Im willing to bet most of the standards data Orbital and SpaceX rely upon and likely refuse to disclose are in fact based upon the START repository.
I don't know about Orbital, but SpaceX routinely credits NASA research for the core of its work. The first Merlin engines, the material for the heat-shield for Dragon. They hired a lot of NASA and Primary-contractor guys, so brought across a lot of ideas. And a lot of their cost-saving manufacturing techniques were originally developed by NASA or through their research contracts. I'm also willing to bet the "pusher" launch-abort system was developed by researchers at, say, JPL, because Boeing & Bigelow adopting the same idea for CST-100.
[The interesting thing is that so little of this work was ever taken up by NASA or the Primes. Orion, for example, doesn't use the newer PICA heatshield material invented by NASA. Instead it uses the older shuttle materials. Similarly it uses an Apollo-style escape-tower instead of a pusher engine. None of the SLS engines will be based on NASA's last 20 years of rocket engine research, but will be refurbished older engines. (Including nine used engines literally taken off the three retired shuttles.)]
Similarly, Bigelow's inflatables were NASA's Transhab research. Sierra Nevada's Dream Chaser is HL-20, with some X-38 thrown in.
Had the shuttle been capable of taking us to the Moon or to at least Lunar orbit
The problem with the shuttle wasn't that it didn't go beyond LEO. It was a space shuttle, that's what they're for, surface to orbit. For longer trips you take the main ship.
The problem was that is was intended to be a low-cost all-purpose reusable truck that would free up funding for other projects. (For example, that "main ship" I mentioned.) But in reality it became the entirety of HSF, consuming vast amounts of funding. Too much to allow its own replacement to be developed, too much to allow iterative development of Shuttle MkII MkIII MkIV... Too much to commercialise. Too much to allow HSF to advance.
By now pushing LEO-work into the commercial sphere, there's a chance to finally turn to other things......Except SLS has been carefully designed to make exactly the same mistakes as the shuttle. The shuttle, okay, they were trying something new, they didn't know better. This time it's wilful and vindictive.
I don't personally know anyone who has lost their GMail account,
I have. It also locked up every google-owned service, such as blogger/blogspot, (and presumably any 3rd party site that uses a google-account for login.)
Sent in the official challenge-form via another email account, next day the block was lifted. Still have no idea what I was actually meant to have done. The only thing I can think of was logging in from someone else's computer (I was at their place when I was blocked) which is surely the whole fucking point of having webmail.
But the best way to do this involves having an asteroid in orbit that the tether hangs from.
Okay, firstly the tether doesn't "Hang" from the counter-weight. The counter-weight isn't in orbit, it's "hanging" from the tether. That's how tethers work. The counter-weight provides centripetal acceleration to balance part of the gravitational force on the other end of the tether. (Or shortens the opposite arm, in a rotator.)
Secondly, as I've said several times now, you don't need a giant mass like an asteroid unless you are dealing with a space elevator.
A lunar L2 space elevator would need to be about 200,000km or more if it didn't have a counter-weight. The "mid-point", in terms of gravity-vs-centripetal force, is at 50,000km. The upper 150,000km provides the necessary centripetal force to overcome the weight of that lower 50,000km, in order to keep the system under tension. The way to cheat that is to put a large mass at a shorter distance above the "mid-point", such as an asteroid at just 100,000km. Because you are trying to create the equivalent force as the 100,000km of cable you are replacing (plus you have a shortened radius), you obviously need a huge mass.
The whole point of short orbital tethers is that they avoid such extremes while providing almost all the advantages (and adding some of their own.). And as I said, for lunar orbital tethers, mass ratios are within a single order of magnitude of the payloads.
And you still need to ship as much down as you ship up.
No, you just have to balance the momentum. This can be with an ion drive. As I said. This alone drops your fuel demand by 4-fold or better.
As I said, the mass:payload ratio is about 5 or 10 to 1, depending on the orbital altitude of the tether's barycentre and how much delta-v you're exchanging. That is, if you had a tether strung from a 5 tonne spent upper-stage (from which it was deployed), you can transfer 500-1000kg payloads.
You do not need an asteroid or similar outrageous mass. That's only for a space elevator, because the whole thing needs to be under outward tension, and you're overcoming the mass of tens of thousands of kilometres of cable/ribbon below the mid-point. The only way of doing that is with tens of thousands more km of cable past the mid-point, or a ridiculously large mass creating the equivalent centripetal force.
(A skyhook is a non-rotating orbital tether. They are easier to work with, but provide less delta-v per metre of length. A reasonable test-bed, but rotators are more effective once you know what you're doing. More bang-for-buck. Better ROI. Skyhooks also don't need giant masses as a counter-weight, in fact, the payload-ratios are slightly better (since there's less momentum exchange.))
[Sigh] And is intended to replace Centaur and DCSS, both of which exist. Not only were they not phased out "in the 70's", but there's ongoing work to develop updated versions.
And SpaceX is also working on Raptor, a Methane/LOx engine to replace their Kero/LOx upper-stage. Being able to supply just LOx in orbit would drastically increase payload capacity of F9/FH.
Getting LOx/LH from LEO might be useful for fuels you intended to burn within a few days
Yes that's the point. Boosting to an escape trajectory.
I'm not talking about, say, a Mars orbital entry burn after 6 months in transit. I'm talking about the major delta-v required to inject into the Earth/Mars transfer trajectory.
and transferring liquid fuels is pretty hard too
And if we ever want to do anything serious in space, it's a technology we're going to have to develop at some point. Every reusable vehicle in space will need fuel transfer.
That means you need to fly up to the contact point without air to support you.
I assume that made sense when you wrote it.
And it means you need rockets [...] to get the altitude.
Except "altitude" is not "orbit". Every bit of delta-v you gain from the tether is less propellant you need to carry on the lander. Since propellant requirements scale exponentially with delta-v, it makes a huge different to payload ratios. It takes about 2000m/s to go from the lunar surface to low lunar orbit, but only about 300m/s to get to low lunar altitude.
As tethers improve, you cut the size of the gap. Eventually, once you get to a few hundred km (still three orders of magnitude shorter than any likely lunar space elevator), you can sync up the orbital altitude and rotation rate to allow the tip to "touch" a limited number of points on the surface of the moon each orbit. At those points you build payload suspending towers.
Payload then gets flicked from LLO to L1, L1-tether to HEO, HEO-tether to LEO, LEO-tether to stationary velocity above the atmosphere.
And you can build every one of those tethers, plus a hundred more throughout the solar system, for less than the cost of a single lunar space elevator. And you can start building them sooner, with vastly less infrastructure in place to justify it. Even a 100m tether provides a delta-v advantage.
As with all skyhooks, you need to ship equal masses up and down over time, or the orbit of the skyhook decays.
"Rotating tethers need to correct for energy lost when flinging payloads, but you can use slow ion drives over time, while the payload gets the entire burst in one hit. The tether therefore acts as a delta-v battery, turning low-thrust solar-powered ion-drive into high-thrust delta-v."
There's no way to use an ion drive to get from Earth's surface to LEO. You must use high-thrust (therefore inefficient) rockets. But with a rotating tether in LEO, you only need to reach the tether tip, making reusable SSTO much easier, since you only need to get above the atmosphere. Say 1 km/s, instead of 8km/s. (Ie, a 15:1 fuel:dry-mass becomes 15:10. And payload:ship-mass ratios improve even more.) The rest of the energy comes from the tether, which is restored by a more efficient system like an ion drive.
And going from a chemical rocket (say, Isp 300s) to an ion drive (Isp 1000s) cuts your fuel requirements by over 4-fold for the same delta-v, not including benefits from reduced tankage and increased reliability.
There is nothing in our path. It's space. Vacuum, radiation, dust.
By putting mining and later manufacturing in space, you gradually eliminate such activities from within Earth's biosphere. That's a good thing. You should be supporting that.
And while rich nations cause pollution, they also have the luxury of caring more about it. As the middle-class grew in the US, they cared more about cleaning up air/water pollution. (As the middle class shrinks recently, they've became mean and shitty. That's a bad thing. You should be worrying about that.) By enriching humanity, you allow the "luxury" of being able to worry about the health of Earth's biosphere. That's a good thing. You should be supporting that.
It also provides resources to uplift more of humanity out of poverty, without overstraining Earth's ability to supply resources. That's a good thing. You should be supporting that.
And who benefits? You think it's western nations. But you're wrong. Rich nations are safe and risk adverse, westerners aren't going to last long working in (or colonising) space. And as Isaac Asimov said, his father didn't come from Russia to the US because he knew how to build ships, but because of he could afford a ticket on someone else's ship. If you lower the price of living and working in space, poorer and poorer people will be able to afford to go. Those people will benefit from the wealth. That's a good thing. You should be supporting that.
A full space-elevator is overkill. You just need a rotating tether. This reduces your material requirements (and hence cost) by many orders of magnitude. And it also allows you to start small and scale up, since any rotating tether provides at least some delta-v advantage. And it can be used in a bunch of different orbits, LEO, L1, LLO, Mars, etc. Even near your favourite asteroid mine to reduce delta-v to/from Earth orbit.
(Rotating tethers need to correct for energy lost when flinging payloads, but you can use slow ion drives over time, while the payload gets the entire burst in one hit. The tether therefore acts as a delta-v battery, turning low-thrust solar-powered ion-drive into high-thrust delta-v.)
Water into LH/LOx. You'll need to be able to handle that for your own operations.
Most upper-stages on large launchers are LH/LOx. Any deep space mission is limited by the capacity of the the launcher. If the upper-stage can be launched empty (or nearly empty, enough to put the payload into LEO), then fueled in orbit, almost all of that saved launch mass can transfer directly to the payload. That means easier engineering (read:cheaper), and/or more instruments. Even if you can only supply LOx (because of the limits of cryo-LH storage), you'll still increase their payload enough to be worth the effort. (Even better, launch to LEO. Refuel in LEO. Boost to L1/etc. Refuel again at L1. Boost to final.)
Those missions are your first clients.
There are also experimental electric drives that use water directly as a propellant. No cryo issues at all. These may be ready by the time you've moved beyond exploration/surveying into actual mining. That not only improves your own transport, it also lends itself to a reusable GEO booster. That increases maximum GEO payload of any launcher by 4-5 times.
For example, the Delta IVH can put about 26 tonnes into LEO. But just 6 tonnes into GEO. Since the F9 can put 10 tonnes into LEO at less than 1/10th the price, you could pay SpaceX $60m and GEOBoostCo $60m and put 10 tonnes into GEO for 1/5th the price of a Delta IVH 6 tonne launch. Or, putting it another way, turn a 3 tonne to GEO Proton-M into a 20 tonne to GEO launcher. Falcon Heavy is meant to put 10 tonnes in GEO, but add a reusable GEO tug, and it can launch five 10 tonne GEO payloads.
If you think there isn't a market for lower cost launches, have a look at SpaceX's launch manifest.
And if we are using raw material from asteroid mining (or lunar ISRU, etc), to expand infrastructure further (which is kinda the whole point), then we'd need to start getting used to shed-level engineering with bulk materials, instead of micron precise aerospace engineering with ultra-advanced composites and alloys.
That's why we need asteroid mining. Being about the create a fuel supply-line that doesn't involve Earth launch will make the "top half" of any subsequent mission much cheaper.
Also, getting the stuff (whatever it is) from the Moon to Earth would require climbing out of Moon's gravity well, which, while much lesser than Earth's, is still significant.
However, there's a delta-v cost for getting to/from the asteroid, not just getting to/from the surface. That was the point of TFA, there are few worthwhile asteroids with low delta-v requirements.
Also, given that space-worthy robots tend to suck, there's a large human component in their control and guidance. So the short time-lag to the moon allows near real-time teleoperation, greatly simplifying work. The time back to Earth is days, instead of months at best and years probably. This particularly matters if there's a reason to send humans (ie, someone has to repair the robots.) Gravity (such as it is) may also simplify the development of some equipment/methods, simply because they are more familiar to us, therefore 2/3rds solved by starting with Earth-analogues.
The moon itself sucks as a resource. The surface is essentially light-slag. But billions of years of asteroid bombardment means it has pretty much anything that you'd find in an asteroid anyway. Run a magnet over the regolith, for example, and you get nickel-iron dust from metallic meteorite impacts (about 1% by mass, apparently). The poles may have water ice in permanent shadows. Possibly. (Man, we seriously need to put a decent lander/rover or ten on the moon again.)
Long term, I think we'd want to mine asteroids. Shorter term, we may find the moon a more convenient place to cut our teeth, and build the resource supply chain into which asteroid mining fits.
Slashdot Mirror
Or set up a greenhouse and grow their own.
That's some pretty fucking expensive bananas.
I think they avoid bananas because the smell tends to go through the whole station for days, and some crew find it off-putting.
Im willing to bet most of the standards data Orbital and SpaceX rely upon and likely refuse to disclose are in fact based upon the START repository.
I don't know about Orbital, but SpaceX routinely credits NASA research for the core of its work. The first Merlin engines, the material for the heat-shield for Dragon. They hired a lot of NASA and Primary-contractor guys, so brought across a lot of ideas. And a lot of their cost-saving manufacturing techniques were originally developed by NASA or through their research contracts. I'm also willing to bet the "pusher" launch-abort system was developed by researchers at, say, JPL, because Boeing & Bigelow adopting the same idea for CST-100.
[The interesting thing is that so little of this work was ever taken up by NASA or the Primes. Orion, for example, doesn't use the newer PICA heatshield material invented by NASA. Instead it uses the older shuttle materials. Similarly it uses an Apollo-style escape-tower instead of a pusher engine. None of the SLS engines will be based on NASA's last 20 years of rocket engine research, but will be refurbished older engines. (Including nine used engines literally taken off the three retired shuttles.)]
Similarly, Bigelow's inflatables were NASA's Transhab research. Sierra Nevada's Dream Chaser is HL-20, with some X-38 thrown in.
Had the shuttle been capable of taking us to the Moon or to at least Lunar orbit
The problem with the shuttle wasn't that it didn't go beyond LEO. It was a space shuttle, that's what they're for, surface to orbit. For longer trips you take the main ship.
The problem was that is was intended to be a low-cost all-purpose reusable truck that would free up funding for other projects. (For example, that "main ship" I mentioned.) But in reality it became the entirety of HSF, consuming vast amounts of funding. Too much to allow its own replacement to be developed, too much to allow iterative development of Shuttle MkII MkIII MkIV... Too much to commercialise. Too much to allow HSF to advance.
By now pushing LEO-work into the commercial sphere, there's a chance to finally turn to other things... ...Except SLS has been carefully designed to make exactly the same mistakes as the shuttle. The shuttle, okay, they were trying something new, they didn't know better. This time it's wilful and vindictive.
So the Year of Linux on the Desktop... in spaaaace?
I have. It also locked up every google-owned service, such as blogger/blogspot, (and presumably any 3rd party site that uses a google-account for login.)
Sent in the official challenge-form via another email account, next day the block was lifted. Still have no idea what I was actually meant to have done. The only thing I can think of was logging in from someone else's computer (I was at their place when I was blocked) which is surely the whole fucking point of having webmail.
The problem is that while gmail might look to you like it is providing "email service" to you, [...] You are gmail's product, not gmail's customer.
Sure, but at least they actually provide a service.
What do I get from the NSA? I can't even get a copy of my own phone records, let alone in an easily searchable format. #bunchajerks
Was that comment specific to this thread or just an observation about Slashdot in general?
They don't need my cell phone to know I'm going to fast. They just need to know I'm on the highway.
Because you never eat after you've been on the highway?
But the best way to do this involves having an asteroid in orbit that the tether hangs from.
Okay, firstly the tether doesn't "Hang" from the counter-weight. The counter-weight isn't in orbit, it's "hanging" from the tether. That's how tethers work. The counter-weight provides centripetal acceleration to balance part of the gravitational force on the other end of the tether. (Or shortens the opposite arm, in a rotator.)
Secondly, as I've said several times now, you don't need a giant mass like an asteroid unless you are dealing with a space elevator.
A lunar L2 space elevator would need to be about 200,000km or more if it didn't have a counter-weight. The "mid-point", in terms of gravity-vs-centripetal force, is at 50,000km. The upper 150,000km provides the necessary centripetal force to overcome the weight of that lower 50,000km, in order to keep the system under tension. The way to cheat that is to put a large mass at a shorter distance above the "mid-point", such as an asteroid at just 100,000km. Because you are trying to create the equivalent force as the 100,000km of cable you are replacing (plus you have a shortened radius), you obviously need a huge mass.
The whole point of short orbital tethers is that they avoid such extremes while providing almost all the advantages (and adding some of their own.). And as I said, for lunar orbital tethers, mass ratios are within a single order of magnitude of the payloads.
And you still need to ship as much down as you ship up.
No, you just have to balance the momentum. This can be with an ion drive. As I said. This alone drops your fuel demand by 4-fold or better.
As I said, the mass:payload ratio is about 5 or 10 to 1, depending on the orbital altitude of the tether's barycentre and how much delta-v you're exchanging. That is, if you had a tether strung from a 5 tonne spent upper-stage (from which it was deployed), you can transfer 500-1000kg payloads.
You do not need an asteroid or similar outrageous mass. That's only for a space elevator, because the whole thing needs to be under outward tension, and you're overcoming the mass of tens of thousands of kilometres of cable/ribbon below the mid-point. The only way of doing that is with tens of thousands more km of cable past the mid-point, or a ridiculously large mass creating the equivalent centripetal force.
(A skyhook is a non-rotating orbital tether. They are easier to work with, but provide less delta-v per metre of length. A reasonable test-bed, but rotators are more effective once you know what you're doing. More bang-for-buck. Better ROI. Skyhooks also don't need giant masses as a counter-weight, in fact, the payload-ratios are slightly better (since there's less momentum exchange.))
How can it be a bubble when nobody is actually doing it yet?
ACES is Proposed, not existing.
[Sigh] And is intended to replace Centaur and DCSS, both of which exist. Not only were they not phased out "in the 70's", but there's ongoing work to develop updated versions.
And SpaceX is also working on Raptor, a Methane/LOx engine to replace their Kero/LOx upper-stage. Being able to supply just LOx in orbit would drastically increase payload capacity of F9/FH.
Getting LOx/LH from LEO might be useful for fuels you intended to burn within a few days
Yes that's the point. Boosting to an escape trajectory.
I'm not talking about, say, a Mars orbital entry burn after 6 months in transit. I'm talking about the major delta-v required to inject into the Earth/Mars transfer trajectory.
and transferring liquid fuels is pretty hard too
And if we ever want to do anything serious in space, it's a technology we're going to have to develop at some point. Every reusable vehicle in space will need fuel transfer.
I think you're confusing tethers with space elevators.
Rotating lunar tethers only need a mass/payload ratio of about 5 or 10:1. You certainly don't need an asteroid as a counter-mass.
And once you have the first, you can leverage it to gather mass bit-by-bit for the counter-weight of the next (larger) tether.
That means you need to fly up to the contact point without air to support you.
I assume that made sense when you wrote it.
And it means you need rockets [...] to get the altitude.
Except "altitude" is not "orbit". Every bit of delta-v you gain from the tether is less propellant you need to carry on the lander. Since propellant requirements scale exponentially with delta-v, it makes a huge different to payload ratios. It takes about 2000m/s to go from the lunar surface to low lunar orbit, but only about 300m/s to get to low lunar altitude.
As tethers improve, you cut the size of the gap. Eventually, once you get to a few hundred km (still three orders of magnitude shorter than any likely lunar space elevator), you can sync up the orbital altitude and rotation rate to allow the tip to "touch" a limited number of points on the surface of the moon each orbit. At those points you build payload suspending towers.
Payload then gets flicked from LLO to L1, L1-tether to HEO, HEO-tether to LEO, LEO-tether to stationary velocity above the atmosphere.
And you can build every one of those tethers, plus a hundred more throughout the solar system, for less than the cost of a single lunar space elevator. And you can start building them sooner, with vastly less infrastructure in place to justify it. Even a 100m tether provides a delta-v advantage.
As with all skyhooks, you need to ship equal masses up and down over time, or the orbit of the skyhook decays.
"Rotating tethers need to correct for energy lost when flinging payloads, but you can use slow ion drives over time, while the payload gets the entire burst in one hit. The tether therefore acts as a delta-v battery, turning low-thrust solar-powered ion-drive into high-thrust delta-v."
There's no way to use an ion drive to get from Earth's surface to LEO. You must use high-thrust (therefore inefficient) rockets. But with a rotating tether in LEO, you only need to reach the tether tip, making reusable SSTO much easier, since you only need to get above the atmosphere. Say 1 km/s, instead of 8km/s. (Ie, a 15:1 fuel:dry-mass becomes 15:10. And payload:ship-mass ratios improve even more.) The rest of the energy comes from the tether, which is restored by a more efficient system like an ion drive.
And going from a chemical rocket (say, Isp 300s) to an ion drive (Isp 1000s) cuts your fuel requirements by over 4-fold for the same delta-v, not including benefits from reduced tankage and increased reliability.
Can't afford a space elevator until you have sufficient launch traffic to justify the economics.
Don't need a space elevator if you already figured out how to get sufficient launch traffic.
we'll simply destroy everything in our path
There is nothing in our path. It's space. Vacuum, radiation, dust.
By putting mining and later manufacturing in space, you gradually eliminate such activities from within Earth's biosphere. That's a good thing. You should be supporting that.
And while rich nations cause pollution, they also have the luxury of caring more about it. As the middle-class grew in the US, they cared more about cleaning up air/water pollution. (As the middle class shrinks recently, they've became mean and shitty. That's a bad thing. You should be worrying about that.) By enriching humanity, you allow the "luxury" of being able to worry about the health of Earth's biosphere. That's a good thing. You should be supporting that.
It also provides resources to uplift more of humanity out of poverty, without overstraining Earth's ability to supply resources. That's a good thing. You should be supporting that.
And who benefits? You think it's western nations. But you're wrong. Rich nations are safe and risk adverse, westerners aren't going to last long working in (or colonising) space. And as Isaac Asimov said, his father didn't come from Russia to the US because he knew how to build ships, but because of he could afford a ticket on someone else's ship. If you lower the price of living and working in space, poorer and poorer people will be able to afford to go. Those people will benefit from the wealth. That's a good thing. You should be supporting that.
Google "ACES upper stage".
If I can offer fuel in orbit and reduce your launch costs or increase your payload-mass 5-fold, you are not going to be fucking around with hydrazine.
We can't do that until we start moving asteroids.
Que? Why do you need to move an asteroid to have an orbital tether?
Or, possibly, a beanstalk
A full space-elevator is overkill. You just need a rotating tether. This reduces your material requirements (and hence cost) by many orders of magnitude. And it also allows you to start small and scale up, since any rotating tether provides at least some delta-v advantage. And it can be used in a bunch of different orbits, LEO, L1, LLO, Mars, etc. Even near your favourite asteroid mine to reduce delta-v to/from Earth orbit.
(Rotating tethers need to correct for energy lost when flinging payloads, but you can use slow ion drives over time, while the payload gets the entire burst in one hit. The tether therefore acts as a delta-v battery, turning low-thrust solar-powered ion-drive into high-thrust delta-v.)
Water into LH/LOx. You'll need to be able to handle that for your own operations.
Most upper-stages on large launchers are LH/LOx. Any deep space mission is limited by the capacity of the the launcher. If the upper-stage can be launched empty (or nearly empty, enough to put the payload into LEO), then fueled in orbit, almost all of that saved launch mass can transfer directly to the payload. That means easier engineering (read:cheaper), and/or more instruments. Even if you can only supply LOx (because of the limits of cryo-LH storage), you'll still increase their payload enough to be worth the effort. (Even better, launch to LEO. Refuel in LEO. Boost to L1/etc. Refuel again at L1. Boost to final.)
Those missions are your first clients.
There are also experimental electric drives that use water directly as a propellant. No cryo issues at all. These may be ready by the time you've moved beyond exploration/surveying into actual mining. That not only improves your own transport, it also lends itself to a reusable GEO booster. That increases maximum GEO payload of any launcher by 4-5 times.
For example, the Delta IVH can put about 26 tonnes into LEO. But just 6 tonnes into GEO. Since the F9 can put 10 tonnes into LEO at less than 1/10th the price, you could pay SpaceX $60m and GEOBoostCo $60m and put 10 tonnes into GEO for 1/5th the price of a Delta IVH 6 tonne launch. Or, putting it another way, turn a 3 tonne to GEO Proton-M into a 20 tonne to GEO launcher. Falcon Heavy is meant to put 10 tonnes in GEO, but add a reusable GEO tug, and it can launch five 10 tonne GEO payloads.
If you think there isn't a market for lower cost launches, have a look at SpaceX's launch manifest.
And if we are using raw material from asteroid mining (or lunar ISRU, etc), to expand infrastructure further (which is kinda the whole point), then we'd need to start getting used to shed-level engineering with bulk materials, instead of micron precise aerospace engineering with ultra-advanced composites and alloys.
Google "neo asteroid".
[Also, 1/17, not 1/27.]
That's why we need asteroid mining. Being about the create a fuel supply-line that doesn't involve Earth launch will make the "top half" of any subsequent mission much cheaper.
It's the gift that keeps on giving.
Also, getting the stuff (whatever it is) from the Moon to Earth would require climbing out of Moon's gravity well, which, while much lesser than Earth's, is still significant.
However, there's a delta-v cost for getting to/from the asteroid, not just getting to/from the surface. That was the point of TFA, there are few worthwhile asteroids with low delta-v requirements.
Also, given that space-worthy robots tend to suck, there's a large human component in their control and guidance. So the short time-lag to the moon allows near real-time teleoperation, greatly simplifying work. The time back to Earth is days, instead of months at best and years probably. This particularly matters if there's a reason to send humans (ie, someone has to repair the robots.) Gravity (such as it is) may also simplify the development of some equipment/methods, simply because they are more familiar to us, therefore 2/3rds solved by starting with Earth-analogues.
The moon itself sucks as a resource. The surface is essentially light-slag. But billions of years of asteroid bombardment means it has pretty much anything that you'd find in an asteroid anyway. Run a magnet over the regolith, for example, and you get nickel-iron dust from metallic meteorite impacts (about 1% by mass, apparently). The poles may have water ice in permanent shadows. Possibly. (Man, we seriously need to put a decent lander/rover or ten on the moon again.)
Long term, I think we'd want to mine asteroids. Shorter term, we may find the moon a more convenient place to cut our teeth, and build the resource supply chain into which asteroid mining fits.