New Mars Forums

Official discussion forum of The Mars Society and MarsNews.com

You are not logged in.

Announcement

Announcement: This forum is accepting new registrations by emailing newmarsmember * gmail.com become a registered member. Read the Recruiting expertise for NewMars Forum topic in Meta New Mars for other information for this process.

#1 2019-02-27 19:27:25

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Interview with Musk...

Wasn't anything too surprising in this for me except Musk's reference to a fun park dome under faceted glass where people could walk "without a suit"...

https://www.popularmechanics.com/space/ … acex-mars/

That seems to suggest a rather cavalier attitude to the radiation danger.

I was just wondering, is he envisaging something with an abundance of vegetation...would that provide protection if you were walking under the canopy? 

Otherwise, it seems to me he hasn't thought this through...

Any thoughts?


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#2 2019-02-27 20:02:48

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 29,204

Re: Interview with Musk...

The SpaceX CEO on food, fuel, and the risk of vaporization.

Suggests underground hydroponics with solar power lighting for food growth.

But yet talks about the remaining life support needs for surface as building blocks of C H O with nothing for the legs of a mars journey.

Talks about gravity with a hint of artifical being used.

Trys the re-entry numbers for how hard it is to stop...

So to sum it up presents the dream but has not the full detailed plan....

Offline

#3 2019-02-27 23:30:55

JoshNH4H
Member
From: Pullman, WA
Registered: 2007-07-15
Posts: 2,551
Website

Re: Interview with Musk...

The short answer to that question is no, vegetation is not enough to protect from radiation.  You can get a good level of radiation protection from a few thousand kg per square meter, and even a tropical rainforest canopy is almost definitely at least an order of magnitude less than that.


-Josh

Offline

#4 2019-02-28 03:21:21

Terraformer
Member
From: Ceres
Registered: 2007-08-27
Posts: 3,827
Website

Re: Interview with Musk...

It depends on what radiation you're talking about. UV requires far less than a few tonnes per square meter to block.

As far as I understand it, an hour a day in such a dome would keep you well within the radiation limits, provided you spent the rest of the time in a well shielded habitat. You should be getting significantly less radiation in that case than airliner crews.


Use what is abundant and build to last

Offline

#5 2019-02-28 03:43:51

elderflower
Member
Registered: 2016-06-19
Posts: 1,262

Re: Interview with Musk...

Earth atmosphere at sea level is approximately 1000 mBar, 15 psi, 1kg/sq cm. That is plenty for humans to live. Humans do not all live at sea level, so a figure of half the above would be adequate for long term living. In Mars terms, that would yield a pressure of approx. 0.4x0.5x1000 =200 mBar as a useable figure for radiation protection. Such an atmosphere would have to be pretty high in Oxygen to meet human minimum breathing needs and would be a severe fire hazard, so actually you need a lot more surface pressure to allow for diluting gases. If you can achieve that you will get all the radiation protection you will need from atmospheric gas.
If you have such conditions in an enclosure, and not outside on the planet's surface the same mass (500 kg/m2) will need to be provided overhead the habitation and excursions will need to be time limited. The  living areas will need to be underground, or mounded or maybe roofed with ice or some massive Mars derived compound. Vegetation doesn't come close to these figures.

Offline

#6 2019-02-28 05:11:18

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

I was thinking more about cosmic radiation...this is a helpful article:

https://www.businessinsider.com/airplan … ?r=US&IR=T

Based on that article, it looks like you are right that an hour a day would keep you within the recommended limits.

So that's good news. Maybe a multi shell dome would help as well.

Terraformer wrote:

It depends on what radiation you're talking about. UV requires far less than a few tonnes per square meter to block.

As far as I understand it, an hour a day in such a dome would keep you well within the radiation limits, provided you spent the rest of the time in a well shielded habitat. You should be getting significantly less radiation in that case than airliner crews.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#7 2019-02-28 05:13:41

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

True but it does sound like anything we've thought about, he's thought about! smile

SpaceNut wrote:

The SpaceX CEO on food, fuel, and the risk of vaporization.

Suggests underground hydroponics with solar power lighting for food growth.

But yet talks about the remaining life support needs for surface as building blocks of C H O with nothing for the legs of a mars journey.

Talks about gravity with a hint of artifical being used.

Trys the re-entry numbers for how hard it is to stop...

So to sum it up presents the dream but has not the full detailed plan....

SpaceNut wrote:

The SpaceX CEO on food, fuel, and the risk of vaporization.

Suggests underground hydroponics with solar power lighting for food growth.

But yet talks about the remaining life support needs for surface as building blocks of C H O with nothing for the legs of a mars journey.

Talks about gravity with a hint of artifical being used.

Trys the re-entry numbers for how hard it is to stop...

So to sum it up presents the dream but has not the full detailed plan....


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#8 2019-02-28 05:18:19

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

Of course cosmic radiation does come in from all directions, so presumably that would provide a good deal of protection since, as long as you were not next to the dome glass, there would always be several tree trunks in the way, blocking the cosmic radiation... In fact, the more I think about it, you'd only really get the full dose if you were in position open to the sky (except for the dome glass that is). So it might have a bigger reduction effect than you might suppose...

JoshNH4H wrote:

The short answer to that question is no, vegetation is not enough to protect from radiation.  You can get a good level of radiation protection from a few thousand kg per square meter, and even a tropical rainforest canopy is almost definitely at least an order of magnitude less than that.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#9 2019-02-28 07:00:31

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,836
Website

Re: Interview with Musk...

louis wrote:

True but it does sound like anything we've thought about, he's thought about! smile

I believe either he or people at SpaceX read our forum. When SpaceX still hadn't successfully landed a stage, Blue Horizon successfully landed one. New Glenn was just a suborbital hop, but it landed. I subscribe to the email list for the Washington DC chapter of the Mars Society. On that email list, I posted my suggestion that SpaceX give up on landing on a barge, instead land on land. They can do a barge in the ocean after they do land. Blue Horizon succeeded because they did land. I also speculated that if NASA doesn't want them to land at KSC, then do a test flight at Boca Chica. Their very next launch landed at KSC. Successfully! After they successfully landed on land, they did so on a barge. Coincidence? Did someone at SpaceX read my post to the email list? Or was it that Blue Horizon landed on land? I would like to believe SpaceX acted on my suggestion. If so, that means someone at SpaceX reads that email list.

Offline

#10 2019-02-28 10:24:58

JoshNH4H
Member
From: Pullman, WA
Registered: 2007-07-15
Posts: 2,551
Website

Re: Interview with Musk...

On Radiation:

I want to point out that on Earth, it's the magnetosphere that blocks radiation, not the atmosphere.  The weight of Earth's atmosphere is therefore irrelevant to any discussion of the mass required for radiation protection.  It's also worth mentioning that a large mass of diffuse matter (such as Earth's thick atmosphere) will do a better job at shielding, kilo-per-kilo, than solid matter.

Musk does not clarify how big of a "park" he envisions so it's hard to say exactly how much radiation protection should be expected, but even if it is a heavily wooded park (something we rarely do in city parks on Earth because open fields are more versatile--also, from where would you get big old trees?) it's hard to imagine a dome that is not very large having enough of them to offer meaningful shielding.  My suggestion on this matter would be to get whatever shielding you can from the dome itself (possibly a multi-layer dome with a layer of water, maybe saltwater, for shielding?) and simply accept that time in the park corresponds to a higher radiation dose and therefore ought to be somewhat limited.

Hey RobertDyck:

Did you consider at any time that the idea of, er, landing on land is not really that hard to come up with?


-Josh

Offline

#11 2019-02-28 11:26:20

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,836
Website

Re: Interview with Musk...

JoshNH4H wrote:

Hey RobertDyck:

Did you consider at any time that the idea of, er, landing on land is not really that hard to come up with?

Why did he refuse to do it so long? It should be obvious; land on land first, barge later. But he didn't. He kept crashing rockets on barges.

Offline

#12 2019-02-28 11:37:36

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

I'm sure some must if only occasionally! 

I've never found other sites where the challenges of Mars colonisation are pursued with such attention to detail over long time periods, involving several "voices" - so it would seem natural for people to gravitate here. If they don't, I think they'll be missing something! 

RobertDyck wrote:
louis wrote:

True but it does sound like anything we've thought about, he's thought about! smile

I believe either he or people at SpaceX read our forum. When SpaceX still hadn't successfully landed a stage, Blue Horizon successfully landed one. New Glenn was just a suborbital hop, but it landed. I subscribe to the email list for the Washington DC chapter of the Mars Society. On that email list, I posted my suggestion that SpaceX give up on landing on a barge, instead land on land. They can do a barge in the ocean after they do land. Blue Horizon succeeded because they did land. I also speculated that if NASA doesn't want them to land at KSC, then do a test flight at Boca Chica. Their very next launch landed at KSC. Successfully! After they successfully landed on land, they did so on a barge. Coincidence? Did someone at SpaceX read my post to the email list? Or was it that Blue Horizon landed on land? I would like to believe SpaceX acted on my suggestion. If so, that means someone at SpaceX reads that email list.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#13 2019-02-28 11:52:06

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

Well you could certainly speed things up by filling up a couple of Starships with large saplings and shipping them out...but you'd probably introduce a lot of unwanted guests that way, so maybe best to be patient...

The current dome record holder has a diameter of over 300 metres. Let's imagine a more manageable 200 metre diameter dome with maybe a 50 metre wide forest zone ring running up to the glass. That would leave a 100 metre diameter circle for your park - with a 300 metre running path on its circumference. The dome could incorporate on the edge of the forested area you could have seating areas and refreshment tables under radiation protection barriers. 

JoshNH4H wrote:

On Radiation:

I want to point out that on Earth, it's the magnetosphere that blocks radiation, not the atmosphere.  The weight of Earth's atmosphere is therefore irrelevant to any discussion of the mass required for radiation protection.  It's also worth mentioning that a large mass of diffuse matter (such as Earth's thick atmosphere) will do a better job at shielding, kilo-per-kilo, than solid matter.

Musk does not clarify how big of a "park" he envisions so it's hard to say exactly how much radiation protection should be expected, but even if it is a heavily wooded park (something we rarely do in city parks on Earth because open fields are more versatile--also, from where would you get big old trees?) it's hard to imagine a dome that is not very large having enough of them to offer meaningful shielding.  My suggestion on this matter would be to get whatever shielding you can from the dome itself (possibly a multi-layer dome with a layer of water, maybe saltwater, for shielding?) and simply accept that time in the park corresponds to a higher radiation dose and therefore ought to be somewhat limited.

Hey RobertDyck:

Did you consider at any time that the idea of, er, landing on land is not really that hard to come up with?


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#14 2019-02-28 11:57:49

Void
Member
Registered: 2011-12-29
Posts: 7,298

Re: Interview with Musk...

Josh,

Although I tend to support artificial light gardening, I really am also a fan of experiments to master surface greenhouses.  I note your thinking.
Quote:

On Radiation:
I want to point out that on Earth, it's the magnetosphere that blocks radiation, not the atmosphere.  The weight of Earth's atmosphere is therefore irrelevant to any discussion of the mass required for radiation protection.  It's also worth mentioning that a large mass of diffuse matter (such as Earth's thick atmosphere) will do a better job at shielding, kilo-per-kilo, than solid matter.
Musk does not clarify how big of a "park" he envisions so it's hard to say exactly how much radiation protection should be expected, but even if it is a heavily wooded park (something we rarely do in city parks on Earth because open fields are more versatile--also, from where would you get big old trees?) it's hard to imagine a dome that is not very large having enough of them to offer meaningful shielding.  My suggestion on this matter would be to get whatever shielding you can from the dome itself (possibly a multi-layer dome with a layer of water, maybe saltwater, for shielding?) and simply accept that time in the park corresponds to a higher radiation dose and therefore ought to be somewhat limited.

And I mention that there are fossil magnetic fields on Mars, I think primarily in the southern hemisphere.  So, it is possible that Mars dwellers would utilize that natural resource.  In addition, I feel that there is the possibility of briny aquifers at the same locations, which to me would be favorable as well.

Otherwise, although an additional expense, I might think that a dome could be given an artificial magnetic field to help.

Done.


Done.

Offline

#15 2019-02-28 12:00:17

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

Has Musk been on the whacky-baccy again?  He's asking whether people whether they want to "make the Mars technocracy real"...erm?  Most of the people voting don't seem to know what a technocracy is and I am wondering if Musk does?

https://twitter.com/elonmusk/status/1100859074764107776


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#16 2019-02-28 13:57:06

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,563

Re: Interview with Musk...

Why are people so fascinated by what Mr. Musk does in his free time?

Work 100+ hours per week for years on end and come back to us and let us know if you need something to take the edge off that.  The man sleeps in his office when he manages to get any sleep at all.  If he wants to smoke a joint, jump out of a perfectly good airplane, or write interesting things on Twitter to cut loose a bit, try walking a mile in his shoes before you judge him.

Offline

#17 2019-02-28 14:21:13

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

It was a joke - but I am concerned by (a) what he means to convey via this tweet and (b) if his understanding of "technocracy" is the same as mine.

kbd512 wrote:

Why are people so fascinated by what Mr. Musk does in his free time?

Work 100+ hours per week for years on end and come back to us and let us know if you need something to take the edge off that.  The man sleeps in his office when he manages to get any sleep at all.  If he wants to smoke a joint, jump out of a perfectly good airplane, or write interesting things on Twitter to cut loose a bit, try walking a mile in his shoes before you judge him.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#18 2019-02-28 18:19:47

JoshNH4H
Member
From: Pullman, WA
Registered: 2007-07-15
Posts: 2,551
Website

Re: Interview with Musk...

louis wrote:

Well you could certainly speed things up by filling up a couple of Starships with large saplings and shipping them out...but you'd probably introduce a lot of unwanted guests that way, so maybe best to be patient...

The current dome record holder has a diameter of over 300 metres. Let's imagine a more manageable 200 metre diameter dome with maybe a 50 metre wide forest zone ring running up to the glass. That would leave a 100 metre diameter circle for your park - with a 300 metre running path on its circumference. The dome could incorporate on the edge of the forested area you could have seating areas and refreshment tables under radiation protection barriers.

How much mass is in a forest?  This paper based on research in Mexican forests, found an average Aboveground Biomass around 80 Mg/Ha with an average canopy height around 15 m.  That's roughly 8 kg/m^2, and with a height of 15 m roughly 0.5 kg/m^3.  That is to say, a forest has roughly double the amount of radiation protection offered by a comparable volume of non-forested air at 1/2 atmosphere (including the radiation protection coming from the air in the forest).

This is to say, not much.  Not much at all.

A key point to remember here is that line-of-sight is not a good metric for radiation protection as (unlike visible light) cosmic rays are barely affected by normal materials.  It's worth remembering that real forests are in fact overwhelmingly composed of air, which is what makes it possible to walk around and see through them.

If what you have in mind is a solid wall of thick-trunked trees you may not have a real-life forest in mind at all but rather an imaginary one.  In the real world trees need space for their root systems, especially big ones.

Given the height limit of the dome ceiling trees will also be of limited utility in protecting from radiation.  More cosmic radiation comes from the zenith than the horizon because the atmosphere provides more shielding horizontally than vertically (this is the same reason that sunsets are red).  Furthermore, thousands of kilograms per square meter are required for adequate shielding, corresponding to a couple meters of regolith.  An overhead structure used for shielding will necessarily be more than a metal roof over an area; it would have to be a pretty thick piece of solid material.

I say all this not to suggest that such a park is impossible or that radiation is an insurmountable problem.  I would, as I said, look to a thicker dome (actually the forces on a 200m pressurized dome would be immense anyway and would require substantial structures to hold in) rather than trees and roofs, as well as simply limiting exposure time.

Radiation at low altitudes on Mars is roughly 50 times higher than Earth.  If I were to design a radiation management strategy, it would be for habitats to be extremely well-shielded so as to have virtually no radiation within, and then for residents to minimize their time in higher-radiation zones to keep their total dosage down.

Given the mental health benefits of open/green space I would say a park like this one is a net win even with higher radiation exposure while you're there.  For what it's worth, if I were designing for maximum effect I would put the vegetation towards the center and make the outer wall an open vista, ideally an impressive crater or canyon.

RobertDyck wrote:

Why did he refuse to do it so long? It should be obvious; land on land first, barge later. But he didn't. He kept crashing rockets on barges.

Here's an entirely reasonable explanation for their actions:

SpaceX wants to land rockets on barges because it requires less fuel than returning to the launch site.

Therefore they try to land rockets on barges.

Landing rockets on barges is hard and their first few tries fail.

They try landing on land (which, as you say, is obvious) as an easier target to develop technology.

Once accomplished, they go back to barges.

The words you used when making the claim initially were as follows: "I would like to believe that SpaceX acted on my suggestion".  I would like to gently suggest to you that in using those words you gave away more than you intended.

On the topic, broadly, of whether Newmars has any influence on technical/policy discussions: I would say that as a default the answer is no but we may show up on a google search every once in a while.  To my knowledge we haven't had a member who was also in a place of power in the aerospace industry while on the forums, but Mr. Musk without a doubt is exposed to many similar sources--Zubrin's writings, the principles of physics and engineering, news articles about space, and the trends in science fiction.


-Josh

Offline

#19 2019-02-28 18:48:14

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

The paper you quote seems to relate to non-trunk biomass (as it's referencing carbon sequestration). When I looked up the mass of big oak and hardwood trees I was seeing figures of 15-45 tons of usable timber - so that would be the trunks and big branches.  That's a lot of mass with a lot of water or other liquids in it (which I have always understood provides good radiation protection).

Take a look at this image of a beech forest -

https://www.alamy.com/stock-photo-ghost … 91468.html

I'd say that is probably 95-98% trunk left to right at a height of up to 10 metres.

There is probably an optimal tree species for any given circumference to provide max radiation protection.

If you are working within a dome, you would obviously plant thick-trunk shorter trees at the periphery and then taller species as you move to the middle. To provide maximum protection you would want species that don't taper too much.  With careful lopping you could no doubt maximise the amount of protective trunk and thick branches.

I agree with you about the mental health benefits of a park environment as weighed against radiation exposure. 

A dome does not necessarily have to carry all the mass of radiation protection.  Given there are 1000 metre plus bridge spans, you could have a 200 metre wide dome with an overarching cable-suspended protective section (ie an entirely separate structure) weighing perhaps  a few thousand tons. Also, we must keep in mind that with the lower G on Mars all this is a lot easier of course.


JoshNH4H wrote:
louis wrote:

Well you could certainly speed things up by filling up a couple of Starships with large saplings and shipping them out...but you'd probably introduce a lot of unwanted guests that way, so maybe best to be patient...

The current dome record holder has a diameter of over 300 metres. Let's imagine a more manageable 200 metre diameter dome with maybe a 50 metre wide forest zone ring running up to the glass. That would leave a 100 metre diameter circle for your park - with a 300 metre running path on its circumference. The dome could incorporate on the edge of the forested area you could have seating areas and refreshment tables under radiation protection barriers.

How much mass is in a forest?  This paper based on research in Mexican forests, found an average Aboveground Biomass around 80 Mg/Ha with an average canopy height around 15 m.  That's roughly 8 kg/m^2, and with a height of 15 m roughly 0.5 kg/m^3.  That is to say, a forest has roughly double the amount of radiation protection offered by a comparable volume of non-forested air at 1/2 atmosphere (including the radiation protection coming from the air in the forest).

This is to say, not much.  Not much at all.

A key point to remember here is that line-of-sight is not a good metric for radiation protection as (unlike visible light) cosmic rays are barely affected by normal materials.  It's worth remembering that real forests are in fact overwhelmingly composed of air, which is what makes it possible to walk around and see through them.

If what you have in mind is a solid wall of thick-trunked trees you may not have a real-life forest in mind at all but rather an imaginary one.  In the real world trees need space for their root systems, especially big ones.

Given the height limit of the dome ceiling trees will also be of limited utility in protecting from radiation.  More cosmic radiation comes from the zenith than the horizon because the atmosphere provides more shielding horizontally than vertically (this is the same reason that sunsets are red).  Furthermore, thousands of kilograms per square meter are required for adequate shielding, corresponding to a couple meters of regolith.  An overhead structure used for shielding will necessarily be more than a metal roof over an area; it would have to be a pretty thick piece of solid material.

I say all this not to suggest that such a park is impossible or that radiation is an insurmountable problem.  I would, as I said, look to a thicker dome (actually the forces on a 200m pressurized dome would be immense anyway and would require substantial structures to hold in) rather than trees and roofs, as well as simply limiting exposure time.

Radiation at low altitudes on Mars is roughly 50 times higher than Earth.  If I were to design a radiation management strategy, it would be for habitats to be extremely well-shielded so as to have virtually no radiation within, and then for residents to minimize their time in higher-radiation zones to keep their total dosage down.

Given the mental health benefits of open/green space I would say a park like this one is a net win even with higher radiation exposure while you're there.  For what it's worth, if I were designing for maximum effect I would put the vegetation towards the center and make the outer wall an open vista, ideally an impressive crater or canyon.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#20 2019-02-28 20:30:30

JoshNH4H
Member
From: Pullman, WA
Registered: 2007-07-15
Posts: 2,551
Website

Re: Interview with Musk...

Hey louis,

I was a bit confused on what exactly they were measuring with "AGB" (Above Ground Biomass) but I went back into the paper and it looks like on page 4 they say "AGB defined as all living vegetation, both woody and herbaceous, above the soil".  I grant that 0.5 kg/m^3 definitely seems low but I think it's a reasonable density to derive from the numbers in that paper.  I have confidence in it as an order of magnitude estimate.  No doubt some forests are higher.

Line-of-sight is not an important factor for radiation protection.  That forest looks quite dense but what that translates to in terms of density ¯\_(ツ)_/¯

One way to approximate total forest density would be to give a very rough guess at tree diameter and spacing.  Let's say the average tree is 1 foot (30 cm) in diameter and is, on average, 3m away from its neighboring trees.  The tree has an area of pi*.3^2/4 or roughly .08 square meters.  The area surrounding the tree has an area of pi*3^2 or roughly 30 square meters.  Divide by two (if the other tree is 3 meters away only half of it "belongs" to the one tree) and you have 15 square meters.  .08/15=0.005, so the forest is 0.5% tree; You might expect a density of 5 kg/m^3.

Is this reasonable? I can honestly tell you that I have no idea.  Maybe next time I'm in a forest I'll bring a tape measure and some string.  But if it's even close to being accurate forests are not good for radiation shielding.  Agreed that there are things you can do that might make them better, but even if you do so you will need additional means to make the park a true low-rad environment.

As far as dome structure:  This is something I harp on a lot but dome weight is not the important structural concern when you're building an indoor dome on Mars.  It's the internal pressure of the dome that matters, pushing upwards and outwards against the outer walls.

Here's a rough calculation:

Let's say the colony operates at half an atmosphere, 50 kPa.  That's 50,000 N per square meter on any surface pushing outwards.  If your dome has a diameter of 200 m, that means that there will be 1.6 billion newtons trying to lift the dome up off the ground.  This is the equivalent to the force of 160,000 tonnes--on Earth.  By way of comparison, The O2 in London (a dome with a diameter of 365 m) weighs  just 4500 tonnes (a half-atmosphere dome of this diameter would have an upwards force of 520,000 tonnes, over 100 times more).  I described how I think buildings in general ought to be built here.  The key idea is that radiation shielding weighing down a ceiling actually reduces the structural load.


-Josh

Offline

#21 2019-03-01 09:44:27

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,563

Re: Interview with Musk...

A dense forest is to an iron ion moving at relativistic speeds what a pallet of paper is to rail gun.  It's almost as if nothing substantial was there to begin with.  Failing to put sufficient mass in front of either can make the secondary effects worse than the primary effect.  That's the nature of the problem.  The constant barrage of high energy protons would kill the trees.  Scientists have actually tested this with particle accelerators.  The plants didn't fare well.  The effects recorded from other forms of radiation are not a suitable analog, either.  The energy levels of GCR's are well in excess of what we've actually shielded against.

We're far better off deflecting relativistic ions with electromagnetic and electrostatic fields than trying to stop them cold with mass of materials.  The obvious solution is to bury habitat modules, but that ignores the quality of life issue of being stuck inside a tube buried beneath the surface of a planet.  That might be perfectly acceptable for astronauts, but normal people will want to go outside and see the sights.

An exploration of the effectiveness of artificial mini-magnetospheres as a potential Solar Storm shelter for long term human space missions

The power and mass requirements are trivial in comparison to the mass and power required for making return propellants or building the O2 dome on Mars.

Edit:

I think projects like this one have the right idea:

Can an Artificial Geomagnetic Field Protect Mars Colonists from Cosmic Rays?!

Last edited by kbd512 (2019-03-01 09:52:15)

Offline

#22 2019-03-01 13:32:53

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,570
Website

Re: Interview with Musk...

There are people living in small cities at ~15,000 feet on this globe.  They do not seem to suffer from radiation or hypoxia any more than most of the rest of us.  The air pressure at that altitude is 56.46% that of sea level,  and that is literally the weight of the atmosphere overhead. 

That weight is 0.5646 * 101.325 KPa = 57.209 KN/sq.m.  Earth's standard gravity acceleration is 9.807 m/s^2,  so the overhead MASS of atmosphere is 5.83  kg/sq.m = 0.583 g/sq.cm.  That's a fairly  small amount of shielding mass compared to 15 cm of water (that being 15 g/sq.cm),  but it is spread out over a linear dimension measured in 10's of km,  not just 15 cm.  That's why it works as well as it does for a radiation shield. 

On Mars,  the overhead atmospheric weight is only about 0.61 KN/sq.m.  At 0.38 gee,  that's about 0.16 kg/sq.m = 0.016 g/sq.cm shielding mass overhead.  Being factor 36 smaller,  that's very small indeed as shielding mass,  but again the linear dimension is 10's of km (about the same 8 km scale height as Earth).  It has some shielding effect,  but nowhere near that of Earth's atmosphere at 15,000 feet altitude.

Them's just the numbers talking.

GW

Last edited by GW Johnson (2019-03-01 13:35:23)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

Offline

#23 2019-03-01 15:36:39

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,415

Re: Interview with Musk...

There is an excellent sample group available to study for the effect of radiation on those living at high altitude: The Sherpas of Nepal. One of my close personal friends did her Ph.D. research on this ethnic group and lived in Rolwaling, Nepal 5 years doing so. The altitude of that village is in XS of 13,000 feet above msl. There is some work already done--collection of DNA samples, for example.

Offline

#24 2019-03-01 15:57:47

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

Interesting - so why do people think you can grow crops under a glass dome on Mars? 

I am sure an electromagnetic barrier would be possible.


kbd512 wrote:

A dense forest is to an iron ion moving at relativistic speeds what a pallet of paper is to rail gun.  It's almost as if nothing substantial was there to begin with.  Failing to put sufficient mass in front of either can make the secondary effects worse than the primary effect.  That's the nature of the problem.  The constant barrage of high energy protons would kill the trees.  Scientists have actually tested this with particle accelerators.  The plants didn't fare well.  The effects recorded from other forms of radiation are not a suitable analog, either.  The energy levels of GCR's are well in excess of what we've actually shielded against.

We're far better off deflecting relativistic ions with electromagnetic and electrostatic fields than trying to stop them cold with mass of materials.  The obvious solution is to bury habitat modules, but that ignores the quality of life issue of being stuck inside a tube buried beneath the surface of a planet.  That might be perfectly acceptable for astronauts, but normal people will want to go outside and see the sights.

An exploration of the effectiveness of artificial mini-magnetospheres as a potential Solar Storm shelter for long term human space missions

The power and mass requirements are trivial in comparison to the mass and power required for making return propellants or building the O2 dome on Mars.

Edit:

I think projects like this one have the right idea:

Can an Artificial Geomagnetic Field Protect Mars Colonists from Cosmic Rays?!


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

#25 2019-03-01 16:10:40

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Interview with Musk...

Obviously people at that height are adapted to living in that environment. I read once about inhabitants of very high altitudes in South America who are able to reproduce at those altitudes whereas inhabitants from lower altitudes were not able to. Something to do with sperm production I seem to recall.

Oldfart1939 wrote:

There is an excellent sample group available to study for the effect of radiation on those living at high altitude: The Sherpas of Nepal. One of my close personal friends did her Ph.D. research on this ethnic group and lived in Rolwaling, Nepal 5 years doing so. The altitude of that village is in XS of 13,000 feet above msl. There is some work already done--collection of DNA samples, for example.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

Offline

Board footer

Powered by FluxBB