Government investigators may be worried about a potentially dangerous defect found in SpaceX’s Falcon 9 rockets — an issue that could compromise the safety of astronauts who are supposed to fly on the vehicle as soon as next year, the Wall Street Journal reports. Specifically, the officials have identified a pattern of cracking in the rocket’s turbine blades, which drive the turbopumps that rapidly funnel propellant into the engines. It’s a hurdle that may require design changes to the Falcon 9, WSJ argues, and could further delay the first launches of the Falcon 9 rocket with people on board.

The concerns are supposedly detailed in a draft of an upcoming report from the Government Accountability Office

The concerns are supposedly detailed in a draft of an upcoming report from the Government Accountability Office, a federal agency that does audits on behalf of Congress. (The Wall Street Journal cites industry and government officials who are “familiar with the matter” in its report.) A representative for GAO confirmed that the agency is working on a report about the Commercial Crew Program, where SpaceX and Boeing are developing vehicles to transport NASA astronauts to and from the International Space Station. “We do have work underway and it is due out later this month,” Charles Young, the managing director of GAO’s public affairs, tells The Verge. “I can’t comment on the contents of the report until it is issued. It is still in draft form and we have not provided copies to any reporters.”

SpaceX is currently modifying its Dragon cargo capsule — a vehicle that the company uses to transport supplies to and from the ISS — so that it can carry NASA astronauts as early as 2018. Once complete, the vehicle, named Crew Dragon, will be able to transport a crew of seven and launch on top of one of SpaceX’s Falcon 9s. Originally, the first crewed flight of the Crew Dragon was supposed to take place this year, but setbacks have forced SpaceX to delay that launch until 2018.

The cracking in the rocket’s turbine blades could cause another delay. NASA has told SpaceX that this cracking pattern in the Falcon 9 is “an unacceptable risk” for future crewed missions, according to the Journal. The WSJ also spoke with NASA’s acting administrator, Robert Lightfoot, who said that the space agency is working with SpaceX on the turbopump problem:

Mr. Lightfoot said “we’re talking to [SpaceX] about turbo machinery,” adding that he thinks “we know how to fix them.” In the interview, Mr. Lightfoot said he didn’t know if the solution would require a potentially time-consuming switch to bigger turbopumps.

However, SpaceX argues that it has designed its engines so that they can withstand cracking in the turbines, but it’s also working on ways to get rid of the problem. “We have qualified our engines to be robust to turbine wheel cracks,” John Taylor, a SpaceX representative, tells The Verge. “However, we are modifying the design to avoid them altogether. This will be part of the final design iteration on Falcon 9. SpaceX has established a plan in partnership with NASA to qualify engines for [crewed] spaceflight.”

“We have qualified our engines to be robust to turbine wheel cracks.”

The GAO report also touches on NASA’s other Commercial Crew partner, Boeing, arguing that the first crewed launches of the company’s capsule, the CST-100 Starliner, will also likely be delayed. Specifically there may be a problem with testing out the capsule’s parachutes, which are needed to land the vehicle after it returns from space. Boeing has already pushed back the first crewed flights of the Starliner twice.

Because the GAO report is just a draft for now, its final iteration could be completely different once it’s released. But if the cracking pattern is mentioned in the final report, however, it wouldn’t be the first time that people have raised concerns about astronaut safety with regard to SpaceX’s rockets. In November, a panel of expert advisors to NASA said they were worried about SpaceX’s plans to fuel the Falcon 9 with people on board, arguing that propellant loading is a “hazardous operation” that shouldn’t be done anywhere near people. During NASA’s Space Shuttle program, astronauts boarded the vehicle after it had been loaded with propellant, but SpaceX is aiming to load the Falcon 9 with propellant after the astronauts have boarded the Crew Dragon on top of the rocket.

At the time, SpaceX argued that it had “designed a reliable fueling and launch process that minimizes" risk to people on board. However, the company also noted that it was open to updating its fueling procedures as needed. "Any additional controls will be put in place to ensure crew safety, from the moment the astronauts reach the pad, through fueling, launch, and spaceflight, and until they are brought safely home," the company said in a statement.

SpaceX’s fueling procedures were called into question by the panel after one of the company’s rockets exploded on a Florida launch pad in September, during a routine fueling procedure. The accident forced SpaceX to ground all of its rockets for more than four months, in order to investigate the cause of the failure. In January, the company revealed that a complex interplay of materials — including liquid oxygen and helium pressure vessels — in the rocket’s upper propellant tank sparked the explosion. SpaceX said it had taken appropriate action to make sure the same failure wouldn’t happen again, and the company successfully returned to flight in January by launching 10 satellites for Iridium from California.

Meanwhile, SpaceX is preparing for its next launch from a newly renovated pad at Cape Canaveral, Florida, known as 39A, which was used for Space Shuttle launches. The company has yet to receive a launch license from the FAA, though SpaceX said it has submitted a license request and is just waiting for approval. “We’ve been working closely with the FAA for six months on getting our vehicles licensed from 39A,” says Taylor. That next launch will transport cargo to the ISS for NASA.