By now, it's common knowledge that SpaceX's Starship super-rocket is key to Elon Musk's plan to colonize Mars.

160 feet tall, with a diameter of 30 feet, the "Starship" transport segment will have the capacity to carry 100 tons of cargo to orbit, or 100 colonists to Mars. Paired with a 223-foot-tall "Super Heavy" rocket booster firing 37 Raptor engines at twice the liftoff thrust (72 meganewtons) of the Saturn V Moon Rocket, Starship/SuperHeavy will be the most powerful rocket ever build by man, and by a large margin. It's literally purpose-built to make mankind an interplanetary species.

And in more ways than one.

Starship testbed Starhopper in flight

Image source: Elon Musk via Twitter.

Starlink first, then Mars

Elon Musk has said he needs to raise $10 billion to conduct a successful manned Mars mission. Unfortunately, although SpaceX is arguably the most successful space company in the world right now, it is not, at present, earning much (or perhaps any) profit. But in 2017, a cache of internal SpaceX documents came to light describing how SpaceX aims to become profitable. Indeed, these documents reveal the key to how SpaceX plans to generate the kind of massive profits it will need to finance a voyage to the Red Planet.

In a nutshell, it all comes down to "Starlink," the company's ambitious plan to put 12,000 (or more) satellites in orbit around Earth, and use them to sell broadband internet to the world. 

SpaceX has in fact already begun deploying Starlink, and once this system becomes operational the company anticipates that selling broadband internet from space will generate operating profits to the order of $4 billion per year by 2021, and as much as $22 billion by 2025 -- at 60% operating profit margins. (Ambitious as those figures might seem, even down here on Earth, S&P Global Market Intelligence data show that Comcast already makes about a 40% EBITDA margin on its internet business. Assuming internet-from-space is even modestly more efficient than internet-buried-under-asphalt, SpaceX's projections might very well turn out to be in the ballpark.)

Of course, in order to earn the profits that will make a mission to Mars possible, SpaceX first has to build the Starlink satellites, and launch them into orbit.

Launch first, then profit from Starlink

But as I said, SpaceX has already begun doing just that.

The first big batch of Starlink satellites went up aboard a Falcon 9 rocket back in May, and to prove that they worked, Musk blasted out this tweet to his followers on October 22:

A second batch of 60 is scheduled to launch on Monday, and next year the company plans to launch 24 similar missions -- growing the number of orbiting Starlinks past 1,500. At that point, says SpaceX, it should have more than enough Starlinks to provide at least some internet coverage everywhere on Earth. 

Of course, even then the work needed for full functionality will only be 13% done. So how does Musk plan to finish up his orbital satellite internet system in time to make all of his planned billions in time for 2025? That's where this story circles back to Starship once again.

How Starship facilitates Starlink

Speaking at an investor conference in New York recently, SpaceX COO Gwynne Shotwell mused that whereas a Falcon 9 rocket can easily carry 60 Starlink satellites into orbit, the much larger "Starship can take 400 satellites at a time." 

Granted, unlike Falcon, Starship hasn't yet reached orbit (emphasis on "yet"). But SpaceX is hoping to conduct an orbital launch either late this year or early next. Assuming it succeeds, well, at 400 satellites per launch, launching roughly once every couple of weeks, SpaceX could theoretically get its 12,000 satellites into orbit in just over one year -- plenty of time to begin making beaucoup bucks by 2025.

Indeed, even SpaceX's recently announced and more ambitious plan to flood the skies with 42,000 Starlinks could become feasible at a rate of 400 Starlinks per Starship launch. Launching twice per month, the 105 launches necessary could be accomplished in roughly four years.

What it means for investors

Long story short, SpaceX's plan for selling broadband internet access from space is ambitious in the extreme -- but the math does work. Crazy as it sounds, a company that made its reputation selling cut-rate space launches for $50 million a pop could soon be making most of its money by growing into the biggest internet provider on the planet.

If that happens, Earth-bound cable companies should start getting nervous -- and Mars should prepare to roll out the welcome mat.