The giant rocket that NASA is building to send astronauts to the Moon will likely be delayed and over budget — yet again. That’s according to a new report from the Government Accountability Office, which reviewed the hardware NASA has been developing for deep space human exploration. The report, originally leaked to The Washington Post, is the latest in a long string of reviews that have identified schedule problems and cost overruns with the rocket’s development program.

For most of the last decade, NASA has been developing two key vehicles to carry humans beyond Earth orbit. One is the Space Launch System, or SLS, a massive rocket capable of sending people to the vicinity of the lunar surface. The other is a crew capsule called Orion, which humans will ride inside when traveling on top of the SLS. The two vehicles were supposed to launch together for the first time back in 2017, but the inaugural flight has been consistently pushed back and is now slated to occur in June 2020. The delays have also led to cost overruns for the SLS program, which have added up to an extra $1 billion, according to NASA.

it’s possible the SLS will fly for the first time as late as June 2021

The new GAO report out today argues that NASA probably won’t meet the June 2020 deadline. Instead, it’s possible the SLS will fly for the first time as late as June 2021, especially if the agency encounters any more issues while piecing together the rocket and testing it. Additionally, the GAO accuses NASA of not being transparent in its cost estimates for both the SLS and Orion. The GAO report finds that the cost of the increase to the SLS program is actually closer to $1.8 billion, because NASA shifted around some associated costs of the rocket to future missions. The cost of Orion is expected to increase, too, but the GAO doesn’t have a good idea of what it’s going to be because NASA hasn’t updated its estimates for the program.

Despite all of these delays and cost overruns, NASA has still been giving “award fees” to Boeing and Lockheed, the primary contractors for SLS and Orion respectively, that have equaled out to $200 million. These fees are usually given out to the agency’s contractors for good performance and maintaining schedule. But the GAO report calls out Boeing for underestimating just how many workers it would need for the SLS build and the complexity of the rocket’s design.

NASA’s William Gerstenmaier, associate administrator for human exploration, responded to the GAO report by reminding the office that the SLS and Orion will be “some of the most sophisticated hardware ever built,” and that “NASA is pushing the boundaries of human exploration.” He argued that while the programs have experienced challenges, the GAO report imagines the “worst-case schedule outcomes.” Gerstenmaier also disagreed with the claim that NASA hasn’t been transparent about costs, arguing that NASA has had to deal with uncertainty in its budgets and direction. That has made it difficult to be efficient and execute programs effectively.

Efficiency will become even more important moving forward. The GAO identified very little room for error in the SLS schedule, since it is jam-packed up until a big test that the program must complete known as the “green run” test. That’s when the main core of the rocket will be fired on the ground, to see if all the components of the rocket work together. Any delay could put NASA’s current ambitions at risk.

the SLS and Orion are instrumental in NASA’s goal of returning humans to the surface of the Moon

Both the SLS and Orion are instrumental in NASA’s goal of returning humans to the surface of the Moon, part of a new initiative named Artemis. In March, Vice President Mike Pence called on NASA to expedite its lunar program and send people to the Moon by 2024, instead of 2028 like the agency had planned. Now, NASA’s administrator Jim Bridenstine is seeking funding from Congress for this accelerated deadline. The agency asked for an additional $1.6 billion for fiscal year 2020, on top of NASA’s requested budget of $21 billion, to fund the Artemis program. And Bridenstine told CNN that he estimates an extra $20 to $30 billion will be needed over the next five years — in addition to NASA’s annual budget — to ensure that the agency makes it to the Moon by 2024.

Even if Congress somehow funds the whole program as desired, meeting the 2024 deadline is reliant on NASA’s hardware being built on time, and this latest report shows that the GAO remains pessimistic about the prospect of Orion and the SLS meeting that five-year goal.

In the meantime, NASA continues to press forward with the program. The agency says it will adhere to some of the recommendations that the GAO advised in its report, including ways to come up with better estimates for the program. However, NASA did not say it will update the estimated launch date for the SLS, so it seems that the agency is still aiming for a launch next year, despite the GAO’s doubts.