better with lower gravity, and some effects get better with higher gravity, and exactly 0.38g is right in an area that is terrible for some reason.

While we're invoking bizarre special pleading arguments, it's also possible that there are alien ghosts on Mars who will be angered by our presence, and will pick us off one by one like in certain Hollywood movies. 

That's not special pleading. We really don't know what level of gravity will mitigate the negative effects of zero g that we have spent the past few decades observing and researching. It could be that Mars gravity (0.37 g) will be sufficient to ameliorate these effects, or it might not. Maybe 0.5 g is the sweet spot. We don't know and we won't know for sure until we either build a rotating space station to study the long term effects of partial g, or we just go there.

Perhaps not relevant, but another big issue is low gravity especially in terms of the longer term if and when colonisation is considered. We don't know to what extent the adverse effects of zero g will be mitigated by 0.38g and what effect it might have on pregnancy and developing children. It could be a show stopper.

No, it can’t, because we already know of methods to mitigate these problems, and future methods will necessarily be better.

Do you have any references to this research?

So just so we're clear, you're asking if we have any references to the fact that people will prefer any superior method that may come along, instead of preferring inferior methods? 

It's obvious that Slarty is asking about the research implied in the statement "we already know of methods to mitigate these problems," which is partly true, we know that vigorous daily exercise and some medications do reduce some of the negative effects of zero g. But we are not able to mitigate all of them. We know nothing about how partial g might affect human pregnancy and childhood development. There have been some studies of mice in partial g (using the rodent habitat in a centrifuge on the ISS) that are promising, however, sometimes research in mice does not pan out when its applied to other animal or human studies.

No. Rotating the whole building like a merry go round would totally mitigate any problems. That’s what tells us for certain this is not a showstopper. It’s probably not the best way, it would suck if this was necessary for kids or whatever but it would for sure work and wouldn’t even be that hard.

It’s extremely unlikely this would the the only possible mitigation. Complex life on Earth developed in the ocean, went to land, then in some cases went back to the land. Life is adaptable to large changes in effective gravity. (Buoyancy and other off-loading methods is not a PERFECT analogue to changes in gravity or zero-gravity, but we’re also not talking about zero gravity but just reduced gravity. Off-loading is considered a close enough analogue to publish peer reviewed studies, so it should not be completely dismissed.) Life, uh, finds a way. Humans, with the benefit of technology, most certainly will.

The habitat on a circular track concept could produce 1 g, but then again that could be much easier to do in Space (no need to go into a gravity well) and surface bases on Mars or the Moon would only be part-time research stations, which isn't necessarily a bad thing except to those who want full scale colonization.

All of which is cart before horse, we still don't know if any of that is necessary or not.

[Robotbeat]

It’s not at all clear that spinning a building is much harder on the ground with all the available resources than in space. It’s certainly much easier on Earth to build a merry go round than to build a spinning merry go round in orbit. Lots of people (including chidlren) live in mobile homes or actual RVs with wheels.

This is one of those “let’s throw objections at Mars settlement to make the whole thing seem doubtful” things. And Slarty1080 succeeded, we were sidetracked successfully with concern trolling about a problem that might not even BE a problem. An ugly solution exists even to worst-case assumptions, we can doubtless do far better, let’s go back to the actual freaking topic.

[Robotbeat]

The REALLY frustrating thing about responding to off topic concern trolls is that if you don’t respond, people think their objections are valid, and if you DO respond with a solution to even their worst case assumptions, you’ve unwittingly gave the impression that such unscientific worst case assumptions are actually likely to be true, which they most certainly are not (many people struggle immensely with understanding hypotheticals). So let’s focus on radiation, and report other directions as off-topic.

[whitelancer64]

It’s not at all clear that spinning a building is much harder on the ground with all the available resources than in space. It’s certainly much easier on Earth to build a merry go round than to build a spinning merry go round in orbit. Lots of people (including chidlren) live in mobile homes or actual RVs with wheels.

This is one of those “let’s throw objections at Mars settlement to make the whole thing seem doubtful” things. And Slarty1080 succeeded, we were sidetracked successfully with concern trolling about a problem that might not even BE a problem. An ugly solution exists even to worst-case assumptions, we can doubtless do far better, let’s go back to the actual freaking topic.

I don't read that as Slarty's intention at all, it's a very reasonable concern and an area of active study.

[whitelancer64]

The REALLY frustrating thing about responding to off topic concern trolls is that if you don’t respond, people think their objections are valid, and if you DO respond with a solution to even their worst case assumptions, you’ve unwittingly gave the impression that such unscientific worst case assumptions are actually likely to be true, which they most certainly are not (many people struggle immensely with understanding hypotheticals). So let’s focus on radiation, and report other directions as off-topic.

If you responded with information rather than just handwaving the concern away, then whining about it and calling people trolls, it would be a more productive conversation.

[ccdengr]

There have been some studies of mice in partial g (using the rodent habitat in a centrifuge on the ISS) that are promising...

The most promising one I found was "Lunar gravity prevents skeletal muscle atrophy but not myofiber type shift in mice" https://www.nature.com/articles/s42003-023-04769-3 and that says "that gravity greater than 1/6 g might be required to prevent slow-to-fast myofiber type transition" but AFAIK they haven't done any testing for levels between 1/6g and 1g.

[Robotbeat]

The REALLY frustrating thing about responding to off topic concern trolls is that if you don’t respond, people think their objections are valid, and if you DO respond with a solution to even their worst case assumptions, you’ve unwittingly gave the impression that such unscientific worst case assumptions are actually likely to be true, which they most certainly are not (many people struggle immensely with understanding hypotheticals). So let’s focus on radiation, and report other directions as off-topic.

If you responded with information rather than just handwaving the concern away, then whining about it and calling people trolls, it would be a more productive conversation.

I did provide information. Reasoned, logical explanation of a pretty clear solution. The whole entire hypogravity issue is off-topic, THAT’S why it’s dismissed.

[Robotbeat]

It’s not at all clear that spinning a building is much harder on the ground with all the available resources than in space. It’s certainly much easier on Earth to build a merry go round than to build a spinning merry go round in orbit. Lots of people (including chidlren) live in mobile homes or actual RVs with wheels.

This is one of those “let’s throw objections at Mars settlement to make the whole thing seem doubtful” things. And Slarty1080 succeeded, we were sidetracked successfully with concern trolling about a problem that might not even BE a problem. An ugly solution exists even to worst-case assumptions, we can doubtless do far better, let’s go back to the actual freaking topic.

I don't read that as Slarty's intention at all, it's a very reasonable concern and an area of active study.

It’s unreasonable when the topic is completely different.

[Dalhousie]

I have started a YouTube channel and have made a video on Mars Radiation, and thought many here would find it interesting.



It would surprise me if I haven't made any errors, so if you spot any - let me know and I'll see if I can pin it in a comment on the video. I know there are a lot of knowledgeable people here, so hopefully no one completely destroys my video.

One issue I am aware of is that not all figures are fully consistent. The video uses estimates from a range of sources and the different sources have made different assumptions. But the big picture should be largely correct.

I decided to make the video because radiation is something I see generating a lot of uninformed discussion (not on this forum in particular), and hopefully it can over time become less uninformed.

Nice work. Good to see consistent use of Sieverts throughout, comparing against natural high radiation areas on Earth (e.g. Ramsar, Gurapari beach),  pointing out that astronauts won't be spending most of the time exposed on the Martian surface but in habitats, and use of ISS and Mir flight experience. Also pointing out that lava caves are not good places and have other issues and that during transit additional shielding can be readily constructed from supplies (illustrated by a great video) if required.

 It would have been good to have:

1) shown mission numbers from Curiosity (surface, solar max transit), TGO (solar min transit, Mars orbit), and ISS data (inside and outside). 

2) remind people that there are levels of shielding to be avoided, because of secondary radiation effects.

3) I would check the amount of regolith needed to provide adequate shielding against GCR.  We don't have to eliminate them, just reduce them to a figure we find acceptable  (equivalent to high altitude habitations on Earth for example). 

Personally I would not have started with a Musk quote or used SS as a baseline, but that may just be me!

[Twark_Main]

if all the cliffs are unstable, you can just ensure that the habitat is set up outside the expected landslide path, for a bit lower shielding effect, but still some shielding, if the cliffs are within view.

In low gravity and atmosphere, the landslides can travel tens of kilometers. So your setback distance has to be at least that far.

Doing the trigonometry, I don't think you'll be able to achieve any meaningful level of shielding this way.

For lava tubes, you are much more at mercy of circumstance. With far fewer options, you may just have to settle for whatever option happens to be remotely close to the area you want to be.

The implicit assumption here is that lava tubes have the same "stability distribution" as cliffs. I see no reason why this should necessarily be true.


For instance, it may be the case that 99% of lava tubes are geologically stable, whereas only 1% of cliff faces are stable. Obviously these numbers are an extreme example, but they're chosen merely to illustrate the point.

[Yggdrasill]

The implicit assumption here is that lava tubes have the same "stability distribution" as cliffs. I see no reason why this should necessarily be true.


For instance, it may be the case that 99% of lava tubes are geologically stable, whereas only 1% of cliff faces are stable. Obviously these numbers are an extreme example, but they're chosen merely to illustrate the point.

I disagree that there is an implicit assumption of the same stability distribution. Even using your numbers, if there are 1000 times more cliffs than lava tubes, there would be ten times more stable cliffs to chose between. That's really what I'm basing it on - the sheer number of potential sites.

However, I would expect that the stability distribution would be skewed in the favour of cliffs. Having rock and regolith directly above your head will tend to be worse than having it piled up to the side of you. And we can see the path of many lavatubes by how they have partially collapsed for large distances.

And while I didn't go too deeply into the potential solutions, you can get to the same solution with an engineered solution - for example, you could have seven Starship placed close to one another. Then fill the center Starship all the way with water. You now have six Starships where one side blocks radiation with a (up to) 9 meter deep water column, and the other Starships would also help. And each Starship would still have a roughly 180 degree unobstructed view of the surface.

[Twark_Main]

The implicit assumption here is that lava tubes have the same "stability distribution" as cliffs. I see no reason why this should necessarily be true.


For instance, it may be the case that 99% of lava tubes are geologically stable, whereas only 1% of cliff faces are stable. Obviously these numbers are an extreme example, but they're chosen merely to illustrate the point.

I disagree that there is an implicit assumption of the same stability distribution.

Mathematically, this is incorrect.

If you ignore the variable altogether, that's an assumption too. By neglecting to account for it, you're implicitly assuming that it doesn't effect the outcome, which means you're implicitly assuming the numbers are the same between cliffs vs. lava tubes.

Even using your numbers

... numbers which I already said were just made up for the sake of illustration?

What could this possibly prove?  That we can both do elementary arithmetic? 

if there are 1000 times more cliffs than lava tubes, there would be ten times more stable cliffs to chose between. That's really what I'm basing it on - the sheer number of potential sites.

And if 100% of rock faces are unstable and 100% of lava tubes are stable, then the decision reverses again.

My point is that you have to account for it. If you neglect it, or (worse) if you blindly accept as true reverse-engineered numbers just because they automatically confirm your previous conclusion, you're not really dealing with it honestly.

However, I would expect that [I'm correct]

Shocking, to be sure. 

Having rock and regolith directly above your head will tend to be worse than having it piled up to the side of you.

Conversely, archways tend to be more stable than unreinforced retaining walls.

And we can see where many lavatubes go by how they is partially collapsed for large distances.

Let's not ignore the baseline. We also see abundant evidence of scree piles and landslide formations, indicating frequent cliff collapses.

And while I didn't go too deeply into the potential solutions, you can get to the same solution with an engineered solution - for example, you could have seven Starship placed close to one another. Then fill the center Starship all the way with water. You now have six Starships where one side blocks radiation with a (up to) 9 meter deep water column, and the other Starships would also help. And each Starship would still have a  greater than 180 degree unobstructed view of the surface.

Now we're talking.

Spoiler alert: this is what real radiation mitigation will look like, not parking your colony right next to The Cliff Face Of Damocles.

[Yggdrasill]

Mathematically, this is incorrect.

If you ignore the variable altogether, that's an assumption too. By neglecting to account for it, you're implicitly assuming that it doesn't effect the outcome, which means you're implicitly assuming the numbers are the same between cliffs vs. lava tubes.

I agree I am making an assumption about it, but the assumption is not that the distribution is *the same*. The assumption I'm making is that the difference in distribution is not significant enough to change the conclusion. And that is in my view a reasonable assumption, even going by the physics-perspective.

And if 100% of rock faces are unstable and 100% of lava tubes are stable, then the decision reverses again.

My point is that you have to account for it. If you neglect it, or (worse) if you blindly accept as true reverse-engineered numbers just because they automatically confirm your previous conclusion, you're not really dealing with it honestly.

That would be an obviously unreasonable assumption, considering the ample evidence that lava tubes often collapse, and cliffs don't always collapse.

Now we're talking.

Spoiler alert: this is what real radiation mitigation will look like, not parking your colony right next to The Cliff Face Of Damocles.

It is an option. However, using what is already there is preferable to engineering a solution.

But if you land in an area with a number of possible cliffs, and the geologist determines they are all unstable, an engineered solution might be the outcome.

[Twark_Main]

Mathematically, this is incorrect.

If you ignore the variable altogether, that's an assumption too. By neglecting to account for it, you're implicitly assuming that it doesn't effect the outcome, which means you're implicitly assuming the numbers are the same between cliffs vs. lava tubes.

I agree I am making an assumption about it, but the assumption is not that the distribution is *the same*. The assumption I'm making is that the difference in distribution is not significant enough to change the conclusion. And that is in my view a reasonable assumption, even going by the physics-perspective.

And over here I almost stooped to using the overly-paranoid phrasing "roughly the same", but I was already running long and I didn't want to clutter it up with additional words, so I assuming you'd give me the benefit of the doubt and realize what I meant. Mea culpa!

I will, in the future, always phrase my responses to you with agonizingly long and unnecessary precision, exhaustively accounting for (and preemptively responding to) every and all conceivable misinterpretation. You asked for it, you got it! 

And if 100% of rock faces are unstable and 100% of lava tubes are stable, then the decision reverses again.

My point is that you have to account for it. If you neglect it, or (worse) if you blindly accept as true reverse-engineered numbers just because they automatically confirm your previous conclusion, you're not really dealing with it honestly.

That would be an obviously unreasonable assumption, considering the ample evidence that lava tubes often collapse, and cliffs don't always collapse.

Your language use here is extremely loaded.

We could equally say that "cliffs often collapse," and "lava tubes don't always collapse."

Now we're talking.

Spoiler alert: this is what real radiation mitigation will look like, not parking your colony right next to The Cliff Face Of Damocles.

It is an option. However, using what is already there is preferable to engineering a solution.

But if you land in an area with a number of possible cliffs, and the geologist determines they are all unstable, an engineered solution might be the outcome.

The suggestion you're obviously hinting at here is that the inverse might also hold true, in which case we'd "use what is already there" i.e. a cliff face.

However I must note that this same inverse might also hold true for lava tubes. That is:

If the geologist determines a lava tube is stable, using what is already there might be the outcome.

[Yggdrasill]

Nice work. Good to see consistent use of Sieverts throughout, comparing against natural high radiation areas on Earth (e.g. Ramsar, Gurapari beach),  pointing out that astronauts won't be spending most of the time exposed on the Martian surface but in habitats, and use of ISS and Mir flight experience. Also pointing out that lava caves are not good places and have other issues and that during transit additional shielding can be readily constructed from supplies (illustrated by a great video) if required.

 It would have been good to have:

1) shown mission numbers from Curiosity (surface, solar max transit), TGO (solar min transit, Mars orbit), and ISS data (inside and outside). 

2) remind people that there are levels of shielding to be avoided, because of secondary radiation effects.

3) I would check the amount of regolith needed to provide adequate shielding against GCR.  We don't have to eliminate them, just reduce them to a figure we find acceptable  (equivalent to high altitude habitations on Earth for example). 

Personally I would not have started with a Musk quote or used SS as a baseline, but that may just be me!

Thanks!

The primary reason I tied it directly to Starship is the transit time. A lot of the proposed NASA missions use longer transit times, which increases the radiation substantially. Though, with the nuclear engines being worked on, Starship may in fact become a conservative scenario!

And there was obviously more I could have covered, but the video already turned out twice as long as I expected. I didn't look much on the options with less regolith, because you need like a meter for the levels to even start dropping, because of secondary particles, and when you're already adding a meter, you might as well go for three meters.

[Yggdrasill]

The suggestion you're obviously hinting at here is that the inverse might also hold true, in which case we'd "use what is already there" i.e. a cliff face.

However I must note that this same inverse might also hold true for lava tubes. That is:

If the geologist determines a lava tube is stable, using what is already there might be the outcome.

That's fine. If we find a good lava tube that meets all our requirements and is in the right place, using it would be an excellent option. My biggest concern is the idea that we *have to* live underground if we go to Mars. If it is treated as a necessity, it imposes huge restrictions on any mission going to Mars. As well as any future base or settlement.

For many (if not most) people, living underground is not an attractive proposition.

[Dalhousie]

Thanks!

The primary reason I tied it directly to Starship is the transit time. A lot of the proposed NASA missions use longer transit times, which increases the radiation substantially. Though, with the nuclear engines being worked on, Starship may in fact become a conservative scenario!

Assuming 4 month (short) vs. 6 month (long) transits, a 26 month synod, and Earth and Mars departure launch windows 24 months apart, I suspect short transit times are most advantageous  for expeditions (12 months out of 30 in transit vs. 8 out of 28).  This would also give an extra two months on the surface.

The fraction of the cumulative radiation dose for permanent stations that would come from shorter transit times is less (12 months out of 56 in transit vs 8 out of 54).  Even more so for permanent settlements (4 months out of 40 years vs 6 months out of 40 years for 4 vs 6 month in transit), assuming people move at age 30 and live to 70.

I have always found it better to assume conservatively, so I generally stick with longer transits and eschew advanced propulsion and EDarth orbit fueling (which come with their own disadvantages).  But that's just me. 

And there was obviously more I could have covered, but the video already turned out twice as long as I expected. I didn't look much on the options with less regolith, because you need like a meter for the levels to even start dropping, because of secondary particles, and when you're already adding a meter, you might as well go for three meters.

But remember three times thickness means three times to mass to be moved, and three times the overhead load on surface structures. Again, by conservatism sees this to be avoided, if possible.

Of course, if the data from Ramsar and Gurpari beach are correct, we may not need extra shielding over the habitat structures at all as the unshielded radiation dose on the martian surface at low altitudes is already less than these places.

Settlements may still want bunkers for decadal and century scale SPEs.

[Dalhousie]

Thanks!

The primary reason I tied it directly to Starship is the transit time. A lot of the proposed NASA missions use longer transit times, which increases the radiation substantially. Though, with the nuclear engines being worked on, Starship may in fact become a conservative scenario!

Assuming 4 month (short) vs. 6 month (long) transits, a 26 month synod, and Earth and Mars departure launch windows 24 months apart, I suspect short transit times are most advantageous  for expeditions (12 months out of 30 in transit vs. 8 out of 28).  This would also give an extra two months on the surface.

The fraction of the cumulative radiation dose for permanent stations that would come from shorter transit times is less (12 months out of 56 in transit vs 8 out of 54).  Even more so for permanent settlements (4 months out of 40 years vs 6 months out of 40 years for 4 vs 6 month in transit), assuming people move at age 30 and live to 70.

I have always found it better to assume conservatively, so I generally stick with longer transits and eschew advanced propulsion and EDarth orbit fueling (which come with their own disadvantages).  But that's just me. 

And there was obviously more I could have covered, but the video already turned out twice as long as I expected. I didn't look much on the options with less regolith, because you need like a meter for the levels to even start dropping, because of secondary particles, and when you're already adding a meter, you might as well go for three meters.

But remember three times thickness means three times to mass to be moved, and three times the overhead load on surface structures. Again, by conservatism sees this to be avoided, if possible.

Of course, if the data from Ramsar and Gurpari beach are correct, we may not need extra shielding over the habitat structures at all as the unshielded radiation dose on the martian surface at low altitudes is already less than these places.

Settlements may still want bunkers for decadal and century scale SPEs.

But again, greaat work!

[Dalhousie]

if all the cliffs are unstable, you can just ensure that the habitat is set up outside the expected landslide path, for a bit lower shielding effect, but still some shielding, if the cliffs are within view.

In low gravity and atmosphere, the landslides can travel tens of kilometers. So your setback distance has to be at least that far.

Doing the trigonometry, I don't think you'll be able to achieve any meaningful level of shielding this way.

The actively degrading cliffs we have seen on Mars to date have all been in polar areas with instability driven by sublimation of dry ice.  This is not going to be a global problem. 

Cliff dwelling on Earth are all in areas of structural stability.  Why should these not exist on Mars?  We already know that landscape degradation is very slow in most places on Mars.

Photos from Setenil (Spain), a town of several thousand inhabited for centuries.

[Yggdrasill]

Settlements may still want bunkers for decadal and century scale SPEs.

It isn't really needed for SPEs, though. A 500 year event would be in the ballpark of 20-50 mSv in a lightly shielded habitat or on EVA. That's low enough and rare enough that you could really just ignore it, and there would be no statistically significant effects.

Of course, if a 500 year event were to occur, you probably would still take shelter, to some extent or other. Because the radiation is relatively low energy, you definitely wouldn't need meters of mass.

Though, we don't fully know what the sun is capable of. Maybe we could need some form of bunker for something like a 10,000-year event. Although the probability of such incredibly powerful events happening is low, it could happen tomorrow.

[DanClemmensen]

Cliff dwelling on Earth are all in areas of structural stability.  Why should these not exist on Mars?  We already know that landscape degradation is very slow in most places on Mars.

In terms of loss of like, the deadliest earthquake in recorded history was the Shaanxi earthquake in 1556.
   https://en.wikipedia.org/wiki/1556_Shaanxi_earthquake
Many (perhaps most) residents of the region lived in caves dug into the loess cliffs. 100,000 died immediately, and up to 700,000 died in the aftermath. It is relatively easy to dig in loess, but loess is not strong enough to resist a strong earthquake. With modern materials and knowledge, caves in loess could be strengthened to survive such an earthquake.

[Slarty1080]

I have started a YouTube channel and have made a video on Mars Radiation, and thought many here would find it interesting.



It would surprise me if I haven't made any errors, so if you spot any - let me know and I'll see if I can pin it in a comment on the video. I know there are a lot of knowledgeable people here, so hopefully no one completely destroys my video.

One issue I am aware of is that not all figures are fully consistent. The video uses estimates from a range of sources and the different sources have made different assumptions. But the big picture should be largely correct.

I decided to make the video because radiation is something I see generating a lot of uninformed discussion (not on this forum in particular), and hopefully it can over time become less uninformed.

You might find this of interest for scaling:
https://xkcd.com/radiation/

[Dalhousie]

Settlements may still want bunkers for decadal and century scale SPEs.

It isn't really needed for SPEs, though. A 500 year event would be in the ballpark of 20-50 mSv in a lightly shielded habitat or on EVA. That's low enough and rare enough that you could really just ignore it, and there would be no statistically significant effects.

Of course, if a 500 year event were to occur, you probably would still take shelter, to some extent or other. Because the radiation is relatively low energy, you definitely wouldn't need meters of mass.

Though, we don't fully know what the sun is capable of. Maybe we could need some form of bunker for something like a 10,000-year event. Although the probability of such incredibly powerful events happening is low, it could happen tomorrow.

I agree. It depends on how the risk is perceived.

Jiggens et al. (2014) observed that the largest known CME, the 1959 “Carrington event” was unusually fast and took 17.5 hrs to each Earth.  While unshielded astronauts would receive over 1.2 Sv in such an event, those behind 40 g/cm2 of shielding would receive only 0.1 Sv. Mars surface values were not calculated, but would probably be about half this dose.

Do you have modelled numbers for a Mars surface dose?

Jiggens, P., Chavy-Macdonald, M. A., Santin, G., Menicucci, A., Evans, H., and Hilgers, A. 2014. The magnitude and effects of extreme solar particle events. Journal of Space Weather and Space Climate 4, A20, DOI: https://doi.org/10.1051/swsc/2014017.

[Robotbeat]

By far the biggest risk of something like that is to electronics. The radiation dose of 20-50mSv or so isn't lethal, but melting electronics, upon which Mars would be especially dependent on, very likely would be.

[LMT]

...you could have seven Starship placed close to one another. Then fill the center Starship all the way with water. You now have six Starships where one side blocks radiation with a (up to) 9 meter deep water column, and the other Starships would also help.

No, shielding is needed above, and hulls don't help. 

Note persistent Martian doses, on and below the surface.  Paris et al. 2019.  20 mSv / year is the longstanding target limit.

1 2 3

Refs.

Paris, A.J., Davies, E.T., Tognetti, L. and Zahniser, C., 2019. Prospective Lava Tubes at Hellas Planitia. Journal of the Washington Academy of Sciences, 105(3), pp.13-36.
 

[Yggdrasill]

...you could have seven Starship placed close to one another. Then fill the center Starship all the way with water. You now have six Starships where one side blocks radiation with a (up to) 9 meter deep water column, and the other Starships would also help.

No, shielding is needed above, and hulls don't help.

The radiation is omnidirectional, so having shielding in any direction helps reduce radiation.

The most interesting thing I came across while researching is the fact that it helps even having water shielding *below* you. Merely being in the vicinity of water and other light materials helps, because there is less scattered secondary radiation. You can see this in the graphs at 24:30 in the video. The radiation up to around 40 km above the surface is affected by the the surface material. I could have mentioned it in the video, but placing your habitat on top of a glacier could help substantially!

And the hulls did help in your source, by 10%. And six ~200 ton Starships would help more.

Note persistent Martian doses, on and below the surface.  Paris et al. 2019.  20 mSv / year is the longstanding target limit.

1 2 3

Refs.

Paris, A.J., Davies, E.T., Tognetti, L. and Zahniser, C., 2019. Prospective Lava Tubes at Hellas Planitia. Journal of the Washington Academy of Sciences, 105(3), pp.13-36.

Rules like 20 mSv are subject to revision. I was more interested in what is actually dangerous.

[Yggdrasill]

By far the biggest risk of something like that is to electronics. The radiation dose of 20-50mSv or so isn't lethal, but melting electronics, upon which Mars would be especially dependent on, very likely would be.

I'd agree that this might be a bigger concern.

I'm not so sure that it would be a huge issue on Mars though. The amount of energetic particles on the Martian surface is pretty low compared to in space during energetic solar particle events. And it's nothing compared to the Van Allen belts and the radiation belts of Jupiter.

Very much can be done through clever engineering. Machines can be designed for the environment, humans cannot.

[Yggdrasill]

I agree. It depends on how the risk is perceived.

Jiggens et al. (2014) observed that the largest known CME, the 1959 “Carrington event” was unusually fast and took 17.5 hrs to each Earth.  While unshielded astronauts would receive over 1.2 Sv in such an event, those behind 40 g/cm2 of shielding would receive only 0.1 Sv. Mars surface values were not calculated, but would probably be about half this dose.

Do you have modelled numbers for a Mars surface dose?

Jiggens, P., Chavy-Macdonald, M. A., Santin, G., Menicucci, A., Evans, H., and Hilgers, A. 2014. The magnitude and effects of extreme solar particle events. Journal of Space Weather and Space Climate 4, A20, DOI: https://doi.org/10.1051/swsc/2014017.

Here: https://www.irpa.net/members/TS10a.2.pdf

I did have it in the sources page at the end of the video, but it sort of ends up behind the suggested videos. For the future I guess I could use two slides, and leave the top half blank. Probably better. (Note that I don't use almost any figures directly from any source. I have made some assumptions of my own.)

[rfdesigner]

By far the biggest risk of something like that is to electronics. The radiation dose of 20-50mSv or so isn't lethal, but melting electronics, upon which Mars would be especially dependent on, very likely would be.

I'd agree that this might be a bigger concern.

I'm not so sure that it would be a huge issue on Mars though. The amount of energetic particles on the Martian surface is pretty low compared to in space during energetic solar particle events. And it's nothing compared to the Van Allen belts and the radiation belts of Jupiter.

Very much can be done through clever engineering. Machines can be designed for the environment, humans cannot.

Rad hardening is what you do, things like adding in discharge paths, error correction, picking one transistor class over another and so on.  You end up with chips that tend to be a little less dense as they have additional or larger structures, but they're reliable for a much much longer period of time in deep space.

See voyager I & II for early examples that REALLY work, decades of functionality has already been done, what you can't do it take a Laptop you bought from your local Tech-Store, well you can, but it might not last.

Yes rad hardened electronics is more expensive, primarily because the market size is tiny.  Make more stuff all using the same designs and the cost per chip will drop like a stone.

[LMT]

...you could have seven Starship placed close to one another. Then fill the center Starship all the way with water. You now have six Starships where one side blocks radiation with a (up to) 9 meter deep water column, and the other Starships would also help.

No, shielding is needed above, and hulls don't help.

The radiation is omnidirectional, so having shielding in any direction helps reduce radiation.

The most interesting thing I came across while researching is the fact that it helps even having water shielding *below* you. Merely being in the vicinity of water and other light materials helps, because there is less scattered secondary radiation. You can see this in the graphs at 24:30 in the video. The radiation up to around 40 km above the surface is affected by the the surface material. I could have mentioned it in the video, but placing your habitat on top of a glacier could help substantially!

And the hulls did help in your source, by 10%. And six ~200 ton Starships would help more.

Note persistent Martian doses, on and below the surface.  Paris et al. 2019.  20 mSv / year is the longstanding target limit.

1 2 3

Refs.

Paris, A.J., Davies, E.T., Tognetti, L. and Zahniser, C., 2019. Prospective Lava Tubes at Hellas Planitia. Journal of the Washington Academy of Sciences, 105(3), pp.13-36.

No, GCRs are not omnidirectional on the surface.  That's why no design places, e.g., water underneath.

Re: hulls, no, the 10% cut wasn't helpful, hence, "a non-starter for in-transit space travel".

Rules like 20 mSv are subject to revision.

Don't fabricate stories; just learn about the topic.

[spacenut]

I've mentioned this before.  Build your habitats under water storage.  Storing water above habitats with about 1m or 3' of water should block out most of the radiation.  Elevated water also allows for water pressure for potable water without constant pumping.  Sure the structure has to be strong enough to hold the water, but if it is built in glass or plexiglass or transparent aluminum daylight can shine through this water to allow light into various buildings.  I know Mars is cold, but LED lighting with some heat should keep the water from freezing. 

Of course, another is to cover habitats with soil or regolith which insulates from cold as well. 

Certain plastics as well as the hydrogen in water protects from radiation. 

Going out exploring in EV suits will be the time of most exposure.  Well designed rovers can allow a lot of protection. 

Again, 0.38g is the only real unknown for long term colonization.  Since SpaceX is going to go to Mars during a 6 month synod when Mars is closest to earth, and not in the 18 months when Mars is further away.  Seems like a 2 year rotation can give a lot of information back for several years, to determine permanent settlement options. 

[LMT]

Rad hardening is what you do, things like adding in discharge paths, error correction, picking one transistor class over another and so on.

Some history and comparisons:

Space-grade CPUs: How do you send more computing power into space?

Figuring out radiation was a huge "turning point in the history of space electronics."

Jacek Krywko - 11/11/2019

[joek]

...
See voyager I & II for early examples that REALLY work, decades of functionality has already been done, what you can't do it take a Laptop you bought from your local Tech-Store, well you can, but it might not last.
...

Blast from the past. I remember that as it was quite the crash program. See Voyager electronic parts radiation program, volume 1; from pg. 77-41:

In the Voyager program, as mentioned earlier, radiation was originally not considered to be a problem. Subsequently, Pioneer Jupiter flybys indicated the presence of strong radiation belts [understatement of the year], which led to an intensive program to harden the existing Mariner design.

(I worked on the Pioneers, not the Voyagers, but there was quite a bit of exchange between the two teams as you might imagine.)

edit: p.s. Mariner 10/11 morphed into Voyager 1/2.

[Twark_Main]

if all the cliffs are unstable, you can just ensure that the habitat is set up outside the expected landslide path, for a bit lower shielding effect, but still some shielding, if the cliffs are within view.

In low gravity and atmosphere, the landslides can travel tens of kilometers. So your setback distance has to be at least that far.

Doing the trigonometry, I don't think you'll be able to achieve any meaningful level of shielding this way.

The actively degrading cliffs we have seen on Mars to date have all been in polar areas with instability driven by sublimation of dry ice.  This is not going to be a global problem. 

Cliff dwelling on Earth are all in areas of structural stability.  Why should these not exist on Mars?  We already know that landscape degradation is very slow in most places on Mars.

Photos from Setenil (Spain), a town of several thousand inhabited for centuries.

I can't help noticing that the surface is stabilized by a bunch of vegetation...   


That's a "con" for Mars. In the "pro" column, there's no (meaningful amount of) running water, other than the extremely occasional recurring slope lineae which may result from deliquescence.

In the "pro" column for Mars is also.....    no vegetation.   Roots and soil can stabilize the land, but they can also split rocks and dissolve minerals.

[Twark_Main]

The most interesting thing I came across while researching is the fact that it helps even having water shielding *below* you. Merely being in the vicinity of water and other light materials helps, because there is less scattered secondary radiation. You can see this in the graphs at 24:30 in the video. The radiation up to around 40 km above the surface is affected by the the surface material. I could have mentioned it in the video, but placing your habitat on top of a glacier could help substantially!

Yes, when I read the (excellent) paper that graph comes from, I immediately though of paving Mars roads with polyethylene-stabilized regolith "concrete." 

Binder and extra shielding for vehicles driving on top!

[Dalhousie]

I agree. It depends on how the risk is perceived.

Jiggens et al. (2014) observed that the largest known CME, the 1959 “Carrington event” was unusually fast and took 17.5 hrs to each Earth.  While unshielded astronauts would receive over 1.2 Sv in such an event, those behind 40 g/cm2 of shielding would receive only 0.1 Sv. Mars surface values were not calculated, but would probably be about half this dose.

Do you have modelled numbers for a Mars surface dose?

Jiggens, P., Chavy-Macdonald, M. A., Santin, G., Menicucci, A., Evans, H., and Hilgers, A. 2014. The magnitude and effects of extreme solar particle events. Journal of Space Weather and Space Climate 4, A20, DOI: https://doi.org/10.1051/swsc/2014017.

Here: https://www.irpa.net/members/TS10a.2.pdf

I did have it in the sources page at the end of the video, but it sort of ends up behind the suggested videos. For the future I guess I could use two slides, and leave the top half blank. Probably better. (Note that I don't use almost any figures directly from any source. I have made some assumptions of my own.)

Most helpful, thank you.  Unfortunately the full citation at the end of your video is covered by ads for additional videos.  Could you give this please (via PM is OK).

[Twark_Main]

I agree. It depends on how the risk is perceived.

Jiggens et al. (2014) observed that the largest known CME, the 1959 “Carrington event” was unusually fast and took 17.5 hrs to each Earth.  While unshielded astronauts would receive over 1.2 Sv in such an event, those behind 40 g/cm2 of shielding would receive only 0.1 Sv. Mars surface values were not calculated, but would probably be about half this dose.

Do you have modelled numbers for a Mars surface dose?

Jiggens, P., Chavy-Macdonald, M. A., Santin, G., Menicucci, A., Evans, H., and Hilgers, A. 2014. The magnitude and effects of extreme solar particle events. Journal of Space Weather and Space Climate 4, A20, DOI: https://doi.org/10.1051/swsc/2014017.

Here: https://www.irpa.net/members/TS10a.2.pdf

I did have it in the sources page at the end of the video, but it sort of ends up behind the suggested videos. For the future I guess I could use two slides, and leave the top half blank. Probably better. (Note that I don't use almost any figures directly from any source. I have made some assumptions of my own.)

Most helpful, thank you.  Unfortunately the full citation at the end of your video is covered by ads for additional videos.  Could you give this please (via PM is OK).

I always forget that people see those. I have my ad blocker configured to hide them. 

[LMT]

The most interesting thing I came across while researching is the fact that it helps even having water shielding *below* you. Merely being in the vicinity of water and other light materials helps, because there is less scattered secondary radiation. You can see this in the graphs at 24:30 in the video. The radiation up to around 40 km above the surface is affected by the the surface material. I could have mentioned it in the video, but placing your habitat on top of a glacier could help substantially!

Yes, when I read the (excellent) paper that graph comes from, I immediately though of paving Mars roads with polyethylene-stabilized regolith "concrete." 

Binder and extra shielding for vehicles driving on top!

The numbers tell a different story.

Site elevation, not water content, has the main surface effect.  Down on Hellas Planitia, annual surface dose is ~ 125 mSv/yr.  1 2

Compare with "icy" Arabia Terra, higher up, Fig. 6.  What do we see?

Even on Hellas Planitia, overhead shielding would be paramount.  --  How deep are lava tubes, btw?

[Robotbeat]

Yeah, people often underestimate how effective Mars’ atmosphere is at shielding.

At low altitudes it should have an effective thickness of over 40 grams/cm^2 of CO2 due to the slant angle most radiation would have to travel through, and CO2 is a much better shield than aluminum.

rem is the same as cSv, or 10mSv.

[Yggdrasill]

The numbers tell a different story.

Site elevation, not water content, has the main surface effect.  Down on Hellas Planitia, annual surface dose is ~ 125 mSv/yr.  1 2

Compare with "icy" Arabia Terra, higher up, Fig. 6.  What do we see?

Even on Hellas Planitia, overhead shielding would be paramount.  --  How deep are lava tubes, btw?

In figure 6, all the different surface materials assume the same atmospheric shielding, at 21 grams/cm^2.

And wouldn't you know it, the first three are arranged by water content, while the dry materials are fairly similar, except for sulphur concrete, which was a bit better than the other options.

If you look at radiation measurements from MARIE and the like, yes, elevation is the major differing factor. But at the same time, water content is also thought to be largely determined by elevation. With more atmospheric pressure, you have less sublimation. So, we don't have the full picture of what we are actually measuring; effects from atmospheric shielding, or effects from water content.

[LMT]

...we don't have the full picture of what we are actually measuring; effects from atmospheric shielding, or effects from water content.

Look at the MARIE map estimate.  Does dose track elevation globally or not?  What do you see at the poles?

[Yggdrasill]

Actually, when I look a bit closer at the source, I believe the data isn't usable for this purpose.

In the way elevation data and radiation data has been merged, I believe we are mostly seeing the elevation data. (And yes, elevation is strongly correlated with elevation!) I believe the MARIE data is much lower resolution than the elevation data, maybe even to an extent that a very similar map could be produced by multiplying elevation data with a single value for the average radiation level. I would like to see a map of only the radiation measurements, not merged with elevation data, just to get an idea of what detail, if any, it is possible to discern. Though I haven't been able to find such a map. (Anyone know if such a map exists?)

Another aspect is that most of the secondary radiation generated by GCRs striking the surface wouldn't reach MARIE. The atmospheric shielding attenuates the secondary radiation to almost nothing, as can be seen in figure 6. At an altitude of 80 km, the difference in radiation is only 12%, while on the surface, the difference is around 45%.

Measuring a small variation with poor resolution would make it very difficult to distinguish any detail from noise.

[LMT]

Actually, when I look a bit closer at the source, I believe the data isn't usable for this purpose.

In the way elevation data and radiation data has been merged, I believe we are mostly seeing the elevation data. (And yes, elevation is strongly correlated with elevation!) I believe the MARIE data is much lower resolution than the elevation data, maybe even to an extent that a very similar map could be produced by multiplying elevation data with a single value for the average radiation level. I would like to see a map of only the radiation measurements, not merged with elevation data, just to get an idea of what detail, if any, it is possible to discern. Though I haven't been able to find such a map. (Anyone know if such a map exists?)

Another aspect is that most of the secondary radiation generated by GCRs striking the surface wouldn't reach MARIE. The atmospheric shielding attenuates the secondary radiation to almost nothing, as can be seen in figure 6. At an altitude of 80 km, the difference in radiation is only 12%, while on the surface, the difference is around 45%.

Measuring a small variation with poor resolution would make it very difficult to distinguish any detail from noise.

You're exaggerating the neutron effect.  Mistakes chase your wish:

My biggest concern is the idea that we *have to* live underground if we go to Mars. If it is treated as a necessity, it imposes huge restrictions on any mission going to Mars. As well as any future base or settlement. 

Shielding requirement is nothing new, Yggdrasill.

Small above-ground neutron differences from water are expected, but no substitute for shielding, as we saw; hence the meaningful mapped dose estimate, and ongoing interest in low-elevation lava tubes.

Do you understand why ions, rather than fast neutrons, pose the main threat?

[ccdengr]

I believe the MARIE data is much lower resolution than the elevation data... I would like to see a map of only the radiation measurements, not merged with elevation data, just to get an idea of what detail, if any, it is possible to discern. Though I haven't been able to find such a map. (Anyone know if such a map exists?)

MARIE was just measuring the isotropic radiation seen in orbit (MARIE wasn't even pointed at the surface), and not at a very high time resolution, so such a map wouldn't show much of anything.  The maps you see are made by taking the average dose in orbit and modulating it with a model of atmospheric absorption.

You can find the raw MARIE data here: https://pds-ppi.igpp.ucla.edu/search/?filter=ODMA&title=Mars%20Odyssey%20Data%20Holdings

[Yggdrasill]

MARIE was just measuring the isotropic radiation seen in orbit (MARIE wasn't even pointed at the surface), and not at a very high time resolution, so such a map wouldn't show much of anything.  The maps you see are made by taking the average dose in orbit and modulating it with a model of atmospheric absorption.

You can find the raw MARIE data here: https://pds-ppi.igpp.ucla.edu/search/?filter=ODMA&title=Mars%20Odyssey%20Data%20Holdings

That's basically what I thought. I was going to dig a bit more into what data was gathered and how it was processed, but thanks for saving me that work!

So yeah, the map just doesn't contain the information needed to say anything about the effects of water prevalence on radiation conditions, because the levels are simply approximated based on elevation.

[Robotbeat]

I just want to address something here. The Mars radiation dose rate at likely landing site altitudes, like those of MSL Curiosity which carries a radiation dosimeter (which can also measure the radiation quality factor, which happens to be virtually identical between ISS and the Martian surface…2.2 and 2.6 respectively) show a radiation level the same as inside ISS, which has a similar radiation dosimeter. 0.213mGray/day Mars Vs 0.240mGray/day ISS. 201mSv/year (full time on the surface) Mars and 193mSv/year *inside* ISS using the respective quality factors.

The dose is pretty small. So much so that as long as you spend no more than 41 hours a week outside of thick shielding, your dose won’t exceed 50mSv/year, which is the terrestrial radiation worker dose rate limit.

The average American spends 93% of their life inside. Meaning less than 12 hours per week outside. This would mean just a 14mSv/year dose from spending the average time outside. This is a tiny dose, about the same amount that the average resident of South Dakota experiences (when you include medical imaging… which is around 3-4mSv/year average, plus 9mSv/year Radon and 1mSv/year other sources).

So you can spend more than three times as much time outside as the average American without exceeding the 50mSv/day terrestrial radiation worker dose rate limit, not to mention the much higher dose rate we allow for astronauts.

This idea that Mars astronauts would be trapped underground all the time due to radiation risk is just not true. They could spend just as much time outdoors as the average American and do just fine as far as dose limits are concerned.

Source for graph and figures (ISS quality factor comes from something else, but you can basically infer it from stuff here): https://www.nasa.gov/sites/default/files/atoms/files/mars_radiation_environment_nac_july_2017_final.pdf

[Robotbeat]

I calculate that roughly 3 meters of water shielding at MSL’s altitude would reduce the dose to about 35mSv/year vs about 201mSv/year unshielded. So spend 7% unshielded, 14mSv/year dose plus 33mSv/year dose from spending 93% of your time indoors under 3 meters of water shielding, giving you an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers. Assuming 30mSv per transit dose (modest shielding from supplies, 80day transit), that means you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

We can do better if we want by just putting more shielding on top, but that’s already extremely good.

[Yggdrasill]

I calculate that roughly 3 meters of water shielding at MSL’s altitude would reduce the dose to about 35mSv/year vs about 201mSv/year unshielded. So spend 7% unshielded, 14mSv/year dose plus 33mSv/year dose from spending 93% of your time indoors under 3 meters of water shielding, giving you an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers. Assuming 30mSv per transit dose (modest shielding from supplies, 80day transit), that means you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

We can do better if we want by just putting more shielding on top, but that’s already extremely good.

30 mSv per transit isn’t very realistic. That requires quite substantial shielding.

But I guess you are assuming solar minimum? For 20 years you should assume solar average.

[MickQ]

Is there a metre for metre comparison between water and regolith, rock etc ?

[whitelancer64]

Is there a metre for metre comparison between water and regolith, rock etc ?

here

https://civil-defence.ca/protection-factor-pf/

[LMT]

...an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers.

...you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

Researchers respect dose limits.  Posters should, too.

[Twark_Main]

Is there a metre for metre comparison between water and regolith, rock etc ?

here

https://civil-defence.ca/protection-factor-pf/

Nuclear bomb fallout and galactic cosmic radiation are two very different things. 

Better sources:

Aluminum and polyethylene (FYI polyethylene and water are quite similar): https://www.sciencedirect.com/science/article/abs/pii/S2214552416300992

Aluminum and polyethylene: https://ntrs.nasa.gov/api/citations/20170005580/downloads/20170005580.pdf

Regolith and regolith+water: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006246


One "gotcha" to look out for is to check which transport model a paper is using. Modern transport models (eg 3DHZETRN) give more accurate results, at the expense of more computation.

[Robotbeat]

I calculate that roughly 3 meters of water shielding at MSL’s altitude would reduce the dose to about 35mSv/year vs about 201mSv/year unshielded. So spend 7% unshielded, 14mSv/year dose plus 33mSv/year dose from spending 93% of your time indoors under 3 meters of water shielding, giving you an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers. Assuming 30mSv per transit dose (modest shielding from supplies, 80day transit), that means you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

We can do better if we want by just putting more shielding on top, but that’s already extremely good.

30 mSv per transit isn’t very realistic. That requires quite substantial shielding.

But I guess you are assuming solar minimum? For 20 years you should assume solar average.

Youre right that 45mSv would be a lot easier, but I’m assuming a very fast but achievable transit. And no, I’m not using solar minimum but solar average.

[Robotbeat]

...an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers.

...you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

Researchers respect dose limits.  Posters should, too.

No, because the dose rates are so incredibly low that the assumptions that went into the 600mSv (ie like that the astronauts are super young) don’t apply. 1000mSv is also a grandfathered dose limit. And quit just linking to past posts of yours. Quit bossing people around. Settlement in space is not the same as being a terrestrial radiation worker, either, where it’s much easier to reduce the dose.

[Robotbeat]

Is there a metre for metre comparison between water and regolith, rock etc ?

here

https://civil-defence.ca/protection-factor-pf/

Nuclear bomb fallout and galactic cosmic radiation are two very different things. 

Better sources:

Aluminum and polyethylene (FYI polyethylene and water are quite similar): https://www.sciencedirect.com/science/article/abs/pii/S2214552416300992

Aluminum and polyethylene: https://ntrs.nasa.gov/api/citations/20170005580/downloads/20170005580.pdf

Regolith and regolith+water: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006246


One "gotcha" to look out for is to check which transport model a paper is using. Modern transport models (eg 3DHZETRN) give more accurate results, at the expense of more computation.

GEANT4 fits incredibly well with MSL-RAD’s data.

[Twark_Main]

I calculate that roughly 3 meters of water shielding at MSL’s altitude would reduce the dose to about 35mSv/year vs about 201mSv/year unshielded. So spend 7% unshielded, 14mSv/year dose plus 33mSv/year dose from spending 93% of your time indoors under 3 meters of water shielding, giving you an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers. Assuming 30mSv per transit dose (modest shielding from supplies, 80day transit), that means you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

We can do better if we want by just putting more shielding on top, but that’s already extremely good.

30 mSv per transit isn’t very realistic. That requires quite substantial shielding.

But I guess you are assuming solar minimum? For 20 years you should assume solar average.

Youre right that 45mSv would be a lot easier, but I’m assuming a very fast but achievable transit. And no, I’m not using solar minimum but solar average.

At 30 mSv per 80 days, that's 137 mSv/year.

I cannot see how this level of shielding is achievable just using supplies. Even assuming a spherical 1 meter thick shield of polyethylene, I'm only getting down to ~250 mSv/year.

Realistic shielding levels are around 20 cm of polyethylene, which gets you down to roughly 350 mSv/year.

[Robotbeat]

I calculate that roughly 3 meters of water shielding at MSL’s altitude would reduce the dose to about 35mSv/year vs about 201mSv/year unshielded. So spend 7% unshielded, 14mSv/year dose plus 33mSv/year dose from spending 93% of your time indoors under 3 meters of water shielding, giving you an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers. Assuming 30mSv per transit dose (modest shielding from supplies, 80day transit), that means you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

We can do better if we want by just putting more shielding on top, but that’s already extremely good.

30 mSv per transit isn’t very realistic. That requires quite substantial shielding.

But I guess you are assuming solar minimum? For 20 years you should assume solar average.

Youre right that 45mSv would be a lot easier, but I’m assuming a very fast but achievable transit. And no, I’m not using solar minimum but solar average.

At 30 mSv per 80 days, that's 137 mSv/year.

I cannot see how this level of shielding is achievable just using supplies. Even assuming a spherical 1 meter thick shield of polyethylene, I'm only getting down to ~250 mSv/year.

Realistic shielding levels are around 20 cm of polyethylene, which gets you down to roughly 350 mSv/year.

Crew surrounded by propellant tanks.

[Twark_Main]

Is there a metre for metre comparison between water and regolith, rock etc ?

here

https://civil-defence.ca/protection-factor-pf/

Nuclear bomb fallout and galactic cosmic radiation are two very different things. 

Better sources:

Aluminum and polyethylene (FYI polyethylene and water are quite similar): https://www.sciencedirect.com/science/article/abs/pii/S2214552416300992

Aluminum and polyethylene: https://ntrs.nasa.gov/api/citations/20170005580/downloads/20170005580.pdf

Regolith and regolith+water: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006246


One "gotcha" to look out for is to check which transport model a paper is using. Modern transport models (eg 3DHZETRN) give more accurate results, at the expense of more computation.

GEANT4 fits incredibly well with MSL-RAD’s data.

That isn't as ironclad as it sounds, because you're really only testing one single value for the shielding thickness.

For polyethylene it doesn't matter so much, since all the models pretty much agree. For aluminum, there's more variation in the overall shape of the curve, where the minimum lies, and what minimum dose rate is achievable.



Note that in the comparison chart they didn't even test 3DHZETRN. At large thicknesses, 3DHZETRN tends to have the biggest deviation from other transport models (especially 1D or modified 1D models).

[Twark_Main]

I calculate that roughly 3 meters of water shielding at MSL’s altitude would reduce the dose to about 35mSv/year vs about 201mSv/year unshielded. So spend 7% unshielded, 14mSv/year dose plus 33mSv/year dose from spending 93% of your time indoors under 3 meters of water shielding, giving you an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers. Assuming 30mSv per transit dose (modest shielding from supplies, 80day transit), that means you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

We can do better if we want by just putting more shielding on top, but that’s already extremely good.

30 mSv per transit isn’t very realistic. That requires quite substantial shielding.

But I guess you are assuming solar minimum? For 20 years you should assume solar average.

Youre right that 45mSv would be a lot easier, but I’m assuming a very fast but achievable transit. And no, I’m not using solar minimum but solar average.

At 30 mSv per 80 days, that's 137 mSv/year.

I cannot see how this level of shielding is achievable just using supplies. Even assuming a spherical 1 meter thick shield of polyethylene, I'm only getting down to ~250 mSv/year.

Realistic shielding levels are around 20 cm of polyethylene, which gets you down to roughly 350 mSv/year.

Crew surrounded by propellant tanks.

Neat concept. Has anyone actually proposed such a vehicle? Last time I checked that was not Starship's configuration, and currently there are no plausible Starship competitors that I'm aware of.


How much thickness are you assuming?

[Robotbeat]

Fine, 45mSv LOL

(But if you must insist, the idea is basically several meters of methane, which is a better shield than even polyethylene in terms of areal density, although not by much.)

Also, you’re modeling the solar minimum whereas I was looking at the average environment over a full solar cycle.

EDIT: Also, if shielding becomes less effective with thickness due to increased secondaries and it's desired to keep getting even lower doses without being deep underground, the solution is nearly always to march down the periodic table. Eventually, liquid hydrogen. The alternative is electromagnetic shielding.

However, remember that EARTH'S terrestrial radiation doses approach about 14mSv/year in some US states, and these do not have the expected increased mortality rates. And in some places like Ramsar, Iran, for instance, doses can be as high as 260mSv/year, and people don't seem to have significantly elevated cancer risk, there. So in terms of settlement, it's not at all clear that hyper-conservative terrestrial radiation worker safety limits are actually important at all. 50-100mSv/year could be just fine.


Very high background radiation areas of Ramsar, Iran: preliminary biological studies
https://pubmed.ncbi.nlm.nih.gov/11769138/

People in some areas of Ramsar, a city in northern Iran, receive an annual radiation absorbed dose from background radiation that is up to 260 mSv y(-1), substantially higher than the 20 mSv y(-1) that is permitted for radiation workers. Inhabitants of Ramsar have lived for many generations in these high background areas. Cytogenetic studies show no significant differences between people in the high background compared to people in normal background areas. An in vitro challenge dose of 1.5 Gy of gamma rays was administered to the lymphocytes, which showed significantly reduced frequency for chromosome aberrations of people living in high background compared to those in normal background areas in and near Ramsar. Specifically, inhabitants of high background radiation areas had about 56% the average number of induced chromosomal abnormalities of normal background radiation area inhabitants following this exposure. This suggests that adaptive response might be induced by chronic exposure to natural background radiation as opposed to acute exposure to higher (tens of mGy) levels of radiation in the laboratory. There were no differences in laboratory tests of the immune systems, and no noted differences in hematological alterations between these two groups of people.

. It was determined that Mamuju was a unique HNBRA with the annual efective dose between 17 and 115 mSv, with an average of 32 mSv. The lifetime cumulative dose calculation suggested that Mamuju residents could receive as much as 2.2 Sv on average which is much higher than the average dose of atomic bomb survivors for which risks of cancer and non-cancer diseases are demonstrated.

https://pubmed.ncbi.nlm.nih.gov/34272409/

(So again, I don't think 20mSv/year is the maximum for settlement. Maybe we limit that for children, but probably 50-100mSv/year is fine for adults...)

Epidemiological studies in several regions of the world (Ramsar, Yangjiang, Kerala and Guarapari) reported no correlation between radiation exposures in the HNBRA and cancer rate or mortality

[LMT]

...an annual dose of about 47mSv/year, under the 50mSv/year annual dose limit for terrestrial radiation workers.

...you could be on Mars for 20 years before getting a 1 Sievert cumulative dose.

Researchers respect dose limits.  Posters should, too.

No, because the dose rates are so incredibly low that the assumptions that went into the 600mSv (ie like that the astronauts are super young) don’t apply. 1000mSv is also a grandfathered dose limit. And quit just linking to past posts of yours. Quit bossing people around. Settlement in space is not the same as being a terrestrial radiation worker, either, where it’s much easier to reduce the dose.

Many mistakes there; you even ignored the radiation worker's actual ICRP dose limit.   

--

Sim exercise gives familiarity with the challenge.  Posters can build free HZETRN shielding sims, with various material layers and historical cosmic ray fluxes, via OLTARIS.

[Robotbeat]

Yeah, I've been doing sims in Oltaris this whole time.

[VSECOTSPE]

Epidemiological studies in several regions of the world (Ramsar, Yangjiang, Kerala and Guarapari) reported no correlation between radiation exposures in the HNBRA and cancer rate or mortality

Not relevant.

Those are areas on Earth with high concentrations of radon, which emits 5.5MeV alpha particles (helium nuclei).  The background radiation threat at Mars is GCR, which is every nuclei on the atomic table from helium to uranium, 90% of which are coming in at energies between 100MeV and 10GeV.  Thus, the energy deposited by a GCR at Mars is 18 to 1800 times higher than the energy deposited by an alpha particle from radon on Earth. 

At the low end, that’s like the difference between getting hit by a ball thrown at 8mph (top speed of a world athlete) and a ball thrown at 144mph (almost the top speed of a typical hypercar in the quarter-mile).  At the high end, that’s like the difference between getting hit by a ball tossed at 8mph (top speed of a world athlete) and a ball thrown at Mach 2.4 (almost the top speed of an F-15 fighter jet).

In each case, we can’t extrapolate the biological impact of the latter from the former.  The energies and physics involved are too different.

[Robotbeat]

This absolutely IS relevant. This is exactly what the “quality factor” is for! Alphas are capable of double DNA breakage.

Additionally, arguably the damage is WORSE for getting hit with a Radon alpha as the lungs are extremely sensitive to radiation and the energy is deposited in an extremely short distance (the Bragg Peak) instead of stretched out over the path of the particle like higher energy particles. Also, by the time Radiation gets through the shielding and atmosphere, most of the effect I believe is from secondaries.

This is all kind of lame excuses to ignore the evidence that low chronic doses don’t have a linear effect. “But it’s complicated” is not an argument to hand-wave away such evidence, and analogies about supersonic travel are just unscientific rhetoric (and work the opposite way the physics of radiation *actually* work, see “Bragg Peak”, but it sounds good and I’m sure you’ll get some likes). Let’s do better.

[VSECOTSPE]

This absolutely IS relevant. This is exactly what the “quality factor” is for! Alphas are capable of double DNA breakage.

Additionally, arguably the damage is WORSE for getting hit with a Radon alpha as the lungs are extremely sensitive to radiation and the energy is deposited in an extremely short distance (the Bragg Peak) instead of stretched out over the path of the particle like higher energy particles.

This misunderstands or misportrays Bragg Curves.  Higher-energy particles deposit more of their energy more deeply in biological tissue, which is _not_ a good thing.  Per this Bragg Curve, the energy deposition of 6MeV proton stream tails off after a centimeter or two, while a 250MeV proton stream tails off around 20 centimeters deep.  The former is in the ballpark of alpha radiation from radon.  The latter is in the ballpark of low-end GCR.

https://en.m.wikipedia.org/wiki/Bragg_peak#/media/File%3ABraggPeak-en.svg

This is all kind of lame excuses to ignore the evidence that low chronic doses don’t have a linear effect. “But it’s complicated” is not an argument to hand-wave away such evidence,

The health threats from the green 6MeV line in that graph above will _not_ be the same as the health threats from the blue and red 250MeV lines in that graph.  They’re literally damaging different parts of the anatomy.  One won’t reach the lungs while the other will.  We cannot equate GCRs with alpha particles from radon.  Just because one type of low-energy particle does not appear to correlate with higher incidences of certain negative health outcomes does not mean that other types of much higher energy particles will have the same health outcomes.

Not all types and energies of radiation are the same.  It’s an easy — not complicated — concept to grasp.

and analogies about supersonic travel are just unscientific rhetoric

It’s not rhetoric.  It’s explaining the differences in the energies involved using velocities that we’re all familiar with.

[Yggdrasill]

Both alpha and heavy ions have a radiation weighting factor of 20. There could well be a difference between these two forms of radiation, and these values will probably be updated in the future, but that is our current understanding.

It is true that alpha radiation from radioactive decay doesn't penetrate deeply, but you can instead compare the effects with 20 times more gamma radiation instead, which penetrates even deeper.

[Yggdrasill]

It's a fair point that the experiences we have with radon on earth aren't quite applicable to space radiation, though, as the radiation doses are not whole body doses, but are instead mostly directed at skin and lung-tissue.

Still, no increased mortality has been proven below 100 mSv/year, for any radiation in any setting.

[VSECOTSPE]

Both alpha and heavy ions have a radiation weighting factor of 20. There could well be a difference between these two forms of radiation, and these values will probably be updated in the future, but that is our current understanding.

The ICRP warns against using their RBE measures to equate low- and high-energy radiation doses.    In part, this is because RBE measures do not take into account tissue weighting factors, and, as discussed above, low-energy radiation sources will impact different tissues than high-energy radiation doses.  So the “current understanding” of the international body that sets the weighting factors talked about in this thread recommends against using those weighting factors in the way that folks are using them in this thread.

Even the same particle will have different radiation weighting factors assigned to it depending on its energy (electron-volts), as the chart linked below for neutrons shows:

https://en.m.wikipedia.org/wiki/Relative_biological_effectiveness#/media/File%3ANeutron_radiation_weighting_factor_as_a_function_of_kinetic_energy.gif

The health threat of any particular radiation dose depends on the particle type(s), the flux, _and_ the  energy spectrum of the radiation.  Equating the biological impact of different particle types with wildly different energy spectra just because they have a similar flux is unsupported by the research, the relevant standards-setting bodies, and common sense physics.  It’s junk science masquerading as astronaut health guidelines.

[sebk]

This absolutely IS relevant. This is exactly what the “quality factor” is for! Alphas are capable of double DNA breakage.

Additionally, arguably the damage is WORSE for getting hit with a Radon alpha as the lungs are extremely sensitive to radiation and the energy is deposited in an extremely short distance (the Bragg Peak) instead of stretched out over the path of the particle like higher energy particles.

This misunderstands or misportrays Bragg Curves.  Higher-energy particles deposit more of their energy more deeply in biological tissue, which is _not_ a good thing.  Per this Bragg Curve, the energy deposition of 6MeV proton stream tails off after a centimeter or two, while a 250MeV proton stream tails off around 20 centimeters deep.  The former is in the ballpark of alpha radiation from radon.  The latter is in the ballpark of low-end GCR.

https://en.m.wikipedia.org/wiki/Bragg_peak#/media/File%3ABraggPeak-en.svg

This is all kind of lame excuses to ignore the evidence that low chronic doses don’t have a linear effect. “But it’s complicated” is not an argument to hand-wave away such evidence,

The health threats from the green 6MeV line in that graph above will _not_ be the same as the health threats from the blue and red 250MeV lines in that graph.  They’re literally damaging different parts of the anatomy.  One won’t reach the lungs while the other will. 

Huh?! Radon is a gas and it's breathed in. Attacking lungs is it's primary damage path.

And GCRs will reach lungs too, of course.

We cannot equate GCRs with alpha particles from radon.  Just because one type of low-energy particle does not appear to correlate with higher incidences of certain negative health outcomes does not mean that other types of much higher energy particles will have the same health outcomes.

Not all types and energies of radiation are the same.  It’s an easy — not complicated — concept to grasp.

Exactly. That's what quality factor is and that's what Robotbeat already included. The little difference between Gray and Sievert units.

and analogies about supersonic travel are just unscientific rhetoric

It’s not rhetoric.  It’s explaining the differences in the energies involved using velocities that we’re all familiar with.

It definitely is. Total BS rhetoric at that. Please stop it.

It just demonstrates the lack of basic understanding of what unit of irradiation is. It's the amount of energy deposited in a unit of mass. It's then multiplied by quality factor (sievert), or not (gray).

1Gy of of alphas is the same amount of deposited energy as 1Gy of electrons which is the same amount of deposited energy as as 1Gy of gammas which is the same amount of deposited energy as as 1Gy of heavy nuclei. Quality factors are different (electrons and gammas are 20x less), but that's why you have units with quality factors included (Sv).

[Yggdrasill]

The ICRP warns against using their RBE measures to equate low- and high-energy radiation doses.    In part, this is because RBE measures do not take into account tissue weighting factors, and, as discussed above, low-energy radiation sources will impact different tissues than high-energy radiation doses.  So the “current understanding” of the international body that sets the weighting factors talked about in this thread recommends against using those weighting factors in the way that folks are using them in this thread.

There are certainly unknowns. But we don't know what we don't know. We can only go by the information we have.

Even the same particle will have different radiation weighting factors assigned to it depending on its energy (electron-volts), as the chart linked below for neutrons shows:

https://en.m.wikipedia.org/wiki/Relative_biological_effectiveness#/media/File%3ANeutron_radiation_weighting_factor_as_a_function_of_kinetic_energy.gif

The health threat of any particular radiation dose depends on the particle type(s), the flux, _and_ the  energy spectrum of the radiation.  Equating the biological impact of different particle types with wildly different energy spectra just because they have a similar flux is unsupported by the research, the relevant standards-setting bodies, and common sense physics.  It’s junk science masquerading as astronaut health guidelines.

The neutron is a fine example. The weighting factor went from simply being 10 back in the days to a much more complicated (and accurate) graph. But it wasn't revised *up*, specifically. For low and high energies, the factor is now close to 2.5, and for energies around 1 MeV, it's around 20.

We may see the factors for protons, alpha and heavy ions also being updated at some point, but we don't know in what way. It might be revised down for the energies we are talking about, or up.

[Robotbeat]

Yup. And I’ve used the ICRP60 equation Quality Factor for modeling work I’ve done in Oltaris. It’s if anything more conservative for neutrons than the newer ICRP-103.

[VSECOTSPE]

Huh?! Radon is a gas and it's breathed in. Attacking lungs is it's primary damage path.

Yes, which is another reason why we can’t project Mars GCR damage based on Earth radon.  We don’t breathe in GCR.

My point above was that even if a 5.5MeV alpha source like radon was placed above a subject’s head like GCR raining down on Mars, those alpha particles will deposit most of their energy in the skull, shoulders and rib cage, while 100MeV+ GCRs will deposit energy in the lungs and other vital, cancer-prone organs (brain, digestive system, reproductive system, endocrine system, etc.)

Different types and energies of radiation vary in their effects on biological systems.  We cannot extrapolate the impact of high-energy GCR from the impact of low-energy alpha radiation.  The governing body on these units actually warns against making exactly that kind of low- versus high-energy comparison.

Exactly. That's what quality factor is and that's what Robotbeat already included. The little difference between Gray and Sievert units.

Sieverts treat all types of tissue damage the same, but they’re not.  To do that, we have to pay attention to tissue weighting factors.

It definitely is. Total BS rhetoric at that. Please stop it.

It just demonstrates the lack of basic understanding of what unit of irradiation is. It's the amount of energy deposited in a unit of mass.

It's then multiplied by quality factor (sievert), or not (gray).

1Gy of of alphas is the same amount of deposited energy as 1Gy of electrons which is the same amount of deposited energy as as 1Gy of gammas which is the same amount of deposited energy as as 1Gy of heavy nuclei.

No, in biological systems, the energy of the individual particles matter for multiple reasons.  This is especially true for the HZE element of GCR.  Besides the international bodies, NASA’s own researchers in this area and medical doctors tell us this:

The quality factor (QF) as defined in International Commission on Radiological Protection report no. 26 or in International Commission on Radiation Units and Measurements report no. 40 is not expected to be a valid method for assessing the biological risk for deep missions where the high-energy heavy ion (HZE) particles of the galactic cosmic rays (GCR) are of major concern.  No human data for cancer induction from the HZE particles exist, and information on biological effectiveness is expected to be taken from experiments with animals and cultured cells.  Experiments with cultured cells indicate that the relative biological effectiveness (RBE) of the HZE particles is dependent on particle type, energy, and the level of fluency.  Use of a single parameter, such as lineal energy transfer (LET) or lineal energy to determine radiation quality will therefor represent an extreme oversimplification for GCR risk assessment.

https://ntrs.nasa.gov/api/citations/19910007668/downloads/19910007668.pdf

[VSECOTSPE]

There are certainly unknowns. But we don't know what we don't know. We can only go by the information we have.

And the information we have (see my prior posts) is that we can’t equate exposure to low-energy background radiation on Earth with exposure to high-energy background radiation at Mars.  We can’t just add up the Grays or Sieverts from GCR or HZEs at Mars and say, well, it’s in the ballpark of the Grays or Sieverts from low-energy background radiation on Earth that show little or no higher incidence of cancer or mortality among high exposure populations on Earth — therefore, we must be safe at Mars.  These different energies impact different tissues, the tracks through the tissues are different, and the damage done to the tissues are different.  For example, former NASA researcher Frank Cucinotta (now at UNLV) has found that the targeted effect model historically used does not work for GCR damage because “the [GCR] damaged cells send signals to the surrounding, unaffected cells and likely modify the tissues' microenvironments. Those signals seem to inspire the healthy cells to mutate, thereby causing additional tumors or cancers.”  The non-targeted effect models that more accurately portray GCR damage in subject tissues have a “two-fold or more increase in cancer risk” versus the targeted effect models.

https://phys.org/news/2017-06-collateral-cosmic-rays-cancer-mars.html

https://www.nature.com/articles/s41598-017-02087-3.pdf

[LMT]

Michel et al. 2018 plots dose limit history.

Refs.

Michel, R., Lorenz, B. and Völkle, H., 2018.  Radiation protection today – success, problems, recommendations for the future.  Fachverband für Strahlenschutz eV.
 

[Twark_Main]

Yup. And I’ve used the ICRP60 equation Quality Factor for modeling work I’ve done in Oltaris. It’s if anything more conservative for neutrons than the newer ICRP-103.

Have you had any success "salting" a hydrogen-rich shield with neutron absorbers, eg boron-10 or gadolinium-157?

[LMT]

Yup. And I’ve used the ICRP60 equation Quality Factor for modeling work I’ve done in Oltaris. It’s if anything more conservative for neutrons than the newer ICRP-103.

Have you had any success "salting" a hydrogen-rich shield with neutron absorbers, eg boron-10 or gadolinium-157?

Quick edit; give it a try and post mSv.  But posters know that ions are the main threat, not fast neutrons.

[Robotbeat]

Neutrons can be like 20-40% the dose.

[LMT]

Neutrons can be like 20-40% the dose.

You made basic radiation mistakes recently; correct mistakes before telling a new story.

[Robotbeat]

Neutrons can be like 20-40% the dose.

You made basic radiation mistakes recently; correct mistakes before telling a new story.

LOL, what “mistake”? You mean that over 5 years, the dose is 20mSv/year limit? Sure. But I wasn’t technically wrong by mentioning the 50mSv/year limit, that’s just for a single isolated year, not for every year.

But I don’t get the obsession with the arbitrary limits for terrestrial workers. These are fundamentally conservative, they do not apply to astronauts, and there’s strong reason to doubt that 50-100mSV/year might be fine, given data from high background radiation areas like Ramsay, Iran and that one place is Sulawesi, Indonesia. (Sulawesi is a wonderful place, BTW…)

I was just using that as an example, not a requirement. But there you go.

As far as neutrons, there’s no changing story. It’s simply factual. After GCRs have passed through shield material like the atmosphere, they tend to make a lot of neutrons and that tends to be a significant part of the dose. For low altitudes on Mars, I’ve found that using a Boron-10 shield about an inch thick beats out polyethylene. Boron-10 is good at absorbing those extra neutrons, especially when they’re slow. Boron-10 is more expensive than I’d like ($5-10/gram for large orders?), but NASA can definitely afford that.

Haven’t tried Gadolinium, but it’s very heavy, so it might produce a lot of secondaries from GCR.

Even a member of the public might receive about 14mSv/year in a place like South Dakota. And some regions are much higher, that’s just for the state level (about 10mSv/year from natural sources, the rest from medical imaging, etc).


Some houses in the US and Canada have radon levels so high that the effective dose can be over 80mSv/year if lower parts of the home (like the basement) are occupied. Which is ironic, as the lower parts or basement of a Mars habitat would have lower radiation dose and likely no radon as it’d be positively pressurized.

[LMT]

You made basic radiation mistakes recently; correct mistakes before telling a new story.

LOL, what “mistake”? You mean that over 5 years, the dose is 20mSv/year limit? Sure. But I wasn’t technically wrong by mentioning the 50mSv/year limit, that’s just for a single isolated year, not for every year.

Multiple mistakes, botching even the definition of a radiation limit, yes.  "Quit bossing people around," with basic definitions, oho. 

Boron-10 is more expensive than I’d like...

Boron shielding on Mars is...  Who will explain?

[Robotbeat]

You’re dismissive and misrepresenting what others say. Terrestrial limits are not applied to astronauts, space agencies develop their own limits. Regulatory bodies also aren’t the laws of physics, their role is to protect workers and the public, not say how the human body responds just by fiat. I only mentioned it as a point of comparison. And the thread doesn’t need to be locked, you need to just stop bossing others around, thankyouverymuch.

EDIT: and fair enough, I could also bring down the temperature of the conversation a bit.

[Slarty1080]

Interesting video - thanks. One point I would make is that there are a lot of unknowns about the effects of some types of space radiation such as heavy ions (Fe⁵⁶⁺) which although very low in numbers, appear to be very damaging. There are also some very complex interactions with some high energy particles creating secondary and tertiary particle cascades. So as things stand there are many unknowns about radiation effects on humans.

The thing is that heavy ions are roughly as prevalent on the ISS as they are on Mars, so we have a pretty decent understanding of the damage they do. And the data thus far is very promising.

We don't know if the increased levels of these heavy ions during transit would be exponentially worse. The levels would be roughly twice as high. It's not impossible that it would be a problem, but at the same time, it could also be completely fine.

We should get more data about this when we start doing research on the lunar gateway. It should have mostly the same radiation environment as deep space.

This is an interesting point do you have any references for the dose of heavy ions that can be expected on the surface of Mars v the ISS v interplanetary space?

[Twark_Main]

After GCRs have passed through shield material like the atmosphere, they tend to make a lot of neutrons and that tends to be a significant part of the dose. For low altitudes on Mars, I’ve found that using a Boron-10 shield about an inch thick beats out polyethylene. Boron-10 is good at absorbing those extra neutrons, especially when they’re slow. ....

Haven’t tried Gadolinium, but it’s very heavy, so it might produce a lot of secondaries from GCR.

It sounds like you've been trying to replace the hydrogen-rich shield with B-10/Ga-157.

When I said "salting a hydrogen-rich shield with neutron absorbers," I meant keep the polyethylene but add in a small amount of neutron absorber material to soak up the neutrons.

Boron-10 is more expensive than I’d like ($5-10/gram for large orders?), but NASA can definitely afford that.

You don't actually have to go through all the expense of separating into isotopically pure B-10 and Ga-157. I just gave the isotopes so it's easier to put in OLTARIS. 

Natural boron contains 20% B-10, and natural gadolinium contains 16% Ga-157. If you're just "salting" with a small amount of these materials it should be fine.

[Robotbeat]

There’s not nearly as much benefit if you’re using the natural isotope mix, tho. Might as well just use polyethylene.

You don’t necessarily need much material if it’s just used as a radiation protection garment on the torso. The torso is the vast majority of the risk of radiation induced death (ie from cancer mostly), with the lungs by themselves having half that risk.

[VSECOTSPE]

... 50-100mSV/year might be fine, given data from high background radiation areas like Ramsay, Iran and that one place is Sulawesi, Indonesia. (Sulawesi is a wonderful place, BTW…)

...Some houses in the US and Canada have radon levels so high that the effective dose can be over 80mSv/year if lower parts of the home (like the basement) are occupied. Which is ironic, as the lower parts or basement of a Mars habitat would have lower radiation dose and likely no radon as it’d be positively pressurized.

We cannot project the health effects of low-energy alpha radiation from inhaled radon onto the health effects of external sources of space radiation, which is dominated by high-energy GCR, especially HZEs.  The physics is different by orders of magnitude and the impact on tissues is different in terms of depth of energy deposition, tracks, and damage to neighboring cells. International standards bodies tell us this.  NASA experts tells us this.  Researchers in academia tell us this.  See my prior three posts in this thread.

[Robotbeat]

... 50-100mSV/year might be fine, given data from high background radiation areas like Ramsay, Iran and that one place is Sulawesi, Indonesia. (Sulawesi is a wonderful place, BTW…)

...Some houses in the US and Canada have radon levels so high that the effective dose can be over 80mSv/year if lower parts of the home (like the basement) are occupied. Which is ironic, as the lower parts or basement of a Mars habitat would have lower radiation dose and likely no radon as it’d be positively pressurized.

We cannot project the health effects of low-energy alpha radiation from inhaled radon onto the health effects of external sources of space radiation, which is dominated by high-energy GCR, especially HZEs.  The physics is different by orders of magnitude

No, it isn't.

and the impact on tissues is different in terms of depth of energy deposition, tracks, and damage to neighboring cells.

No, the damage is comparable and long term effects are likely to be similar. And you seem to have hopped onto this train before understanding that radon's dose gets absorbed directly IN the lungs where the alpha particle's short range actually makes the impact WORSE as you get the maximum of the Bragg Peak right in the most radiation-sensitive part of the body (lung tissue).

International standards bodies tell us this.  NASA experts tells us this.

I am a NASA expert who has studied radiation. I've had to take safety courses on radiation. I've went to school where some of the classes were on various types of radiation, including doing experiments with radiation. I've modeled space radiation doses as part of my job and helped test multiple different radiation shielding methods. Who even are you?

Yes, there may be subtle differences, but Radon is fundamentally doing very similar types of damage, and the ratio from energy received to actual effect is fairly well (although not perfectly) captured by the Quality Factor.

[VSECOTSPE]

No, it isn't... No, the damage is comparable and long term effects are likely to be similar.

I’m sorry, but statements like those are false and have been shown so by models and experiments for a long time:

For galactic cosmic rays (GCR), biophysical response models indicate that track structure effects lead to substantially different assessments of shielding effectiveness relative to assessments based on LET-dependent quality factors... High-energy and charge (HZE) ion can produce tissue events resulting in damage to clusters of cells in a columnar fashion, especially for stopping heavy ions. Grahn (1973) and Todd (1986) have discussed a microlesion concept or model of stochastic tissue events in analyzing damage from HZE's. Some tissues, including the CNS, maybe sensitive to microlesions or stochastic tissue events in a manner not illuminated by either conventional dosimetry or fluence-based risk factors. HZE ions may also produce important lateral damage to adjacent cells...

https://ntrs.nasa.gov/citations/20000101087

With relevance to the risk of carcinogenesis, we investigated, in model C3H 10T½ mouse embryo fibroblasts (MEFs), modulation of the spontaneous frequency of neoplastic transformation in the progeny of bystander MEFs that had been in co-culture 10 population doublings earlier with MEFs exposed to moderate doses of densely ionizing iron ions (1 GeV/nucleon) or sparsely ionizing protons (1 GeV). An increase (P<0.05) in neoplastic transformation frequency, likely mediated by intercellular communication through gap junctions, was observed in the progeny of bystander cells that had been in co-culture with cells irradiated with iron ions, but not with protons.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3125249/

However, in terms of the breakpoints making up exchange events, the majority of damage registered following HZE particle irradiation was due to complex aberrations involving multiple chromosomes. This adds a decidedly nonlinear component to the overall breakpoint response, giving it a significant degree of positive curvature, which we interpret as being due to interaction between ionizations of the primary HZE particle track and long-range δ rays produced by other nearby tracks. While such track interaction had been previously theorized, to the best of our knowledge, it has never been demonstrated experimentally.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3580060/

Significantly, the methylation status of 56Fe ion sensitive sites, but not those affected by X ray or 28Si ions, discriminated tumor from normal tissue for human lung adenocarcinomas and squamous cell carcinomas. Thus, high-LET radiation exposure leaves a lasting imprint on the epigenome, and affects sites relevant to human lung cancer.

https://www.nature.com/articles/s41598-018-24755-8#content

Brookhaven even commissioned a multi-beam simulator in 2020 to get at the different biological effects of GCR/HZE versus single-ion beams:

https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000669

And you seem to have hopped onto this train before understanding that radon's dose gets absorbed directly IN the lungs where the alpha particle's short range actually makes the impact WORSE as you get the maximum of the Bragg Peak right in the most radiation-sensitive part of the body (lung tissue).

Whether emitted externally or internally, a 6MeV alpha particle is a lousy model for 100xMeV or GeV heavy ions.  The latter deposits energy 10x more deeply in biological tissue than the former.

And blanket statements like lung tissue is the most “radiation-sensitive” part of the body are meaningless.  Even in the narrow context of carcinogenesis (setting aside other biological effects) and even with the same type and energy of radiation, we still get different sensitivities in different tissues depending on the dose:

https://www.env.go.jp/en/chemi/rhm/basic-info/1st/03-07-02.html

I am a NASA expert who has studied radiation. I've had to take safety courses on radiation. I've went to school where some of the classes were on various types of radiation, including doing experiments with radiation. I've modeled space radiation doses as part of my job and helped test multiple different radiation shielding methods.

Maybe you are.  Maybe you’re not.  There seems to be some debate on that upthread that I was not involved in.

Regardless, “safety courses on radiation” and “school where some of the classes were on various types of radiation” is not the same as having expertise on the biological effects of radiation, like the folks who authored the papers I’ve quoted and linked in this thread.  Someone who has “modeled space radiation doses” and “helped test multiple different radiation shielding methods” is not someone who researches and performs experiments on the biological effects of radiation, like the folks who authored the papers I’ve quoted and linked in this thread.  Just because someone shoots firearms at different types of ballistic protection and models the effects does not mean that person is a surgeon qualified to repair gunshot wounds in an ER or is a researcher on the effects gunshot wounds and medical countermeasures.  They are adjacent areas of expertise, but they are not the same thing.

Who even are you?

I’m a quarter-century veteran of the space sector.  I oversaw every NASA program area over seven years in the EXOP during the Clinton and Bush II administrations.  My last duty before leaving was visiting east Texas and justifying the budget for the Columbia recovery effort.  I then wrote the VSE and started the COTS program as a NASA HQ civil servant.  And I’ve been involved in human space exploration management and studies on and off ever since.  That kind of work requires fluency across a range of technical fields, often with the aim of surfacing key issues and stumbling blocks that need to be tackled, like the difference between the biological effects of high-energy GCR/HZEs and the effects of radiation of other types and lower energy levels.

[Robotbeat]

...

With relevance to the risk of carcinogenesis, we investigated, in model C3H 10T½ mouse embryo fibroblasts (MEFs), modulation of the spontaneous frequency of neoplastic transformation in the progeny of bystander MEFs that had been in co-culture 10 population doublings earlier with MEFs exposed to moderate doses of densely ionizing iron ions (1 GeV/nucleon) or sparsely ionizing protons (1 GeV). An increase (P<0.05) in neoplastic transformation frequency, likely mediated by intercellular communication through gap junctions, was observed in the progeny of bystander cells that had been in co-culture with cells irradiated with iron ions, but not with protons.

...

This actually validates my point. Alpha particles are densely ionizing, being 4 times the mass per nucleonparticle of the protons, and a similar mass to charge ratio as the iron ions, and they deposit all their energy in a shallow spot, right into the lung tissue, the most sensitive tissue in the body for carcinogenesis. Most radiation, including most GCR, is actually protons (to start with).

[Robotbeat]

...

Significantly, the methylation status of 56Fe ion sensitive sites, but not those affected by X ray or 28Si ions, discriminated tumor from normal tissue for human lung adenocarcinomas and squamous cell carcinomas. Thus, high-LET radiation exposure leaves a lasting imprint on the epigenome, and affects sites relevant to human lung cancer.

https://www.nature.com/articles/s41598-018-24755-8#content
...

Yet another thing which validates my point about alpha particles from Radon (and daughter products), WHICH ARE ALSO HIGH-LET: "High LET radiation includes particles with substantial mass and charge such as alpha particles. Low energy neutrons, which carry no electrical charge, are also a high-LET radiation. The distribution of energy in cells has a marked influence on the amount of biological damage done by a fixed amount of radiation. High-LET radiation deposits a large amount of energy in a small distance. For alpha particles, all the particles’ energy can be deposited in a few cells. Using our ammunition analogy, we can compare the alpha particle to a hollow point bullet. A hollow point bullet is designed to expand on impact. It disperses most of the energy close to the surface of impact."

https://ce4rt.com/rad-tech-talk/explaining-linear-energy-transfer/

[Robotbeat]

...
Whether emitted externally or internally, a 6MeV alpha particle is a lousy model for 100xMeV or GeV heavy ions.  The latter deposits energy 10x more deeply in biological tissue than the former.

Deeper is irrelevant in the context where the very tissue that is most sensitive is precisely where the alpha particles will hit! In fact, it's WORSE that it's shallow because the energy all gets absorbed by the lungs and doesn't hit less-sensitive tissue.

And blanket statements like lung tissue is the most “radiation-sensitive” part of the body are meaningless. ...

No, they aren't. I am speaking from experience, you are just rapidly googling things to try to justify your incorrect points. You can check for yourself by running some simulations on OLTARIS.NASA.GOV. Pick all different types of scenarios, from GCR to SPE, in free space or on Mars or behind shielding. Lungs alone account for about half of the "Risk of Exposure Induced Death", and in fact they seem to be more important for the higher energy GCR than for SPE.

[Robotbeat]

...

Regardless, “safety courses on radiation” and “school where some of the classes were on various types of radiation” is not the same as having expertise on the biological effects of radiation, like the folks who authored the papers I’ve quoted and linked in this thread.  ...

Did you literally just claim your desperate googling beats experience and training? We're all capable of googling, here, and subtle claims pulled out of context just to try to ignore some of the only long-duration dose rate data we have is very disappointing.

Of course we do not know for certain, there are subtle parameters to understand. But to claim we know nothing is just fundamentally false and unscientific.

[Robotbeat]

...That kind of work requires fluency across a range of technical fields, often with the aim of surfacing key issues and stumbling blocks that need to be tackled, like the difference between the biological effects of high-energy GCR/HZEs and the effects of radiation of other types and lower energy levels.

Yeah, you seem to confuse many aspects of radiation, for instance not realizing that alpha particles are high-LET particles, being unaware of the particular sensitivity of the lungs (the very organs attacked most by radon) to GCRs, and several other things. You can't compensate for this by rapidly googling things outside your experience just to smear some of the only data that we have on the topic.

Look, it's fine to disagree on this or to say we still don't know enough to be highly certain (that would be totally correct). I just don't think that long-duration evidence from Radon (which is high-LET radiation targeting the same organ that is responsible for about half of the Risk of Exposure Induced Death for GCR) should be just completely dismissed out of hand and with so very little reflection. It seems to betray a lack of scientific curiousity.

[Lampyridae]

Damn, I missed out on a good discussion here. Space Twitter is going to rot my brain.

...
Whether emitted externally or internally, a 6MeV alpha particle is a lousy model for 100xMeV or GeV heavy ions.  The latter deposits energy 10x more deeply in biological tissue than the former.

Deeper is irrelevant in the context where the very tissue that is most sensitive is precisely where the alpha particles will hit! In fact, it's WORSE that it's shallow because the energy all gets absorbed by the lungs and doesn't hit less-sensitive tissue.

And blanket statements like lung tissue is the most “radiation-sensitive” part of the body are meaningless. ...

No, they aren't. I am speaking from experience, you are just rapidly googling things to try to justify your incorrect points. You can check for yourself by running some simulations on OLTARIS.NASA.GOV. Pick all different types of scenarios, from GCR to SPE, in free space or on Mars or behind shielding. Lungs alone account for about half of the "Risk of Exposure Induced Death", and in fact they seem to be more important for the higher energy GCR than for SPE.

I think part of that may be attributable to the fact that lungs have almost no self-shielding from tissue. An organ such as the liver has a significant amount of protection from other solid organs, visceral fat and its own mass to an extent.

We have a lot of evidence on lung irradiation from radiotherapy for breast cancer – an acute vs chronic dose, usually in the Grays and of course higher for the lung next to the breast receiving radiotherapy.

Research has shown that there are potentiating factors: being a smoker *massively* increases the risk of dying from lung cancer, from 0.3% to 4% in this sample*. Microgravity and low gravity might have a similar influence because of the way they suppress the immune system (theoretically in the case of low gravity). Or microgravity might suppress cancers. Then there's high CO2 levels, a closed environment, etc.

https://www.breastcancer.org/research-news/rads-risks-much-higher-for-smokers

Acute radiotherapy doses also cause lung injury such as scarring which reduces lung capacity, but that's not relevant here.

*Over the existing lung cancer risk from smoking/nonsmoking

[Robotbeat]

Yeah, and because of how NASA’s radiation regulations work. Women tend to be more radiosensitive (in part because they live longer!) so they have a lower dose threshold for the same radiation induced risk of death (although women also are smaller and with fewer consumables requirements, so it evens out as far as mission mass goes if you include modest shielding), and the regulations work such that all astronauts are given the same dose limit regardless of age or gender, so the dose limits of young women tend to be the limiting factor, and for them, lungs are the main limit as far as GCR on Mars is concerned.

Now this is regulation and it doesn’t change the physics or biology of effects, but we do want Mars to be a place where men and women can live fairly safely for long periods, so it makes sense to use a similar approach.

But it is, of course, still important to note that at the low doses of GCRs, hormesis is plausible and it’s likely the risk isn’t increased linearly with time. But we don’t know this with high confidence.

[Twark_Main]

After GCRs have passed through shield material like the atmosphere, they tend to make a lot of neutrons and that tends to be a significant part of the dose. For low altitudes on Mars, I’ve found that using a Boron-10 shield about an inch thick beats out polyethylene. Boron-10 is good at absorbing those extra neutrons, especially when they’re slow. ....

Haven’t tried Gadolinium, but it’s very heavy, so it might produce a lot of secondaries from GCR.

It sounds like you've been trying to replace the hydrogen-rich shield with B-10/Ga-157.

When I said "salting a hydrogen-rich shield with neutron absorbers," I meant keep the polyethylene but add in a small amount of neutron absorber material to soak up the neutrons.

Boron-10 is more expensive than I’d like ($5-10/gram for large orders?), but NASA can definitely afford that.

You don't actually have to go through all the expense of separating into isotopically pure B-10 and Ga-157. I just gave the isotopes so it's easier to put in OLTARIS. 

Natural boron contains 20% B-10, and natural gadolinium contains 16% Ga-157. If you're just "salting" with a small amount of these materials it should be fine.

There’s not nearly as much benefit if you’re using the natural isotope mix, tho. Might as well just use polyethylene.

Just so we're clear, what sort of error bars should I assign to this statement?

Should I interpret this as an "I have a hunch" type, or as "I tried many possible thicknesses and layering options combining PE/B/Ga, and none of them beat the equivalent mass in polyethylene" type, or something in-between? You did mention simulating pure boron, but I didn't see a definitive yes/no about simulating hybrid shielding with PE. 

If we need to go back to isotopic refinement, that's fine! It's not too costly. How does using isotopically-pure B/Ga change the analysis?

[Robotbeat]

Big error bars, I haven’t compared them directly.

[Coastal Ron]

...
As far as neutrons, there’s no changing story. It’s simply factual. After GCRs have passed through shield material like the atmosphere, they tend to make a lot of neutrons and that tends to be a significant part of the dose. For low altitudes on Mars, I’ve found that using a Boron-10 shield about an inch thick beats out polyethylene. Boron-10 is good at absorbing those extra neutrons, especially when they’re slow. Boron-10 is more expensive than I’d like ($5-10/gram for large orders?), but NASA can definitely afford that.

I see Wikipedia has an entry in their article on Boron that says:

In future crewed interplanetary spacecraft, ¹⁰B has a theoretical role as structural material (as boron fibers or BN nanotube material) which would also serve a special role in the radiation shield. One of the difficulties in dealing with cosmic rays, which are mostly high energy protons, is that some secondary radiation from interaction of cosmic rays and spacecraft materials is high energy spallation neutrons. Such neutrons can be moderated by materials high in light elements, such as polyethylene, but the moderated neutrons continue to be a radiation hazard unless actively absorbed in the shielding. Among light elements that absorb thermal neutrons, ⁶Li and ¹⁰B appear as potential spacecraft structural materials which serve both for mechanical reinforcement and radiation protection.

When you mentioned that using a Boron-10 shield about an inch thick, were you thinking about an inch of boron solid metal, or where you thinking about something like Boron impregnated material, like tape?

For my Mars-gravity rotating space station I was planning to use lots of polyethylene for the station structure, but now it seems like I should be planning to use a layer of Boron-10 too. I'm just thinking of the cost, assuming that Boron impregnated structural tape would cost a lot, and obviously solid Boron metal would likely cost the most, but there is a way for me to use it in a non-structural location while depending on polyethylene like Dyneema for the structural material.

Any thoughts?

[Robotbeat]

...
As far as neutrons, there’s no changing story. It’s simply factual. After GCRs have passed through shield material like the atmosphere, they tend to make a lot of neutrons and that tends to be a significant part of the dose. For low altitudes on Mars, I’ve found that using a Boron-10 shield about an inch thick beats out polyethylene. Boron-10 is good at absorbing those extra neutrons, especially when they’re slow. Boron-10 is more expensive than I’d like ($5-10/gram for large orders?), but NASA can definitely afford that.

I see Wikipedia has an entry in their article on Boron that says:

In future crewed interplanetary spacecraft, ¹⁰B has a theoretical role as structural material (as boron fibers or BN nanotube material) which would also serve a special role in the radiation shield. One of the difficulties in dealing with cosmic rays, which are mostly high energy protons, is that some secondary radiation from interaction of cosmic rays and spacecraft materials is high energy spallation neutrons. Such neutrons can be moderated by materials high in light elements, such as polyethylene, but the moderated neutrons continue to be a radiation hazard unless actively absorbed in the shielding. Among light elements that absorb thermal neutrons, ⁶Li and ¹⁰B appear as potential spacecraft structural materials which serve both for mechanical reinforcement and radiation protection.

When you mentioned that using a Boron-10 shield about an inch thick, were you thinking about an inch of boron solid metal, or where you thinking about something like Boron impregnated material, like tape?

For my Mars-gravity rotating space station I was planning to use lots of polyethylene for the station structure, but now it seems like I should be planning to use a layer of Boron-10 too. I'm just thinking of the cost, assuming that Boron impregnated structural tape would cost a lot, and obviously solid Boron metal would likely cost the most, but there is a way for me to use it in a non-structural location while depending on polyethylene like Dyneema for the structural material.

Any thoughts?

I think Boron-10 is cheap enough for NASA to use. You can just straight buy it for $100/gram. $50/gram if you get a contract. I think $10-20/gram might be feasible if you needed a lot of it (helps a lot if you can find cheap electricity). That's comparable to mission launch costs, so I don't think it'd be that expensive for NASA Mars missions. But expensive for settlers...

And I was thinking of solid Boron-10. Boron-10 mixed with polyethylene matrix wouldn't be bad.

Boron fiber is actually a pretty high performance fiber, too. Boron-10 would be the same thing but about 8% less mass. (You want to use the boron fibers with a carbon thread, though, not the tungsten thread one, as tungsten is very heavy and would produce more secondaries than you'd like.

[Lampyridae]

When you mentioned that using a Boron-10 shield about an inch thick, were you thinking about an inch of boron solid metal, or where you thinking about something like Boron impregnated material, like tape?

For my Mars-gravity rotating space station I was planning to use lots of polyethylene for the station structure, but now it seems like I should be planning to use a layer of Boron-10 too. I'm just thinking of the cost, assuming that Boron impregnated structural tape would cost a lot, and obviously solid Boron metal would likely cost the most, but there is a way for me to use it in a non-structural location while depending on polyethylene like Dyneema for the structural material.

Any thoughts?

The most efficient boron-based material I found (and one of the best bar liquid hydrogen, neat) was lithium borohydride. Though that's not something you'd want to see outside of a propellant tank.

I think gadolinium would be an interesting material to use... there might be a certain thickness where its neutron-stopping power outweighs the spalling radiation.

Since these radiation vests are like 5cm thick in places, and Robotbeat mentioned the one he tried got rather warm, it would probably be better to have these things as overlapping plates for ventilation.

I just checked Oltaris and found that it doesn't have gadolinium as one of the available elements. Boo!

[VSECOTSPE]

This actually validates my point.

No.  Upthread you were comparing alpha emissions from radon measured in MeV.  That paper is on iron particles measured in GeV.

Yet another thing which validates my point

No.  That paper shows that 56Fe particles are significantly more damaging than 28Si particles (or X-rays).  Even if alpha particles from radon were in the same energy spectrum (and they’re not by orders or magnitude) as the 56Fe particles in GCR/HZEs, the alpha particles are still much less massive than the 28Si particles in that paper, forget the 56Fe particles.

Physics matters for biological impact, especially when dealing with particles that are several orders of magnitude more energetic and an order of magnitude more massive.

I am speaking from experience, you are just rapidly googling things to try to justify your incorrect points. You can check for yourself by running some simulations on OLTARIS.NASA.GOV.

I did not rapidly Google anything.  I pulled up an old file.  Those are among the research papers showing that GCR/HZEs are more damaging and more cancer-inducing than other particles and energy levels.  They and others underpinned the decision to develop the multi-beam simulator at Brookhaven because they told us that we could not rely on non-GCR/HZE models for the biological impact of GCR/HZEs.

I’m not trying to insult you here, but using Oltaris does not give you expertise in the biological effects of GCR/HZEs.  Rather, the half-dozen citations that I’ve provided upthread provide (some of) that expertise.  And, again, the international bodies that govern this stuff and NASA’s own researchers and medical experts warn that applying the same QF as other radiation types/energies to GCR/HZEs — or comparing other radiation types/energies to GCR/HZEs with similar LET or other figures — will create misleading results.  Using Oltaris in this way is misapplying the tool.

[Lampyridae]

No.  That paper shows that 56Fe particles are significantly more damaging than 28Si particles (or X-rays).  Even if alpha particles from radon were in the same energy spectrum (and they’re not by orders or magnitude) as the 56Fe particles in GCR/HZEs, the alpha particles are still much less massive than the 28Si particles in that paper, forget the 56Fe particles.

Physics matters for biological impact, especially when dealing with particles that are several orders of magnitude more energetic and an order of magnitude more massive.

In addition to the cancer risk, there is also structural damage caused by the individual Fe ions, especially in the brain.

The transport models used in the Oltaris simulations show that most of the Fe-56 flux is absorbed within the first 10cm of low-Z shielding. High energy Fe-56 remains but I don't think there's enough to swiss cheese the brain like unprotected doses seem to do.

[Slarty1080]

No.  That paper shows that 56Fe particles are significantly more damaging than 28Si particles (or X-rays).  Even if alpha particles from radon were in the same energy spectrum (and they’re not by orders or magnitude) as the 56Fe particles in GCR/HZEs, the alpha particles are still much less massive than the 28Si particles in that paper, forget the 56Fe particles.

Physics matters for biological impact, especially when dealing with particles that are several orders of magnitude more energetic and an order of magnitude more massive.

In addition to the cancer risk, there is also structural damage caused by the individual Fe ions, especially in the brain.

The transport models used in the Oltaris simulations show that most of the Fe-56 flux is absorbed within the first 10cm of low-Z shielding. High energy Fe-56 remains but I don't think there's enough to swiss cheese the brain like unprotected doses seem to do.

This is an interesting point. I know that heavy ions like Fe-56+ are very damaging but only form a very small proportion of the flux. But I had always assumed whatever Fe_56+ existed was mostly very high energy? Is this not the case?

[VSECOTSPE]

In addition to the cancer risk, there is also structural damage caused by the individual Fe ions, especially in the brain.

The transport models used in the Oltaris simulations show that most of the Fe-56 flux is absorbed within the first 10cm of low-Z shielding. High energy Fe-56 remains but I don't think there's enough to swiss cheese the brain like unprotected doses seem to do.

My point upthread was not about shielding.  It was about an assumption that the carcinogenic effects of GCR/HZE exposure would be similar to the carcinogenic effects of radon exposure.  Research and experts tells us this is a bad assumption.  That said, as long as the participants and their medical gatekeepers are willing to accept cancer risks that are in the neighborhood of what ex-smokers accept, I’m sure shielding options exist and can be deployed that enable missions with two- to five-year durations.

We know from recent rodent experiments that HZE exposure interferes with cognition over the short-term (for at least two to six months after exposure in the case of the mice in these studies):

https://www.nature.com/articles/s41598-021-83447-y.pdf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3534034/

To the extent that rodent cognition deficit translates to human brains, it obviously raises mission operations risks.  The traditional way around this is mission controllers with full faculties back on Earth.  But that doesn’t necessarily apply to missions to distant targets, like Mars, with lengthy communications delays.  20 or 40 minutes is a long time for a confused crew to press a lot of wrong buttons.

The obvious way forward on this is to study the cognition of, and nervous system changes in, astronauts sent to near targets outside the Van Allen Belts, like the Moon, where we can safely study these impacts while keeping crews close enough for mission controllers on Earth to take over in real-time if/when cognition deficits emerge.  This research area should be a clear and major driver of the Artemis Program.  But you won’t find it in the breakdown of NASA’s Moon-to-Mars Objectives for Human and Biological Science.  See HBS-1 thru 3 in the spreadsheet below:

https://www.nasa.gov/sites/default/files/atoms/files/m2m-objectives-mapping-table-acr22.xlsx

Instead, NASA’s Moon-to-Mars Objectives for Human and Biological Science have little to nothing to do with research goals and are instead comprised of junk like ten ”Move cargo...” and “Transport cargo...” objectives.  Just mindless, third-rate engineering bureaucracy utterly divorced from the research that should be driving the program. 

And as a result, we have Artemis mission durations that will top out at 30 days vice the multi-hundred day durations that will be required for Mars conjunction- and opposition-class missions.  We’re going to blow hundreds of billions of dollars on an Artemis Program with objectives that do not, and an architecture that cannot, tackle the key human health hurdles to manned Mars missions.  Dumb, dumb, dumb...

But I digress...

This is an interesting point. I know that heavy ions like Fe-56+ are very damaging but only form a very small proportion of the flux. But I had always assumed whatever Fe_56+ existed was mostly very high energy? Is this not the case?

The energy of HZE particles is along a spectrum, they are a small part of the flux, but they are responsible for the majority of the carcinogenic damage/risk, per NASA’s own research roadmap in this area:

The energy spectrum of galactic cosmic rays (GCRs) peaks near 1,000 MeV/ nucleon; consequently, these particles are so penetrating that shielding can only partially reduce the doses that are absorbed by the crew (Cucinotta et al., 2006). Thick shielding poses obvious mass problems to spacecraft launch systems, and would only reduce the GCR effective dose by no more than 25% using aluminum, or about 35% using more efficient polyethylene. Therefore, with the exception of solar proton events, which are effect- ively absorbed by shielding, current shielding approaches cannot be considered a solution for the space radiation problem (Cucinotta et al., 2006; Wilson et al., 1995). In traveling to Mars, every cell nucleus within an astronaut would be traversed by a proton or secondary electron every few days, and by an HZE ion every few months (Cucinotta et al., 1998b). The large ionization power of HZE ions makes them the major contributor to the risk, in spite of their lower cell nucleus hit frequency compared to protons.

https://humanresearchroadmap.nasa.gov/evidence/reports/Carcinogenesis.pdf

[Robotbeat]

You made several claims, some of which I proved untrue, for instance the implication that Radon exposure is not high-LET, therefore the effects wouldn’t be similar. I disproved that.

There is always going to be some uncertainty in these comparisons, however your stance that we should ignore the insight of long term Radon studies entirely is unfounded. You’re misinterpreting the researchers looking at the subtle effects of GeV ions as if that’s justification for ignoring some of the best data we have. No one is saying there isn’t some difference, I’m just saying you cannot blanket ignore that research as if it were irrelevant because it most certainly is not.

This is a common mistake people make with scientific research. They interpret research on subtle effects and the tendency of scientists to make qualifying statements on validity with the idea we have to throw away all other related research and ignore it. That is just bad science.

We need to take the radon research seriously as it is some of the only research we have on comparable doses.

And another thing: the paradox of high-energy GeV particles is that they don’t actually deposit that much energy over a given millimeter of particle track. The biggest energy deposition per unit distance occurs right at the end, where the particle has been slowed down to MEV energies. That is the Bragg Peak, which occurs right at the end. Right when it is most comparable to… *drumroll please* alpha particles emitted by Radon and its decay products deep inside the body, in sensitive lung tissue.

[Robotbeat]

I also think you are vastly overstating the cognitive effects. To actually have enough of a dose to cause noticeable short term cognitive effects, you’d have to expose astronauts to an unethically high dose, and this would violate the ALARA principle.

This is a major problem with the idea of using astronauts as Guinea pigs to study long term risks from space radiation. The effects are very subtle at the doses that we can ethically allow for astronauts, and you’d need a HUGE sample size to see anything through the statistical noise. Thousands or tens of thousands of astronaut-flight-years to have a statistically useful data set.

And the ISS already experiences much of this dose. INCLUDING GCR. The GCR dose on Mars at likely landing sites is the same as the radiation dose on ISS. (Note the units here are the wrong ones in the graph, but the quality factor between ISS and MSL are very close, such that the dose rates in mSv/day are the same within about 5-10%.)

Note that the Earth’s magnetic field actually only shields from the LOWER energy GCRs (I believe the value is roughly 10GeV per nucleon for heavy ions at the equator at the top of the Earth‘s atmosphere… at higher latitudes like where ISS hangs out, this can be much less and in fact the Earth’s magnetic field can actually FOCUS high energy particles at higher latitudes…). This is a pretty simple consequence of the fact that the gyro radius of the highest energy particles in Earth’s magnetic field is larger than the extent of that magnetic field.

[VSECOTSPE]

You made several claims, some of which I proved untrue, for instance the implication that Radon exposure is not high-LET, therefore the effects wouldn’t be similar.

I did not write that alpha radiation from radon is low-LET.  If you want to disprove an “implication” that exists in your head, be my guest.  Just please do not attribute your “implication” to another poster like me.

There is always going to be some uncertainty in these comparisons, however your stance that we should ignore the insight of long term Radon studies entirely is unfounded. 

I did not write that we should “ignore” radon studies.  I wrote that we cannot predict the biological effects of GCR/HZE radiation from high radon exposure populations.

You’re misinterpreting the researchers looking at the subtle effects of GeV ions...

There’s nothing subtle about what the research has stated in this area since the 90s.  It unequivocally states that models, metrics, and measures for other types of radiation and energy levels do not apply to GCR/HZE risks.  Per Cucinotta et al:

The quality factor (QF) as defined in International Commission on Radiological Protection report no. 26 or in International Commission on Radiation Units and Measurements report no. 40 is not expected to be a valid method for assessing the biological risk for deep missions where the high-energy heavy ion (HZE) particles of the galactic cosmic rays (GCR) are of major concern.  No human data for cancer induction from the HZE particles exist, and information on biological effectiveness is expected to be taken from experiments with animals and cultured cells.  Experiments with cultured cells indicate that the relative biological effectiveness (RBE) of the HZE particles is dependent on particle type, energy, and the level of fluency.  Use of a single parameter, such as lineal energy transfer (LET) or lineal energy to determine radiation quality will therefor represent an extreme oversimplification for GCR risk assessment.

https://ntrs.nasa.gov/api/citations/19910007668/downloads/19910007668.pdf

I also think you are vastly overstating the cognitive effects. To actually have enough of a dose to cause noticeable short term cognitive effects, you’d have to expose astronauts to an unethically high dose, and this would violate the ALARA principle.

I did not write that we should aim ion beams at human brains.  What I wrote is that we should test cognition and take data on CNS changes in Artemis astronauts, that this should be one of the research drivers for the program (but it’s not), and that the program should use this and other factors to drive a number of long-duration Artemis missions (but they’re not).

This is a major problem with the idea of using astronauts as Guinea pigs to study long term risks from space radiation. The effects are very subtle at the doses that we can ethically allow for astronauts, and you’d need a HUGE sample size to see anything through the statistical noise. Thousands or tens of thousands of astronaut-flight-years to have a statistically useful data set.

Paucity of human samples is an issue for practically all human space research.  See the Kelly twins study, for example.  This issue has not stopped us from understanding and defining the risks. 

And the ISS already experiences much of this dose. INCLUDING GCR. The GCR dose on Mars at likely landing sites is the same as the radiation dose on ISS.

Transit is the larger issue for Mars conjunction/opposition and similar couple/few-year missions.

We need to take the radon research seriously as it is some of the only research we have on comparable doses.

Even when they do make careful comparisons to get indications of what damage GCR/HZEs might do to the human body, experts do _not_ cite high radon population studies in conjunction with GCR/HZE risks.  They cite studies of nuclear weapon survivors, nuclear workers, and certain radiation therapy patients:

Human epidemiology studies that provide evidence for cancer risks for low-linear energy transfer (LET) radiation such as X rays or gamma rays at doses from 50 to 2,000 mSv include: the survivors of the atomic-bomb explosions in Hiroshima and Nagasaki, nuclear reactor workers (Cardis et al., 1995; 2007) in the United States, Canada, Europe, and Russia, and patients who were treated thera- peutically with radiation. Ongoing studies are providing new evidence of radiation cancer risks in populations that were accidentally exposed to radiation (i.e., from the Chernobyl accident and from Russian nuclear weapons production sites), and continue to analyze results from the Japanese atomic-bomb survivors from Hiroshima and Nagasaki. These studies provide strong evidence for cancer morbidity and mortality risks at more than 12 tissue sites, with the largest cancer risks for adults found for leukemia and tumors of the lung, breast, stomach, colon, bladder, and liver.

https://humanresearchroadmap.nasa.gov/evidence/reports/Carcinogenesis.pdf

[Robotbeat]

…which is even less applicable as those typically are extreme acute doses, not long duration. Natural high background radiation environments are pretty much our only data source with any kind of statistical power for the duration of exposure we’re talking about. It tends to be the radiation hormesis folks who cite these chronic exposure data sets.

[VSECOTSPE]

…which is even less applicable as those typically are extreme acute doses, not long duration. Natural high background radiation environments are pretty much our only data source with any kind of statistical power for the duration of exposure we’re talking about. It tends to be the radiation hormesis folks who cite these chronic exposure data sets.

A United Nations committee, the National Council on Radiation Protection and Measurements, and the National Research Council have all reviewed the “evidence” for hormesis — some 30 quality epidemiological studies and a 16-year review, among others — and found none.

[Lampyridae]

No.  That paper shows that 56Fe particles are significantly more damaging than 28Si particles (or X-rays).  Even if alpha particles from radon were in the same energy spectrum (and they’re not by orders or magnitude) as the 56Fe particles in GCR/HZEs, the alpha particles are still much less massive than the 28Si particles in that paper, forget the 56Fe particles.

Physics matters for biological impact, especially when dealing with particles that are several orders of magnitude more energetic and an order of magnitude more massive.

In addition to the cancer risk, there is also structural damage caused by the individual Fe ions, especially in the brain.

The transport models used in the Oltaris simulations show that most of the Fe-56 flux is absorbed within the first 10cm of low-Z shielding. High energy Fe-56 remains but I don't think there's enough to swiss cheese the brain like unprotected doses seem to do.

This is an interesting point. I know that heavy ions like Fe-56+ are very damaging but only form a very small proportion of the flux. But I had always assumed whatever Fe_56+ existed was mostly very high energy? Is this not the case?

At least in Oltaris, the *median* flux is 180MeV, but the higher range skews higher. The most energy comes from the 1GeV range - graph 1. Protons tend have a lower energy distribution.

Graphs 2 and 3. These is for a slab of 100g/cm^2 thick Al at 1AU at Solar Minimum. You can see how the Fe56 dose equivalent drops off fairly quickly. It's also the single largest contributor to the unshielded cosmic ray dose.

From what I understand, magnetic shielding is pretty much nucleon agnostic in effectiveness and would cut out a lot of the lower-energy stuff.

[Lampyridae]

We know from recent rodent experiments that HZE exposure interferes with cognition over the short-term (for at least two to six months after exposure in the case of the mice in these studies):

https://www.nature.com/articles/s41598-021-83447-y.pdf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3534034/

To the extent that rodent cognition deficit translates to human brains, it obviously raises mission operations risks.  The traditional way around this is mission controllers with full faculties back on Earth.  But that doesn’t necessarily apply to missions to distant targets, like Mars, with lengthy communications delays.  20 or 40 minutes is a long time for a confused crew to press a lot of wrong buttons.

Personal cerebral shielding should likely be tested.

[Robotbeat]

I worked on that. I honestly don’t think it’s worth it. The torso is the main problem. The lungs alone are half the problem.

[MickQ]

Would an outer garment, like a bulletproof vest made of polyethylene, provide measurable protection?

[whitelancer64]

Would an outer garment, like a bulletproof vest made of polyethylene, provide measurable protection?

Yes, some.

https://www.nasa.gov/feature/orion-passengers-on-artemis-i-to-test-radiation-vest-for-deep-space-missions

[MickQ]

Good. Do you know if any results have come out yet ?

[Lampyridae]

Good. Do you know if any results have come out yet ?

The Astrorad vest flew on Artemis I, validating it in a true interplanetary cosmic radiation environment, but I haven't seen any results published. Those will likely take a while.

https://stemrad.com/astrorad-4/

[Robotbeat]

Would an outer garment, like a bulletproof vest made of polyethylene, provide measurable protection?

Yes. The benefit is bigger in transit than on the surface, as the surface already has a bunch of shielding from the atmosphere. At low altitude sites, the atmosphere may be roughly equivalent to about 25 cm (10 inches) of polyethylene.

[Twark_Main]

I worked on that. I honestly don’t think it’s worth it. The torso is the main problem. The lungs alone are half the problem.

Covering of the torso and hips seems quite sensible. Protects the vital organs, gonads, and about 85% of the blood-forming tissue (bone marrow).

Any concerns incorporating high neutron cross-section materials (boron, hafnium, gadolinium) in a shielding garment?

[Slarty1080]

I see there is a new public release of the  NASA software catalogue some of which may be of interest to those who like making calculations on the effects of raddiation:
https://software.nasa.gov/software/category/crew_and_life_support

[Lampyridae]

I worked on that. I honestly don’t think it’s worth it. The torso is the main problem. The lungs alone are half the problem.

Covering of the torso and hips seems quite sensible. Protects the vital organs, gonads, and about 85% of the blood-forming tissue (bone marrow).

Any concerns incorporating high neutron cross-section materials (boron, hafnium, gadolinium) in a shielding garment?

Boron is fine; desirable even since it's fairly low-Z. Hafnium and gadolinium probably just aren't worth it due to spalling. A gadolinium shielding jacket behind very thick shielding to mop up neutrons may be worth it.

[Robotbeat]

The high neutron cross section is for a smallish energy band of Neutrons, tho. Boron, boron-10 in particular, is probably the better bet.

[Twark_Main]

That's good news. Looks like enriched (and "depleted" ) boron is readily available commercially.

https://en.wikipedia.org/wiki/Boron#Commercial_isotope_enrichment

3M™ 10B Enriched Boron

3M™ 11B Enriched Boron

 
Concentrations are available "exceeding 99% isotopic purity," but given the exponential enrichment cost curve and falling launch costs I can't imagine it's economical to go much beyond 80-90% B-10.

For any interior use you probably will want to use relatively high concentration (>95% B-11) depleted boron to minimize secondary spallation, but B-11 is a lot cheaper.

[Robotbeat]

Boron-11 isn’t very good. Much better off with hydrogen-rich material like polyethylene.

Note that for this graph, it’s per-atom, not per-unit-mass. Hydrogen has a tenth the mass of Boron-10, and even in the form of polyethylene, the effective mass per hydrogen atom is still just 70% that of Boron-10. (For methane, it’s 40%.)

At high energies, hydrogen has a higher per-atom cross section even.

Gadolinium has about 30 times the cross section of Boron-10 per atom at very low neutron energies, but at those energies the neutrons aren’t nearly that high dose. Gadolinium 157 is also 157 times the mass of a hydrogen atom.

[Robotbeat]

Gadolinium-157 has at best ~33 times the neutron cross section of B-10 at low energy but weighs 15.7x as much, so the benefit is much smaller, only a factor of 2. And it’s much worse for other types of radiation and may produce a lot of secondaries, like other heavier metals do.

I wouldn’t think it’d actually be useful except in very niche cases.

Boron-10, on the other hand, is okay as a shielding material for high energy protons, low enough atomic mass to not produce a bunch of secondaries, and is much better against neutrons per unit mass than Gd-157 at the more destructive higher energies, so I think it has much broader use.

And you can’t really go wrong with hydrogen, if you can get a lot of hydrogen atoms.

[Twark_Main]

Boron-11 isn’t very good. Much better off with hydrogen-rich material like polyethylene.

The question is more about to what extent (ie percent isotopic concentration) it's worth the large expense to filter out more boron-11 "chaff" leaving behind the boron-10 "wheat."

Boron-11 could be used for any interior applications calling for boron, precisely because it has a low cross-section ("isn't very good" at shielding), so it gives off a lot fewer secondary radiation particles.

[Robotbeat]

There’s no advantage to using Boron-11 instead of polyethylene.

[Twark_Main]

There’s no advantage to using Boron-11 instead of polyethylene.

There's no advantage to intentionally adding additional boron-11 instead of polyethylene. Yes that's true.

There is however an advantage to not removing (at great expense!) that last little bit of boron-11 from your already-pretty-enriched boron-10 product. The advantage is cost.

[Robotbeat]

There’s no advantage to using Boron-11 instead of polyethylene.

There's no advantage to intentionally adding additional boron-11 instead of polyethylene. Yes that's true.

There is however an advantage to not removing (at great expense!) that last little bit of boron-11 from your already-pretty-enriched boron-10 product. The advantage is cost.

There is a mass advantage to doing it versus natural boron. If you mean using 95% B10 instead of 99.9%B10, then sure, small benefit from going to 99.9%.

…

Boron-11 could be used for any interior applications calling for boron, ..

Boron is not a common structural material (although Shuttle used it). So your comment doesn’t make much sense. Why would you be using Boron if not for its ability to mop up neutrons?

(And no, having a low cross section isn’t an advantage in this case, either.)

[Twark_Main]

There’s no advantage to using Boron-11 instead of polyethylene.

There's no advantage to intentionally adding additional boron-11 instead of polyethylene. Yes that's true.

There is however an advantage to not removing (at great expense!) that last little bit of boron-11 from your already-pretty-enriched boron-10 product. The advantage is cost.

There is a mass advantage to doing it versus natural boron.

My point is that at Starship level launch costs, this advantage does seem to be far outweighted by the cost of isotope separation.

If you mean using 95% B10 instead of 99.9%B10, then sure, small benefit from going to 99.9%.

I mean precisely that you shouldn't do that.

The cost of 99.9% isotopic purity would be astronomical. Far better to just "bite the bullet" and launch a slightly larger quantity boron with lower enrichment.

Regular boron is only 20% boron-10. Even 95% boron-10 is already considered a high level of enrichment, and is almost certainly uneconomic given Starship launch costs. 99.9% is just plain ridiculous.

…

Boron-11 could be used for any interior applications calling for boron, ..

Boron is not a common structural material (although Shuttle used it). So your comment doesn’t make much sense. Why would you be using Boron if not for its ability to mop up neutrons?

Did I stutter? "Any" applications.   I intentionally didn't specify, because we can't necessarily predict it ahead of time.

This includes, apparently, what you wrote in bold. So to borrow a phrase your comment doesn’t make much sense.    Always nice when people answer their own question however!

Yes if you need to build a neutron absorber assembly inside the shielded hab (not sure why you'd do that, vs simply locating your radiation source outside the GCR shield) then obviously you're not going to use boron-11. But if all you need is the chemical properties of boron (fire retardants etc) then you should consider whether to use depleted boron.

(And no, having a low cross section isn’t an advantage in this case, either.)

Oh sorry, I thought you'd read the article (at least the relevant sections) when I linked to it.

https://en.wikipedia.org/wiki/Boron#Radiation-hardened_semiconductors

[Robotbeat]

There’s no advantage to using Boron-11 instead of polyethylene.

There's no advantage to intentionally adding additional boron-11 instead of polyethylene. Yes that's true.

There is however an advantage to not removing (at great expense!) that last little bit of boron-11 from your already-pretty-enriched boron-10 product. The advantage is cost.

There is a mass advantage to doing it versus natural boron.

My point is that at Starship level launch costs, this advantage does seem to be far outweighted by the cost of isotope separation.

If you mean using 95% B10 instead of 99.9%B10, then sure, small benefit from going to 99.9%.

I mean precisely that you shouldn't do that.

The cost of 99.9% isotopic purity would be astronomical. Far better to just "bite the bullet" and launch a slightly larger quantity boron with lower enrichment.

Regular boron is only 20% boron-10. Even 95% boron-10 is already considered a high level of enrichment, and is almost certainly uneconomic given Starship launch costs. 99.9% is just plain ridiculous.


…

Yes, I pretty clearly was *acknowledging* this.

[Twark_Main]

I'll take yes for an answer. 

I was surprised at the level of controversy over (what I considered to be) a set of relatively uncontroversial statements about boron shielding. Looks like just "loudly agreeing with each-other" in this case.

[Robotbeat]

Yup, many such case.

I do want to point out that even if the costs are fairly high per unit mass, in some cases there are other mass considerations. I'm thinking of enriched Boron-10 for use on a radiation protection vest. At very low altitudes of Mars, 1 inch of polyethylene shielding (i.e. like a vest) gets you 0.45mSv/day dose but 1inch of Boron-10 gets you 0.35mSv/day dose. Might cost a million dollars, but that's probably cheap if it reduces the dose by ~100mSv, allowing you to reduce transit speed dramatically.

[Twark_Main]

Haha agreed. The vest is an interesting case, thanks.

Times of Israel had a good article on the AstroRad vest from Artemis 1. No boron as far as I know, but it does have polyethylene with variable thickness to best protect individual organs. See Paige, Newman & Lombardo 2020.

https://www.timesofisrael.com/israels-stemrad-gears-up-for-major-demo-of-anti-radiation-suit-on-nasas-artemis-i/

https://ieeexplore.ieee.org/abstract/document/9172794




EDIT Also good news everyone, our new excuse just dropped. "I'm not fat, I'm self-shielded."   

[LMT]

At very low altitudes of Mars, 1 inch of polyethylene shielding (i.e. like a vest) gets you 0.45mSv/day dose but 1inch of Boron-10 gets you 0.35mSv/day dose.

Bare skin gets ~ 0.34 mSv/day, as we saw in thread.   

[Robotbeat]

At very low altitudes of Mars, 1 inch of polyethylene shielding (i.e. like a vest) gets you 0.45mSv/day dose but 1inch of Boron-10 gets you 0.35mSv/day dose.

Bare skin gets ~ 0.34 mSv/day, as we saw in thread.   

Yeah, you’re right, but our values are not inconsistent. I was looking at -5km altitude, Hellas Basin is greater depth than that, altitude of -7km or lower.

[LMT]

At very low altitudes of Mars, 1 inch of polyethylene shielding (i.e. like a vest) gets you 0.45mSv/day dose but 1inch of Boron-10 gets you 0.35mSv/day dose.

Bare skin gets ~ 0.34 mSv/day, as we saw in thread.   

Yeah, you’re right, but our values are not inconsistent. I was looking at -5km altitude, Hellas Basin is greater depth than that, altitude of -7km or lower.

Notice your own post, and quantify the actual shielding effect.

[Robotbeat]

? How are we even in disagreement?

[Lampyridae]

? How are we even in disagreement?

Even moreso when you consider the variation of cosmic radiation flux over years and decades.

Yup, many such case.

I do want to point out that even if the costs are fairly high per unit mass, in some cases there are other mass considerations. I'm thinking of enriched Boron-10 for use on a radiation protection vest. At very low altitudes of Mars, 1 inch of polyethylene shielding (i.e. like a vest) gets you 0.45mSv/day dose but 1inch of Boron-10 gets you 0.35mSv/day dose. Might cost a million dollars, but that's probably cheap if it reduces the dose by ~100mSv, allowing you to reduce transit speed dramatically.

This paper suggests a price of $45/g for 99% B-10. Comparable to gold. So a square metre of 5g/cm^2 Boron-10 works out to $2.25 million.

Boron-10 carbide seems a lot cheaper for some reason, and it's 80% boron atoms.

[spacenut]

Rovers can be shielded.  Robotic arms can be used off rovers.  Rovers can be shielded heavier.  Only go outside when necessary, otherwise stay in rovers and in habitats.  In the future of a Mars colony, satellites can provide shielding by creating a radiation belt like the Van-Allen belt on earth.  These same satellites might be able to do double duty by being similar to Starlinks for communication.  Satellites might be placed in the Mars-Sun LaGrange point to deflect radiation from the sun.  There are many options.  Polyethylene is cheap, and lightweight.  Is boron heavy?  I know it can be expensive and the carbon based boron molecule would be heavier.  Then, Mars is 0.38 earths gravity, so what might be heavy on earth would be lighter on Mars. 

[Slarty1080]

Rovers can be shielded.  Robotic arms can be used off rovers.  Rovers can be shielded heavier.  Only go outside when necessary, otherwise stay in rovers and in habitats.  In the future of a Mars colony, satellites can provide shielding by creating a radiation belt like the Van-Allen belt on earth.  These same satellites might be able to do double duty by being similar to Starlinks for communication.  Satellites might be placed in the Mars-Sun LaGrange point to deflect radiation from the sun.  There are many options.  Polyethylene is cheap, and lightweight.  Is boron heavy?  I know it can be expensive and the carbon based boron molecule would be heavier.  Then, Mars is 0.38 earths gravity, so what might be heavy on earth would be lighter on Mars.

Is a satellite based artificial Van-Allen radiation belt a realistic possibility? It sounds highly suspect to me (but I would love to be proved wrong). The density of boron is greater than than of polyethylene, but presumably it is more effective at absorbing radiation than polythene gram for gram.

It is true that they would weigh less on Mars, but they would both be launched from Earth for the foreseeable future so It wouldn't make any difference. Longer term polyethylene could fairly easily be produced on Mars, but Boron would be a lot harder to source/extract locally.

[Robotbeat]

The Van Allen Belt doesn’t provide shielding. The Earth’s magnetic field does.

[Twark_Main]

The Van Allen Belt doesn’t provide shielding.

That's not exactly true.

https://www.researchgate.net/publication/270653683_An_impenetrable_barrier_to_ultra-relativistic_electrons_in_the_Van_Allen_Radiation_Belt

https://scitechdaily.com/van-allen-probes-reveal-impenetrable-barrier-space/

[Greg Hullender]

The Van Allen Belt doesn’t provide shielding. The Earth’s magnetic field does.

I think he's talking about the idea proposed in How to create an artificial magnetosphere for Mars" (R.A. Bamford et al, Acta Astronautica, Volume 190, January 2022, Pages 323-333). The idea is to create an artificial Van Allen belt of charged particles and then to run an electrical current through that loop, generating a magnetic field. (See section 8, starting on page 16.)

Plasma structures such as radiation belts naturally occur around planets like the Earth. In these cases, the co-rotating ions and electrons are formed as a result of the rotation of the planet and complex interactions of its natural magnetic field. Here we do the opposite, artificially driving a current in a plasma torus to create a resultant magnetic field.

[Twark_Main]

The Van Allen Belt doesn’t provide shielding. The Earth’s magnetic field does.

I think he's talking about the idea proposed in How to create an artificial magnetosphere for Mars" (R.A. Bamford et al, Acta Astronautica, Volume 190, January 2022, Pages 323-333). The idea is to create an artificial Van Allen belt of charged particles and then to run an electrical current through that loop, generating a magnetic field. (See section 8, starting on page 16.)

Plasma structures such as radiation belts naturally occur around planets like the Earth. In these cases, the co-rotating ions and electrons are formed as a result of the rotation of the planet and complex interactions of its natural magnetic field. Here we do the opposite, artificially driving a current in a plasma torus to create a resultant magnetic field.

Anyone care to comment on whether this is more or less difficult than the "standard" buried superconducting loop plan?

https://inis.iaea.org/collection/NCLCollectionStore/_Public/40/084/40084971.pdf

Clearly the buried conductors plan requires more work to build the "wires," but for the other parts of the system the relative feasibility is less clear.

[Robotbeat]

The Van Allen Belt doesn’t provide shielding. The Earth’s magnetic field does.

I think he's talking about the idea proposed in How to create an artificial magnetosphere for Mars" (R.A. Bamford et al, Acta Astronautica, Volume 190, January 2022, Pages 323-333). The idea is to create an artificial Van Allen belt of charged particles and then to run an electrical current through that loop, generating a magnetic field. (See section 8, starting on page 16.)

Plasma structures such as radiation belts naturally occur around planets like the Earth. In these cases, the co-rotating ions and electrons are formed as a result of the rotation of the planet and complex interactions of its natural magnetic field. Here we do the opposite, artificially driving a current in a plasma torus to create a resultant magnetic field.

Anyone care to comment on whether this is more or less difficult than the "standard" buried superconducting loop plan?

https://inis.iaea.org/collection/NCLCollectionStore/_Public/40/084/40084971.pdf

Clearly the buried conductors plan requires more work to build the "wires," but for the other parts of the system the relative feasibility is less clear.

I think Jim Greene's orbital magnetosphere plan is less effective than burying wires. Burying wires can also act as a global energy storage and distribution system for Mars.

[Lampyridae]

FYI, there is finally a paper on active + passive radiation shielding.

https://www.sciencedirect.com/science/article/pii/S2214552423000391

What's interesting is that they were able to compute a simple scaled reduction factor for the various ions and energies and then feed them into HZTERN. Hopefully NASA can implement this feature with OLTARIS if we agitate enough.

Note: this is for electrostatic shielding, which isn't going to be great for Mars surface and its low pressure, dusty, highly conductive atmosphere.

[LMT]

Note: this is for electrostatic shielding, which isn't going to be great for Mars surface and its low pressure, dusty, highly conductive atmosphere.

I think it can't work there at all, no.  Electrical conductivity is ~ 2 orders of magnitude higher than Earth's.  The shield would discharge far below the required electric potential.