Settling other planets isn’t going to be cheap. That’s why Elon Musk, after setting out to develop lower-cost rockets at SpaceX, decided to make money with them by launching a satellite network called Starlink to sell broadband internet access to ruralites. “Starlink is how we are paying for humanity to get to Mars,” he wrote on his social network X last year.

Starlink’s progress has been stunning. In March, less than five years after starting service, it reached 5 million customers, more than doubling the market of the previous satellite communications incumbents, Viasat and Hughes, at their height. Sunny expectations for Starlink are one of the main reasons investors have been eager to pump money into SpaceX. Its valuation hit $350 billion in December in a sale of insider shares, making it the most valuable private company in the world.

That valuation has largely held steady on secondary markets this year even as shares in Musk’s electric car maker Tesla have plummeted 55% from a record high reached in mid-December amid faltering sales and public fury over his role in the Trump administration and embrace of right-wing nationalists in Europe.

But some fear SpaceX, too, could face a reckoning, with the upside for Starlink not as high as investors seem to be betting. As with Tesla, it’s partly a question of how much they’re buying into Musk’s grand vision and their willingness to overlook financials.

“He keeps pulling rabbits out of hats, whether you believe them or not, about his robots or his self-driving cars or his city on Mars or his AI plans,” independent telecom consultant Tim Farrar told Forbes. “But I don’t think that Starlink alone as it exists today and the reasonable view of its future growth is going to support that sort of valuation.”