I read the article on shielding and the radiation versus inclination due to the South Atlantic Anomaly makes me think the station could get buy with a very small shielded area where people shelter for a few minutes twice a day when they pass through it. Such a shelter could also double as the sleeping area.
But that brings up a point about shielding a small volume. High density polyethylene is slightly less dense than water (0.97 SG), so to get 4 tons per square meter requires a thickness of 13.5 feet of poly. If you went with depleted uranium (19 SG) you’d only need 8.2 inches to get 4 tons/m^2. This becomes really important if you’re shielding a small sphere.
A 6 foot diameter sphere has 10.5 square meters of surface area, so 4 tons/m^2 would have a mass of 42 tonnes. An 8 foot diameter sphere would have an area that requires a mass of 75 tons to shield. But the shield’s own thickness makes for a larger sphere, and although 8.2 inches per wall doesn’t add much, 13.5 feet (27 feet total) adds a tremendous extra volume and mass. The six foot-internal sphere’s outer diameter is 7.38 feet with depleted uranium but 33 feet with polyethylene.
So the 6 foot shielded sphere weighs 52.5 tonnes with DU but 516 tonnes with polyethylene or water. The 8 foot shielded sphere weighs 89 tonnes with DU but 614 tonnes with poly. The DU isn’t as good per mass as poly, but for small spaces the disparity in relative weight gives cause to reanalyze the material selection.
Anyway, years ago I ran some numbers on a mini-settlement which assumed that material costs remained extremely high and wondered what a viable settlement would look like in a competitive environment where the construction cost per person is the driving factor.
So I assumed something akin to a pair of airliner fuselages being spun on the end of a long boom. Given that windows are problematic, I went with solar cells providing power for interior grow lights, but either way a lot of heat gets dumped on the plants. I used that heat to drive natural air circulation between the crop/habitation area and cooling radiators mounted closer to the axis. The big pipes that carry the airflow to the radiators and back also double as the twin booms that support the two spinning habitats, and they make a fine place to mount all the solar cells.
I tilted the two habitats a bit nose up relative to the occupants so warming would drive the airflow along. The cool return air from the radiators is introduced at the low end and slowly travels up-gradient, picking up heat from the equipment, plants, and grow lights, before exiting at the higher end to enter the chimney duct. The air then heads up toward the axis, splitting off into the slightly down-sloping radiators along the way, with the radiators dumping the air into the cold-air return duct. Since the two booms are also air ducts, it’s trivial to have them serve as elevators to get to and from the axis, as long as the elevators have perforated floors and ceilings so they don’t overly impeded the airflow.
You do NOT want depleted Uranium, or indeed any heavy element, for your radiation shielding. With heavy elements, cosmic rays striking your shield would cause lethal secondary radiation.
That’s why I’d go with something like barium boride (BaB6) for the inner lining. Barium is a great X-ray absorber and boron is a neutron absorber.
And of course we’re talking about 4 tonnes per square meter, which is very dense shielding against the secondaries, too.
Perhaps I can dig up some nuclear codes and have a look, but the point is mainly based on geometry. For the six foot diameter polyethylene shell, with is 33 foot outer diameter, only 3 percent of what strikes the outer shell was on a path that would’ve taken it into the inner shell in the first place, so the shield is undergoing 30 times the number of GCR collisions (and the subsequent secondaries) than it would have if the shielding was small and dense.
And of course a 52 tonne, 7-foot diameter sphere is a lot easier to launch, install, and work around than a 516 tonne, 33-foot diameter sphere.
For charged particle radiation, which dominates in space, you want low atomic number. Polyethylene, with lots of hydrogen and carbon, is excellent, as is water. But presuming extraterrestrial materials you use whatever lower atomic number materials are handy. High atomic number materials are generally inferior radiation shielding unless you’re dealing with high energy photons.
Is there any possibility that having the shielding be a plasma, a moving plasma, or a plasma with a substantial electrical current is of any use?
And why is the brute-force approach of ‘sealed blocks of ice’ with the goal of eventually ending up with an iceball while providing an exceedingly deep emergency reservoir of fuel, air, and water not viable?
I’m unaware of any plasma configuration that is any use as a radiation shield. There are electromagnetic field configurations that should work, though they would take constant power input to maintain. One I have in mind charges the settlement with a high positive potential to block most cosmic rays, and uses a magnetic field to reduce discharge to electrons to an acceptable rate.
That’s they way I’d normally go when we’re talking about something like a Mars mission, where an older astronaut is going to fly one mission and accept a significant increase in cancer risk with poly shielding that’s maybe six to eighteen inches thick, or somewhere in the range of 0.2 tonnes per square meter. But what Al Globus is discussing is shielding sufficient for children and pregnant women to live full lives in space without significantly raising their risks, with shielding densities ten to forty times higher (and thus much, much thicker). So when the shield gets 10 to 20 feet thick for low Z materials, the geometry becomes unwieldy for shielding small spaces.
For shielding spent nuclear radiation DU concrete and tungsten are often used, with tungsten far outperforming lead. For linear accelerators in the low-end GCR range of megavolts, concrete, lead, and steel are the norm. I’d have to get much deeper into it to see what the trade-offs would be, but in the thicknesses Al Globus is talking, the low-Z materials are coming in six or more times heavier for the same density coverage (in tonnes/m^2), and a small shielded space the size of a bathroom is too heavy and bulky to launch even with the SLS.
$2m each person to orbit (and back) is within reach now simply by sending more at a time (not my idea, others with the right credentials have pointed this out years ago.) If $200k is required, then we twiddle thumbs until it’s achieved. It is simply not productive to say if only costs were lower we could do more. Is anybody denying this truth? Does acknowledging this truth make it happen any faster?
There is another way to look at it. Crew rotation multiples the cost. Sending ten (or 100) people in series costs the same as one person at ten (or 100) times the cost. Permanent settlers needs to be our initial mindset. Rotation should come only after costs have been established at a lower level.
The other weakness of the argument is basing it on tourism which requires that rotating crew cost in spades. A different income source can eliminate this problem (which again requires us to sit on our thumbs until magic happens.)
We need to eliminate mass transfer as completely as possible. The only mass transfer that is required for colony growth is more colonists (which means choosing a destination that already has sufficient and diverse mass already.)
Or we could just bypass our solar system and fantasize about colonizing an exoplanet? That way we don’t have to ever accomplish anything and yet still keep pretending it’s an accomplishment.
Of course you start small (but no smaller than viable.) The economics only makes sense if they can live off the land when they get there. The cost of getting there get’s lost in the noise over time.
On a railroad enthusiast forum there is a discussion about a report of an Amtrak employee being paid for 40 hours work during a single calendar day amounting to $1500. The consensus is that the time card wasn’t fraudulent, rather, the Amtrak has negotiated a Byzantine set of overtime rules for onboard service (OBS) workers on long-distance trains to make up for long away-from-home-but-not-on-duty hours these people put in. Face it, jets cost less because the dominant cost is labor and jets complete long trips much more quickly than trains.
There is this big flame war over there between people who work for Amtrak or are Amtrak retirees and one passenger train advocate that is angry that this makes Amtrak look bad before Congress and the tax paying public.
Are we going to have a flame war regarding a space tourism employee collecting 15 million dollars during a trip because of overtime pay and union craft rules (I’m a doctor, not a brick layer!)
Tourism is fine for those businesses that want to take the risk to pursue it, but growing colonies should be based on the most fundamental of economics. So fundamental that it is both vast and invisible. Without it you have no colony at all.
Anyone looking only at mining and export will completely miss it. The reason people can’t see it today is because the world is so interconnected they can’t imagine anything else even though it still dominates and always will. It’s simple internal growth.
You start small by trading in your community until the day you find things to profitably export. Those that think export is required for economic growth are simply blind and ignorant. Before you object, note that I never say that profitable export doesn’t enhance an economy, just that it’s common to the point of approaching universal to only see external trade. It’s how trade is measured (completely ignoring the bulk of it.)
If you start with the assumption of no external trade it eliminates nonviable destinations. Your destination must already have abundant and diverse mass and no critical element missing.
It also eliminates short term thinking. Profit will come over the lifetime of the colonists, not next quarter. That there will be profit only requires a moments thought. Distance does not hinder sharing in these profits because sharing in profits is done electronically just as it is on earth.
I riffing on my notion of NASA being “Amtraak in spaaaaccce!”
If labor rules allowed paying an Amtrak dude working on a train $1500 for a day, were NASA to run a space operation serving passengers — tourists, colonists, etc. –would they end up paying a spacecraft attendedant tourists 15 million? Sorta like the NASA cost structure of $10,000/lb to orbit deal and the anticipated multi-billion price tag per SLS mission?
Paul, you don’t happen to work in the Greek gov, do ya?
I agree with those who say low atomic number materials are better shielding against solar wind – the major component of the radiation in space. I think it’s worth mentioning that this mass doesn’t have to be inert; putting all the stored water, waste for recycling and even food outside the crew would dual-purpose the shielding.
“Crew rotation multipl[i]es the cost. Sending ten (or 100) people in series costs the same as one person at ten (or 100) times the cost. Permanent settlers needs to be our initial mindset.” – it also multiplies the revenue, justifies the extra investment in making vehicles reusable, and creates economies of scale in the transport system.
it also multiplies the revenue
That’s Nancy Pelosi economics. You can’t lose on every transaction and make it up in volume. The return on investment requires we first get a viable colony going which is going to be a sunk cost. We keep that cost as low as possible by sending as little as possible… just the colonists and their personal provisions, some of which they trade for ISRU life support when they arrive. First landers will need presupply with ISRU water, oxygen, methane, power, tools, etc., already waiting.
An incremental island hopping strategy might work as well but will take much longer (beyond our lifetime) and have periods of thin support. Put a dozen on first landing on mars and several dozen on the next launch window and support at a minimal level is assured.
Never mind about how to build them (space settlements). Build them! This is what the focus should be on: To build them. Let others debate. Build them! Stop talking about it. If anyone here knows anyone who is ambitious, then refer them to me. I define ambitious as wanting to do large manned projects out there including but not limited to settlements. I define large as more than ten people a year. If you know someone who wants to get such a business, a space company going, then please refer them to me. Thanks all!
I read the article on shielding and the radiation versus inclination due to the South Atlantic Anomaly makes me think the station could get buy with a very small shielded area where people shelter for a few minutes twice a day when they pass through it. Such a shelter could also double as the sleeping area.
But that brings up a point about shielding a small volume. High density polyethylene is slightly less dense than water (0.97 SG), so to get 4 tons per square meter requires a thickness of 13.5 feet of poly. If you went with depleted uranium (19 SG) you’d only need 8.2 inches to get 4 tons/m^2. This becomes really important if you’re shielding a small sphere.
A 6 foot diameter sphere has 10.5 square meters of surface area, so 4 tons/m^2 would have a mass of 42 tonnes. An 8 foot diameter sphere would have an area that requires a mass of 75 tons to shield. But the shield’s own thickness makes for a larger sphere, and although 8.2 inches per wall doesn’t add much, 13.5 feet (27 feet total) adds a tremendous extra volume and mass. The six foot-internal sphere’s outer diameter is 7.38 feet with depleted uranium but 33 feet with polyethylene.
So the 6 foot shielded sphere weighs 52.5 tonnes with DU but 516 tonnes with polyethylene or water. The 8 foot shielded sphere weighs 89 tonnes with DU but 614 tonnes with poly. The DU isn’t as good per mass as poly, but for small spaces the disparity in relative weight gives cause to reanalyze the material selection.
Anyway, years ago I ran some numbers on a mini-settlement which assumed that material costs remained extremely high and wondered what a viable settlement would look like in a competitive environment where the construction cost per person is the driving factor.
So I assumed something akin to a pair of airliner fuselages being spun on the end of a long boom. Given that windows are problematic, I went with solar cells providing power for interior grow lights, but either way a lot of heat gets dumped on the plants. I used that heat to drive natural air circulation between the crop/habitation area and cooling radiators mounted closer to the axis. The big pipes that carry the airflow to the radiators and back also double as the twin booms that support the two spinning habitats, and they make a fine place to mount all the solar cells.
I tilted the two habitats a bit nose up relative to the occupants so warming would drive the airflow along. The cool return air from the radiators is introduced at the low end and slowly travels up-gradient, picking up heat from the equipment, plants, and grow lights, before exiting at the higher end to enter the chimney duct. The air then heads up toward the axis, splitting off into the slightly down-sloping radiators along the way, with the radiators dumping the air into the cold-air return duct. Since the two booms are also air ducts, it’s trivial to have them serve as elevators to get to and from the axis, as long as the elevators have perforated floors and ceilings so they don’t overly impeded the airflow.
You do NOT want depleted Uranium, or indeed any heavy element, for your radiation shielding. With heavy elements, cosmic rays striking your shield would cause lethal secondary radiation.
That’s why I’d go with something like barium boride (BaB6) for the inner lining. Barium is a great X-ray absorber and boron is a neutron absorber.
And of course we’re talking about 4 tonnes per square meter, which is very dense shielding against the secondaries, too.
Perhaps I can dig up some nuclear codes and have a look, but the point is mainly based on geometry. For the six foot diameter polyethylene shell, with is 33 foot outer diameter, only 3 percent of what strikes the outer shell was on a path that would’ve taken it into the inner shell in the first place, so the shield is undergoing 30 times the number of GCR collisions (and the subsequent secondaries) than it would have if the shielding was small and dense.
And of course a 52 tonne, 7-foot diameter sphere is a lot easier to launch, install, and work around than a 516 tonne, 33-foot diameter sphere.
For charged particle radiation, which dominates in space, you want low atomic number. Polyethylene, with lots of hydrogen and carbon, is excellent, as is water. But presuming extraterrestrial materials you use whatever lower atomic number materials are handy. High atomic number materials are generally inferior radiation shielding unless you’re dealing with high energy photons.
Is there any possibility that having the shielding be a plasma, a moving plasma, or a plasma with a substantial electrical current is of any use?
And why is the brute-force approach of ‘sealed blocks of ice’ with the goal of eventually ending up with an iceball while providing an exceedingly deep emergency reservoir of fuel, air, and water not viable?
I’m unaware of any plasma configuration that is any use as a radiation shield. There are electromagnetic field configurations that should work, though they would take constant power input to maintain. One I have in mind charges the settlement with a high positive potential to block most cosmic rays, and uses a magnetic field to reduce discharge to electrons to an acceptable rate.
That’s they way I’d normally go when we’re talking about something like a Mars mission, where an older astronaut is going to fly one mission and accept a significant increase in cancer risk with poly shielding that’s maybe six to eighteen inches thick, or somewhere in the range of 0.2 tonnes per square meter. But what Al Globus is discussing is shielding sufficient for children and pregnant women to live full lives in space without significantly raising their risks, with shielding densities ten to forty times higher (and thus much, much thicker). So when the shield gets 10 to 20 feet thick for low Z materials, the geometry becomes unwieldy for shielding small spaces.
For shielding spent nuclear radiation DU concrete and tungsten are often used, with tungsten far outperforming lead. For linear accelerators in the low-end GCR range of megavolts, concrete, lead, and steel are the norm. I’d have to get much deeper into it to see what the trade-offs would be, but in the thicknesses Al Globus is talking, the low-Z materials are coming in six or more times heavier for the same density coverage (in tonnes/m^2), and a small shielded space the size of a bathroom is too heavy and bulky to launch even with the SLS.
$2m each person to orbit (and back) is within reach now simply by sending more at a time (not my idea, others with the right credentials have pointed this out years ago.) If $200k is required, then we twiddle thumbs until it’s achieved. It is simply not productive to say if only costs were lower we could do more. Is anybody denying this truth? Does acknowledging this truth make it happen any faster?
There is another way to look at it. Crew rotation multiples the cost. Sending ten (or 100) people in series costs the same as one person at ten (or 100) times the cost. Permanent settlers needs to be our initial mindset. Rotation should come only after costs have been established at a lower level.
The other weakness of the argument is basing it on tourism which requires that rotating crew cost in spades. A different income source can eliminate this problem (which again requires us to sit on our thumbs until magic happens.)
We need to eliminate mass transfer as completely as possible. The only mass transfer that is required for colony growth is more colonists (which means choosing a destination that already has sufficient and diverse mass already.)
Or we could just bypass our solar system and fantasize about colonizing an exoplanet? That way we don’t have to ever accomplish anything and yet still keep pretending it’s an accomplishment.
Of course you start small (but no smaller than viable.) The economics only makes sense if they can live off the land when they get there. The cost of getting there get’s lost in the noise over time.
On a railroad enthusiast forum there is a discussion about a report of an Amtrak employee being paid for 40 hours work during a single calendar day amounting to $1500. The consensus is that the time card wasn’t fraudulent, rather, the Amtrak has negotiated a Byzantine set of overtime rules for onboard service (OBS) workers on long-distance trains to make up for long away-from-home-but-not-on-duty hours these people put in. Face it, jets cost less because the dominant cost is labor and jets complete long trips much more quickly than trains.
There is this big flame war over there between people who work for Amtrak or are Amtrak retirees and one passenger train advocate that is angry that this makes Amtrak look bad before Congress and the tax paying public.
Are we going to have a flame war regarding a space tourism employee collecting 15 million dollars during a trip because of overtime pay and union craft rules (I’m a doctor, not a brick layer!)
Tourism is fine for those businesses that want to take the risk to pursue it, but growing colonies should be based on the most fundamental of economics. So fundamental that it is both vast and invisible. Without it you have no colony at all.
Anyone looking only at mining and export will completely miss it. The reason people can’t see it today is because the world is so interconnected they can’t imagine anything else even though it still dominates and always will. It’s simple internal growth.
You start small by trading in your community until the day you find things to profitably export. Those that think export is required for economic growth are simply blind and ignorant. Before you object, note that I never say that profitable export doesn’t enhance an economy, just that it’s common to the point of approaching universal to only see external trade. It’s how trade is measured (completely ignoring the bulk of it.)
If you start with the assumption of no external trade it eliminates nonviable destinations. Your destination must already have abundant and diverse mass and no critical element missing.
It also eliminates short term thinking. Profit will come over the lifetime of the colonists, not next quarter. That there will be profit only requires a moments thought. Distance does not hinder sharing in these profits because sharing in profits is done electronically just as it is on earth.
I riffing on my notion of NASA being “Amtraak in spaaaaccce!”
If labor rules allowed paying an Amtrak dude working on a train $1500 for a day, were NASA to run a space operation serving passengers — tourists, colonists, etc. –would they end up paying a spacecraft attendedant tourists 15 million? Sorta like the NASA cost structure of $10,000/lb to orbit deal and the anticipated multi-billion price tag per SLS mission?
Paul, you don’t happen to work in the Greek gov, do ya?
I agree with those who say low atomic number materials are better shielding against solar wind – the major component of the radiation in space. I think it’s worth mentioning that this mass doesn’t have to be inert; putting all the stored water, waste for recycling and even food outside the crew would dual-purpose the shielding.
“Crew rotation multipl[i]es the cost. Sending ten (or 100) people in series costs the same as one person at ten (or 100) times the cost. Permanent settlers needs to be our initial mindset.” – it also multiplies the revenue, justifies the extra investment in making vehicles reusable, and creates economies of scale in the transport system.
it also multiplies the revenue
That’s Nancy Pelosi economics. You can’t lose on every transaction and make it up in volume. The return on investment requires we first get a viable colony going which is going to be a sunk cost. We keep that cost as low as possible by sending as little as possible… just the colonists and their personal provisions, some of which they trade for ISRU life support when they arrive. First landers will need presupply with ISRU water, oxygen, methane, power, tools, etc., already waiting.
An incremental island hopping strategy might work as well but will take much longer (beyond our lifetime) and have periods of thin support. Put a dozen on first landing on mars and several dozen on the next launch window and support at a minimal level is assured.
Never mind about how to build them (space settlements). Build them! This is what the focus should be on: To build them. Let others debate. Build them! Stop talking about it. If anyone here knows anyone who is ambitious, then refer them to me. I define ambitious as wanting to do large manned projects out there including but not limited to settlements. I define large as more than ten people a year. If you know someone who wants to get such a business, a space company going, then please refer them to me. Thanks all!