2009 BD, the minable asteroid

Earth isn't scheduled to have any interesting asteroid encounters over the next while (as far as we know, that is - they often appear out of nowhere just days before they fly by us) except for one asteroid that is very small, as well as with an extremely low relative velocity. It's an asteroid barely a dozen metres in diameter called 2009 BD, and it will be making its closest encounter (nine times the distance from the Earth to the Moon) in six days. Compare it to a few other more typical asteroid encounters:

Object Name	Close Approach Date	Miss Distance (AU)	Miss Distance (LD)	Estimated Diameter*	H (mag)	Relative Velocity (km/s)
(2010 GU6)	2010-May-01	0.1277	49.7	200 m - 450 m	20.6	17.79
(2007 TD71)	2010-May-01	0.1914	74.5	540 m - 1.2 km	18.5	28.77
(2009 YF)	2010-May-02	0.1492	58.1	31 m - 69 m	24.7	3.71
(2010 GT6)	2010-May-02	0.1361	53.0	130 m - 290 m	21.6	15.81
(2007 DB61)	2010-May-02	0.0899	35.0	55 m - 120 m	23.4	9.96
(2009 WA)	2010-May-03	0.1980	77.1	150 m - 330 m	21.3	16.22
(2010 HV20)	2010-May-04	0.0939	36.5	110 m - 250 m	21.9	24.64
(2010 HS20)	2010-May-05	0.0779	30.3	59 m - 130 m	23.3	10.84
(2010 GU21)	2010-May-05	0.0205	8.0	160 m - 360 m	21.1	10.60
(2010 FA81)	2010-May-05	0.0454	17.7	89 m - 200 m	22.4	8.34
(2008 TE)	2010-May-06	0.1165	45.3	7.7 m - 17 m	27.7	15.27
(2009 BD)	2010-May-07	0.0235	9.1	5.7 m - 13 m	28.3	0.89

This combination of tiny size and low relative velocity is what makes this type of asteroid an ideal candidate for mining in the future, as the low relative velocity is what makes it that much easier to capture into Earth orbit, and the small size guarantees it will burn up in the atmosphere if something were to go wrong. Still, an asteroid 9 metres in diameter would have a mass of 1500 tonnes, almost five times that of the International Space Station. By comparison, the Atlas V heavy launch vehicle can send up to 30 tonnes to LEO. The Falcon 9 Heavy is expected to be able to take 32 tonnes to LEO, at a price tag of $95 million per launch, so the mass of an asteroid like 2009 BD would require 47 launches, or $4.4 billion.

Read more on the idea of mining small asteroids here, and to see the asteroid and Earth next to each other as they orbit the Sun, see here (warning: that page always crashes Firefox for me and only Opera will show it).

Personally though I can't say I'm that excited about the idea of asteroid mining, simply because lowering launch costs is a more practical idea. Mining asteroids is only really worth it if 1) the asteroid happens to have a lot of precious metals, and/or 2) the cost of launching a kilogram to LEO remains high. Take out 2) and only 1) remains worthwhile.

More exciting than this would be the idea of bringing in an asteroid like this in as a second moon, perhaps at an orbit some 50000 ~ 100000 km from the Earth (4 to 7 times closer than the Moon). A permanent new target in the sky for astronomy would be created, it could be visited fairly easily by astronauts, and history textbooks would have Did you know? Earth used to only have one moon. The second one was brought into Earth orbit in 2015 in a tiny infobox somewhere.