Goldman Sachs is bullish on space mining with "asteroid-grabbing spacecraft." In a 98-page note for clients seen by Business Insider, analyst Noah Poponak and his team argue that platinum mining in space is getting cheaper and easier, and the rewards are becoming greater as time goes by.

"While the psychological barrier to mining asteroids is high, the actual financial and technological barriers are far lower. Prospecting probes can likely be built for tens of millions of dollars each and Caltech has suggested an asteroid-grabbing spacecraft could cost $2.6bn," the report says.

$2.6 billion (£2 billion) sounds like a lot, but it is only about one-third the amount that has been invested in Uber, putting the price well within reach of today's VC funds. It is also a comparable to the setup cost for a regular earthbound mine. (This MIT paper estimates a new rare earth metal mine can cost up to $1 billion, from scratch.)

The price of spacecraft is plummeting, thanks to reusable rockets from Elon Musk's SpaceX and Jeff Bezos's Blue Origin. It used to cost $35 million (£28 million) to send one person up on a Soyuz rocket. Today, Virgin Galactic hopes to get space tourists into space for something like $250,000 (£200,000), Goldman says. More broadly, the price of all new rockets is falling over time:

Those economics make going into space more feasible. The rewards would be vast: just one asteroid might contain $50 billion (£40 billion) of platinum:

"Space mining could be more realistic than perceived. Water and platinum group metals that are abundant on asteroids are highly disruptive from a technological and economic standpoint. Water is easily converted into rocket fuel, and can even be used unaltered as a propellant. Ultimately being able to stockpile the fuel in LEO [low earth orbit] would be a game changer for how we access space. And platinum is platinum. According to a 2012 Reuters interview with Planetary Resources, a single asteroid the size of a football field could contain $25bn- $50bn worth of platinum."

There is just one problem: That same asteroid would instantly tank the entire platinum market: "Successful asteroid mining would likely crater the global price of platinum, with a single 500-meter-wide asteroid containing nearly 175X the global output, according to MIT's Mission 2016."

Nonetheless, Goldman is bullish. "We expect that systems could be built for less than that given trends in the cost of manufacturing spacecraft and improvements in technology. Given the capex of mining operations on Earth, we think that financing a space mission is not outside the realm of possibility."