One of Elon Musk's central goals in founding SpaceX has always been to make space more accessible by making it less expensive to escape Earth's gravity well. This week, company President Gwynne Shotwell provided some sense of just how much cheaper it hopes to make spaceflight when it finally begins to re-use its rockets.

For much of the history of space exploration on Earth, the powerful rockets used to propel people and cargo to orbit or beyond typically end up in a watery grave at the bottom of the ocean or eventually burning up in the atmosphere. That's part of the reason that even today, rocket launches by SpaceX competitors like the United Launch Alliance can cost hundreds of millions of dollars each.

SpaceX has been working to develop rockets with a first stage designed to make a soft landing back on Earth, or on a floating drone barge in the ocean, so that they can be reconditioned, refueled and ultimately, relaunched.

Shotwell told an audience at a satellite conference that the cost of using a previously launched SpaceX Falcon 9 rocket to get to space could be as much as 30 percent less when compared to a new Falcon 9 flight. That translates to around $40 million for the launch in a recycled rocket.

To be fair, rockets and their missions vary widely, but $40 million for a launch still represents a relative bargain in the industry.

Exactly when SpaceX might begin to re-use its rockets is hard to say. So far they've only managed to successfully recover one Falcon 9 that was part of a successful commercial mission. That historic landing happened in December at Florida's Cape Canaveral launch complex on dry ground. 

According to SpaceNews, Shotwell told the audience that she had the opportunity to inspect the recovered rocket in person.

"It was extraordinary how great it looked. In fact we didn't refurbish it at all. We inspected it and then three days later we put it on the test stand and fired it again. "

SpaceX has also tried to recover its rockets by landing them on unmanned landing pads on barges at sea. All four of those attempts so far have landed hard, creating fiery explosions that destroyed the rockets.