On November 12, 2014 Philae became the first robotic spacecraft to land on a comet nucleus, which is the solid part of a comet usually composed of rock, dust and frozen gases. As part of the Rosetta mission, the European Space Agency launched Philae, mounted on an Ariane 5 rocket, over a decade ago. The rocket traveled to Comet 67/P, otherwise known as Churyumov-Gerasimenko , and on August 6, 2014, the Rosetta spacecraft arrived at its destination. Four months later it released the Philae lander. Unfortunately, Philae had a bouncy landing and landed in shadow near a rocky outcropping, with two of its feet on the ground and one reaching out into space—two days later its solar batteries ran out of power .
Although the landing did not follow the ESA’s initial plans, the mission to Churyumov-Gerasimenko still achieved 80 percent of its goals , providing valuable insight into the asteroid itself as well as helpful information for future missions. The data acquired from Philae are significantly important for asteroid mining, which is a possible method of obtaining essential and rare materials from asteroids. These materials—like minerals and metals—could be used back on Earth or elsewhere in space. The need for materials, such as platinum, cannot be satisfied from just the Earth, where resources will inevitably be depleted . For example, if all cars were to be replaced with fuel cell equipped cars, platinum recourses would be exhausted within just 15 years. In addition, if the materials necessary for space missions could be harvested from asteroids, the cost of such missions would be dramatically reduced . There are many plausible ways to carry out asteroid mining, including transporting the raw asteroid material to Earth, processing the raw material on the asteroid and returning the processed materials to Earth or transporting the asteroid to an orbit around Earth or the moon and processing the material there .
In order to get a better idea of the economic aspect of asteroid mining, it is important to provide a brief overview of asteroid types. This is because asteroid composition and proximity to the Sun are two factors that could influence the turnover of an asteroid mining mission. Scientists have categorized comets into 3 main types of asteroids :
1) C-type asteroids are the most common and contain up to 22 percent water, but they are the furthest from the Sun.
2) S-type asteroids are made up of stony material, nickel-iron and more precious metals like gold, platinum, and rhodium. Those asteroids are the closest to the Sun.
3) M-type asteroids consist mostly of metals and occupy the middle region of the asteroid belt.
However, what elements are we looking for in asteroids? The answer to this question is by no means clear and it depends on the way we want to use them. For example, the rate of occurrence of platinum on the Earth is very low, and the procedure of mining it is costly. This means that platinum is very rare and expensive, making research of new ways to mine it from asteroids worthwhile. Platinum metal currently costs more than 30 euros per kilo , making it a potential metal to mine. On the other hand, water is abundant on the Earth. Therefore, it would be reasonable to acquire it from space only when it is needed for space missions. Because the launch cost for space shuttle cargo is about $10,000 per pound, water can be extremely expensive to transport to the International Space Station. Perhaps asteroid-mined water could be used in the International Space Station or for other manned missions. Or, possibly, that water, with the aid of solar power, could be broken down to hydrogen and oxygen and be used as fuel. Using water and minerals directly from space, rather than transporting it, could be very cost-effective .
Even though the technology needed for asteroid mining at least partially exists, the process must become faster and cheaper in order for it to be actually viable. The Rosetta mission had to use gravitational assist two times from Earth and once from Mars to catch Churyumov–Gerasimenko. This illustrates the fact that it was not even able to propel its own mass at the required velocity without gravity. So, what about having to carry the mass of an asteroid? It is extremely costly in terms of energy to transport such a huge mass in space back to Earth or even just the Earth’s orbit. Maybe our best bet is a small M-type platinum rich asteroid that we could set into earth orbit and start mining there.
References “Rosetta on the way to Comet 67/P”. ESA: Space in Videos. 30 March 2004. http://www.esa.int/spaceinvideos/Videos/2004/03/Rosetta_on_the_way_to_Comet_67_P  Tim Sharp. “Rosetta Spacecraft: To Catch a Comet”. Space.com. 17 November 2014. http://www.space.com/24292-rosetta-spacecraft.html  Katherine J.Mack. “Sleep now for Rosetta’s comet probe after a bouncy landing”. The Conversation. 18 November, 2014. http://theconversation.com/sleep-now-for-rosettas-comet-probe-after-a-bouncy-landing-34122  David Cohen. “Earth’s natural wealth: an audit”. NewScientist. Magazine issue 2605. 23 May, 2007. http://www.theengineer.co.uk/aerospace/in-depth/your-questions-answered-asteroid-mining/1015966.article  Stephen Shaw. “Asteroid mining”. Astronomy Source (e-pub). 21 August, 2012. http://theconversation.com/sleep-now-for-rosettas-comet-probe-after-a-bouncy-landing-34122  “In-Line Water Filtration: Better Hygiene, Less Expense”. NASA. 28 September, 2009. http://www.nasa.gov/topics/nasalife/pure_water.html