I don’t think we’ll be doing space mining in the time frame of my OP, however:
[QUOTE=MichaelEmouse]
How can they dwarf anything we could extract on earth?
[/QUOTE]
It is getting harder and harder to extract certain resources from the Earth…all of the low hanging fruit has already been extracted, and we have to dig or drill deeper and deeper to continue extraction. The best iron deposits in the US have been used up already, which is one of the reasons we aren’t a major steel producer anymore. Recycling helps, but there is still the issue of only so much to go around. Asteroids, however, are a completely untapped resource with huge potential. There are literally millions of them out there, many with concentrations of rare metals and water. You have to remember that a lot of the resources we actually use on the earth came originally from asteroid impacts, since much of the heavier metals that were here sunk into the core during formation.
Asteroids. Many, MANY more times the amount of resources of the Earth…orders of magnitude more.
Well, I think that mostly what you’d do is use the resources, especially the water up in space and only send down finished or refined products, but it’s fairly trivial to send down bulk materials to the Earth without having them burn up. Since you don’t need to worry as much about it as sending down something fragile like a human, you merely have to put some sort of ablative heat shield on the cargo, give it a nudge so it falls into the gravity well, and then put a few parachutes on it to slow it down enough so it doesn’t crater the landing spot and there you go. None of this is technically difficult. It’s the cost model that isn’t there, not the ability, and based on the fact that several companies have been formed in the last 5 years to start exploring the possibilities (at least one of them plans to start sending up probes to explore which are the richer asteroids by 2016), I’d say that at least some folks are looking into this seriously.
For the cost of putting on a Superbowl or a single Bond movie (~US$200M), nearly the entire population of Africa could be provided potable water. For the cost of a single F-35 fighter, the population of Bangladesh could be educated to a high school level. For the annual budget of the Transportation Security Administration (US$7.6B) the entire population of Southeast Asia could be fed for a year at a level exceeding the minimum dietary energy requirements. Arguing that any particular program is at fault for poverty, famine, and illiteracy ignores the larger, systematic problem that we absolutely have the fiscal means to deal with such problems, but not the political will.
However, it should be pointed out that by virtue of Earth surveillance by satellites we have comprehensive information about climate impacts on ocean populations, surface and subsurface agricultural water depletion, and variations in solar incidence at surface level. By using tools such as surveillance and GPS we can optimize crop yields, identify ocean areas that are overfished and need to recover, et cetera, which already have and will continue to allow us to maintain sustainable yields of food stocks. This is one of many benefits to mankind overall that have been provided by space utilization and exploration. That the benefits are not shared in egalitarian fashion is, again, a political problem, not a technical one.
Let me state this very clearly; China is not doing anything new in space travel or exploration. They are not developing new technologies. They are not investing significant resources in space exploration. They are using conventional technology to do what the US and Soviet Union did thirty odd years ago, and they are doing so for the same reason that they maintain a nuclear arsenal–so that they can claim the mantle of being a “superpower”. There is zero indication that the PRC will establish a permanent base on the Moon or any other body. They certainly aren’t putting in the kind of resources necessary to advance the state of the art in propulsion, nor are they engaging in the kind of astronomy or planetary science that is the hallmark of a comprehensive space exploration program intent on gaining a sufficient understanding of the Solar System and beyond to prepare for eventual crewed exploration. The Chinese space program is a vanity effort akin to the wife of a tycoon running a boutique organic bathworks shop. The day we see China do anything in space that isn’t either focused on military/orbital superiority or a by-the-numbers repeat of what other superpowers have already done, then we can consider China as a potential innovator in space exploration and technology.
The cost value of reusability in space launch vehicles is typically overstated, in part because of assumptions of how little it is expected to cost to refurbish reused equipment, but in large measure because of how little of the cost of a rocket launch is actually presented in the hardware. The cost of a typical orbital space launch for a liquid propellant vehicle is generally less than 10% in the fabrication of the vehicle hardware; the bulk of cost is in various labor categories such as transportation, vehicle and payload integration, range approvals and interfaces, addressing processing anomalies, et cetera. (Propellants are typically less than 1% of the total cost except for hypergolics).
And reusability comes with its own costs; designing a high performance rocket propulsion system and reentry systems to be sufficiently robust that it can be reused without extensive refurbishment and acceptance testing is extraordinarily expensive, as NASA discovered with both the STS Orbiter Vehicle and the Solid Rocket Motors. Antonio Elias describes how Orbital Sciences investigated the requirements for a reusable vehicle and came to the same conclusion that NASA did in 1970, to wit that reusability only becomes cost effective at a rate of 50-60 flights per vehicle per year. Designing a rocket launch vehicle capable of operating at this rate without refurbishment or replacement is well beyond the current state of the art, and while it isn’t physically impossible would require advances in material science, propulsion technology, and reentry systems.
There is another approach, and that is to trade performance for robustness. This is the tact taken by Bob Truax with the Sea Dragon/SEALAR concept, in which a relatively low performing, gigantic rocket, built to shipbuilding tolerances, is launched from the ocean (no launch platform; it is just erected using ballast and launched with the base submerged). Although the payload to propellant ratio is unimpressive (and therefore the propellant costs are higher) and theoretically predicted reliability is lower because of the lack of redundancy, the overall launch costs are dramatically lower (a crew of a few dozen people to tow, erect and launch, and it is launched into broad ocean area not requiring range services or flight termination systems) and, at least for bulk payloads, the vehicle is far more cost effective. However, this is not the approach taken by SpaceX with the Falcon vehicles which are relatively high performance, conventional gas generator engines which will likely require refurbishment between flights. If SpaceX could get per-flight costs down to the single millions of dollars that would be incredible, but so far they’ve invested so much labor into every launch that it is doubtful that they’re even in the black at the current base cost schedule of $61.2M (not $56M) per flight. (Note that cost is only a “manifest” cost, e.g. it buys you a slot on a rocket; if you need extra services such as health and status monitoring of the payload, contamination control, spacecraft propellant loading, multiple coupled load analyses for payload stack design maturation, et cetera, these are all additional significant costs in addition to the base cost.) It’s easy for Elon Musk or Gwynne Shotwell to claim that they’ll be relaunching rockets at $5M to $7M, but until they are actually doing that on a regularly scheduled basis it’s about as substantial as a politician’s campaign promise.
You’ve got this turned around; a solar orbiting space habitat which uses solar power (whether photoelectric, concentrated thermal, et cetera) can be selective as to how much energy they absorb and use a shade to deflect the rest, thereby maintaining passive thermodynamic balance and with out having to produce a significant amount of power by internal processes. A “generation ship” on the other hand, has to produce all of the energy needed for propulsion, habitation, resource recycling, food production, et cetera, which will produce a large amount of waste heat at temperatures below a level useful for power production but above what can be tolerated environmentally.
Achieving even a fraction of c would require an extraordinary amount of energy and for any system with an I[SUB]sp[/SUB] < 80,000 s would also require an untenable propellant-to-payload ratio (see previous discussions [POST=16382736]here[/POST], [POST=16494836]here[/POST], and [POST=16974132]here[/POST]). The necessity of carrying a habitat and all that entails capable of reliable operation for hundreds (at least) years is simply prohibitive using any extant or plausible propulsion and power generation technology.
The Earth is certainly large but we can only access a very, very thin shell of it (down to at most the upper 4000 meters). Most of the really valuable metals are far deeper than that, so we can only get to what was ejected near the surface during eruptions or what was deposited in the crust by meteorite impacts. On the other hand, it is no great trick to completely disassemble a small asteroid, or melt a comet in order to gain complete access to all of its contents. Many metal-rich bodies have already been identified and more are estimated. However, water is probably the most precious resource in space, and fortunately many objects appear to be comprised almost entirely of water ice. Developing the technology to intercept and utilize these resources is challenging but entirely plausible, and delivering bulk materials to Earth is a matter of providing ablative shielding (fabricated from the slag left over from extraction) sufficient to slow the payload to a non-hazardous speed (e.g. one that won’t create a seismic event like a tsunami) and dropping it in the ocean like a giant-sized Apollo capsule. Unlike delicate payloads and crewed vehicles, a delivery of bulk materials doesn’t have to be carefully protected against impact.
I’m not sure why you think hazardous or polluting manufacturing should be located “underground, in the desert or Siberia/Northern Canada” but I’ll point out that virtually none of this is done now, both because it is logistically complex, nobody wants to travel or live there, underground caves are generally near water tables, and deserts and tundra are delicate ecosystems that can easily be disrupted by pollutants and traffic. In space, metals, radioactive fuels, and rare earth materials, and radio can be chemically or thermally smelted without any concerns about the residual material affecting habitats, threatening wildlife, or creating a persistent hazard to human populations.
But the real reason to create material processing capability using space resources is to support a sustainable space manufacturing and habitation infrastructure. Having to pull materials up out of a gravity well–even that of Earth’s Moon or other smaller bodies–is still expensive and labor consuming versus using materials already in a “freefall” solar orbit which can be moved to other orbits with a limited and distributed expenditure of energy.
Project Orion (the bomb-propulsion system) would be feasible, but only as an interplanetary propulsion system.
A somewhat more advanced and speculative version, Project Daedalus, was devised in the Seventies,
a system which has already been mentioned upthread. This version would have used tiny pellets of deuterium/helium-3 mix that would be detonated by electron beam.
More recently an updated version has been proposed, Project Icarus;
the details on this one have been less comprehensive than the original (so far); but there have been some very nice images made by Adrian Mann of various versions.
