It was a speech short on financial details but long on big ideas. In a 42-minute presentation to the International Astronautical Congress (IAC) in Adelaide, Australia, this past week, SpaceX CEO Elon Musk updated investors on the latest iteration of his plan to make humans a "multiplanetary" species -- by landing astronauts on Mars for the first time and returning them to the moon.

The upshot? Just years after introducing Earth to the concept of a reusable Falcon 9 rocket, and before even successfully launching its bigger brother, the Falcon Heavy, SpaceX is ready to junk both rocket ships and make them redundant with an even bigger spacecraft: the BFR.

BFR rocketship docked at International Space Station

How big will Elon Musk's "BFR" be? Big enough to all but dwarf the International Space Station in comparison. Image source: SpaceX.

Space is expensive

Musk couched his talk as an update to the ideas initially introduced at the IAC conference in Guadalajara, Mexico, last year. Specifically, he promised to tell people "how do we pay for this thing" -- this "thing" being sending astronauts on Mars for a price less than the $500 billion that experts estimate it would cost NASA to do it.

Musk aims to get the ball rolling for $10 billion -- just 2% of what it would cost NASA to do it. Problem is, as we now know, SpaceX doesn't actually have $10 billion lying around to do it. It does have $350 million, thanks to a funding round conducted in July, but even that's just a down payment on the Mars project.

The solution to this problem, as Musk explained, is to gradually phase out use of its Falcon family of reusable rockets and replace them with just one big rocket model -- a rocket that can be used for everything from resupplying the space station, to round-trip unrefueled missions to the moon, to colonizing Mars. He calls it the BFR (picture above). SpaceX intends to build a small fleet of Falcon 9 and Falcon Heavy launchers for customers who want to fly on them, but then it intends to focus all its future investments on refining the design of this single, one-size-fits-all rocket ship, the BFR.

What is BFR?

In a series of slides, Musk depicted BFR as a massive 106-meter-tall, 4,400-ton rocket comprising two main parts: a 58-meter-tall, 3,200-ton first-stage booster section, and a 48-meter-tall, 1,200-ton spaceship atop it. Most of the mass of both sections will be liquid methane fuel and oxygen. The reason the first stage's mass is so much greater than the second stage is that it's going to be made up primarily of fuel. Both sections will be fully reusable, launching and landing from Earth -- or the moon, Mars, or an asteroid -- under their own power.

Why is this important? Because if its experience with Falcon 9 has taught SpaceX anything, it's that reusability makes a rocket cheap. Instead of building an entire rocket and then throwing it away after each mission, as is the current practice among space incumbents such as Airbus's (NASDAQOTH:EADSY) Arianespace, and Boeing (NYSE:BA) and Lockheed Martin's (NYSE:LMT) United Launch Alliance, SpaceX's BFR will fly multiple missions before needing replacement. The primary cost of each mission, therefore, will be fuel. And because, as Musk explains, the costs of oxygen and methane are "extremely low," it follows that the cost of putting things in space aboard BFR will also be extremely low.

How low, you ask? Despite being significantly bigger than the Saturn V rocket that took us to the moon, the "marginal cost per launch accounting for reusability" of BFR will be cheaper than that of any rocket ever before built. BFR launches will come cheaper than Boeing's Delta IV rocket, cheaper than Lockheed Martin's Atlas V and Airbus's Ariane 5 -- even cheaper than SpaceX's own Falcon 9 rocket, and including its upcoming Falcon Heavy.

That's just amazing.

How cheap is BFR?

Of course, Musk didn't say exactly how cheap BFR launches will be. Nor was he specific on whether he was referring to the cost of an entire launch or perhaps the cost per ton of payload launched. Notably, BFR will carry 150 tons of payload, several times  more than anything Boeing, Lockheed, or Airbus can manage currently.

But this is why I say Musk was a bit short on financial details in giving his presentation. That being said, Musk seems to think that launch costs will be cheap enough that, in the not too distant future, BFR could become commercially viable for point-to-point rocket-ship flights around Earth itself. If he's right about that, then we could be talking about launch costs similar to the cost  of buying a ticket on the Concorde.

And if he could do that for a ticket to Mars, that would be a bargain indeed.

Rich Smith has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.