On May 11th, SpaceX launched the inaugural mission of its powerful new Falcon 9 rocket, called the Block 5 — the same vehicle the company will use to send astronauts to the International Space Station. However, it turns out the vehicle used for that first launch wasn’t in its final configuration to fly crew members for NASA, Quartz reports, though it was believed to be.

Before the launch, SpaceX CEO Elon Musk was asked if the Block 5 rocket met NASA’s requirements for flying astronauts, and he said he thought so. “That’s my understanding, but I could be mistaken,” Musk said. However, the rocket was missing some upgraded tanks that will have to be installed long before crewed flights can take place. And that means SpaceX will have to fly even more flights of the Block 5 before astronauts can board it.

The Block 5 is meant to be the final major iteration of SpaceX’s Falcon 9 rocket. It’s designed with higher thrust and more robust landing capabilities, which will make it easier for SpaceX to reuse the vehicle quickly after each launch. It’s also the vehicle that SpaceX plans to use to send astronauts to the International Space Station, as part of NASA’s Commercial Crew program. But first, NASA is requiring that SpaceX fly the Falcon 9 Block 5 at least seven times in a frozen “crew configuration” before the space agency will allow astronauts on board. That means no major design changes can be added between flights.

the Falcon 9 that flew on May 11th won’t be counted toward the seven flight requirement

But it turns out the Falcon 9 that flew on May 11th won’t be counted toward the seven flight requirement. That’s because it was missing key upgraded hardware known as COPVs — composite overwrapped pressure vessels. These bottles sit inside the main propellant tanks of the rocket, filling them with helium when the fuel is rapidly gobbled up during flight. The COPVs have been a headache for SpaceX: in September 2016, one of these bottles caused a Falcon 9 to explode on a launch pad during fueling. The material wrapped around the COPV caused the super cold propellants inside the tank to ignite.

SpaceX has since been fortifying the COPVs to make sure they are up to NASA’s rigorous safety standards, according to SpaceX CEO Elon Musk. “The amount of testing and research that’s gone into COPV safety is gigantic,” he said during a press conference before the first Block 5 flight. “This is by far the most advanced pressure vessel developed by humanity. It’s nuts.”

Testing and development of these enhanced COPVs is complete, according to SpaceX, however the bottles won’t be incorporated into the Falcon 9 Block 5 until the company does its first Commercial Crew demonstration mission in August. That flight, called Demo-1, is meant to test out SpaceX’s upgraded Dragon crew capsule, by launching it without crew to the International Space Station. The first crewed flight of the Dragon is scheduled for December. So after Demo-1, SpaceX will need to fly six more Block 5s before December to meet that schedule. SpaceX has been launching more frequently, so that may be doable. Plus, it’s possible the dates for the Commercial Crew program will be delayed, according to government auditors, so that may give SpaceX more time to get all its flights done.

SpaceX and NASA confirmed to the The Verge that the May 11th flight does not count toward the seven flight requirement. Yet, they both say that data from the first Block 5 flight will be used to make sure future crewed missions are safe. “Falcon 9 Block 5’s first flight serves as an important milestone toward flying crew to the International Space Station later this year,” a SpaceX spokesperson said in a statement to The Verge. NASA says that all Block 5 flights without the new COPVs will be important. “Early Falcon 9 Block 5 flights will provide important insight into the rocket, and will contribute to the certification efforts for the Falcon 9 Block 5 configuration for crew,” a NASA spokesperson said to The Verge in a statement.

“Falcon 9 Block 5’s first flight serves as an important milestone toward flying crew to the International Space Station later this year.”

SpaceX’s COPVs are of particular concern to NASA because of how SpaceX plans to fuel its rockets for future crewed missions. When astronauts fly on the Falcon 9, SpaceX plans to load crew members onto the rocket, quickly fill the vehicle up with super-cold propellant, and then launch shortly afterward. This process, called “load and go,” can save SpaceX time when launching rockets, but it has been criticized by many within the aerospace industry. Fueling is a dangerous procedure that shouldn’t be done in close proximity to people, according to safety experts. On the Space Shuttle, for instance, propellant was loaded many hours before crew boarded the vehicle. And since a COPV caused one of SpaceX’s Falcon 9s to explode during fueling, NASA wants to make sure these bottles are extra safe.

When asked about the controversy surrounding “load and go,” Musk said SpaceX doesn’t have to fuel the rocket after astronauts board. “I think that issue has been somewhat overblown,” he said. “We certainly could load the propellants and then have the astronauts board Dragon. That’s certainly something we could do.” However, he said he doesn’t think that course of action will be necessary. He also noted that if the COPVs don’t work, the company has a backup plan of switching to more resistant spheres made of alloy.

Since testing on the new COPVs is complete, it seems that option also won’t be needed. A group of NASA safety experts recently said that it’s possible the “load and go” approach could work, as long as the risks are minimized. However, the new COPVs need to prove themselves, and it’ll be at least a few months before they fly, meaning SpaceX’s final Falcon 9 upgrade isn’t totally complete just yet.