Plans for asteroid mining

Aidyan

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

D H

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

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

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

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

NSTAR Ion Engine - Boeing - 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

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

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.

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

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

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.

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.

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.

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

Not if it as bigger than some specific size.

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

D H

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.


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.


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

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

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.