Artist concept of a mission to bring an asteroid to Earth

It has been proposed that NASA go out, grab an asteroid, and bring the asteroid to Earth. It would be placed into high lunar orbit (not directly in Earth orbit).  Once there, astronauts can go out to visit it.

This would demonstrate key technologies like the solar electric propulsion and the ability to move asteroids, which could be important someday if we see the big one heading toward the Earth.  The relocated asteroid will become a destination for astronauts in the new Orion space capsule.  Such a trip will be a test of our ability to go farther than we ever have before without going all the way to Mars.  It would be much healthier than going all the way out to the asteroid in its original orbit around the sun, which would give the crew an unacceptably huge dose of cosmic radiation. (That’s a problem we still need to solve.)

The proposed mission will also give us the best opportunity EVER to study an asteroid, a fundamental building block of planets and an historical record of our solar system. So you can count on really awesome science coming from it!  And as if that weren’t enough, it will give us the opportunity to mine a real asteroid in weightlessness, demonstrating our ability to gather space resource that enable even more ambitious activities in space.

There are many, many kinds of rocks in space, so before we bring an asteroid to Earth we need to think which kind will accomplish all these purposes.  The next few posts will cover some important asteroid characteristics to consider.

An Asteroid’s Size

Size matters when considering how to bring an asteroid to Earth

One of the most important features is the asteroid’s size.  It would be absolutely fantastic if we could bring back a huge asteroid, a dwarf planet like Ceres, one that has enough gravity for Bruce Willis and a team of oil drillers to drive around on their asteroid buggy shooting its Gatling gun.  But that would require too huge a spacecraft to haul back to the Earth, too much fuel, and too much money.  Furthermore, it would be a bit dangerous.  What happens if we make a mistake while hauling it back and accidentally hit the Earth instead?  Larger than 25 to 30 meters, a portion of the asteroid could survive entry through the Earth’s atmosphere and hit the surface.  Pow!  That could be really bad.  But smaller than 10 meters an errant asteroid will completely burn up, causing nothing more than a brilliant display of light and color in the sky.  We are considering an asteroid in the range of 7 – 10 meters in diameter if we can find a good one.  That’s plenty small enough for safety.

By the way, if we bring back a rock smaller than 1 meter, then technically it’s not an asteroid; it’s a meteoroid.  Visiting such a rock would not fulfill the President’s direction to visit an asteroid.  We have to draw the lines somewhere.  Before 2010, a space rock had to be bigger than 10 meters to be considered an asteroid.  After a bunch of really big space rocks smaller than 10 meters were discovered, scientists decided they should be called asteroids, so the limit was moved down to 1 meter to be more inclusive.  This was four years after Pluto had been kicked out from being a planet, so maybe they were feeling guilty and tried to make up for it.  Anyhow, a 7 meter space rock now counts as an asteroid, and it’s small enough to bring to Earth economically so astronauts can visit it without exposure to too much cosmic radiation.

Some chondritic asteroids are believed to have as much as 20% water by weight.

One last consideration about the size:  can we get enough resources from a 7 meter asteroid to really do anything with it?  Well, some asteroids are as much as 22% water by mass (in the form of hydrated minerals).  That means a 7 meter asteroid could yield up to 83 metric tons of water!  That’s enough propellant to send a Human-class, 52 ton spacecraft from low Earth orbit to Mars (Δv=4.3 km/s).  To launch that much propellant from Earth up to low Earth orbit would cost more than a third of a billion dollars on the least expensive launcher available today!  That’s not enough savings to recoup the development cost of the asteroid retrieval mission, but it’s a good start toward setting up an in-space capability that can pay back a million-fold or even a billion-fold in the longer run.  And that doesn’t account for the value of the other materials in the asteroid, such as metals for 3D printing of spaceships.  So I’d say a 7 meter asteroid is big enough for a first mission!  It gives us a great opportunity to develop and test some very important technologies.

Next topic:  what type of trajectory the asteroid should be on when we go out to get it?

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Phil Metzger

Phil Metzger is a physicist/planetary scientist who works on technologies for mining the Moon, Mars, and asteroids; for developing extraterrestrial spaceports; and starting for robotic industry in space. He recently took early retirement from NASA, where he co-founded the KSC Swamp Works. He is now with the planetary science faculty at the University of Central Florida. Subscribe to the email list to get notified of updates to this blog!

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At the most recent count, I found eight companies with a focus on space mining. They are at various stages:  seeking capital, developing technologies, and planning missions.  These companies have similar visions for the long-term:  robust human civilization in space.  To do this, they plan to initiate an industry that utilizes the resources of space.  That’s the key, because launching out of a planet’s gravity field is expensive and dangerous.  If we ever want civilization beyond the Earth, we need to avoid launching everything from Earth.

RASSOR, a NASA robot designed to mine space, working in very low gravity environments

To accomplish their goal, these companies that plan to mine space will need some profit in the near term:  to support their families and to raise capital toward the big vision.  They have different strategies to do this.  Four of them plan to mine the Moon, and four plan to mine asteroids.  At least three have discussed mining metals like platinum to sell down here on the Earth.  Others have discussed mining water, splitting it into hydrogen and oxygen, and selling it to other space-faring entities as rocket propellant so they can boost satellites into higher orbits or send humans on missions to Mars, for example. Both of these mining products, metal and water, can be obtained by mining the Moon or by mining an asteroid.

A NASA concept to mine space: a method to pull asteroids back to Earth by tether.

Already some of the companies have discussed plans to manufacture things in space like communication satellites that are bigger and have greater capacity than anything we could fit onto a rocket launched from Earth.  The metals and other materials they mine in space would therefore not be sold on Earth. In this Information Age, beaming the data alone is a very lucrative business.  And some have discussed plans to build giant solar power plants that will beam energy to Earth.  These general strategies were discussed in an earlier post, “How Do You Make Money in Space?”

So here is a summary of the companies I found that plan to mine space.  The nearer-term strategies listed here are according to on-line resources.  I am sure they all plan to do more than this, and I will update the table as I find out more.  My hope is that by providing this brief overview the world will see that this is an active and growing sector because bright minds are realizing the time is now to mine space.

To this list we could add SpaceX, because they plan to have Mars colonies, which implies they will need to obtain resources on Mars.  Also, there are many companies that plan to directly support these space mining companies with other in-space services.  I love the vision of all these companies!

(Please note:  these posts are completely my own private musings and do not represent the views of any organization, including my employer.)

Author information

Phil Metzger

Phil Metzger is a physicist/planetary scientist who works on technologies for mining the Moon, Mars, and asteroids; for developing extraterrestrial spaceports; and starting for robotic industry in space. He recently took early retirement from NASA, where he co-founded the KSC Swamp Works. He is now with the planetary science faculty at the University of Central Florida. Subscribe to the email list to get notified of updates to this blog!

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