There's gold in them thar asteroids – also iron, nickel, copper and, most valuable of all, water. According to the proponents of asteroid mining, these space rocks are a virtual El Dorado in the sky with more obtainable minerals in the largest three in our solar system than on the entire Earth. The question is, where exactly is all this mineral wealth and how do you get it without going broke in the process?

There's something of an international race to the asteroids underway at the moment, with countries from the United States to Luxembourg backing missions. On the surface it seems like a two-tier race – NASA and ESA are sending giant spacecraft and even manned missions, while private firms are concentrating on tiny probes that look like scale models. But while these approaches to asteroid exploration are very different, they are far from mutually exclusive.

Before we examine these exploration plans, let's look at the asteroids and why anyone would be interested in spending billions to visit a far flung rock.

Rich pickings

Asteroids are the debris from the formation of the Solar System, when a vast ring of gas and dust condensed to form the Sun and a surrounding disc that became a collection of planetoids that crashed together over millions of years to create the planets and moons.

Asteroids such as Vesta could be treasure troves of minerals NASA

The asteroids are concentrated in the famous asteroid belt between Mars and Jupiter, where the gravitational pull of the latter prevented them from forming a planet, slinging some of them into the inner Solar System, while others migrated in from beyond Pluto.

Italian priest and astronomer Giuseppe Piazzi first spied Ceres in 1801, and this is cited as the first asteroid discovered (though these days Ceres is classified as a dwarf planet). By the 20th century the asteroids were recognized as a potential treasure trove and Russian space pioneer Konstantin Tsiolkovsky speculated that asteroids might be laden with gold, platinum, and diamonds.

This was a romantic notion, but Tsiolkovsky wasn't too far off. Studies indicate that an asteroid 1,000 m (3,280 ft) across could yield about 100,000 tons of platinum – which already has miners in South Africa worried because we only mine a measly 130 tons of the metal on Earth each year.

By the 1950s, asteroid miners were a common trope in science fiction. Robert Heinlein depicted them as repeating the gold rushes of the 19th century, with grizzled prospectors in clapped-out spaceships hunting for uranium instead of gold.

One application of asteroid mining could be to build giant space colonies NASA

In 1976, Cornell University physicist Gerard K. O'Neil published The High Frontier: Human Colonies in Space, where he outlined his ideas for building giant colonies with tens of millions of people in them. Built mostly from lunar materials, these colonies would eventually use the asteroids for raw materials such as silica, carbon, hydrogen, nitrogen, and even petrochemicals, as well as metals in quantities far beyond anything available on Earth.

Modern would-be miners also see rich pickings in the asteroids, though initially the likes of Planetary Resources and Deep Space Industries (DSI) are not going after gold or platinum or uranium, but plain, ordinary water.

This is the economics of asteroid mining. Even after almost 60 years, space travel is still horribly expensive. In a recent court case involving the theft of lunar samples recovered by the Apollo 17 mission in 1972, a US federal judge determined that the Apollo Moon rocks are worth US$50,800 per gram due to the immense costs of going to the Moon and bringing the rocks back to Earth. At that price, even if asteroids were made of flawless blue-white diamonds, it might not be worth going after them.

Robotic probe using its gravity to tow an asteroid NASA

Today, the price of getting into orbit has dropped, but not as much as was hoped. The cost of reaching geosynchronous orbit stands at about US$27,063 per kg (2.2 lb), so the economics of asteroid mining are still daunting.

This is why asteroid mining companies are focusing on near-Earth asteroids. These are asteroids that have been thrown out of their regular orbit by the gravity of Jupiter and now make eccentric passages through the inner solar system. Reaching these and returning to Earth with your plunder takes less propellant than going to the asteroid belt.

It also seems logical to try to avoid the costs of bringing materials back to Earth and concentrate on things that space missions need, but are expensive to bring from Earth. In the case of Deep Space industries and Planetary Resources, this is water, which is vital for space travelers, but costs US$10,000 per liter to send to the ISS. If the a near-Earth asteroid could be turned into a cheaper source, the water could be used for drinking and bathing, as well as split into hydrogen and oxygen for use as fuel. In addition, acting as a space-based supplier for the International Space Station or satellites could form the basis for a new orbital economy.

Artist's concept of a fuelling plant Deep Space Industries

In the long run, many would-be asteroid miners see this new space economy as the real bonanza. Returning asteroid materials to Earth, even in refined form, is expensive. It may even unsettle Earthlings by reminding them of unpleasant science fiction novels where asteroids are deliberately fired at Earth, hitting with the force of large H-bombs.

It might be more profitable and safer to leave the asteroid products in space and use them there by means of 3D printing and other advanced production methods. Why go to the trouble of sending steel and copper back to Earth when they could be used to build satellites or space stations or more mining equipment?

Stepping stones

But even that is a very large leap in a field where even the most basic of infrastructure needs to be built. It's one thing for NASA to build an entire space travel system from scratch and put a man on the Moon in less than a decade. It's quite another for a private company to do the same in order to stake a claim on Ceres. Private companies need to keep money coming in and the lights on while making sure investors are happy – or at least not too nervous. Companies need to reduce the costs of working in space and find a way to make it pay off in the short term.

Artist's concept of an asteroid mining station Deep Space Industries

One way to do this is to develop technology for mining and prospecting that can be repurposed for use on Earth. Call it the Teflon and Tang option, named after NASA's PR offensive in the 1970s to sell itself on the grounds of all the spinoffs it produced (though neither Teflon nor Tang were among them).

Currently, the main asteroid mining firms are concerned less with recovering minerals from asteroids than they are with remote prospecting to identify which asteroids are promising targets for exploitation and what they might contain.

Planetary Resources bases much of its surveying strategy on its Arkyd satellites. These are a series of platforms that act as technology demonstrators, culminating in the Arkyd 100, which is a small orbital telescope designed to hunt for and identify prospective asteroids. Eventually, the company hopes to have a constellation of these satellites in orbit and, if successful, they'll be joined by the Arkyd 200, a deep space probe for rendezvousing with asteroids for close observation, and Arkyd 300, which would act in swarms for detailed prospecting.

Planetary Resources' Arkyd 100 Planetary Resources

It's a bold plan, but it doesn't answer the question of how to pay the bills, so Planetary Resources has decided that when it deploys its Arkyd 100 constellation, one of its first missions will be to turn around and look at the Earth. Called Ceres, this program will allow Earthbound customers in industries such as oil, gas and agriculture to hire the constellation of 10 satellites to make detailed twice-daily observations using infrared and hyperspectral sensors.

Deep Space Industries (DSI) is another firm that hopes to achieve success by starting small, keeping things cheap and going for short-term goals, but is also faced with the problem of making that first profitable step. Satellite propellants may be worth US$25 million a ton to send into orbit and replacing them with space-based equivalents is tempting, but with DSI estimating that its first satellites will cost US$20 million, that's a pretty wide margin to span.

Like Planetary Resources, DSI is planning on repurposing some of its technology for non-mining efforts. One of the company's major efforts is Prospector-1, which is an asteroid lander mission that will "only" cost something in the neighborhood of US$10 million. Since Prospector-1 isn't due to launch for a decade and there are bills to pay, DSI is offering the platform to other companies to develop their own low-cost missions.

Prospector-1 Deep Space industries

DSI's other approach is to partner with the government of Luxembourg. Under this agreement, DSI will establish a new headquarters in the country and the Luxembourg space program, (LuxIMPULSE) will co-fund R&D projects beginning with DSI's Prospector-X technology demonstrator satellite. This low-Earth orbit minisatellite is designed to prove the practicality of DSI's technology for deep space missions to seek out, survey, and mine asteroids for water and minerals.

Mixing it with the big boys

But the question remains, what chance do these tiny private companies have? For all their ambitions, the missions being planned by the likes of Planetary Resources and DSI look like student projects compared to the efforts of NASA and other space agencies. Are these entrepreneurs out of their league?

In one sense, the answer is yes. Where the private ventures work in budgets of millions, NASA's OSIRIS-REx mission alone cost almost a billion dollars and uses a spacecraft the size of a truck. If all goes well, it will return the first samples from the asteroid Bennu by 2023, as well as providing a detailed study of the asteroid's composition and other properties. All this will be much more, and long before, anything the private companies can deliver.

Artist's concept of OSIRIS-REx NASA

But OSIRIS-REx's mission isn't about space mining. Its purpose is mainly pure science, and the samples coming back to Earth have as much to do with asteroid mining as the Apollo mission samples did with lunar mining. They might produce useful information, but they're not directly concerned with commercial exploitation.

OSIRIS-REx is designed to carry out many different functions with a suite of instruments for everything from infrared spectronomy to cosmic ray analysis. Such deep space probes are built with a high-degree of survivability to protect the investment, so they have redundant systems and shielding.

But that doesn't mean the information brought back by OSIRIS-REx will be of no use to asteroid miners. An interesting aspect of this is one of the probe's secondary mission objectives – to study asteroid deflection. Bennu is wider than the Empire State Building is tall and the asteroid has a slight chance of impacting the Earth in the future, so NASA is studying what it would take to deflect it from its present trajectory. It's an important question not only from the viewpoint of planetary security, but for asteroid miners, who will certainly need such a capability.

Orion spacecraft configured for asteroid rendezvous NASA

This ability to redirect asteroid also has a more immediate purpose. One of NASA's flagship projects is the manned Orion space capsule, which is designed for deep-space missions, but is currently lacking any plausible destination. One way to solve this is the space agency's proposed Asteroid Redirect Mission.

If it can be funded, it will launch a robotic spacecraft in December 2020 that will not only rendezvous with a near-Earth asteroid, but capture it with a huge tarp and ferry it back to cislunar orbit using a solar-electric propulsion system similar to the one on the Dawn mission.

After the boulder has been placed into lunar orbit in the mid-2020s, NASA will launch an Orion spacecraft with two astronauts aboard on a 25-day mission to rendezvous with the asteroid fragment for study and collecting samples. Not only will this provide new insights into the asteroids, but NASA regards the mission as a rehearsal for an eventual manned mission to Mars.

Artist's concept of astronauts taking asteroid samples NASA

These and other missions, such as the US-European Asteroid Impact and Deflection mission (AIDA), put asteroids high on the list of space destinations in the 21st century, though for many different reasons. Some are going for pure science, some to stave off earthly disaster and some to mine. One day these missions might even include colonists bound for the asteroid belt.

At present the planned missions fit into two distinct categories with different priorities and different approaches. Space agencies like NASA are answerable to governments and taxpayers while asteroid miners take their orders from stockholders and customers. Space agencies have larger budgets, much broader mandates, and carry out missions that could have an impact on national security or prestige. In addition, they tend to be very risk adverse because a major disaster could throw a wet blanket on future projects for decades.

On the other hand, private miners work on shoestring budgets, have very specific goals, and, though they are driven by a need to stay in the black, they are more likely to take on risk. Mistakes will be made, but others will learn from them and the commercial imperative may drive space exploration forward faster and in unforeseen ways.

Rather than a gold rush, asteroid mining might be more aptly compared to oil and gas exploration, where pure geological research spills over into the hunt for new drilling fields. If asteroid mining does prove to be viable in coming decades, it will be on the back of lessons learned from both government and private missions. Only time and the balance sheet will tell.