Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Loud Whispers]

We seem to be making a pretty good shot at it. Hem.

"Coming to your neighbourhood soon."

Gotta love NASA.

[Leafsnail]

When... when you say "can't" there, are you saying that in a sort of theoretical sense or are you referring to actual technical limitations you know of? If the latter, could you toss some links out so we can educate ourselves?

You could also interpret those questions as a simple, "Why not?" We have some pretty impressive computers nowadays.

Technical limitations in terms of just not being able to see them?  We don't have the telescopic resolution to see tiny rocks thousands of miles away that barely reflect any light.  No amount of computing power would help there.  I guess we could send lots of probes over to try and map them all but that would add even more expense.

You'd be surprised.

I might be if there's evidence of us being able to spot tennis ball sized rocks thousands of miles away, I guess?

[MetalSlimeHunt]

You don't actually have to be thousands of miles away. We have sent things out into space with cameras on them before, and we'll do it again.

[DJ]

I thought the standard sci-fi method of propelling asteroids is lasers. You simply shoot the asteroid, and the resulting jet of debris acts as a jet engine of sorts.

[palsch]

I thought the standard sci-fi method of propelling asteroids is lasers. You simply shoot the asteroid, and the resulting jet of debris acts as a jet engine of sorts.

Can work, but more with smaller objects. A plan for dealing with bits of space junk is using a laser to sap velocity so they fall into the atmosphere and burn up. One problem with that is you would have a significantly powerful laser in orbit. The other is getting a significantly powerful laser in orbit that will last long enough to make a difference before becoming space junk itself.

For asteroids you are talking about massive delta-V. The most direct method would be strapping on an ion engine with a decade or two's worth of fuel and relying on a slow burn. If you only need to make a small adjustment (say, enough to make it miss earth), then flying a significant but more easily flown mass alongside it close enough could have enough gravitational pull to adjust it's path, but then there is the problem of getting that mass up there early and long enough. Having some captured asteroid mass to play with would be a nice start.

[DJ]

Wait, I'm getting tangled in terminology here. Are we talking about asteroids that have stable orbits with relatively constant distance from the sun (well, as constant as your run of the mill planet), or ones that have highly elliptical orbits that come close to Earth's orbit now and then? If it's the latter, wouldn't a relatively small course adjustment bring them close enough to mine? Ie, a laser should be able to do it.

[Eagleon]

I thought the standard sci-fi method of propelling asteroids is lasers. You simply shoot the asteroid, and the resulting jet of debris acts as a jet engine of sorts.

Wait, I'm getting tangled in terminology here. Are we talking about asteroids that have stable orbits with relatively constant distance from the sun (well, as constant as your run of the mill planet), or ones that have highly elliptical orbits that come close to Earth's orbit now and then? If it's the latter, wouldn't a relatively small course adjustment bring them close enough to mine? Ie, a laser should be able to do it.

I don't think anything short of fusion could make the sustained thrust from that significant, and you'd be throwing out what you're hoping to recover. 'Close' is a relative term here, and if you were working with elliptical NEOs, there's probably a ton of speed involved. There aren't a lot of proposals I can say this for, but I'd be worried about accidents if we tried that.

Speaking of, talking with friends, I came up with an interesting idea that I'm not sure has been considered about how we might refine what we want on-site without anything terribly complex - CVD (chemical vapor deposition) using lasers. Now, I know, lasers use lots of energy so it would be slow, but we've got some interesting advantages there. Relative vacuum removes the need for expensive pumps to maintain a clean space. Microgravity means you can work in some fine-tuned magnetic filtering without worrying about the speed of the process too much, which means you could potentially filter all sorts of gasses into their own compartments to deposit how you like. And if you can come up with parts that can be 'grown' by vapor deposition, you have some primitive manufacturing capability. I'm not exactly sure how primitive, but I imagine at least enough to make replacement motors for a flywheel driven by solar panels, and maybe just enough to make engines for smaller cargo containers to ship back home.

Hell, if you can make pure enough vapors you might be able to make parts for another laser. At the very least you could start building the framework to accept parts you can't make using CVD, and those can be shipped over at reduced cost to amplify the rate of returns.

[palsch]

Wait, I'm getting tangled in terminology here. Are we talking about asteroids that have stable orbits with relatively constant distance from the sun (well, as constant as your run of the mill planet), or ones that have highly elliptical orbits that come close to Earth's orbit now and then? If it's the latter, wouldn't a relatively small course adjustment bring them close enough to mine? Ie, a laser should be able to do it.

You are still talking about a significant velocity change that needs to be carefully controlled. Long and slow, at the point of the asteroid, gives you far more control than a remote laser would.

A laser would work either by direct photon pressure (very weak, especially over significant distances) or by burning material off the surface and using that expelled material as effective reaction mass. The latter would probably be needed for the sorts of delta-V we are talking about, being roughly comparable to an ion engine for the duration of the laser being on, but is less reliably consistent (very dependent on the material being shot) and requires a hell of a lot more power. I'd expect it to be energetically favourable to burn a rocket getting your engines to the asteroid compared to firing your laser.

The laser still has some theoretical advantages, but laser propulsion makes more sense for man made objects than for natural asteroids.


From my previous post, the stable orbits in the asteroid belt aren't even worth talking about right now. At least not without the sort of orbital materials base we would want to capture asteroids for in the first place.

[mainiac]

The early American colonies were a financial disaster for the proprietors too.

True in the sense that this statement is so wrong that it becomes right.  The early american colonies were so profitable that they caused the collapse of the Spanish economy three times because they had too much gold.

I strongly doubt they would shoot for an asteroid belt operation.

The energy cost of sending something out there, let alone bringing anything back, would be obscene enough to make it unrealistic. This post does some basic maths on the energetics of shifting something from the asteroid belt to earth orbit.

Still plenty of room to think outside the box though.  Use the mass of the object being mined itself to create propellant.  Who cares if you lose 90% in transit?  10% is still a bounty.  That turns your delta-v budget problem into a mere energy density problem, far easier to tackle.  Build a mass accelerator on an asteroid and proceed to mine it out.  As your energy budget affords it, send your minerals back.  Leave the rest of it floating far out beyond earth.

Also the Near Earth Asteroid delta-v to earth orbit is about 1 km/s not 5 km/s.  So if you can get your means of propulsion to the NEA resources and mine them out, it's actually pretty easy to get them to earth orbit.

[palsch]

Also the Near Earth Asteroid delta-v to earth orbit is about 1 km/s not 5 km/s.  So if you can get your means of propulsion to the NEA resources and mine them out, it's actually pretty easy to get them to earth orbit.

Which is why I've been talking about NEO capture and giving methods...

As for burning asteroid resources to bring them into orbit, it is the only real method I can imagine working. But I don't especially care for it in much the same way I don't care to drop resources into Earth's atmosphere unless we really, really need them. It's taking a resource with some additional value and burning away that value to try to make it more immediately useful. Unless you have an immediate use that makes the result far more valuable into the future than the total burned away I'm not sure it's a good trade. Not to mention you are still dropping resources we could use for further exploration and expansion deeper into a gravity well. Again, not a fan.

In any case, that still runs into the other problems of time delay. Unless you specifically track down an asteroid that has the exact resources needed for a high-impulse rocket you are probably talking about converting part of the material into a solar sail or reaction mass in an ion engine or similar. I'm not sure you could create effective rockets from most worthwhile targets, and the other methods have an extreme time cost associated.

[mainiac]

The "extreme cost" associated with mass accelerators being...?

[palsch]

The "extreme cost" associated with mass accelerators being...?

Mass tradeoff and time of travel. Same as the others.

The are two main options with mass drivers. Either you sacrifice the vast majority of your interesting mass and energy rich material to make a launch platform or you use a smaller fraction of mass as reaction mass during transit, with the driver acting as the engine.

In the latter case things reduce the ion engine problem.

In the former case you are extremely limited in the amount of mass you can send back. I'd actually go with this option if a belt mining operation were established, simply because I'm not interested in sending much back to earth. But for those who want a significant return on a commercial investment you aren't talking about a good option.

And frankly it doesn't change the energetics of the problem at all.

[RedKing]

The early American colonies were a financial disaster for the proprietors too.

True in the sense that this statement is so wrong that it becomes right.  The early american colonies were so profitable that they caused the collapse of the Spanish economy three times because they had too much gold.

We're talking about different colonies (specifically, I was thinking of the early English colonies, most of which either failed spectacularly or kinda limped along for decades before becoming sustainable). Roanoke vanished completely. Jamestown lost 75% of its population in the first 3 years. Plymouth lost half its population in the first six months. The 1500's are littered with failed French and British colonies in the Caribbean. The southern colonies were not initially founded to grow tobacco, but rather to harvest sassafras bark. It was only sheer dumb luck that John Rolfe had brought some tobacco seeds from the Caribbean to Jamestown, and it was only after they tried growing and harvesting tobacco that Jamestown became profitable.

My point being, it may be that asteroid mining won't be profitable for decades, but then somebody will discover that asteroids make great places to do zero-G medicine, or biotech, or high-energy physics, or something else lucrative. But they won't get that far unless a group of investors is willing to take losses early until that pivot point is reached. Governments are too fickle a source of funding. That's why I'm kinda jazzed at the prospect of a bunch of engineers and geeks with loads of money hitching up to this wagon.

I know can determine the elements on the surface of a far-away object by observing the exact wavelength of the light that reflects off of it. There are probably some other methodologies I'm missing as well.

I would've thought that for something as relatively tiny and far away as an asteroid that would be fairly difficult.  And you'd only get the surface, although I guess you could hope it's the same all the way through.

No, we've done it for things as far away as planets orbiting other stars.

We've determined atmospheres. Not crust composition. Atmospheres you can partially determine because of absorption spectra, and some educated guesses based on mass and temperature (which is its own guess based on insolation and distance). But determining the crustal composition is nearly impossible without a direct sample or (as someone suggested) spectrographic analysis of ejecta.

Up close, we could use things like ground-penetrating radar and sonar to get an idea of the mass distribution/density of the rock and make some more educated guesses about what the composition is based on knowledge of geology, but the best bet is still going to be a core sample of some kind.

[mainiac]

The "extreme cost" associated with mass accelerators being...?

Mass tradeoff and time of travel. Same as the others.

The are two main options with mass drivers. Either you sacrifice the vast majority of your interesting mass and energy rich material to make a launch platform or you use a smaller fraction of mass as reaction mass during transit, with the driver acting as the engine.

In the latter case things reduce the ion engine problem.

In the former case you are extremely limited in the amount of mass you can send back. I'd actually go with this option if a belt mining operation were established, simply because I'm not interested in sending much back to earth. But for those who want a significant return on a commercial investment you aren't talking about a good option.

And frankly it doesn't change the energetics of the problem at all.

Yes it does, it eliminates the propellant entirely.

On the asteroid side you use surface launches on two different schedules.  "Direct" launches take months of unpowered flight to get to earth.  "Indirect" launches take more then a year of unpowered flight and balance out the momentum effects of the direct launches.  With careful timing over the orbital period, maintaining orbit would be easy.

On the earth side, you have a capture station that does the same thing in reverse.  It uses minimal amounts of maneuver fuel weeks or months in advance to rendezvous with cargo.  It intercepts this cargo at different times in it's orbital cycle in order to to maintain it's orbit without the use of counteracting propellant.  The cargo is then either used in space or air-braked to earth surface.

Yes it would be insanely uneconomical if you used propellant.  This is why you would never in the love of science seriously consider using propellant.  Stop your earth thinking and start thinking like a spaceman!

[palsch]

On the asteroid side you use surface launches on two different schedules.  "Direct" launches take months of unpowered flight to get to earth.  "Indirect" launches take more then a year of unpowered flight and balance out the momentum effects of the direct launches.  With careful timing over the orbital period, maintaining orbit would be easy.

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?

Yes it would be insanely uneconomical if you used propellant.  This is why you would never in the love of science seriously consider using propellant.  Stop your earth thinking and start thinking like a spaceman!

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