# Bringing iron asteroids down to Earth?

1. Sep 20, 2010

### rrw4rusty

Hi,

I'm writing a science fiction story and in the future we are having to bring iron asteroids down to Earth. These asteroids are 1 to 3 miles in diameter and shaped charges brake up the asteroid and push it down into the atmosphere in such a way that the house size chunks land in an unpopulated area.

But... will they burn up in the atmosphere? I know natural ones do but these are traveling at great velocities. How could I bring iron asteroid material down to Earth in such a way that there's enough left to make it worth the effort?

Is there a better forum or place to ask this?

Thanks,
Rusty

2. Sep 20, 2010

### DaveC426913

Asteroids that large will not burn up so much as they will tend to explode.

3. Sep 20, 2010

### BobG

Here's a link to a book that discusses it. A portion of the book is available for viewing on line.

Dynamics of Atmospheric Reentry

Nickel-iron meteorites surviving reentry are fairly common. However, slowing it down and controlling where it lands is a problem. You could slow it down enough to orbit the Earth (vs a high speed hyperbolic orbit). Any decreases beyond that lower the satellite's altitude and, as the altitude decreases, the atmosphere becomes thicker and the satellite will continue to decelerate and lose altitude, but will still reenter the atmosphere at a pretty high rate of speed.

You won't have any fine control of where a rock with an uneven surface will land. In fact, there's no fine control of where most satellites will land when they reenter the atmosphere, since they're designed to live in space, not reenter the atmosphere (in fact, almost all of a satellite burns up in the atmosphere - spherical titanium fuel tanks, however, seem to survive reentry quite well). When satellites are deorbited at the end of their life, the operators aim for big targets, such as the Pacific Ocean.

Without a shape specifically designed for reentry, the best you'll be able to hope for is to aim for a continent with very few inhabitants and then search the continent for your 'meteorite'. Monitoring the rock before reentry and the telltale streak of a flaming rock falling from the sky makes it something that's at least possible, but it will still entail a large overhead for operations - especially for insurance to cover the rare few that land in a city instead of a remote area.

In addition to the linked book, check out how hard it was to solve the controlled reentry problem during the early days of the space age. For the US's first reconnaissance satellites, it wasn't until the 13th try that they got one to land close enough to it's target for it to be recovered. (The recovery of the film cannisters is a pretty interesting operation in itself, as they used to be snatched out of the sky as they fell by a C-119 airplane. It would be so cool to tell people your job was flying around in a plane and catching objects falling from outer space.)

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4. Sep 20, 2010

### DaveC426913

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5. Sep 20, 2010

### Max™

6. Sep 20, 2010

### DaveC426913

7. Sep 20, 2010

### Office_Shredder

Staff Emeritus
Launching something into space and landing something from space are not equivalent problems Max

I'm envisioning a magnet based system... the asteroid is magnetized in space, and then magnets are used to push it around to control/slow its descent. Unfortunately any plane with a magnet attached flying close enough to actually push the asteroid would have to have a hell of an engine to get close enough (equal force against the plane, which pales in comparison in terms of mass)

8. Sep 20, 2010

### Max™

Pretty sure you could bring something in on a suitable trajectory to dock with a launch loop/follow it down.

Remember, this thing would be 50 miles up, damn near halfway to the lowest space shuttle orbit, and with enough accelerative ability to toss payloads into those orbits, or receive them.

More importantly, you could get the processing equipment needed to actually work with asteroids in space up with a loop, and land craft with just processed material as needed.

Think it would be wonderful for more sci fi stories and whatnot to mention them instead of dweeby elevator ideas, maybe even shape some future policy makers towards an achievable real world launch system.

9. Sep 20, 2010

### rolerbe

Rusty,

Since it's SF, perhaps you can also use the notion of a space elevator (look it up in Wiki). Manuever the asteroid into geosync orbit, match positions to the nearest space elevator, chunk it up to suitable sizes in space, haul it down the elevator.

Not a crazy notion if you have very high tensile strength wires like (non-existant) nano-fibers.

Good luck with the story.

10. Sep 20, 2010

### Max™

*screams*

That is exactly what I was trying to avoid, by suggesting a realistic alternative.

We could build a launch loop with real world materials (check out the site, about $2 billion from estimates), we will need magical fairies spewing unobtainium to build an elevator. 11. Sep 20, 2010 ### Evo ### Staff: Mentor In the sci-fi books I've read, they carry out mining of the asteroid itself, while it's in space. I wonder which would be more realistic, mining in space or bringing them to the ground on earth? What would be the difference in getting one to the surface of the moon for mining, then bringing the smaller fragments of ore to earth? In case it's not already obvious, I have no clue about this stuff, but I like science fiction. Last edited: Sep 20, 2010 12. Sep 20, 2010 ### JaredJames Or take the Red Dwarf style approach and build a mining ship which processes asteroids. (I think it took them in through the front) 13. Sep 20, 2010 ### BobG I agree that there would be huge problems with a space elevator. It's a great idea in theory (a perfectly spherical Earth, no wind or other stresses, a way to make a cable thousands of kilometers in length while still being stronger than any in existence, plus an incredibly cheap energy source). Your solution has the same problems. For one, I think your loop would have to be at least twice as high. It has to intersect the orbit of the asteroid before the atmosphere is causing heating and perturbations to the orbit of the asteroid. The asteroid has to be traveling at an orbital speed (approximately 7800 meter/sec at a heighth of 200 km). The vehicle in your launch loop has to accelerate to match the asteroids orbital speed in order to catch it, and then your vehicle has to slow down without burning up. I can understand how a 'cable' moving 14,000 meters/sec can accelerate the catch vehicle, but I don't see how the vehicle is going to slow down. There's a reason it's called a launch loop. The disadvantage of breaking up the asteroid in space is that you have to launch vehicles into space to catch the pieces and bring them down. That's an awful lot of launches with an awful lot of fuel or a few launches with really big spacecraft and an awful lot of fuel. Or, if the launch loop lowers the launch cost enough, break up the asteroid and the launch loop launches the spacecraft that will bring the asteroids to Earth. The key to all solutions is that the fuel used for any solution costs less than the iron that burns up in the atmosphere (keeping in mind the free reentry solution has that pesky problem of unpredictability that has to be overcome). Planing and shaping the asteroid to form a nice balanced shape with a bottom shaped like a space capsule and coating it with something similar to the tiles on the space shuttle would provide some possibility, with the difficulty that all of this would have to be done on an asteroid orbiting the Earth. I'm not sure that would be a cheaper option than just breaking the asteroid up and shipping it down in spacecraft if the launches are cheap, but at least it offers a cool job (asteroid sculpting) and offers some drama with the occasional reentry malfunction that takes out a city (if you want them to make a movie from your book, then I think taking out a city is essential). Last edited: Sep 20, 2010 14. Sep 20, 2010 ### DaveC426913 Funny that you disparage elevators. Contary to this launch sytem, which requires a vast energy source, space elevators are basically free energy-wise. And they work both ways up and down. 15. Sep 20, 2010 ### JaredJames Out of curiosity, are there really that many asteroids that could be broken down into chunks the size of houses coming within a reasonable range to earth? (At least so far as being able to make a business out of it goes.) Would it not just be easier to send something to Mars and mine that? (I'm not trying to change your story, I'm just curious about the asteroid count.) 16. Sep 20, 2010 ### Office_Shredder Staff Emeritus I like Evo's idea. Crash the asteroid into the moon and pick up the pieces at your leisure. I only wonder if there's potential for destroying all life by knocking the moon out of orbit (speaking of a movie idea: They have 72 hours to stop the moon from crashing into the planet! .... oh, that's been done already?) 17. Sep 20, 2010 ### BobG Really?! What movie was that? (I want to see it! I don't care if it is a stupid premise!) How about if we just knock it into an elliptical orbit that comes closer to the Earth, providing us with some awesome waves for surfing! I want to see Annette Funicello in a sci fi movie! 18. Sep 20, 2010 ### BobG Really big asteroids are rare. However we just had a couple in the 20 to 65 meter size pass close by earlier this month (Sep 9). Apophis, a 350 meter asteroid, passes close by about every 7 years. Apophis would definitely have to be broken up and brought in in several smaller pieces. It's real hard to find a good landing spot for a 350 meter asteroid. There is no accurate count of how many asteroids come close to the Earth, seeing as we haven't been tracking them for very long. Near Earth Asteroid Discoveries 19. Sep 20, 2010 ### Office_Shredder Staff Emeritus Well, it wasn't a movie per se. The video game Majora's Mask was based on the premise of the moon hitting the planet 20. Sep 20, 2010 ### Evo ### Staff: Mentor I will go on record as saying that the moon hitting the earth would be bad. 21. Sep 20, 2010 ### DaveC426913 Citations? 22. Sep 20, 2010 ### JaredJames I agree with Dave, I can foresee there being some minor issues, but without a full scale government funded study into the matter I would be hesitant to comment on the 'major' issues that such an event may or may not cause! 23. Sep 21, 2010 ### Max™ http://launchloop.com/slides/launchloop.pdf Includes a breakdown of materials based on current prices, something like$540 million (page 37/40 of the pdf), with the \$2 billion number listed below as a ballpark for the first one + research costs.
http://ap1000.westinghousenuclear.com/index.html [Broken]

These aren't exactly absurd energy requirements, and an elevator would still require energy for the payload climbers.

An elevator also requires advances in material sciences beyond what we currently have available, while a launch loop does not.

You could bring something down to meet the loop and let it brake by accelerating the rotors in the loop directly, then haul it down to a base station as usual.

It is of course quite a bit easier to get down into a gravity well than to leave one, but that is why the effort should be devoted to more effective methods of going up, isn't it?

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24. Sep 21, 2010

### DaveC426913

You miss the point. Construction is a one-time cost. It's the operating costs that add up.

Yes, which makes one wonder why you would turn your nose up at the opportunity to go up basically "for free".

25. Sep 21, 2010

### rolerbe

Well, at the risk of more *screams*, another (future, SF) thought would be to machine the incoming asteroid into (one or more) lifting bodies. Yes, they're heavy and dense (or they're not worth much), but consider the recent space shuttle -- really very small wing area, and you would not have to have even that much lift for an unmanned body.

So, assume elliptical asteroid. Split in half to have reasonably smooth underbody. Carve away some of the upper edges to create stubby winglets. Attach computer controls (or even real pilots for dramatic potential), and some pretty modest reaction jets, and 'fly' (as in controlled crash) the thing down. Pilots guide to selected impact area and jettison just before crashdown.

I won't do the calculations of required lift, etc., but might be worth an hour or two of the OP's time.