Do you like space? Would you like to see Mankind return to the moon? Well, hold onto your pocketbooks, folks -- because it's going to cost you.

Rapidly growing SpaceX and its Falcon 9 rocket fleet may have cut the cost of space launch to Low Earth Orbit to $50 million. But as we've been saying for months, the new Space Launch System (SLS) that Boeing (NYSE:BA) and Lockheed Martin (NYSE:LMT), Northrop Grumman, and Aerojet Rocketdyne are building to help NASA return to the moon will cost $1 billion every single time it launches.

And now it turns out we may have been wrong about that price: SLS may cost more than $1 billion. A lot more.

Artist's depiction of SLS taking off

Image source: Getty Images.

OMB spills the beans

In a letter to the Senate Appropriations Committee last month, acting director of the Office of Management and Budget Russell Vought estimated the cost of a single SLS launch at "over $2 billion per launch" -- and that's excluding "development" costs. (Hint: Development costs to-date are estimated at $14 billion or more, and continuing to pile up at the rate of $2 billion to $3 billion per year. To get the true cost of each rocket, you need to amortize all these development costs across all eventual SLS launches, and then add this development cost pro rate to each "launch" cost.) 

Admittedly, NASA says it's "working to bring down" that cost "as the agency continues negotiations with Boeing," according to a report out last week on Ars Technica. Still, if development continues for another year or so, then even if SLS eventually launches as many times as the Apollo program did (17), that arguably raises the rocket's true cost to nearly $3 billion per launch -- triple what taxpayers had been led to believe.

And it doesn't even end there.

What good is a rocket without a spaceship?

After all, the raison d' etre of the SLS is not to fly unmanned -- we have plenty of rockets that do that already. SLS was designed from the get-go to carry humans into deep space, to the moon, to Mars, and even beyond. And for that it's going to need to carry a space capsule of some sort -- a "spaceship."

NASA's candidate for this role is the Orion space capsule being developed by Lockheed Martin. At an estimated cost of $600 million to $900 million a pop, adding Orion to the SLS will push the cost of each launch closer to $4 billion than to $3 billion.

And you've got to factor in the development costs for Orion as well. Ars puts that figure at $16 billion, so over the course of 17 or so missions, we're now looking at a per-launch cost of close to $5 billion.

Is it worth it?

Now compare that cost to the cost of the alternatives. SpaceX advertises launches of its reusable Falcon Heavy rocket -- currently the most powerful rocket on Earth that is actually flying -- at just $90 million each. An "expendable" Falcon Heavy -- one SpaceX would not expect to get back and be able to reuse -- could be bought for just a bit more, specifically $150 million according to Elon Musk. 

SpaceX's latest project, Starship, hasn't yet been proven capable of reaching orbit (though it's getting closer to an orbital test flight) and its development, production, and launch costs aren't yet known. That being said, last year Musk promised that Starship would offer the "lowest marginal cost per launch" of any SpaceX vessel -- which, incredibly, seems to imply that Starship might cost even less than SpaceX's other rockets.

Indeed, OMB notes that using an unspecified "commercial launch vehicle" other than SLS could "provide over $1.5 billion in cost savings" per launch. It's not clear what other vehicle OMB is referring to here. But it's possible that SpaceX's Starship could be significantly cheaper to build and launch than SLS.

What does this mean for the future of SLS?

And that could be key, because $5 billion is quite simply too much money to spend on a single rocket launch -- especially if SpaceX can get the job done for $90 million, $150 million, $500 million ... pretty much any number ending in "million" instead of "billion."

No matter how hard it works to bring SLS's cost down, I fear that NASA (and its contractors Boeing and Lockheed) have their work cut out for them convincing Congress that costs aren't rapidly spiraling out of control. If they fail to make their case, I see a very real possibility that SLS -- and perhaps Orion as well -- will end up getting canceled in favor of more economical alternatives being developed faster and cheaper by commercial space firms like SpaceX.

To be clear, I still believe that mankind will go to the moon and beyond ... but at these prices, we're unlikely to get there on SLS.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.