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#26 2019-03-01 17:16:25

JoshNH4H
Member
From: Pullman, WA
Registered: 2007-07-15
Posts: 2,526
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Re: Interview with Musk...

Hey GW,

Seems to me there's an error in your math there.

57 kN/m^2 corresponds to 5.8 tonnes of atmosphere, not kilograms.  This corresponds, in turn, to 5.8 meters of water, not 0.58 centimeters.

While Earth's atmosphere probably would be adequate shielding to protect us from most cosmic radiation it does not have to serve that purpose because Earth has a strong magnetic field which protects us in its stead.

Kbd512,

I'd be interested in having a look at the studies you mentioned.  As louis pointed out they have a direct bearing on whether we can use natural light greenhouses or not.  My assumption thus far is that the radiation would not be a big issue for agriculture (agrifacturing?), but obviously if research paints a different picture I will have to update that.

On the topic of artificial magnetospheres, the first source notes (on page 7) that the system being described depends on a plasma environment to work.  Mars's atmosphere is thin, but not that thin.  I'm not sure that particular paper applies.

The second article mentions a system designed for Mars.  I believe we had a member of that Lake Matthew Team right here on the fora.  I don't totally understand how the system is supposed to work, but it seems that the basic idea is to use a large, superconducting loop (much larger than the area being protected) to generate a big magnetic field to push charged particles away.

The theory is sound, and I suppose I trust their math, but superconducting loops and carbon nanotubes are a substantial investment as far as infrastructure goes.  Is this better than burying things under dirt and ice?  Probably, I guess, if you're building on a big scale anyway.  It does also require continuous power though which is a substantial drawback.


-Josh

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#27 2019-03-01 17:55:45

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,228

Re: Interview with Musk...

Louis,

If there's an electromagnetic or electrostatic deflector shield to route incoming ions around the dome, then there's no reason why we can't grow crops there and also give the inhabitants a lush garden to enjoy using the agricultural techniques developed in The Netherlands (genetically engineered crops, no soil at all, water recycling, special spectrum LED lighting, and elevated levels of CO2 optimized for plant growth).  Sulfacrete has the strength of steel reinforced concrete, but without the steel.  Throw in CNT reinforcement (this has also been developed and tested) using C obtained from the CO2 atmosphere and you have seriously strong composite concrete.  Those crater beds are almost certainly sitting atop ice.  The ice will supply the colonists and their food source with water.  There won't really be any need to leave the dome.  The dome itself can be made of CNT-infused silica.

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#28 2019-03-01 18:20:24

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 26,753

Re: Interview with Musk...

The field produced in the coil is from AC or RF energy charging the coil to create the field. A dc field would decay once the coil saturates. CNT are conductive but carbon is a resistive element in electronics and is not magnetic.

Back before the constellation redirection there was some work being done on the electrostatic shield for the moon.

The real issue for any field created from the power source for man is you need more energy to have one.

If we have nuclear powered satelites in orbit then a field is a matter of transimitting the RF energy between them to creat the grid of energy to deflect the in coming particles.

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#29 2019-03-01 20:58:01

kbd512
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Registered: 2015-01-02
Posts: 6,228

Re: Interview with Musk...

Josh,

Here's a couple papers or links to more papers.  I did have a paper where they basically irradiated plants using particle accelerators until they killed them, but I had that on my other hard drive before it bit the dust.  Along with the various nuclear regulatory agencies, NASA, ESA, and ROSCOSMOS have all studied this topic intensively because it's a major factor regarding whether or not humans can live in space indefinitely.

Space radiation effects on plant and mammalian cells

Effects of Ionizing Radiation on Plants and Animals at Levels Implied by Current Radiation Protection Standards

Apparently plants don't like microwave radiation, so the communications array should probably be outside the dome:

Electromagnetic Fields Impact Tree And Plant Growth

Somewhat encouraging results (basically states that the problems can be dealt with):

Effects of the Extraterrestrial Environment on Plants: Recommendations for Future Space Experiments for the MELiSSA Higher Plant Compartment

As would be expected, not all plants respond the same to ionizing radiation.  The food crops will probably be fine because their chronic radiation exposure is so short, but there would inevitably be some DNA alterations that produce deleterious results in unpredictable ways.  Some plants even seem to grow a little better at slightly elevated levels of ionizing radiation.  But the trees?  Not so much.  Oak and pine are sensitive to ionizing radiation.  There are specific species that aren't.  My takeaway is that the answer to the question of how much radiation damage to expect and what the ultimate result will be is that it depends greatly on the species in question.  In general, plants are more resilient than most animals.  However, there are exceptions.  Even so, shielding is a good idea.

Regarding the superconducting electromagnetic loop, the cryocooler is what requires continuous power.  After the conductor has been energized, it requires very little to no power to keep it energized.  MRI machines consume power to keep their LHe2 cold, but after the coil is energized no more power is consumed to maintain the magnetic field.  A small amount of power from the superconducting coil is lost over the course of multiple months, but the major energy input is the cryocooler.

SpaceNut,

My commentary about the various forms of Carbon is that those materials are ideal for structures or structural reinforcement of metals and in composites.  As we figure out how to make longer and longer strands of CNT, much sooner rather than later, there won't be an aircraft or spacecraft structure or electrical cable made without them.  It'll be too costly in terms of fuel not to use them.  In another 10 years or so, we'll have well-developed Carbon-based functional meta-materials that serve as sensors and embedded electronics.

Doped multi-stranded CNT wires are already as good or better than Copper is as a bulk electrical conductor, at a fraction of the weight, but right now the satellite and military / commercial aviation industries are using flat CNT tapes, from fibers or strands processed into tapes (think of it as black Teflon tape), as conductive EMI shielding that meets military standards instead of the traditional but much heavier copper braid.  NASA's big meta-materials push included CNT's that conduct as well as or better than copper in multi-stranded conductor configurations (successful, but not presently used for carrying electricity), disposable biological sensors to monitor astronaut metabolic function (successful and now in use aboard ISS), and spacecraft composites and radiation shielding (in progress).  NASA also figured out how to mass manufacture multi-kilogram quantities of CNT tapes for COPV reinforcement, but now they're working on BNNT tapes as electrical / thermal insulators and GCR shielding.

The doped multi-stranded / braided CNT wires aren't superconductors, but their ampacity ratings are so high per unit mass that they can carry similar current to superconducting tapes for less weight (that still doesn't help you get rid of the waste heat, though).  Similarly, recent advances in ordinary Copper conductors have achieved ampacities on par with superconductors (same waste heat problem).  This is important for development of electric motors and generators that generate large amounts of power using lightweight components.  Electron Labs uses a 50hp+ motor the size of a coke can (and if you use CO2 to spin it, you get 37kWe as output).  That's the kind of technology we need for Mars.

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#30 2019-03-01 22:12:37

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,952
Website

Re: Interview with Musk...

Josh:

Are you sure about tons of atmosphere?  Maybe on a square meter,  but not a square cm,  which is where I was trying to go,  in order to compare to "the usual" shielding masses,  typically expressed as grams per square cm. 

57 KN/sq.m = 57,000 N/sq.m by definition.  W = mg says  N = kg * 9.807 m/s^2,  which in turn says kg = N / 9.807 m/s^2.  So 57,000 N/sq.m corresponds to 5812 kg/sq.m = 5.812 metric ton/sq.m.  There's 100 cm in a meter,  so there's 10,000 sq.cm in a sq.m.   That means (5812 kg/sq.m)/(10,000 sq.cm/sq.m) = 0.5812 kg/sq.cm = 581 g/sq.cm.

That's my error,  I forgot to convert from kg to grams.  I was reporting 0.58 g/sq.cm. The 15 cm of water radiation shield corresponds to 15 g/sq.cm. I thought the thin air at altitude air had less shielding mass overhead;  it really has more. 

Thanks,  Josh.

GW

Last edited by GW Johnson (2019-03-01 22:16:16)


GW Johnson
McGregor,  Texas

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

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#31 2019-03-01 22:18:35

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,952
Website

Re: Interview with Musk...

As for people living at very high altitudes,  there are a lot more than many folks think,  and they are not significantly different from any of us.

Wikipedia has a list of the 47 highest-elevation airports in the world.  The title of the Wikipedia article is “List of Highest Airports”.  Each is associated with a city name,  which means there are large,  permanent,  reproducing populations in the vicinities of these airports. 

The lowest in the list is Mariscal Lamar International Airport,  located at Cuenca,  Ecuador.  Its IATA code is CUE,  and its ICAO code is SECU.  Field elevation is 2532 meters = 8307 feet above MSL. 

The highest in the list is Daocheng Yading Airport,  at Daocheng,  in Sichuan Province,  China.  Its IATA code is DCY,  and its ICAO code is ZUDC.  Field elevation is 4411 meters = 14,472 feet above MSL. 

The most common countries in the list are China,  Bolivia,  and Peru.  The top 10 in the list are all at or above 3788 m = 12,428 ft MSL.

La Paz,  Bolivia,  is a city often visited by tourists,  without serious acclimatization problems.  Its airport is El Alto International Airport,  IATA code LPB,  ICAO code SLLP,  and field elevation 4061 m = 13,323 ft MSL. 

There are two US airports on this list.  One is Leadville,  Colorado’s Lake County Airport,  IATA code LXV and ICAO code KLXV,  field elevation 3026 m = 9928 ft MSL.  The other is Telluride Regional Airport near Telluride,  Colorado,  IATA code TEX and ICAO code KTEX,  field elevation 2767 m = 9078 ft MSL.

There are no cities or settlements known at altitudes approaching 6096 m = 20,000 ft MSL,  but there are mountain herders in the Andes who work that high.  Those are the people who show significant genetic adaptation.  The rest of us are probably good,  with relatively minimal acclimatization,  to 4572 m = 15,000 ft MSL.

From the US 1962 Standard Atmosphere table at 15,000 feet:  pressure 0.5646 of sea level standard,  temperature -14.7 C = 5.5 F,  density 0.6295 of sea level standard.  At 20.94 volume percent oxygen,  that means the ambient partial pressure of oxygen in the air you breathe at 15,000 feet is 0.1182 atm,  vs 0.2094 atm at sea level.   For the record,  at sea level,  the standard atmospheric pressure is 1 atm = 101.325 KPa = 14.696 psia.

If a pure oxygen mask,  helmet,  or suit were pressurized to 0.1182 atm oxygen pressure,  that pressure corresponds to an altitude of about 15,074 m = 49,456 ft in the standard atmosphere.  About 40,000 to 45,000 ft is considered about the max practical pure oxygen mask altitude for steady-state flying.  Surprise,  surprise!
 
GW


GW Johnson
McGregor,  Texas

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

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#32 2019-03-01 22:25:16

JoshNH4H
Member
From: Pullman, WA
Registered: 2007-07-15
Posts: 2,526
Website

Re: Interview with Musk...

kbd512 wrote:

My takeaway is that the answer to the question of how much radiation damage to expect and what the ultimate result will be is that it depends greatly on the species in question.  In general, plants are more resilient than most animals.  However, there are exceptions.  Even so, shielding is a good idea.

Quoted because I think this is a great synopsis of the state of our understanding.  Reflected light into shielded greenhouses may in fact be necessary.

On the topic of radiation shielding: I don't like it (I think the need for continuous refrigeration is something of a kludge) but it probably would work


-Josh

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#33 2019-03-03 12:25:09

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,952
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Re: Interview with Musk...

On the moon there is no atmospheric or magnetic field shielding.  You have only the planet beneath your feet blocking half the sky,  with the whole sky the source of GCR.  GCR is a dilute exposure to highly-energetic particles.  It varies with the 11-year sunspot cycle from about 24 REM per year to 60 REM per year.  About 15 cm of something like water will cut that toward the 50 REM per year exposure limit,  but if you use metal shells,   or very modest thicknesses of regolith,  you get secondary showers of particulate radiation.  You need at least a couple of meters of regolith for a shield,  and you'll still get some low-rate exposure. 

The solar flare storm is quite different.  It is way-lower-energy particulate radiation far easier to shield,  but it comes in very concentrated doses.  Those vary quite erratically from a couple of hundred REM picked up in a few-hour event to tens of thousands of RM picked up in a few hours.  500 REM in a "short time" is just about 100% fatal to all so exposed,  and it is an ugly death within hours,  to at most a day.

Fortunately,  the same 15 cm of water is an order-of-magnitude or better shield.  Spacecraft hulls are also a factor-of-2-ish shield.  Pretty much a meter or more of regolith will work great,  and there are no secondary shower effects from solar flare radiation.  The lesson here for lunar bases and settlements is pile a couple of meters of regolith on the roof,  and if you need sunlight inside,  reflect it in through windows on the side,  underneath a roof overhang.  That's simple enough for anyone to understand.

Mars has an atmosphere to help shield from these things,  but it is lots thinner than Earth's atmosphere,  and so inherently has to be a less effective shield than Earth's atmosphere.  Mars has no shielding magnetic field,  unlike Earth. 

Earth sea level air at 101.3 KPa = 14.7 psia and 1 full gee corresponds to 10.33 metric tons per sq.m = 1000.3 g/sq.cm of shielding mass per it area.  Even at half nominal sea level pressure,  that's still 5-ish tons/sq.m = ~500 g/sq.cm:  quite a bit of shielding mass per unit area.  You reach only 15 g/sq.cm equivalent at a pressure of 0.015 atm,  and that's around 93 kft altitude (28 km).

Nominal surface Mars atmosphere at 6.1 mbar and 0.38 gee corresponds to a shielding mass per unit area of 163 kg/sq.m = 16.3 g/sq.cm.  That's a lot less shielding effect potential,  and it is similar to the remaining shielding effect on Earth at altitudes near 28 km. The whole average-plain surface atmosphere of Mars looks to be about as effective as 16 cm of water,  if all that matters is mass per unit area (and there's more to it than just that). 

What that really says is that on Mars,  you must do the same things you do on the moon for radiation shielding for your bases and settlements.  You might get away with a bit thinner regolith layer on your roof,  but you will NOT get away with none! 

Such recommendations will change some as we gain in-situ experience with actual bases and settlements.  But I bet they don't change a whole lot.  Radiation physics is just radiation physics after all. 

Josh: please double-check my figures.  But I think you will find I got them right,  this time.

GW

Last edited by GW Johnson (2019-03-03 12:48:53)


GW Johnson
McGregor,  Texas

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

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#34 2019-03-03 14:35:30

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,228

Re: Interview with Musk...

There are specific locations on the moon that provide some electromagnetic shielding, albeit very localized, but relying on those small somewhat protected locations is not a viable long-term survival strategy.

Though obviously geared towards nuclear war, this document is a general primer for treatment of radiological casualties that describes the observed effects in affected radiation casualties:

MULTISERVICE TACTICS, TECHNIQUES, AND PROCEDURES FOR TREATMENT OF NUCLEAR AND RADIOLOGICAL CASUALTIES

Here's the website it came from:

US Department of Health & Human Services - Radiation Emergency Medical Management

There's a wealth of information available for anyone who wants to read it.

According to NRC, the average American receives a radiation dose of .62 REM per year.  Assuming GW's figures are correct, that means that the dose rate can be up to 100 times higher on the moon.  Thought of another way, it's as if the radiation you'd receive over a 100 year lifetime was received in just one year by living unprotected on the moon.  That's before solar storms are taken into account, which can produce exposure rates up to tens of thousands of times higher than what you'd receive in a year on Earth.

The effects from radiation exposure depend greatly on type (ionizing, gamma ray, neutron), exposure area (whole body or confined to a particular area of the body), and exposure rate (how fast the dose is absorbed and at what total power level).  Medicine routinely uses radiation levels that would be lethal in days to treat cancer, for example, but those treatments are typically not lethal because the powerful radioactive isotopes used direct that radiation to very specific points within the body containing the cancerous cells.  The source us shielded in all other directions not in line with the cancer growth.  The radiation environment in space is fairly complex.  The Sun throws off a combination of electrons, ions, neutrons, high energy x-rays, and low energy gamma rays.  The remnants of stellar supernovae primarily contribute extremely high energy ions.

If anybody needs an analogy to understand the mechanism of injury and death from high radiation dose rates, you can think of it as death by trillions of atomic or subatomic paper cuts.  Any single paper cut would be easily and swiftly repaired by the body and life would go on without issue.  Repeat that process many times in a very short amount of time and the overall injury overwhelms the ability of the body to repair itself.

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#35 2022-09-26 05:36:52

Mars_B4_Moon
Member
Registered: 2006-03-23
Posts: 4,782

Re: Interview with Musk...

NASA and ESA sign lunar cooperation statement
https://spacenews.com/nasa-and-esa-sign … statement/

'Destruction Event' From Sun Annihilated Dozens of SpaceX Satellites
https://www.newsweek.com/spacex-satelli … er-1743539

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