Mars Radiation

[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.