On Friday, SpaceX founder Elon Musk revealed his grand vision for the future of his company, including a new mega-rocket titled the “BFR (Big Fucking Rocket)”, which would theoretically ferry humans to Mars and — if all goes according to plan — around the world in less than an hour, with an ultra-fast passenger rocket service meant to compete with airlines.

Though this would require building an entire network of super expensive rockets, Musk claimed in a follow-up Instagram the cost per seat “should be about the same as full fare economy in an aircraft.” Early calculations from experts suggest this is almost definitely bullshit.

“I think that’s pretty much wishful thinking without backing it up with solid data,” Ella Atkins, a professor in the Department of Aerospace Engineering at the University of Michigan, tells Inverse. “What’s being ignored in addition to fuel — not just the processing and loading — is who’s going to build the launchpads? What will the infrastructure look like for building, maintaining, and dealing with [these launchpads] in bad weather look like?”

It’s incredibly exciting that Musk is exploring alternatives to long-distance travel from continent to continent. Anyone who has the same flight-induced anxiety I have will tell you that the shorter travel time can be, the better. But there’s no evidence to support the claim that this unprecedented technology would cost around the same as a standard plane ticket.

Atkins did a quick calculation to determine what a round trip between Detroit, Michigan, and Perth, Australia, would cost on Delta Airlines and found that it ranged from $2,574 to $7,762, depending on how many layovers a person was willing to take. She also found that a nonstop round trip in that same time frame between Detroit and Beijing would cost $984 at the lowest.

“It is clear that a rocket ticket will not be the low price (~$1K) of the round-trip ticket Detroit to Beijing,” Atkins says. “It is also not clear the rocket will be able to hold enough passengers to offer each a $7.7K price. Remember that in addition to the actual cost of the rocket (which might be subsidized by investors/government), each rocket ‘flight’ will also incur substantial expense for rocket fuel and between-flight rocket servicing and preparation.”

It’s unclear how many passengers the BFR will actually be able to hold — the number of folks on board will definitely help determine the cost of a ticket. But no matter how you slice it, it’s pretty unlikely that a trip around the world in under an hour will cost you the same as an economy ticket on board your average airplane — at least to start. Be sure to stretch before you reach for the stars, Elon.

If you liked this article, check out this video of the nerdy way Elon Musk comes up with names for his inventions.