What happened

Space tourism company Virgin Galactic Holdings (SPCE -10.02%) has been rocketing higher since its public market debut earlier this year, largely due to investor excitement about its long-term potential. Goldman Sachs sees that potential, but it just published a note reminding everyone of the challenges the company faces.

That dose of reality sent Virgin Galactic shares downward in morning trading on Friday. As of noon EDT, they were off by more than 6%.

So what

Virgin Galactic aims to sell tourists brief trips into space at ticket prices of $250,000 or more apiece. The company has a backlog of deposits and lots of potential, but is still very much a speculative venture.

In a note initiating coverage, Goldman Sachs analyst Noah Poponak said that Virgin has "a substantial head start" in a new market that has "significant long-term revenue prospects."

Interior shot of Virgin Galactic's space craft.

Image source: Virgin Galactic.

But it is going to take a lot of time to realize that opportunity, the overall market size is still uncertain, and the potential for competition "is not insignificant," Poponak notes. "Spaceflight technology is not an easy feat, many timeline delays have already occurred, and more could," the analyst wrote.

Poponak believes Virgin Galactic will not hit the cash-flow breakeven point for years. Given that combination of opportunities and challenges, he initiated Goldman's coverage of Virgin Galactic with a neutral rating.

Now what

It's hard to quibble with much that Poponak had to say. Virgin Galactic could turn into a high-flying growth stock. But at best, its evolution from speculative venture to profitable business will take a lot of time, and a large number of things could go wrong along the way.

The idea of space tourism is cool, and given its potential, an investor couldn't be blamed for making Virgin Galactic shares a small part of a well-diversified portfolio. But be mindful of the risks, and don't expect this to be an overnight success story.