A recent report by NASA's chief watchdog raised new doubts about the readiness of contractors to deliver astronauts to space, even before Thursday's explosion of a SpaceX rocket.

Any further delay, NASA's Inspector General found, could mean a continued reliance on Russia to deliver American astronauts to space, a ferry ride that has been growing steadily more expensive.

Since the last shuttle mission blasted off from the Kennedy Space Center in 2011, NASA’s astronauts have had to hitch rides to the International Space Station with Russia, the country America bested in the Cold War race to the moon.

That has come with a pricetag that grew precipitously after the shuttle was retired in 2011. A report issued this week by NASA’s Inspector General found the cost Russia charged to ferry U.S. astronauts jumped 384 percent over the last decade, growing from $21.3 million in 2006 to $81.9 million last year.

Before the shuttle was retired, Russia kept its costs relatively consistent, with the prices growing modestly, the report found. But after the U.S. couldn’t get to space on its own, the prices jumped from an average of $26.4 million a seat in 2010 to $51 million in 2012. In all, the U.S. has paid Russia $3.4 billion for rides on its Soyuz rocket, and the IG said NASA could have saved $1 billion of that if it had met its original goal of flying human missions in 2015.

The agency’s watchdog said that Russia will rake in even more taxpayer money if there are additional delays to NASA’s efforts to fly again from U.S. soil. In 2014, NASA awarded contract to Boeing and SpaceX to fly its astronauts to the station. But the so-called “commercial crew” program is facing delays, the IG found, so that “NASA may need to buy additional seats from Russia to ensure a continued U.S. presence" on the space station.

The report was written before SpaceX’s Falcon 9 rocket blew up as it sat on the launchpad at Cape Canaveral Air Force Station Thursday. It’s unclear whether that failure will contribute to any delays in the commercial crew program. But it was the second time one of SpaceX’s rockets has blown up in the last 15 months, raising concerns about its ability to fly people safely and whether it will be able to meet its timeline.

NASA has stood by SpaceX through both failures, saying it recovered quickly after the first. And on Thursday agency officials said they "remain confident in our commercial partners."

In its report, the IG noted that SpaceX did not think its first failure, which happened in June 2015 on a mission to resupply with space station with $118 million worth of cargo, would cause a delay in the commercial crew program. The company said “it had built sufficient margin into the schedule,” according to the report.

But it also said SpaceX “noted the lack of margin remaining to accommodate any additional unexpected issues that may arise.” The report was released on the same day SpaceX’s rocket exploded.

Boeing has already said it would have to push back its first crewed flights to early 2018. SpaceX has maintained that it would fly by the end of 2017.

But the IG investigators weren’t buying either of those timetables: “Notwithstanding the contractors’ optimism, based on the information we gathered during our audit, we believe it unlikely that either Boeing or SpaceX will achieve certified, crewed flight to the ISS until late 2018.”

In the past, funding shortfalls led to the delays, the IG said. But “technical challenges with the contractors’ spacecraft designs are now driving the schedule slippages,” it said.

Boeing’s spacecraft, the Starliner, has had problems with its mass and the effects of vibrations during launch. SpaceX’s delays came when it changed its capsule design to land in the water instead of on land, it said.

SpaceX declined comment. In a statement, Boeing said that, "as in any development program, issues can stress the schedule and we are working shoulder-to-shoulder with NASA to overcome them. Boeing has been a partner with NASA on the Starliner system since 2010 and we’ve made significant progress on the maturity of our design."

The report also blamed NASA for the delays, saying that in some cases it was taking as long as six months to review reports issued by the contractors when the process should take eight weeks.

If the company's don't launch until late 2018, the hiatus in human space flight would be seven years--even longer than the last of the Apollo-era missions in 1975 to the first space shuttle flight in 1981.

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