soft landiing an asteroid at the south pole

khoopes01

can a small nickel/iron asteroid brought near Earth (matching its solar orbital velocity) and soft landed at the south pole where Earth's rotation is not an issue?

Ryan_m_b

The Earth's rotation is not an issue, the Earth's gravity is. Because of that anything that's near enough to feel its gravitational pull is going to plummet down. Considering the south pole is where so much water is kept I doubt dropping an asteroid at terminal velocity on it would do us any favours.

Lsos

Unless you hold it back somehow, that asteroid will be going at least 11km/s by the time it gets near the earth. Earth's rotation or not, that's going to do some damage.

khoopes01

ok - so the asteroid free falls to its terminal velocity - remember, it is not in orbit but starting from rest. Could a system of parachutes slow it down enough to let it crash land (remember, we don't care if it is damaged.) 100 meters/sec would not do much damage on the south pole.

Ryan_m_b

You might as well consider the whole thing a giant parachute. As it falls it is encountering resistance from the atmosphere across the entirety of its surface but that would not be enough by far to slow down an asteroid. It would hit the south pole at many kilometres per second. Also I would contend with your point that damage isn't an issue, Antarctica constitutes some 70% of the worlds fresh water. We'd hardly want to heat that and start dumping it into the sea.

khoopes01

The asteroid in question is not an ELE sized rock but a carefully selected nickel/iron
asteroid as big as a house. Since it is starting from rest and not going 17,000 mph,
the use of steerable parachutes is feasible. Remember, Antarctica is a continent so
there is lots of places to land. A house sized asteroid (15 by 15 by 15 or 1000 cubic
meters would weigh 3375 *(450 lbs/cubic foot) = 1518750 pounds. Now that's a lot,
but multiple drogue parachutes could probably slow its descent. If not, we would select a smaller asteroid, or use solid rocket motors to slow it down.
An Asteroid One one tenth that size weighing 700,000 pounds would be worth 700,000*5.00/lb
=3,500,000 dollars (that buys a LOT of parachutes)

Ryan_m_b

Ok, if you are proposing an asteroid that small there are a few more considerations;

• How are you going to attach parachutes to this asteroid?
• How are you going to manoeuvre this asteroid to Earth?
• If you are going to slow it down that much and it is that small do you really need to do it on Antarctica?
• How much is all this going to cost?

Regarding the cost assuming this 1000cm3 asteroid was a 1:1 mix of nickel and iron that gives you 4451 tonnes of nickel and 3935 tonnes of iron. That gives a value of $90,043,730* for the nickel and $461,536.15** for the iron. Do you think that all of this could be done (that's the technology both developed and implemented) in an economically viable way?

* Value of iron in dollars per tonne (times the amounts worked out)
** Value of nickel in dollars per tonne (times the amounts worked out)

gregtomko

Just as a ballpark figure, on the Kennedy Space Center's FAQ section, they say it costs $450 million for a space shuttle mission. You would need a pretty big asteroid to cover that.

Lsos

If an object from space is accelerated towards the earth by earth's gravity, it will be moving AT LEAST 11km/s by the time it hits the atmosphere and you have any hope or slowing it aerodynamically. This is also earth's escape velocity. So, "starting from rest" means starting from 11km/s. Assuming that the asteroid in not just chilling parked there in space, then this value will be higher.

khoopes01

Assuming we can land it without burning it up, it is still an immense undertaking. I think the
following steps would be required:
- getting the stuff for the 'asteroid mission' up there at a minimum cost. Perhaps an
air breathing, tail first reusable craft to get the stuff into low Earth orbit.
- Can we use solar sails to get a robot to the asteroid belt to find 'candidates' of
the right size and composition?
- Before going further, the candidate will have to have steering rockets at the end of tow
cables installed as well as hooks for sails and parachutes.
- Can we sling shot the asteroid around Jupiter under sail to direct it back to Earth

All in all a very expensive mission (especially the first one.) It also may be possible to impact the asteroid on the moon and send the cut up pieces back to earth by solar powered linear accelerators. Those asteroids could be big enough to be economically more feasible.

Ryan_m_b

That's a big assumption depending on the asteroid.
Big undertaking. But if we assume something like Skylon succeeds then we're looking at a cost of ~600,000 dollars per tonne to launch to LEO with a 15 tonne payload per launch. From then on you're probably going to need something like an ion drive or VASIMR to launch equipment around the solar system.
I don't think solar sails would be good enough. It would need some sort of propulsion.
If you want to land it you're going to need more than that! You'll need to attach significant rockets and fuel (probably more massive than the asteroid itself) to land it safely. Remember you are talking about shunting around kilo-megatonnes of mass!
Er...maybe. Depends where it is.
I don't see why impacting the moon and shooting smaller chunks to Earth would be desirable as you still have the problem of how fast they are going.

This really does seem horrifically expensive. This plan sounds like it would cost 10s-100s of billions for R&D and running costs! That means that for the 1000m3 asteroid you suggested before the amount of money you would get from the sale would be ~0.001% of the cost of getting it.

All in all this seems like far too much effort for little benefit. Apart from the fact that the back-of-the-envelope value I gave above as to how much you could sell an asteroid for injecting so many resources into the world economy would significantly reduce the value. Supply and demand, if you get a huge asteroid of iron the cost of iron will plummet. You might as well spend that 10s-100s of billions on new mines, recycling technologies and re-designing products to run without costly/scarce resources.

The only way I can see this as being a good idea was if the mining were as a by product of another project. For example, we knock a couple of asteroids into orbit to construct a space elevator.

D H

Nonsense, for several reasons.

1. "Since it is starting from rest and not going 17,000 mph" is just wrong. 17,000 mph is the minimum speed at which your object will the atmosphere.
2. "the use of steerable parachutes is feasible" is just wrong, too. One reason is that you are facing a cube-square law problem here. Chutes don't scale up to handle large objects. The 12 foot long ants in the movie Them! are physically impossible thanks to the cube-square law, as are parachutes to slow a house-sized asteroid.
3. Another problem with using parachutes is that a solid metal, house-sized asteroid will never fall below the speed of sound. (The cube-square law comes into play here, also). Parachutes don't work above the speed of sound; you'll never be able to deploy the chutes.
4. Drogue chutes don't do very much. They aren't steerable and they only slow the reentering vehicle a bit. Drogue chutes are used for one reason only: To slow the reentering vehicle just enough so that the main chutes can be deployed without tearing themselves to shreds. That nasty cube-square law comes into play here as well. Drogue chutes on a solid metal, house-sized asteroid will only slow the asteroid by a tiny smidge. They will never slow the vehicle down enough to enable deploy main chutes (and you can't use drogue chutes because of reason #3).

Which is it? 15 meters × 15 meters × 15 meters, or 1000 m³? Do your math right! Fortunately, Ryan did your math right for you in post #7.


Space mining might eventually become a going venture, but never for something as common as iron, or even something like nickel which is about 20 times less common than iron (and hence about 20 times more expensive). It might be worthwhile for those common elements if the mined material is used to manufacture items in space, never bring them back to Earth. Mining things in space and bringing the refined material back to Earth might be worthwhile, but only for substances such as gold, iridium, and tritium that are several orders of magnitude more valuable than iron and nickel. And then it will be treated as the precious (and small) cargo that it is. It will not be dropped like a rock on Antarctica.

khoopes01

First, I would like to thank everybody on this thread for their input. I think we can put the Earth landing to rest as being impractical. However, there are 3 more logical targets out there - the moon, Mars, and Earth orbit where the nickel and iron would be very valuable. Someone is already thinking of mining lunar water and selling it in low Earth orbit (Shakleton mission.) So getting materials for space exploration from non-terrestrial sources is a very practical mission.

Ryan_m_b

I really don't see how any of that is economically viable. The sheer cost of the project would outweigh any gains. Think of it this way, every billion spent on pulling a few tonnes in space is a billion that could be spent on efforts on Earth prospecting/mining new deposits, recycling old materials and redesigning systems to run with less.

As for the moon water thing that leaves me gobsmacked. There is no way that regular Earth-to-Moon and back again mass transport as well as water mining in what is essentially a desert would be cheaper than a desalination station on the coast.

D H

You're missing the point, Ryan. Raw materials mined in space could eventually become very valuable in space if that material is refined in space and then used in space to manufacture things. It costs a lot of money to launch anything into space. In-situ resource utilization is and has been a hot research topic in NASA. It is for the most part far term research of course; we won't see a space refinery and space metallurgy any where in the near future.

Here you are really missing the point. Water is far too common on Earth to ever make mining water in space and shipping it back the Earth an economically viable endeavor. However, just because water is cheap on Earth does not make it cheap in space. Launching water into space is expensive; launching anything into space is expensive. Water is one of those in-situ resource utilization capabilities that is not far into the future science fiction. Mining water on the Moon for use on the Moon could significantly reduce the costs of an extended lunar outpost.

Ryan_m_b

D H I didn't realise we'd swapped the conversation onto in situ resource allocation. Considering that's a world away from landing an asteroid on Earth for mining I'd say this thread is going slightly off topic.

shashankac655

Asteroid mining
The figures given in this link makes me think that asteroid mining can become a reality ... probably by the 2nd half of this century or by the beginning of the 22nd century.