What happened

For the second day in a row -- and the sixth session out of the last eight -- shares of Virgin Galactic (SPCE 3.15%) are heading lower on Friday, down by 7.3% as of 1:40 p.m. ET.

That's kind of a surprise given that this week was a pretty great week for Virgin Galactic on the news front. The company finally -- after years of waiting -- launched a revenue-generating commercial space tourism flight, and brought all three of its passengers back home safe and sound.

So what

In its press release announcing the success of said spaceflight -- dubbed "Galactic 01" -- Virgin Galactic also confirmed that it's on track to launch "Galactic 02" in August, and then proceed to monthly launches thereafter, using its VMS Eve mothership and VSS Unity spaceplane.  

That sounds like good news. The problem for investors, though, is that it also makes the math on the company incredibly easy to calculate:

(1 spaceplane) x ($250,000 per ticket) x (no more than 6 paying passengers per flight) x (1 flight per month) = $1.5 million in potential monthly revenue for Virgin Galactic.

Unfortunately, it's spending closer to $40 million per month on its operating costs, leading to the inevitable conclusion: Unless Virgin Galactic finds a way to fly a whole lot more often than it's currently promising to, there's no mathematical way this company can make a profit for the foreseeable future.

Now what

Admittedly, Virgin Galactic has a solution to this math problem in mind: Build more spaceplanes.

The company's new Delta class spaceplanes are being designed to fly as frequently as once per week, and if it can build enough of them, there actually is a mathematical chance for it to become profitable. Unfortunately, the Delta spaceplanes in question aren't expected to be ready for flight before 2026, which means Virgin Galactic will probably keep losing money for at least that long.

And each of these planes is expected to cost Virgin Galactic as much as $50 million to $60 million to build -- which will make it necessary to fly even more frequently to recoup those additional costs.

It's kind of looking like a Catch-22 situation for Virgin Galactic. And the fact that investors are selling the stock suggests that they are having no trouble at all doing the math.