By Christian Davenport / The Washington Post

The spacecraft Boeing plans to use to fly NASA astronauts to the International Space Station suffered a significant setback when, during a test of its emergency abort system in June, officials discovered a propellant leak, the company confirmed.

In a statement to The Washington Post, Boeing said it has “been conducting a thorough investigation with assistance from our NASA and industry partners. We are confident we found the cause and are moving forward with corrective action.”

The leak is likely to delay its launch schedule and is another setback for a program that has faced a number of problems. The trouble also comes as Vice President Mike Pence is expected to announce the crews for the first missions during a ceremony in early August at the Kennedy Space Center in Florida.

Along with SpaceX, Boeing is under contract from NASA to fly astronauts to the space station. The “Commercial Program” would restore NASA’s ability to fly humans from the United States — a capability that was lost when the Space Shuttle was retired in 2011. Since then, the space agency has had to rely on Russia to fly its astronauts to space, at a cost of more than $80 million per seat.

Under the program, Boeing’s contract was worth as much as $4.2 billion; SpaceX’s was $2.6 billion for the same number of flights.

The program’s first test launches with crews on board were supposed to occur this year. But a recent report from the Government Accountability Office said that the company’s schedules “are aggressive” and that Boeing “set ambitious-rather than realistic-dates, only to frequently delay them.”

SpaceX, the rocket company founded by Elon Musk, also has faced challenges and is working to show NASA that it has corrected a problem that caused one of its uncrewed Falcon 9 rockets to explode during fueling in 2016.

In its report, the GAO said further delays in the program could “disrupt access to” the space station-which would be an enormous embarrassment for NASA. The space agency has been counting on Boeing and SpaceX to fly astronauts there. But the GAO said the delays could mean the companies’ spacecraft are not certified before the last flights NASA has secured for its astronauts on Russian rockets, which would keep an American presence on the station through early 2020.

In other words: Should delays persist, NASA could find itself with no way to get to the station, the orbiting laboratory that has cost NASA $100 billion to build and operate.

In a statement, NASA said that “flying safely has always taken precedence over schedule. As our partners are finalizing their systems, we’re assessing remaining technical details and schedules for flight tests with and without crew.”

The agency said it plans to announce an update on the test-flight schedules next month.

Boeing said it discovered the propellant leak during the emergency abort test in June at the White Sands Test Facility in New Mexico.

“The engines successfully ignited and ran for the full duration,” the company said in a statement. “During engine shutdown, an anomaly occurred that resulted in a propellant leak.”

The GAO report cited concern about another problem with the abort system, an issue that caused it to “tumble, which could pose a threat to the crew’s safety.”

Boeing has said that it corrected that problem and that it would “meet or exceed all NASA requirements.”