The used rockets of tech billionaires just might save humanity from doom - here's how

The way Elon Musk sees it, humanity is either on the cusp of its greatest revolution - or risking its own annihilation.

But now, after 15 years of work through his rocket company, SpaceX, Musk's rosier scenario may have finally started to take root.

On March 30, SpaceX proved it can launch satellites, cargo, and eventually people into orbit around Earth using previously flown Falcon 9 rocket boosters.

The technology could make obsolete an industry-wide practice of trashing multi-million-dollar rockets after every launch, drastically lowering the cost of access to space in the process.

"This is a very helpful proof point that it's possible, and I hope people start to think of it as a real goal to which we should aspire, to establish a civilization on Mars," Musk told Business Insider during a post-launch press teleconference. "This is not just about humanity, it's about all the life that we care about."

Musk's SpaceX isn't the only company working on reusable rocket systems: Blue Origin, a company owned by Amazon.com founder Jeff Bezos, is also in the game.

Here's what the future of reusable spaceflight might soon look like, why Musk and others are pushing hard for it, and what it might mean for our species' future.