This article was updated on June 8, 2016. 

SpaceX just might be the hottest stock that everyone wants to own but no one can buy.

Asiasat Launch
SpaceX sent the AsiaSat 6 satellite sent into orbit aboard a Falcon 9 rocket on Sept. 8, 2014. Image source: SpaceX.

PayPal co-founder and serial high-tech entrepreneur Elon Musk is juggling leadership roles at three of the 21st century's hottest enterprises: electric-car maker Tesla (NASDAQ:TSLA), solar panel lessor SolarCity (NASDAQ:SCTY), and space launch company SpaceX. Over the past 12 months, SolarCity has incurred $62 million in losses, and Tesla lost 16 times that -- more than $1 billion. SpaceX, in contrast, is said to be both profitable on a generally accepted accounting principles basis, and cash flow positive to boot.

Unfortunately, you can't own it. So far, Musk is keeping SpaceX private. Of his three companies, SpaceX is the only one that's making money... and the only one that has not IPO'ed.

But what if it did?

The good news for investors is that for one reason or another, companies -- even profitable, popular companies like SpaceX, which probably don't really need to -- very often eventually go public. One day, we might all have a chance to own a piece of SpaceX. But if and when that day arrives, how much should we pay for this stock?

Up until last year, the most recent known sale of SpaceX equity had occurred in November 2010, when the company raised $50.6 million in capital from an equity offering. This offering followed a March 2009 offering of $60 million worth of SpaceX equity.

Prior to that, the company raised $29 million in August 2008, $30 million in March 2007, $50 million in March 2005, and $10.1 million and $15 million in August and December 2002, respectively. Tally it all up, and add in both the original $100 million initial investment from Elon Musk himself, and the most recent 2015 investment of $1 billion by Google and Fidelity, and we can assume that, because SpaceX is known to be profitable, its stock is worth at least the $1.345 billion put in by its investors.  

In fact, SpaceX stock is probably worth quite a bit more than that. Figuring out how much more, though, is tricky.

Crunching the numbers 

SpaceX "declines to disclose" its annual revenue or profits -- at least officially. In a job advertisement on its website, however, the company boasts of being a "nearly $5B revenue operation." 

Let's assume for a moment that this number refers to annual revenues. Rival space launch companies Boeing (NYSE:BA) and Lockheed Martin (NYSE:LMT) sell for market capitalizations of 0.9 and 1.5 times annual sales, respectively. So if we apply, say, a 1.2 times sales valuation to SpaceX, the stock should be worth approximately $6 billion today.

Crunching more numbers

SpaceX also boasts a backlog of "over 70 launches on its manifest, representing over $10 billion in contracts" to be performed for its customers, launching satellites into outer space, ferrying supplies to the International Space Station, and soon, transporting astronauts to ISS as well. To compare, at last report, S&P Global Market Intelligence pegged Boeing's backlog at $479.9 billion, while Lockheed Martin had a backlog of $99.6 billion.

Now, with a market capitalization of $84.7 billion, investors are valuing Boeing at about 18% of the value of its backlogged work. If we apply a similar valuation "price-to-backlog" ratio to SpaceX, the company might be worth as little as $1.8 billion.

But now look at Lockheed: At a $73.2 billion market cap, investors think Lockheed Martin is worth roughly 73% of its backlog. Apply this valuation to SpaceX's $10 billion backlog, and presto-change-o, the stock's implied value leaps as high as $7.3 billion.

Elon Musk's magic multiple

So you see: The more valuation calculations we throw at SpaceX, the higher the valuation seems to march. We saw this again last January, when Google -- now Alphabet (NASDAQ:GOOGL) (NASDAQ:GOOG) -- blew all preceding valuation guesses out of the water. As part of a group of investors participating in a $1 billion round of funding, it anted up $900 million for a 7.5% stake in SpaceX stock. This means that SpaceX stock is now worth $12 billion in market capitalization. At least, according to Google, it is.

So why would Google pay so much? Here's a thought: Maybe Google loves Elon Musk. Maybe they think the guy's simply magic.

After all, the two companies that Musk has already brought public, Tesla and SolarCity, both sell for valuations that are truly immense multiples of their respective annual sales. And these are the two Musk companies that are not earning a profit. So how much more valuable will SpaceX stock become when it IPOs? Fast-growing, space tech-sexy, and profitable SpaceX stock?

If you ask Google, the answer seems to be: "A lot."

Spacex Launch
Up, up, and away goes SpaceX's rocket ... and SpaceX stock, too? Image source: SpaceX.

Rich Smith does not own stock in SpaceX (but wishes he could). He has no position in any other stocks mentioned above, either. You can find him on CAPS, publicly pontificating under the handle TMFDitty, where he's currently ranked No. 335 out of more than 75,000 rated members.

Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool’s board of directors. The Motley Fool owns shares of and recommends Alphabet (A and C shares), SolarCity, and Tesla Motors. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.