Can Asteroid Mining Technology Serve as a Global Defense System?

[D H]

A ten mile diameter nickel-iron asteroid has more ore on it than has been mined on Earth in all of history.

The subject of this thread, Planetary Resources, is not talking about mining nickel or iron. Mining nickel or iron simply is not feasible yet, and won't be for a long, long time.

This thread (and this site) is not the place for fanciful scifi dreams.

 

[Ryan_m_b]

This thread (and this site) is not the place for fanciful scifi dreams.

AKA near-verbatim reiterations of the Mars Trilogy

 

[Higgs Boson]

The subject of this thread, Planetary Resources, is not talking about mining nickel or iron. Mining nickel or iron simply is not feasible yet, and won't be for a long, long time.

This thread (and this site) is not the place for fanciful scifi dreams.

Sooooo ... exercising one's imagination is verboten around here, these days, Delta Hotel?

 

[redrum419_7]

Sooooo ... exercising one's imagination is verboten around here, these days, Delta Hotel?

Apparently so.

 

[Ryan_m_b]

Sooooo ... exercising one's imagination is verboten around here, these days, Delta Hotel?

Apparently so.

Of course not, speculation and imagination are welcomed. So long as they stay within the rules. Arch's post would have been acceptable if he backed anything he said up with some actual science to validate his points rather than just wishy-washy SF claims. For example: what are the potential candidates for a space shuttle replacement and is there a business argument for their production? Could a single space tourist module on a small space station pay for the program? What are the energy costs of propelling large fuel tankers to space and how are they suitable for spacecraft construction? etc etc etc.

 

[lpetrich]

Asteroid mining? Seems like a nonstarter. I seriously suspect that there won't be much by way of ore deposits in the asteroid belt, because of the lack of geological activity in most asteroids. To see why, let's review how how ore bodies form. Geologists have now gotten a good understanding of that, and we can use that understanding to see what one can expect of elsewhere.

Ore genesis - Wikipedia
Processes of Ore Formation

• Fractional crystallization of magma bodies.
• Sorting of immiscible components of magma bodies.
• Hydrothermal processes: water dissolving some minerals in hotter rocks and those minerals precipitating out in cooler rocks.
• Diffusion of minerals into cracks and the like ("lateral secretion").
• Precipitation from bodies of water, like salt being left behind when water evaporates.
• Mechanical sorting.
• Being left behind by other materials getting leached away by water flowing through.
• Release by volcanoes.

Most of these processes require liquid water, and only the Earth and Mars have such processes near their surfaces. There is even some evidence of such processes on Mars, in the form of evidence of carbonates and sulfates.

So we are stuck with igneous processes, rock melting. By the square-cube law, only a relatively large object can have such processes, so have any asteroids had them? The evidence, surprisingly, is yes. Certain meteorites, the "HED meteorites", have spectra similar to Vesta's surface, meaning that they likely came from Vesta.


So the smaller asteroids are unlikely to contain useful ores, except perhaps if they are fragments of some larger one that had had magma differentiation.


One could get the rarer elements by chewing through large quantities of asteroid, but it would be cheaper to do that with Earth rocks or seawater. But there *might* be some elements where mining asteroids might be worthwhile: the rarer "siderophiles". These are elements with a chemical affinity for iron, like gold and the platinum-group elements. The Earth's crust is depleted in them relative to stony and especially to iron asteroids, so one could mine gold by chewing through some iron asteroids.
Goldschmidt classification - Wikipedia
Mineralogy Notes 3
Abundances of the elements 3.1.3

 

[Aidyan]

But would it not be less costly to mine a very small asteroid (say only few dozens of meters wide) ON Earth than mining it in space? One has to de-orbit it, splash it into the ocean and retrive it. Then we can mine it easily at home. Obviously safety is the big issue here, if it wrongly hits a city it is a disaster. But I think atmospheric reentry is a complex but not impossible science.

 

[D H]

But would it not be less costly to mine a very small asteroid (say only few dozens of meters wide) ON Earth than mining it in space? One has to de-orbit it, splash it into the ocean and retrive it.

No. Nobody sane is discussing the concept of de-orbiting an asteroid. Think about it.

 

[SHISHKABOB]

basically: you'd need A LOT of energy to take something going many km/s and slow it down to zero along with the energy needed to compensate for gravitational potential energy

it'd be silly

 

[thorium1010]

No. Nobody sane is discussing the concept of de-orbiting an asteroid. Think about it.

It maybe a silly/insane question .why is it impossible to bring small asteroids back to earth?
would it destabilise the asteroid belt or we cannot control the velocity it enters Earth's atmosphere. Or the energy required is too great for it to viable.

 

[SHISHKABOB]

It maybe a silly/insane question .why is it impossible to bring small asteroids back to earth?
would it destabilise the asteroid belt or we cannot control the velocity it enters Earth's atmosphere. Or the energy required is too great for it to viable.

it's because you're talking about taking a GIGANTIC ROCK from *space* to the *ground* without it just crashing and blowing some stuff up

we don't even have our spacecraft re-enter the atmosphere at slow speeds. How do you suggest we give an asteroid a "soft landing"? It's a totally unpractical idea.

also: no it wouldn't destabilize the asteroid belt, the only thing stabilizing the asteroid belt is the sun

 

[lpetrich]

It's possible to work out the numbers -- soft-landing an asteroid is TOTALLY impractical. Let's see what one needs to do.

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This asteroid will be accelerated by the Earth's gravity, and when it reaches the Earth's atmosphere, it will be traveling at a little over the Earth's escape velocity, about 11.2 km/s. How much propellant will one need to consume to soft-land it?

Over a century ago, Konstantin Tsiolkovsky showed how to find how much. His rocket equation, for initial mass m_i, final mass m_f, effective exhaust velocity v_e, and velocity change v:

v = v_e * log(m_i/m_f)

Relation to specific impulse: v_e = I_sp*g_E, where I_sp is the specific impulse, and g_E is the acceleration of the Earth's gravity at its surface, about 9.81 m/s^2.

So to avoid consuming much more propellant than asteroid, the rocket must have an exhaust velocity more than the Earht's escape velocity.

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The asteroid must be supported by the rocket engines as it makes its landing. That requires that the thrust be greater than (asteroid mass)*g_E.

So for a thousand-ton asteroid, that requires a thrust of a million kilograms-force or 10 million Newtons. Bigger asteroids require more thrust, of course. I won't get into English-system mass and force units.

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So let's see what's available. Spacecraft propulsion - Wikipedia has a big compendium of numbers in its "Propulsion methods" table, and Wikipedia's articles on various rocket engines often list the engines' numbers.

The highest-thrust engines that have been successfully run are chemical-combustion ones, at 1 to 2 million Newtons, and hydrogen-oxygen ones can get about 4.5 km/s of exhaust velocity. Ones with non-cryogenic propellants can get as much as 3 km/s. Because of the nature of their energy sources, it's difficult to get much more exhaust velocity than that.

So they are unsuitable.

One can get more energy per unit mass with nuclear reactions, and thus greater exhaust velocity, but there are problems here also. A nuclear reactor heating hydrogen can get around 9 km/s or thereabouts, which is still too low to be suitable. It cannot get much more than that without melting the reactor. Nuclear-bomb propulsion can get greater exhaust velocity, but it has certain other problems. Inertial confinement fusion would also get high exhaust velocity, but that mechanism has yet to produce energy breakeven in the lab.

So they are unsuitable also.

In contrast to these thermal systems, there are various nonthermal propulsion systems, like ion engines, that are in various stages of development. The Dawn spacecraft , currently at Vesta, has 3 ion engines, each with exhaust velocity 30 km/s and thrust 0.09 Newtons. Most other nonthermal engines have similarly low thrust.

These are still more unsuitable ones.

So there's no way that soft landing an asteroid is going to work.

 

[Higgs Boson]

So there's no way that soft landing an asteroid is going to work.

Unless someone engineers a really big catcher's mitt.

(Sorry, had to throw a little humor in there.)

Seriously though, from what I have read it appears to me, (and this remains no less feasible imho), that their intention is to manipulate said asteroid into some sort of orbit where it may be mined in space.

It is pie in the sky scifi though, I agree.

 

[Antiphon]

It will take a Dutch metallurgical genius to solve this problem. Someone who loves goooooold.

 

[Aidyan]

Why making things complicate? De-orbit slightly a NEO asteroid between the Earth and the Sun so that it takes the path towards Venus (not much thrust needed for that), 'aereobrake' it in Venus' atmosphere such that inserts itself into a synchronous orbit with the Earth + a component for Venus-Earth orbit transferal, and then, once it reaches Earth (at zero orbital velocity) let the thing simply fall freely and splash somewhere in a safe place in the ocean. It would be something like a Tunguska event, but at thousands of miles away from any inhabitated region. Maybe there is a problem with a Tsunami wave, but I think that if the asteroid is not too big, it will not harm. So, why not?

 

[SHISHKABOB]

Why making things complicate? De-orbit slightly a NEO asteroid between the Earth and the Sun so that it takes the path towards Venus (not much thrust needed for that), 'aereobrake' it in Venus' atmosphere such that inserts itself into a synchronous orbit with the Earth + a component for Venus-Earth orbit transferal, and then, once it reaches Earth (at zero orbital velocity) let the thing simply fall freely and splash somewhere in a safe place in the ocean. It would be something like a Tunguska event, but at thousands of miles away from any inhabitated region. Maybe there is a problem with a Tsunami wave, but I think that if the asteroid is not too big, it will not harm. So, why not?

remind me of how much asteroid was left after the Tunguska event

 

[Aidyan]

remind me of how much asteroid was left after the Tunguska event

It was too small. Choose an asteroid with the right size.

 

[D H]

Why making things complicate? De-orbit slightly a NEO asteroid between the Earth and the Sun so that it takes the path towards Venus (not much thrust needed for that),

Do the math. A lot of thrust is needed for that.

'aereobrake' it in Venus' atmosphere such that inserts itself into a synchronous orbit with the Earth + a component for Venus-Earth orbit transferal, and then, once it reaches Earth (at zero orbital velocity)

Zero orbital velocity? Try again. That meteor will hit the Earth's atmosphere with a speed of 13.7 kilometers per second.

let the thing simply fall freely and splash somewhere in a safe place in the ocean. It would be something like a Tunguska event, but at thousands of miles away from any inhabitated region. Maybe there is a problem with a Tsunami wave, but I think that if the asteroid is not too big, it will not harm. So, why not?

Maybe? There is a huge problem with a tsunami. There is also a huge problem with the asteroid breaking up in the atmosphere. If the asteroid is 100% gold, that breakup is definitely not a desirable outcome. There is also a huge problem with the impact. Water is downright solid to an object hitting it at 13+ km/s. Whatever is left of the asteroid after the atmospheric breakup will most likely vaporize.

If the asteroid is iron/nickel there isn't enough value to pay back the huge cost of your maneuvers. Iron and nickel are too cheap. You need something extremely valuable to justify bringing the outputs of space mining down to Earth. Even gold and platinum are dubious. If this is done, it won't be accomplished by splashing the asteroid in the ocean. It will be accomplished instead by mining the asteroid in space and carrying the precious cargo as payload in a vehicle designed for re-entry.

There is potential future value in iron/nickel asteroids, but that value would be realized by mining the asteroid in space and utilizing the resultant resources in space. That requires an in-space manufacturing capability. This might happen eventually, but that is not the subject of this thread.

 

[SHISHKABOB]

It was too small. Choose an asteroid with the right size.

bigger asteroid means bigger impact event

we don't want big impact events

 

[lpetrich]

One can make a best-case estimate for a rocket engine's acceleration by dividing its thrust by its mass. I'll call it the engine's self-acceleration. Let's do so for some rocket engines.

Space Shuttle Main Engine - Wikipedia
Combustion engine: hydrogen and oxygen
Mass = 3.5 metric tons
Thrust = 2.279*10⁶ Newtons
EEV = 4.437 km/s
Self-acceleration = 650 m/s = 66 g_E
Good thrust, bad EEV

http://www.boeing.com/defense-space/space/bss/factsheets/xips/nstar/ionengine.html - used in the Dawn spacecraft
Electrostatic ion engine: xenon
Mass = 8 kg
Thrust = 0.092 Newtons
EEV = 30 km/s
Self-acceleration = 0.012 m/s = 0.0012 g_E
Good EEV, bad thrust

EEV = Effective Exhaust Velocity

 

[twofish-quant]

Is it worth spending billions for some technology for deep mining in space.

A billion dollars isn't that much money. Oil and mining companies *routinely* spend billions on Earth based mining. A deep sea oil platform in the Gulf of Mexico has a total investment of a billion dollars.

The problem with asteroid mining isn't the total cost. It's the technology uncertainty. Oil companies are willing to spend one billion on Earth because the costs, returns, and risks are predictable.

Also, the article talks about "millions". In this sort of thing, several million dollars is pocket change.

 

[twofish-quant]

Many of the investors in this project are not looking for an ROI in the next few decades.

Or no ROI at all.

And they are talking about pocket change. The amounts of money they are talking about will get you a nice apartment in NYC or a luxury yacht. Several tens of millions of dollars is cheap enough so that there are people that will do stuff for the hell of it.

Which is good for astrophysicists, since telescopes get funded this way. Mauna Kea cost about $1 billion which came from private donors.

All of these people have a history of spending huge amounts of money on things they think are exciting, beneficial for humanity/science, and/or have a small chance of paying off huge in the long run.

Anything less than a billion, and it's pocket change. We aren't talking about huge sums of money.

However, there are other rare minerals that can be mined as well. It may be possible to produce net profit without flooding any particular market, especially when combined with the sale of water and other chemicals to other space programs.

Or it could be a total financial disaster. Many of the early efforts at making money in the New World turned out to be financial bombs, but it didn't matter. If they get space infrastructure going to do asteroid mining, and then it turns out that it's a financial bomb, that infrastructure is still there and could be used for other things.

My big concern is that several million isn't enough, but if they can get things to the point where it costs *only* say $10 million to send a probe to an NEO asteroid, that would be revolutionary. If it costs *only* $10 million to send a robot to NEO asteroid, then you can do stuff like shoot science fiction movies *on location*, since the budget for a Hollywood blockbuster is $100 million.

 

[Aidyan]

Do the math. A lot of thrust is needed for that.

There are lots of NVOs (Near Venus Objects), a de-orbiting of few hundreds of m/s are sufficient. The difficult part is not the energy, but the aero-braking math.

Zero orbital velocity? Try again. That meteor will hit the Earth's atmosphere with a speed of 13.7 kilometers per second.

In co-orbital configuration (Earth and asteroid moving in parallel on the same orbit). What you probably mean is the Earth's escape velocity (11.2 km/s). But it can be reduced to an equivalent free fall from about say 50 km height by adequate atmospheric entry angle, speed and aero-braking. Should not be much more than few hundreds of km/h of terminal velocity.

Maybe? There is a huge problem with a tsunami.

Did you do the math? An object of about 500 tons falling in the ocean does not create giant Tsunami wave if it falls with moderate speeds.

There is also a huge problem with the asteroid breaking up in the atmosphere. If the asteroid is 100% gold, that breakup is definitely not a desirable outcome.

Ok, this is the only good point I could see so far that could possibly invalidate the theory...

Whatever is left of the asteroid after the atmospheric breakup will most likely vaporize.

Not if it as bigger than some specific size.

If the asteroid is iron/nickel there isn't enough value to pay back the huge cost of your maneuvers. Iron and nickel are too cheap. You need something extremely valuable to justify bringing the outputs of space mining down to Earth. Even gold and platinum are dubious. If this is done, it won't be accomplished by splashing the asteroid in the ocean. It will be accomplished instead by mining the asteroid in space and carrying the precious cargo as payload in a vehicle designed for re-entry. There is potential future value in iron/nickel asteroids, but that value would be realized by mining the asteroid in space and utilizing the resultant resources in space. That requires an in-space manufacturing capability. This might happen eventually, but that is not the subject of this thread.

And this should be considered a 'cheap' option? It is much more expensive to develop such technology than splashing.

 

[D H]

There are lots of NVOs (Near Venus Objects), a de-orbiting of few hundreds of m/s are sufficient.

Baloney. Name one. Keep in mind that asteroid orbits tend to have significant eccentricity (changing the shape of an orbit is expensive) and significant inclination with respect to the invariant plane (plane changes are extremely expensive). With this in mind, try to find one near Venus object whose orbital velocity vector with respect to the Sun is within a few hundred m/s of that of Venus.

In co-orbital configuration (Earth and asteroid moving in parallel on the same orbit). What you probably mean is the Earth's escape velocity (11.2 km/s). But it can be reduced to an equivalent free fall from about say 50 km height by adequate atmospheric entry angle, speed and aero-braking. Should not be much more than few hundreds of km/h of terminal velocity.

Nonsense. Of course I'm talking about Earth's escape velocity. That plus the 2.3 to 2.7 km/s v_∞ (typical value: 2.5 km/s) with your asteroid's Venus to Earth transit orbit and you get 13.7 km/s. There is no escaping this without the use of thrusters.

Did you do the math? An object of about 500 tons falling in the ocean does not create giant Tsunami wave if it falls with moderate speeds.

An object of 500 tons will not hit the Earth at moderate speeds. There's one exception, which is that the asteroid does a skip re-entry. This is just about the only explanation for the Hoba meteorite's lack of a crater. NASA has had contingency plans for a single skip reentry. These were never used because even a single skip is just too touchy -- and that's for a vehicle with well-known aerodynamics. To have an asteroid hit the Earth at terminal velocity as opposed to a hyperbolic velocity would require multiple skips. There is no telling whether it would work, and if it did work, where it would hit. Think back to the reentries of Phobos-Grunt and UARS. There was no telling where they were going to hit, right up to their final orbits. You want to hit a precise spot, and that means coming in hot and heavy. The notion is ludicrous.

 

[lpetrich]

From conservation of energy,

v_arrival = sqrt(v_escape² + v_{interplanetary}²)

So even if the asteroid is moving in nearly the same orbit as the Earth's, it will crash down at great speed -- v_escape ~ 11.2 km/s.

One could get it into Earth orbit and gradually lower it, and try for a soft landing that way. But even then, it'll likely crash into the Earth's surface at close to low-Earth-orbit velocity, about 7.9 km/s.

 

[HopDavid]

The initial goal isn't landing platinum on Earth's surface.

Rather, parking a propellant source high on the slopes of Earth's gravity well.

The forum's not letting me post a link. Google: kiss caltech asteroid_final_report

 

[HopDavid]

From conservation of energy,

v_arrival = sqrt(v_escape² + v_{interplanetary}²)

So even if the asteroid is moving in nearly the same orbit as the Earth's, it will crash down at great speed -- v_escape ~ 11.2 km/s.

One could get it into Earth orbit and gradually lower it, and try for a soft landing that way. But even then, it'll likely crash into the Earth's surface at close to low-Earth-orbit velocity, about 7.9 km/s.

Using 3 body mechanics, there are some bodies that can be captured at EML1 or 2 with relatively small delta V.

From EML1 a .7 km/s acceleration suffices to drop the perigee into Earth's upper atmosphere. Once this is accomplished, each perigee pass through the upper atmosphere sheds a little velocity. Thus circular low Earth orbit can be accomplished with relatively little reaction mass.

Low Earth orbit is about 7.9 km/s as you say. But this doesn't mean the object would hit the Earth's surface at 7.9 km/s. You have to take into account ballistic coefficient which includes, among other things, ratio of object's mass to cross sectional surface area.

 

[lpetrich]

There is a certain problem with aerobraking: the square-cube law.

(acceleration) ~ (force)/(mass) ~ (area)/(volume) ~ 1/(size)

This explains why large objects reach the Earth's surface while small objects burn up in the upper atmosphere.

 

[HopDavid]

There is a certain problem with aerobraking: the square-cube law.

(acceleration) ~ (force)/(mass) ~ (area)/(volume) ~ 1/(size)

This explains why large objects reach the Earth's surface while small objects burn up in the upper atmosphere.

If you're arguing against soft landing kilometer sized asteroids, this argument's valid. But that's not what Space Resources is suggesting.

Again, nobody seems to have done much research. The KISS paper proposes returning ~7 meter rocks and parking in high lunar orbit.

For two reasons:

1) Parking rocks this size at EML1 is doable.
2) It's much safer. 300,000 kilometers is fairly distant from Earth's surface so an accidental impact is unlikely. In the unlikely event of such an impact, a 7 meter rock would burn up in the upper atmosphere.

 

[alensmith4]

Asteroid mining could result in costs so high that it would be better to find those elements the other way.

 

[negativzero]

Regardless of whether the industry paid off initially, the technology required for mining would provide the requisite super-structure for a world-wide asteroid defense. Protection needs to be in situ. Trajectories of known asteroids are difficult to predict with precision, and "new" asteroids can pop up.
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It would be foresighted to practice various means of moving asteroids around too.
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On the subject of both, i suggest a version of Clarke's elevator could be used. Most asteroids spin. That spin could be used with an elevator, perhaps a cable or cable on a tower, to launch ore projectiles beyond escape velocity.
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i'm dubious how much such a technique could deflect the orbit though. Because it seems like the launches would use up the spin rather than the velocity. i guess the average distribution of ore on the cable might shift the center of gravity a little. i can't figure out how much the orbit would change as a result of using an elevator as a mass thrower. The overall effect would look kind of like a bolo lasso. The more massive and longer the cable is, the more complicated the whole thing would be. It boggles. Yet if all that changes is the rate of rotation and the mass, the orbit should be substantially the same, assuming the center of gravity doesn't move around.
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i assume every asteroid will be unique, in orbit, size, composition, spin, and that a panoply of techniques will be needed to deflect any dangerous examples.
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A world-wide subsidization would be necessary to seriously fund asteroid defense. The world should be happy to survive if mining even brings back a fraction of the initial investment because the alternative is unacceptable.