why are you talking about speed pulling things apart?
it's 1 g.
we build shit all the time in one g,
and really, it would probably be closer to .25-.5g until we get really good at it.
The hoop stress for a spinning ring generating 1 G will exceed the tensile strength of steel once the structure gets over about 50 km in diameter. That's without having anything on the ring. Anything bigger requires exotic materials.
Fortunately, there's a wonderful material called Carbon Fiber Composite which we're pretty great at making into all kinds of things, like these drive shafts: https://www.youtube.com/watch?v=hjErH4_1fks
Properly woven, its ultimate tensile strength can be as high as 3.5GPa, which dwarf's 4130 steel at 670MPa (or 0.670GPa). Though this doesn't get around the real reason we aren't doing any of this in space yet: you have to build at least a couple different kinds of manufacturing plants in space first, which is very expensive.
Is that a unidirectional UTS? How is it's stress perpendicular to the lay? I've seen carbon fiber composites get up to very high UTS in one or two dimensions, but never all three.
Also, carbon fiber composites have a lot of issues that have to be solved before they can be used in space, like the elastic-plastic transition temperature of the bonding agent, off-gassing effects, and the like.
*edit* Also we have materials like Inconels that can have a UTS of over 250 ksi (1.7 GPa).
https://en.wikipedia.org/wiki/Centripetal_force#Formula
Centripetal acceleration is a = v*v/r
If we want earth gravity (9.81 m/s/s) at geostationary orbits (~36000 km, 3 km/s orbital velocity) v is 18800 m/s, which would tear any material we know of apart
Rigid ring-like structures are fundamentally unstable. Assuming they don't break under the stress, there is zero net gravitational pull from Earth. Any deviation (caused by say the Moon) will cause it all to crash into the planet or break apart very quickly. Even the theoretical Niven setup of sun + ringworld + completely cleared system is unstable
I wouldn't want to use a reaction wheel to spin an asteroid. If that thing were to ever fail a whole hell of a lot of kinetic energy would be released instantly
Scrith says hi. He had to retcon Ringworld because MIT noticed that.
why are you talking about speed pulling things apart?
it's 1 g.
we build shit all the time in one g,
and really, it would probably be closer to .25-.5g until we get really good at it.
The hoop stress for a spinning ring generating 1 G will exceed the tensile strength of steel once the structure gets over about 50 km in diameter. That's without having anything on the ring. Anything bigger requires exotic materials.
Fortunately, there's a wonderful material called Carbon Fiber Composite which we're pretty great at making into all kinds of things, like these drive shafts:
Properly woven, its ultimate tensile strength can be as high as 3.5GPa, which dwarf's 4130 steel at 670MPa (or 0.670GPa). Though this doesn't get around the real reason we aren't doing any of this in space yet: you have to build at least a couple different kinds of manufacturing plants in space first, which is very expensive.
I was using high-tensile steel values of 1.8 GPa, so that's only twice as strong. You do get benefits from the 6 times lower density, which means at best you could get something 600 km in diameter. However, the original discussion was for a geostationary ring around earth which would be 84,000 km in diameter and hoop stress is proportional to radius. You'd need an exotic material 140 times stronger than nanotube composite to do it, or around 490 GPa. But again, that's a absolute minimum value. Safety margins alone means you would probably need 2000 GPa, and again that does not include the strength increase needed if you want to actually put stuff on that ring. The best we can do with multiwall carbon nanotubes is 63 GPa and we can't make those in a size that doesn't require a microscope to see.
Just remember that half the people you meet are below average intelligence.
why are you talking about speed pulling things apart?
it's 1 g.
we build shit all the time in one g,
and really, it would probably be closer to .25-.5g until we get really good at it.
The hoop stress for a spinning ring generating 1 G will exceed the tensile strength of steel once the structure gets over about 50 km in diameter. That's without having anything on the ring. Anything bigger requires exotic materials.
Fortunately, there's a wonderful material called Carbon Fiber Composite which we're pretty great at making into all kinds of things, like these drive shafts: https://www.youtube.com/watch?v=hjErH4_1fks
Properly woven, its ultimate tensile strength can be as high as 3.5GPa, which dwarf's 4130 steel at 670MPa (or 0.670GPa). Though this doesn't get around the real reason we aren't doing any of this in space yet: you have to build at least a couple different kinds of manufacturing plants in space first, which is very expensive.
Is that a unidirectional UTS? How is it's stress perpendicular to the lay? I've seen carbon fiber composites get up to very high UTS in one or two dimensions, but never all three.
Also, carbon fiber composites have a lot of issues that have to be solved before they can be used in space, like the elastic-plastic transition temperature of the bonding agent, off-gassing effects, and the like.
*edit* Also we have materials like Inconels that can have a UTS of over 250 ksi (1.7 GPa).
Yeah, that's for something that's anisotropic as hell. Generally speaking, the density advantage ends up being what makes CF beat the shit out of steel, especially because you can make up for most of the issues with the material being anisotropic by adding more of it in different directions. As for the resins, I think NASA has made progress on that though it was one of the problems that delayed the James Webb space telescope. They ended up finding a cyanate ester thermoset that would remain very dimensionally stable through repeated heating and cooling cycles and most importantly at extremely low temperatures.
Inconel is also attractive, especially with the recent improvements in using it for additive manufacturing purposes (which would simplify the total equipment count for orbital construction hardware).
why are you talking about speed pulling things apart?
it's 1 g.
we build shit all the time in one g,
and really, it would probably be closer to .25-.5g until we get really good at it.
The hoop stress for a spinning ring generating 1 G will exceed the tensile strength of steel once the structure gets over about 50 km in diameter. That's without having anything on the ring. Anything bigger requires exotic materials.
Fortunately, there's a wonderful material called Carbon Fiber Composite which we're pretty great at making into all kinds of things, like these drive shafts:
Properly woven, its ultimate tensile strength can be as high as 3.5GPa, which dwarf's 4130 steel at 670MPa (or 0.670GPa). Though this doesn't get around the real reason we aren't doing any of this in space yet: you have to build at least a couple different kinds of manufacturing plants in space first, which is very expensive.
I was using high-tensile steel values of 1.8 GPa, so that's only twice as strong. You do get benefits from the 6 times lower density, which means at best you could get something 600 km in diameter. However, the original discussion was for a geostationary ring around earth which would be 84,000 km in diameter and hoop stress is proportional to radius. You'd need an exotic material 140 times stronger than nanotube composite to do it, or around 490 GPa. But again, that's a absolute minimum value. Safety margins alone means you would probably need 2000 GPa, and again that does not include the strength increase needed if you want to actually put stuff on that ring. The best we can do with multiwall carbon nanotubes is 63 GPa and we can't make those in a size that doesn't require a microscope to see.
Oh yeah, orbital rings (Niven or otherwise) are way beyond what we're capable of. I'm more interested in Bernal Spheres and O'Neill Cylinders, which have a lot fewer hurdles and question marks between where we are today and actually building one.
The original O'Neill Cylinder designs were 8 km in diameter precisely because he was factoring in the practicalities of building it with existing materials.
Just remember that half the people you meet are below average intelligence.
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TraceGNU Terry Pratchett; GNU Gus; GNU Carrie Fisher; GNU Adam WeRegistered Userregular
what we really should be doing is sticking some sort of space station into orbit around Earth that can hold 50-100 people so we can perfect the technologies associated with living in a space station so we don't need to immediately go and terraform Mars or what-have-you
why are you talking about speed pulling things apart?
it's 1 g.
we build shit all the time in one g,
and really, it would probably be closer to .25-.5g until we get really good at it.
The hoop stress for a spinning ring generating 1 G will exceed the tensile strength of steel once the structure gets over about 50 km in diameter. That's without having anything on the ring. Anything bigger requires exotic materials.
Sure, but that the fact that this is occurring at what seems like a large linear velocity really doesn't play into that. It's just a G. It's like trying to build a space elevator you can live on, it needs to be able to support it's own mass.
So, the max size would scale linearly with your desired G force and tensile, so if you double the strength or halve the acceleration, you get double the... circumference?
It's like building a self-supporting 70000 km arch bridge. Switching to carbon fiber isn't going to help much, you get a 5x improvement in tensile strength but you need much more than that
If we reduce it to 3.5 GPa ω becomes 5.11e-5 which gives an orbital period of 123000 s and a speed of 1823 m/s. This is actually slower than normal orbital velocity for this orbit; I'm not 100% sure how this would work, maybe you'd get normal orbital velocity "for free" and this would be extra - if this is the case you'd get a bit more than 5% of Earth gravity, or around a quarter to a third of the Moon
To build a ring around the Earth with close to Earth gravity you don't necessarily need exotic materials if you instead use exotic building techniques, namely active structure techniques.
Instead of spinning up your ring, leave it non-rotating, not even at orbital velocities, just stationary. At low Earth orbit heights, you would still have around 90% of the gravity you would have on the surface of the planet. You would be living on the outer surface of the ring instead of the inside. That itself doesn't solve the building problems, since you're still supporting things under nearly 1g, but it makes the next part easier.
For the next part, build a second ring inside the first, and spin it up to a high velocity. You now have two rings with a common, but opposite, problem. The first, stationary, ring would collapse inwards under it's own weight without support, the second, rotating, ring would fly apart outwards without support. So you set up a system of electromagnetic repulsion between the two of them. The stationary ring pushes inward against the rotating ring, preventing it from flying apart. In turn, the rotating ring pushes outwards against the stationary ring, supporting its weight evenly across the whole structure.
In practice, you would build both rings at the same time, at orbital velocities, and then, you can spin one of them up at the same time you spin the other one down. These two rings don't have to be the same mass either, Your stationary ring might be a large colony structure, while your rotating ring might simply be structure with much less mass, but rotating very fast. The rotating component could even just be something like a set of cables, or even discrete projectiles, embedded within the structure of the ring.
The design principles are similar in concept to a Space fountain. Perhaps a bit simpler, given that you could have constant force applied the whole time, and everything contained within a structure the whole way. And you can extend these techniques to essentially build structures of arbitrary size.
It's still not statically stable, since the ring could drift from its position. Given that you're already using a lot of electromagnets, you could possibly set it up to push against the Earth's magnetic field for stationkeeping maneuvers.
The original O'Neill Cylinder designs were 8 km in diameter precisely because he was factoring in the practicalities of building it with existing materials.
One of the things Gerard O'Neill never thought up (because he was making his proposals about 10 years too early) was the benefit of large space habitats paired with Aldrin Cyclers. Buzz Aldrin proposed the use of cycler orbits - almost perpetual orbits between two bodies in space, passing very near each one - as a means to situate support infrastructure for travel between those bodies in 1985. If you built a Bernal Sphere at the original spec for Island One - a 500m diameter habitation sphere, plus agricultural toruses on the ends along the axis, with the whole thing spinning at 1.9 RPM for 1g at the equator - you could support up to 10,000 people aboard it at any given time. If you then had that habitat set on a Mars Cycler orbit, you could transport thousands of people between the two planets in an ideal environment on a very regular basis with far greater safety than other proposed interplanetary cruise vehicles.
In fact, I'd bet chartering an early such habitat as a university or research institute campus would be a compelling choice, especially since the concept is almost like what the ISS does now but about three orders of magnitude moreso on all fronts.
Ninja Snarl PMy helmet is my burden.Ninja Snarl: Gone, but not forgotten.Registered Userregular
I don't see spaceborne mega-structures happening without being able to couple structural strength with actual power output in some way, unless the structures are zero-G. Material physics do not at all scale in a linear fashion; oscillations of a magnitude that would be virtually undetectable in something the size of a rotating beer can would annihilate any kind of solid or semi-solid planetary ring. Even just the variations in the topology of the Earth and how that would influence the effects of gravity would probably make a planetary ring unstable, and the effects of the Moon's gravity would definitely make for lethal instability. Without material technologies far, far beyond what we have now, crazy huge artificial rings or stations are just not a possibility. The physics are just not on our side for that sort of endeavor.
Which loops back to the discussion of why terraforming Mars to be livable is a better prospect for humans in space than mega-stations. Take the technology we have right now and add being able to build on a large scale in space, and we could drop enough material onto Mars to make it semi-habitable (albeit at hideous expense and the process would probably take decades, if not centuries).
Short of that, we could still definitely build artificial structures which would let us mine the planet for resources. And since the gravity is so much lower on Mars, we could get away with much larger structures as well, without having to worry about providing gravity.
I don't see spaceborne mega-structures happening without being able to couple structural strength with actual power output in some way, unless the structures are zero-G. Material physics do not at all scale in a linear fashion; oscillations of a magnitude that would be virtually undetectable in something the size of a rotating beer can would annihilate any kind of solid or semi-solid planetary ring. Even just the variations in the topology of the Earth and how that would influence the effects of gravity would probably make a planetary ring unstable, and the effects of the Moon's gravity would definitely make for lethal instability. Without material technologies far, far beyond what we have now, crazy huge artificial rings or stations are just not a possibility. The physics are just not on our side for that sort of endeavor.
Which loops back to the discussion of why terraforming Mars to be livable is a better prospect for humans in space than mega-stations. Take the technology we have right now and add being able to build on a large scale in space, and we could drop enough material onto Mars to make it semi-habitable (albeit at hideous expense and the process would probably take decades, if not centuries).
Short of that, we could still definitely build artificial structures which would let us mine the planet for resources. And since the gravity is so much lower on Mars, we could get away with much larger structures as well, without having to worry about providing gravity.
Which again, is why I'm firmly in favor of "small" (0.1 km to 10 km radius) stations and planetary installations. Eventually, we may be able to pull a Kuat somewhere but until then keeping things to a smaller scale is both more feasible and less prone to catastrophe.
I... Actually totally forgot that underwater welding was a thing.
I feel real dumb now.
Underwater welding requires a lot of technical knowledge and prerequisite supporting technology. Without the ability to create or use fire, the only energy source capable of showing a primitive underwater society the concept of welding or metalworking in general would be an active lava flow. But building any type of primitive industry around such a random, unpredictable, unreliable, and difficult to use energy source would be extremely difficult and stunt the growth of said civilization. That's not to say cephalopods couldn't develop other technologies that allow them to progress along other avenues to become an advanced society , but if they develop metalworking at all, in my opinion it would come very late.
High quality modern industrial welding requires a lot of technical knowledge and prerequisite supporting technology. Man developed welding techniques long before understanding the science behind doing so or having access to technology beyond fire and hammer. While modern welding involves things like electrical equipment (welding machine), filler metal (wire, usually coated in flux), and controlled conditions, this is a result of our need to have rapid high quality joining methods. Heating up two pieces of metal and bashing them until they are a single piece is also a welding method, it's just that smithing doesn't satisfy our current needs.
Magma vents at the ocean bottom provide more than enough energy and stability to allow for the development of a metalworking society. If anything, the reason that cephalopods will not develop metalworking isn't due to a lack of resources, but due to a lack of evolutionary demand. They are an apex predatory, and don't require tools to uplift them further.
The temperature coming out of a hydrothermal vent is not near hot enough for forge welding. That's why I said they'd need actual open lava for it.
even if you had open lava, i don't think an underwater forge weld would work. for one the water would suck the heat out of the workpieces too fast to have any time to do anything with them. even more importantly, the faces you want to join need to be extremely clean for the weld to take, having salt water and whatever other minerals are introduced by the lava boiling off the workpiece and leaving residue would corrode the shit out of it and wouldn't leave a clean enough surface to produce a good joint
MayabirdPecking at the keyboardRegistered Userregular
So... what this is all telling me is that long-term, habitats are best, but if we want an off-planet semi-sustainable presence anytime in the near future we'll need to plop colonies on physical bodies that already exist, like the Moon and/or Mars, even if we can't terraform them.
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Ninja Snarl PMy helmet is my burden.Ninja Snarl: Gone, but not forgotten.Registered Userregular
So... what this is all telling me is that long-term, habitats are best, but if we want an off-planet semi-sustainable presence anytime in the near future we'll need to plop colonies on physical bodies that already exist, like the Moon and/or Mars, even if we can't terraform them.
With the technology immediately available, yeah, building in a gravity well works best and is probably the most feasible thing if a population of any notable size is intended. Even then, there would be long-term health concerns due to microgravity, especially if anybody ever wants to go to Earth from those environments. At the moment, the longest consecutive time spent in space is under a year and a half, so there could be a lot of health issues from microgravity that we haven't even encountered yet.
But if we figure out how to stop bone and muscle wastage in microgravity, which is very much a possibility since both of those problems seem to occur due to biological systems not balancing against gravity any longer, then there might not be a medical need to simulate gravity on a station. Then we could build large habitable structures in space, because we wouldn't have to worry about the enormous stresses of rotating structures.
what we really should be doing is sticking some sort of space station into orbit around Earth that can hold 50-100 people so we can perfect the technologies associated with living in a space station so we don't need to immediately go and terraform Mars or what-have-you
edit: mind you, this is the proposal/target for the least cost-efficient of the US space companies. The others could do this too (or parts of it, and probably will) for less.
The "lift everyone on earth out of poverty" line is kind of comical, it should have been bookended with "I mean it won't be used for that, but it will make various business owners and investors very rich."
The "lift everyone on earth out of poverty" line is kind of comical, it should have been bookended with "I mean it won't be used for that, but it will make various business owners and investors very rich."
I think the idea is that the big counterweight to altering the economy with respect to climate change is cheap energy is one of the big ways to get serious industry going in a developing country. A lot of that cheap energy isn't very clean, so if you could eliminate that as a problem [while making your investors filthy rich] it's a no-brainer for a company to pursue.
(The real first customer of these satellites is almost certainly going to be the US military because they love anything that lets them improve logistical efficiency. Not having to ship as much diesel for bases would be a big deal, Air Conditioning costs alone are $20 Billion in Afghanistan and Iraq.)
The "lift everyone on earth out of poverty" line is kind of comical, it should have been bookended with "I mean it won't be used for that, but it will make various business owners and investors very rich."
That won't be how it is directly applied, but a massive increase in resources would reduce their cost and inevitably improve the lives of a huge number of people. A hundred years ago, living in poverty meant starving to death and dying from colds no matter where you were. Nowadays, being below the poverty line in a developed country means you still probably have things like a place to live, air conditioning and heat, food, TV, etc. And that's because making those things got so cheap to make.
Wow, it will make some rich people more rich, big deal. Far more importantly, it could change living conditions for the better on a scale even larger than with the Industrial Revolution, simply by virtue of driving down the cost of a lot of materials.
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MayabirdPecking at the keyboardRegistered Userregular
Okay, we were just talking about terraforming not being highly practical, but I was thinking about those perchlorates on Mars - there are bacteria and archaea right now on Earth that eat perchlorates for their metabolic processes. There are multiple ways that they do it, but one of the pathways liberates O2 in the process. Make some organisms that don't die when released on Mars, and they could not just bioremediate (biomediate?) the soil a bit as they feast, but start building up oxygen in the atmosphere which could help speed up/simplify the terraforming process.
Okay, we were just talking about terraforming not being highly practical, but I was thinking about those perchlorates on Mars - there are bacteria and archaea right now on Earth that eat perchlorates for their metabolic processes. There are multiple ways that they do it, but one of the pathways liberates O2 in the process. Make some organisms that don't die when released on Mars, and they could not just bioremediate (biomediate?) the soil a bit as they feast, but start building up oxygen in the atmosphere which could help speed up/simplify the terraforming process.
Ok, but the atmosphere is well below the Armstrong limit and won't get much denser due to a lack of magnetic fiend, plus the surface is radioactive.
Okay, we were just talking about terraforming not being highly practical, but I was thinking about those perchlorates on Mars - there are bacteria and archaea right now on Earth that eat perchlorates for their metabolic processes. There are multiple ways that they do it, but one of the pathways liberates O2 in the process. Make some organisms that don't die when released on Mars, and they could not just bioremediate (biomediate?) the soil a bit as they feast, but start building up oxygen in the atmosphere which could help speed up/simplify the terraforming process.
Ok, but the atmosphere is well below the Armstrong limit and won't get much denser due to a lack of magnetic fiend, plus the surface is radioactive.
what we really should be doing is sticking some sort of space station into orbit around Earth that can hold 50-100 people so we can perfect the technologies associated with living in a space station so we don't need to immediately go and terraform Mars or what-have-you
edit: mind you, this is the proposal/target for the least cost-efficient of the US space companies. The others could do this too (or parts of it, and probably will) for less.
bah and humbug on that.
the moment we get to the point where we can manufacture/produce the heavy duty equipment and parts for space station construction -in space- itself those costs plummet.
if I had any real say about the matter we'd already have some sort of experimental factory up in space producing things as a proof of concept for this.
if we can get a move on with capturing an asteroid composed of a bunch of heavy metals it'll be even cheaper.
what we really should be doing is sticking some sort of space station into orbit around Earth that can hold 50-100 people so we can perfect the technologies associated with living in a space station so we don't need to immediately go and terraform Mars or what-have-you
edit: mind you, this is the proposal/target for the least cost-efficient of the US space companies. The others could do this too (or parts of it, and probably will) for less.
bah and humbug on that.
the moment we get to the point where we can manufacture/produce the heavy duty equipment and parts for space station construction -in space- itself those costs plummet.
if I had any real say about the matter we'd already have some sort of experimental factory up in space producing things as a proof of concept for this.
if we can get a move on with capturing an asteroid composed of a bunch of heavy metals it'll be even cheaper.
Well, they defunded NASA's Asteroid Redirect Mission, so right now the plan isn't for 2017-2018, it's 2021 or further.
what we really should be doing is sticking some sort of space station into orbit around Earth that can hold 50-100 people so we can perfect the technologies associated with living in a space station so we don't need to immediately go and terraform Mars or what-have-you
edit: mind you, this is the proposal/target for the least cost-efficient of the US space companies. The others could do this too (or parts of it, and probably will) for less.
bah and humbug on that.
the moment we get to the point where we can manufacture/produce the heavy duty equipment and parts for space station construction -in space- itself those costs plummet.
if I had any real say about the matter we'd already have some sort of experimental factory up in space producing things as a proof of concept for this.
if we can get a move on with capturing an asteroid composed of a bunch of heavy metals it'll be even cheaper.
Well, they defunded NASA's Asteroid Redirect Mission, so right now the plan isn't for 2017-2018, it's 2021 or further.
The real story behind the Asteroid Redirect was to just have goal stated for what NASA has been working on for a long time now: their solar electric propulsion tug. It's been in development for what might be a decade now if not more, and the "active" part they slap on the front just changes from time to time to keep funding flowing. I think the current version specifically is meant to be able to separate from whatever it is pushing around so that it can be used over and over to move all kinds of large things around the inner solar system.
what we really should be doing is sticking some sort of space station into orbit around Earth that can hold 50-100 people so we can perfect the technologies associated with living in a space station so we don't need to immediately go and terraform Mars or what-have-you
edit: mind you, this is the proposal/target for the least cost-efficient of the US space companies. The others could do this too (or parts of it, and probably will) for less.
bah and humbug on that.
the moment we get to the point where we can manufacture/produce the heavy duty equipment and parts for space station construction -in space- itself those costs plummet.
if I had any real say about the matter we'd already have some sort of experimental factory up in space producing things as a proof of concept for this.
if we can get a move on with capturing an asteroid composed of a bunch of heavy metals it'll be even cheaper.
Well, they defunded NASA's Asteroid Redirect Mission, so right now the plan isn't for 2017-2018, it's 2021 or further.
The real story behind the Asteroid Redirect was to just have goal stated for what NASA has been working on for a long time now: their solar electric propulsion tug. It's been in development for what might be a decade now if not more, and the "active" part they slap on the front just changes from time to time to keep funding flowing. I think the current version specifically is meant to be able to separate from whatever it is pushing around so that it can be used over and over to move all kinds of large things around the inner solar system.
Well, no, not really, it was intended to test a lot of different systems and craft, especially the planned SLS and Orion vehicle in the lead up to manned missions to Mars. They would use manned missions to the object in orbit and manned survey missions of NEOs in the Orion to prepare and test the systems. In addition they would use it to test possible planetary defense plans, and to examine the viability of space mining in real world tests.
what we really should be doing is sticking some sort of space station into orbit around Earth that can hold 50-100 people so we can perfect the technologies associated with living in a space station so we don't need to immediately go and terraform Mars or what-have-you
edit: mind you, this is the proposal/target for the least cost-efficient of the US space companies. The others could do this too (or parts of it, and probably will) for less.
bah and humbug on that.
the moment we get to the point where we can manufacture/produce the heavy duty equipment and parts for space station construction -in space- itself those costs plummet.
if I had any real say about the matter we'd already have some sort of experimental factory up in space producing things as a proof of concept for this.
if we can get a move on with capturing an asteroid composed of a bunch of heavy metals it'll be even cheaper.
Well, they defunded NASA's Asteroid Redirect Mission, so right now the plan isn't for 2017-2018, it's 2021 or further.
The real story behind the Asteroid Redirect was to just have goal stated for what NASA has been working on for a long time now: their solar electric propulsion tug. It's been in development for what might be a decade now if not more, and the "active" part they slap on the front just changes from time to time to keep funding flowing. I think the current version specifically is meant to be able to separate from whatever it is pushing around so that it can be used over and over to move all kinds of large things around the inner solar system.
Well, no, not really, it was intended to test a lot of different systems and craft, especially the planned SLS and Orion vehicle in the lead up to manned missions to Mars. They would use manned missions to the object in orbit and manned survey missions of NEOs in the Orion to prepare and test the systems. In addition they would use it to test possible planetary defense plans, and to examine the viability of space mining in real world tests.
Real Talk: NASA has wanted that tug for long before any asteroid mission was planned. Had the prior White House actually been interested in doing something more interesting with SLS (which it very obviously was not), they would have pushed for more funding to design an additional payload for SLS beyond Orion itself. As that project stands, we have a rocket and a capsule that can go nowhere of particular interest compared to robotic exploration in those same areas.
edit: in fact, as it stands the most compelling use for SLS is as a means to launch very heavy (or high dV) robotic payloads, like the proposed Europa lander and ATLAST [Advanced Technology Large-Aperture Space Telescope] (a 1:1 replacement in terms of sensors on the Hubble, but with either an 8m or 9.2m aperture compared to Hubble's 2.4m aperture).
Is it wrong that I read that as Advanced Technology Large Aperture Science Telescope?
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MayabirdPecking at the keyboardRegistered Userregular
Corvids are great. Ravens have just been shown to genuinely be able to plan ahead for the future and delay gratification, and even performed better in a trading game than great apes. Sure, ravens cache food, but this experiment was meant to show it wasn't just some instinctual habit like squirrels being driven to horde nuts, but deliberate planning.
What's even better is that one of the ravens figured out how to hack the experiment by wedging the device open that released the treats and had to be removed before he taught the rest of the ravens how to do it.
Corvids are great. Ravens have just been shown to genuinely be able to plan ahead for the future and delay gratification, and even performed better in a trading game than great apes. Sure, ravens cache food, but this experiment was meant to show it wasn't just some instinctual habit like squirrels being driven to horde nuts, but deliberate planning.
What's even better is that one of the ravens figured out how to hack the experiment by wedging the device open that released the treats and had to be removed before he taught the rest of the ravens how to do it.
Corvids are great. Ravens have just been shown to genuinely be able to plan ahead for the future and delay gratification, and even performed better in a trading game than great apes. Sure, ravens cache food, but this experiment was meant to show it wasn't just some instinctual habit like squirrels being driven to horde nuts, but deliberate planning.
What's even better is that one of the ravens figured out how to hack the experiment by wedging the device open that released the treats and had to be removed before he taught the rest of the ravens how to do it.
wut?
They would trade bottle caps for food, and Corvids picked up on the process quicker and with more regularity than apes.
Corvids are great. Ravens have just been shown to genuinely be able to plan ahead for the future and delay gratification, and even performed better in a trading game than great apes. Sure, ravens cache food, but this experiment was meant to show it wasn't just some instinctual habit like squirrels being driven to horde nuts, but deliberate planning.
What's even better is that one of the ravens figured out how to hack the experiment by wedging the device open that released the treats and had to be removed before he taught the rest of the ravens how to do it.
wut?
They would trade bottle caps for food, and Corvids picked up on the process quicker and with more regularity than apes.
I somehow read that as trading card game.
Which left me a bit puzzled, i guess the game part lead my thoughts in a wrong direction.
Corvids are great. Ravens have just been shown to genuinely be able to plan ahead for the future and delay gratification, and even performed better in a trading game than great apes. Sure, ravens cache food, but this experiment was meant to show it wasn't just some instinctual habit like squirrels being driven to horde nuts, but deliberate planning.
What's even better is that one of the ravens figured out how to hack the experiment by wedging the device open that released the treats and had to be removed before he taught the rest of the ravens how to do it.
wut?
They would trade bottle caps for food, and Corvids picked up on the process quicker and with more regularity than apes.
I somehow read that as trading card game.
Which left me a bit puzzled, i guess the game part lead my thoughts in a wrong direction.
At this point, I am starting to believe we could teach Corvids to play MTG.
Corvids are great. Ravens have just been shown to genuinely be able to plan ahead for the future and delay gratification, and even performed better in a trading game than great apes. Sure, ravens cache food, but this experiment was meant to show it wasn't just some instinctual habit like squirrels being driven to horde nuts, but deliberate planning.
What's even better is that one of the ravens figured out how to hack the experiment by wedging the device open that released the treats and had to be removed before he taught the rest of the ravens how to do it.
wut?
They would trade bottle caps for food, and Corvids picked up on the process quicker and with more regularity than apes.
I somehow read that as trading card game.
Which left me a bit puzzled, i guess the game part lead my thoughts in a wrong direction.
"Ca-caw!*"
*You've activated my trap card!
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Metzger MeisterIt Gets Worsebefore it gets any better.Registered Userregular
You'd think ravens would play a swamp deck, but I bet those tricky fuckers are all about that blue counter/control type stuff.
Corvids are great. Ravens have just been shown to genuinely be able to plan ahead for the future and delay gratification, and even performed better in a trading game than great apes. Sure, ravens cache food, but this experiment was meant to show it wasn't just some instinctual habit like squirrels being driven to horde nuts, but deliberate planning.
What's even better is that one of the ravens figured out how to hack the experiment by wedging the device open that released the treats and had to be removed before he taught the rest of the ravens how to do it.
wut?
They would trade bottle caps for food, and Corvids picked up on the process quicker and with more regularity than apes.
I somehow read that as trading card game.
Which left me a bit puzzled, i guess the game part lead my thoughts in a wrong direction.
At this point, I am starting to believe we could teach Corvids to play MTG.
Maybe one of the older editions bu I suspect they'd look at modern day MtG and caw "This is some bullshit right here"
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Is that a unidirectional UTS? How is it's stress perpendicular to the lay? I've seen carbon fiber composites get up to very high UTS in one or two dimensions, but never all three.
Also, carbon fiber composites have a lot of issues that have to be solved before they can be used in space, like the elastic-plastic transition temperature of the bonding agent, off-gassing effects, and the like.
*edit* Also we have materials like Inconels that can have a UTS of over 250 ksi (1.7 GPa).
Scrith says hi. He had to retcon Ringworld because MIT noticed that.
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I was using high-tensile steel values of 1.8 GPa, so that's only twice as strong. You do get benefits from the 6 times lower density, which means at best you could get something 600 km in diameter. However, the original discussion was for a geostationary ring around earth which would be 84,000 km in diameter and hoop stress is proportional to radius. You'd need an exotic material 140 times stronger than nanotube composite to do it, or around 490 GPa. But again, that's a absolute minimum value. Safety margins alone means you would probably need 2000 GPa, and again that does not include the strength increase needed if you want to actually put stuff on that ring. The best we can do with multiwall carbon nanotubes is 63 GPa and we can't make those in a size that doesn't require a microscope to see.
Yeah, that's for something that's anisotropic as hell. Generally speaking, the density advantage ends up being what makes CF beat the shit out of steel, especially because you can make up for most of the issues with the material being anisotropic by adding more of it in different directions. As for the resins, I think NASA has made progress on that though it was one of the problems that delayed the James Webb space telescope. They ended up finding a cyanate ester thermoset that would remain very dimensionally stable through repeated heating and cooling cycles and most importantly at extremely low temperatures.
Inconel is also attractive, especially with the recent improvements in using it for additive manufacturing purposes (which would simplify the total equipment count for orbital construction hardware).
Oh yeah, orbital rings (Niven or otherwise) are way beyond what we're capable of. I'm more interested in Bernal Spheres and O'Neill Cylinders, which have a lot fewer hurdles and question marks between where we are today and actually building one.
The original O'Neill Cylinder designs were 8 km in diameter precisely because he was factoring in the practicalities of building it with existing materials.
It's like building a self-supporting 70000 km arch bridge. Switching to carbon fiber isn't going to help much, you get a 5x improvement in tensile strength but you need much more than that
http://www.engineeringtoolbox.com/stress-rotation-disc-ring-body-d_1752.html
σz = ω^2 ρ ( r1^2 + r1 r2 + r2^2) / 3
ρ for carbon fiber composite is around 1550 kg/m^3
r1 = r2 = 36000 km
ω = 0.0005 (I think)
Stress would be about 334 GPa
If we reduce it to 3.5 GPa ω becomes 5.11e-5 which gives an orbital period of 123000 s and a speed of 1823 m/s. This is actually slower than normal orbital velocity for this orbit; I'm not 100% sure how this would work, maybe you'd get normal orbital velocity "for free" and this would be extra - if this is the case you'd get a bit more than 5% of Earth gravity, or around a quarter to a third of the Moon
edit: mathed wrong
Instead of spinning up your ring, leave it non-rotating, not even at orbital velocities, just stationary. At low Earth orbit heights, you would still have around 90% of the gravity you would have on the surface of the planet. You would be living on the outer surface of the ring instead of the inside. That itself doesn't solve the building problems, since you're still supporting things under nearly 1g, but it makes the next part easier.
For the next part, build a second ring inside the first, and spin it up to a high velocity. You now have two rings with a common, but opposite, problem. The first, stationary, ring would collapse inwards under it's own weight without support, the second, rotating, ring would fly apart outwards without support. So you set up a system of electromagnetic repulsion between the two of them. The stationary ring pushes inward against the rotating ring, preventing it from flying apart. In turn, the rotating ring pushes outwards against the stationary ring, supporting its weight evenly across the whole structure.
In practice, you would build both rings at the same time, at orbital velocities, and then, you can spin one of them up at the same time you spin the other one down. These two rings don't have to be the same mass either, Your stationary ring might be a large colony structure, while your rotating ring might simply be structure with much less mass, but rotating very fast. The rotating component could even just be something like a set of cables, or even discrete projectiles, embedded within the structure of the ring.
The design principles are similar in concept to a Space fountain. Perhaps a bit simpler, given that you could have constant force applied the whole time, and everything contained within a structure the whole way. And you can extend these techniques to essentially build structures of arbitrary size.
It's still not statically stable, since the ring could drift from its position. Given that you're already using a lot of electromagnets, you could possibly set it up to push against the Earth's magnetic field for stationkeeping maneuvers.
One of the things Gerard O'Neill never thought up (because he was making his proposals about 10 years too early) was the benefit of large space habitats paired with Aldrin Cyclers. Buzz Aldrin proposed the use of cycler orbits - almost perpetual orbits between two bodies in space, passing very near each one - as a means to situate support infrastructure for travel between those bodies in 1985. If you built a Bernal Sphere at the original spec for Island One - a 500m diameter habitation sphere, plus agricultural toruses on the ends along the axis, with the whole thing spinning at 1.9 RPM for 1g at the equator - you could support up to 10,000 people aboard it at any given time. If you then had that habitat set on a Mars Cycler orbit, you could transport thousands of people between the two planets in an ideal environment on a very regular basis with far greater safety than other proposed interplanetary cruise vehicles.
In fact, I'd bet chartering an early such habitat as a university or research institute campus would be a compelling choice, especially since the concept is almost like what the ISS does now but about three orders of magnitude moreso on all fronts.
Which loops back to the discussion of why terraforming Mars to be livable is a better prospect for humans in space than mega-stations. Take the technology we have right now and add being able to build on a large scale in space, and we could drop enough material onto Mars to make it semi-habitable (albeit at hideous expense and the process would probably take decades, if not centuries).
Short of that, we could still definitely build artificial structures which would let us mine the planet for resources. And since the gravity is so much lower on Mars, we could get away with much larger structures as well, without having to worry about providing gravity.
Which again, is why I'm firmly in favor of "small" (0.1 km to 10 km radius) stations and planetary installations. Eventually, we may be able to pull a Kuat somewhere but until then keeping things to a smaller scale is both more feasible and less prone to catastrophe.
even if you had open lava, i don't think an underwater forge weld would work. for one the water would suck the heat out of the workpieces too fast to have any time to do anything with them. even more importantly, the faces you want to join need to be extremely clean for the weld to take, having salt water and whatever other minerals are introduced by the lava boiling off the workpiece and leaving residue would corrode the shit out of it and wouldn't leave a clean enough surface to produce a good joint
hitting hot metal with hammers
With the technology immediately available, yeah, building in a gravity well works best and is probably the most feasible thing if a population of any notable size is intended. Even then, there would be long-term health concerns due to microgravity, especially if anybody ever wants to go to Earth from those environments. At the moment, the longest consecutive time spent in space is under a year and a half, so there could be a lot of health issues from microgravity that we haven't even encountered yet.
But if we figure out how to stop bone and muscle wastage in microgravity, which is very much a possibility since both of those problems seem to occur due to biological systems not balancing against gravity any longer, then there might not be a medical need to simulate gravity on a station. Then we could build large habitable structures in space, because we wouldn't have to worry about the enormous stresses of rotating structures.
About that:
and the Overview PDF
edit: mind you, this is the proposal/target for the least cost-efficient of the US space companies. The others could do this too (or parts of it, and probably will) for less.
I think the idea is that the big counterweight to altering the economy with respect to climate change is cheap energy is one of the big ways to get serious industry going in a developing country. A lot of that cheap energy isn't very clean, so if you could eliminate that as a problem [while making your investors filthy rich] it's a no-brainer for a company to pursue.
(The real first customer of these satellites is almost certainly going to be the US military because they love anything that lets them improve logistical efficiency. Not having to ship as much diesel for bases would be a big deal, Air Conditioning costs alone are $20 Billion in Afghanistan and Iraq.)
That won't be how it is directly applied, but a massive increase in resources would reduce their cost and inevitably improve the lives of a huge number of people. A hundred years ago, living in poverty meant starving to death and dying from colds no matter where you were. Nowadays, being below the poverty line in a developed country means you still probably have things like a place to live, air conditioning and heat, food, TV, etc. And that's because making those things got so cheap to make.
Wow, it will make some rich people more rich, big deal. Far more importantly, it could change living conditions for the better on a scale even larger than with the Industrial Revolution, simply by virtue of driving down the cost of a lot of materials.
Ok, but the atmosphere is well below the Armstrong limit and won't get much denser due to a lack of magnetic fiend, plus the surface is radioactive.
Also that's how you get giant martian roach men.
And that would be a ... bad? ... thing?
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Wilds of Aladrion: [https://forums.penny-arcade.com/discussion/comment/43159014/#Comment_43159014]Ellandryn[/url]
bah and humbug on that.
the moment we get to the point where we can manufacture/produce the heavy duty equipment and parts for space station construction -in space- itself those costs plummet.
if I had any real say about the matter we'd already have some sort of experimental factory up in space producing things as a proof of concept for this.
if we can get a move on with capturing an asteroid composed of a bunch of heavy metals it'll be even cheaper.
Well, they defunded NASA's Asteroid Redirect Mission, so right now the plan isn't for 2017-2018, it's 2021 or further.
The real story behind the Asteroid Redirect was to just have goal stated for what NASA has been working on for a long time now: their solar electric propulsion tug. It's been in development for what might be a decade now if not more, and the "active" part they slap on the front just changes from time to time to keep funding flowing. I think the current version specifically is meant to be able to separate from whatever it is pushing around so that it can be used over and over to move all kinds of large things around the inner solar system.
Well, no, not really, it was intended to test a lot of different systems and craft, especially the planned SLS and Orion vehicle in the lead up to manned missions to Mars. They would use manned missions to the object in orbit and manned survey missions of NEOs in the Orion to prepare and test the systems. In addition they would use it to test possible planetary defense plans, and to examine the viability of space mining in real world tests.
Real Talk: NASA has wanted that tug for long before any asteroid mission was planned. Had the prior White House actually been interested in doing something more interesting with SLS (which it very obviously was not), they would have pushed for more funding to design an additional payload for SLS beyond Orion itself. As that project stands, we have a rocket and a capsule that can go nowhere of particular interest compared to robotic exploration in those same areas.
edit: in fact, as it stands the most compelling use for SLS is as a means to launch very heavy (or high dV) robotic payloads, like the proposed Europa lander and ATLAST [Advanced Technology Large-Aperture Space Telescope] (a 1:1 replacement in terms of sensors on the Hubble, but with either an 8m or 9.2m aperture compared to Hubble's 2.4m aperture).
What's even better is that one of the ravens figured out how to hack the experiment by wedging the device open that released the treats and had to be removed before he taught the rest of the ravens how to do it.
They would trade bottle caps for food, and Corvids picked up on the process quicker and with more regularity than apes.
Which left me a bit puzzled, i guess the game part lead my thoughts in a wrong direction.
At this point, I am starting to believe we could teach Corvids to play MTG.
"Ca-caw!*"
*You've activated my trap card!
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Pfft, nah. The most powerful card.
Maybe one of the older editions bu I suspect they'd look at modern day MtG and caw "This is some bullshit right here"