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[mainiac]

Uh, way to move the goalposts much? 

The entire point I was getting across was that those propellant cost numbers are a load of crock.  Propellant costs shouldn't even figure into things if you calculate them correctly.  This isn't rocket science, it's orbital mechanics.

And what exactly are the numbers that you want to see?

I spoke about reaction mass. You can't have propulsion without reaction mass. Momentum is conserved. Even solar sails work by momentum transfer.

No propellant.  No propellant.  No propellant.  You get all your delta v at launch.  We are talking about speeds in the range of the muzzle velocity of a gun.  And the acceleration can be done over a much longer length than that of a gun (kilometers feasibly).  Once that velocity is imparted you do not need any propellant.  The only "propellant" that you have is the asteroid you are mining.

[sluissa]

I can see the point wanting to leave them in the belt. But why send the whole thing back to Earth? Other than having a source of labor here, I don't really understand what can be done in earth orbit that can't be done elsewhere better. Move closer to the sun, you can pick up more solar energy. Move outwards and you have gas giants and their moons to feast on. Even mars could be a better choice if you absolutely needed somewhere to land. It's smaller than the earth with less gravity and has a lot less atmosphere to contend with if you want to regularly launch from it.

Face it, the earth has been a good cradle for us, and definitely still has its uses. (I doubt we'll perfect large scale farming in space or on any other planets anytime soon.) But there are definitely better places to work.

[andrea]

the reason to move asteroids in earth orbit would be that it is (relatively) easy and MUCH less expensive to send more equipment and people to mine the asteroid.
furthermore, whatever use we have for the minerals and metals, in the near future it will be needed either in earth orbit or on earth itself.

you can turn a tree into planks on the spot, but often a trip to the sawmill is worth the effort.

[Sowelu]

People who personally invest into the future of mankind in space, and almost more importantly in the hopes and dreams of mankind, are the highest form of heroes.

[mainiac]

What about the people who don't have a billion dollars, because they were gifted with a rather trivial skill and the luck to be born into the exact conditions were that skill is ridiculously rewarded, but still help the world in far less visible ways?  Perhaps they are heroes even higher?  Higherest heroes?

[Sowelu]

Not every soldier on the battlefield can earn a Medal of Honor:  In addition to the incredible luck and skill that it takes to pull off a heroic stunt and succeed, you have to be in the right place at the right time, or you'll never even have the opportunity.  Most soldiers go through their entire careers without ever being in a clusterfuck that is both that bad and also salvagable.  Plenty of them have the will, but not the chance.

Not every businessman can take space travel from a joke to a true business enterprise:  You have to be obscenely wealthy.  Also, you need the experience and skill at business management and technology, the willpower to push it to success, and no small amount of luck.

Being a hero on this vast of a scale involves both having the opportunity and taking it.  Most of us aren't born with the opportunity.

And yeah, short of "preventing all-out nuclear war or some other effective end of the human race", those who get us off this rock ARE the highest of heroes.  That includes all the astronauts who will surely die in the process, and all the ones who will live, but the people who fund them are the most necessary of all.

[Eagleon]

I'm assuming you have numbers for this? What are the energy costs? How can that energy be generated? What materials are needed to make each launch? How can those materials be gathered and processed?

What sort of asteroid are you targeting? What resources are you targeting within that? What mass of resources are you returning and at what rate?

And why bother with dozens of launches of insignificant masses from what will need to be a highly sophisticated launch base, making use of only a small fraction of the asteroid's mass when you could use the same principles to ditch a small fraction of the asteroid's mass and retrieve the whole thing?

Flywheels are awesome, especially with modern materials. If they aren't planning to use them now, they'll end up using them later, because there's just no other storage for power that can store energy from something small like solar over long periods and still release it on scales batteries and capacitors can't reach, barring significant breakthroughs. They're perfect for space - low friction, low gravity, and built in gyroscopic stabilization. A good flywheel can supply all the power you'd need. It's totally what Hank Hill would grill with if he had to live in space. They'd also probably be comparatively simple to manufacture for a self-expanding operation (versus finding suitable materials for reaction mass), which would be very nice to have if Mr. Cameron doesn't hit up the moon first.

For mass drivers, keep in mind the scale and gravity of the asteroid involved. They also don't need to be straight, or even aimable - you could conceivably build a ring-track circling (or partially circling) the object, with releases at each half or quarter degree, and accelerate your package gradually then release at any angle you like. It's not my personal favored option, since you'd still need to build a fairly long and complex bit of equipment with its own maintenance issues, but it is feasible. It's just that if you can build a mass driver, you can also build an ion engine, which can use your least valuable collected resource as propellant - whatever you decide that may be.

[Nilik]

Everyone's talking about asteroid mining as if that's absolutely definitely what this is going to be. I hear a lot about how much space junk there is floating about in orbit... what would be the feasibility of salvaging some of that? You put a disposible robot into orbit, gather up as many broken satelites, used booster rockets and astronaut soda cans as you can into a big ball of junk and then drop the sucker to earth. There's got to be a lot of precious metals in those satelites.

I'm envisaging a sort of sphere with booster rockets and a dozen or so telescoping arms. Once each arm has grabbed hold of a chunk of space-junk, the boosters fire and propel it to earth. And they can call it "Project: Katamari".

[Eagleon]

I know you're probably joking, but it's fun to speculate anyway. If I were looking at recycling what we've got up there, I'd personally rather make a giant foam wall. Capture satellite, use solar collectors for heat and a small adaptable chemistry kit to foam up all the materials (all of them!), use extending sharp metal probes to suck back and store the toxic gasses I've made for foaming agents, and vent them strategically to navigate to the next object. Then when I've collected enough foamed up crap to survive reentry I'd nail Greenpeace with a kinetic barrage of captured micrometeorites, steaming partially decomposed PVC, and heavy metals.

There, I just saved the world.

[Rose]

http://www.foxnews.com/scitech/2012/04/24/company-aims-to-strike-it-rich-by-mining-asteroids/

Looks like they are, in fact, planning on harvesting asteroids, using... scoops.

Announcement will be shown live at 10:30am, PDT, at http://www.spacevidcast.com/live/

[palsch]

Uh, way to move the goalposts much? 

What were the goalposts? I have always been focusing (well, since my first post that discussed the things I actually think are possible and sensible) on the energetic costs of moving heavy metals from the asteroid belt into earth orbit. These costs are what are are prohibitive, regardless of how you propose to pay them. If you genuinely have a method to reduce them then well done, but I'm entirely sceptical. Because I have never seen such numbers, despite spending a couple hours yesterday looking around the internet for them.

My main view on this kind of thing is without numbers, it's science fiction. Which is fun, but probably worth flagging as such.


In any case, this is the study they are basing the early stages on. Targeting a C-class near earth asteroid, approximately seven meters in diameter and with a total mass of around 500,000 kg. The goal is to bring it into lunar orbit. Estimated costs there are ~$2.6bn

Note three things;
1) We don't know of many any suitable asteroids. The actual mission outline involves early space based telescopes (spiking the costs above those of the study) to find such targets.
2) The asteroid type is carbonaceous. The primary benefit from these is they contain water, if usually locked up in other minerals. Water is expensive to put into orbit.
3) Even so, how cost effective this is depends on the useful mass fraction. The same costs would put ~20 Heavy Falcon rockets into lunar orbit, worth 320,000kg of payload. You get an extra 180,000kg from the asteroid mission, but if it's more cost effective depends on just how useful that mass is.

Oh, and the expected return is in 2025. For an estimated $0 return on investment. This isn't a profitable venture. The good news is that it isn't expected to be. The early news stories spoke about it being worth billions. That was always bullshit. Even the long term goal of this project is supply depots in space. A series of asteroids with resources pre-prepared for future missions or projects, making future exploration cheaper.

[Another]

A proposal for economically profitable space mining may involve extracting He3 from Moon surface. Once we have commercial fusion energy plants it can be an efficient fuel component for that. So - just 30 years away in the future from now (or from any other point in time we will call 'now' for some time).

By the way - correcting Near-Earth asteroid trajectories years in advance so that they will perform precise 'slingshot' manoeuvre near Earth on their way to a Moon orbit (and a small additional impulse to make it a closed orbit) or near Moon for later Earth orbit would greatly reduce needed delta-Vs. I think that high eccentricity elliptic orbit is sufficient for an orbital raw materials stockpile.

[mainiac]

What were the goalposts? I have always been focusing (well, since my first post that discussed the things I actually think are possible and sensible) on the energetic costs of moving heavy metals from the asteroid belt into earth orbit.

No, you have been focused like a laser beam on the amount of propellant (or equivalent) necessary in order to make a round trip using conventional rockets.  This is not the same thing as the energetic costs of space mining.  Not all means of changing delta-v require a conventional rocket.

[sluissa]

the reason to move asteroids in earth orbit would be that it is (relatively) easy and MUCH less expensive to send more equipment and people to mine the asteroid.
furthermore, whatever use we have for the minerals and metals, in the near future it will be needed either in earth orbit or on earth itself.

you can turn a tree into planks on the spot, but often a trip to the sawmill is worth the effort.

There's also a reason they tend to build sawmills in and around forests, rather than, say, the middle of New York City.

A moot point at the new information, however. A near earth asteroid meant for supplies really doesn't have much elsewhere it could be useful at the moment.

[palsch]

No, you have been focused like a laser beam on the amount of propellant (or equivalent) necessary in order to make a round trip using conventional rockets.  This is not the same thing as the energetic costs of space mining.  Not all means of changing delta-v require a conventional rocket.

I had one quote dismissing that idea in my original post. The only other mention of a rocket was looking at constructing one from materials on an asteroid (sceptically) to get enough delta-V to get the rock home quickly. The other mentions of fuel were in reference to ion engines, which I used as a gold standard of mass driver style thrust.

Everything else was talking about mass driver reaction mass, with reference back to the ion engine.

A proposal for economically profitable space mining may involve extracting He3 from Moon surface. Once we have commercial fusion energy plants it can be an efficient fuel component for that. So - just 30 years away in the future from now (or from any other point in time we will call 'now' for some time).

Commercial fusion plants of the first generation (or third if you count from modern tokamaks) will be burning D-T. He3 fusion requires far higher temperatures to work. They have significant advantages, but are distant enough that I can't pretend that they are a viable energy source. Tritium (and so lithium) are far more important right now.