It began with just 12 contracts.

In 2014, NASA embarked upon a three-year mission to explore new ways of sending astronauts to the International Space Station (ISS) and to seek out new partnerships with private industry, tasking SpaceX and Boeing (BA -0.65%) with a request to build two new spaceships for a combined $6.8 billion. SpaceX would receive $2.6 billion to design and build a Crew Dragon spacecraft by 2017, and use it to send astronauts to ISS six times. Boeing would be paid $4.2 billion to do the same thing.

Ultimately, it would take SpaceX not three but six years to launch its first crewed spaceflight (Demo-2, in 2020). But once that was accomplished, SpaceX quickly hit its stride, launching four new fully certified "Crew" missions over the next two years. Boeing is taking a bit longer to fulfill its contract, finally completing an uncrewed test flight just last month, and Boeing has yet to send up its "Starliner" spacecraft with astronauts actually aboard. 

And this tardiness is going to cost Boeing -- big time.

SpaceX: 14, Boeing: 6

With SpaceX the only space contractor that had proven itself capable of launching astronauts to orbit safely (something that remains true today), NASA awarded SpaceX three additional crewed space missions last year at a price of roughly $300 million per launch.

But Boeing is now mere months away from completing its test flights with a crewed demonstration mission, and proving itself a viable competitor to SpaceX. You'd think NASA would want to pause at this point and see how Boeing performs on its upcoming "Boeing Crew Flight Test" before handing out any more contracts. But no. Instead, on June 1, NASA announced it was awarding five more crew missions -- and all of them are going to SpaceX. 

NASA has decided to keep ISS operational through 2030, you see. As a result, "there is a need for additional crew rotation missions to sustain a safe and sustainable flight cadence throughout the remainder of the space station's planned operations." The plan going forward is for "each commercial provider [to fly] alternating missions once per year." That appears to mean that every year from now through 2030 -- i.e. eight more years -- each of SpaceX and Boeing will fly once per year. 

The math doesn't work out exactly like that, however.

Consider: So far, SpaceX has flown four Crew missions to ISS. Boeing has flown zero. Two missions remain in SpaceX's original six-mission allotment, plus the three missions awarded last year, plus the five missions just awarded this month -- so SpaceX still has 10 missions to go. Boeing has all of its original six missions remaining.

Together, it's true the two companies have 16 missions awarded -- two per year, times eight years. But it looks like SpaceX will be flying slightly more frequently than once per year through 2030, and Boeing slightly less often.

The upshot for Boeing investors

Although NASA reserves the right to make "additional contract modifications in the future for additional transportation services as needed," right now it looks like the space agency has bought all the crewed launch missions it needs through the end of ISS's lifespan in 2030. Thus, Boeing won't get a chance to bid for any more contracts beyond the six launches that it originally won back in 2014.

Now, there's still the question of what happens after ISS is retired in 2030. A handful of space companies have, for example, floated the prospect of building private space stations. Boeing might want to provide space taxi services to and from those after ISS goes dark. So far, though, the company making the most progress toward building a private space station is Axiom Space -- and Axiom has already performed one flight to ISS aboard a SpaceX Crew Dragon, and contracted for three more such flights with SpaceX. 

What does this mean for Boeing and its future in space?

One possibility is that Boeing convinces Axiom to diversify its space taxi providers by hiring Boeing's Starliner for some future flights. Boeing is also a partner on Jeff Bezos's Orbital Reef space station concept, though, in cooperation with Blue Origin and Sierra Space. While it's anyone's guess whether "Orbital Reef" will actually happen, if it does that station might provide a second market for Boeing's Starliner.

Absent Boeing landing Axiom or Orbital Reef as a customer, though, there's a very real risk at this point that Starliner will become a product in search of a buyer -- and a huge sunk cost for Boeing. And that would not be good news at all for Boeing stock.