KENNEDY SPACE CENTER, Fla. — The two companies developing commercial crew transportation systems for NASA are experiencing problems that will likely push back the beginning of regular flights until at least late 2018, an agency report warned.

The report by the NASA Office of Inspector General (OIG), released Sept. 1, also concluded that those delays may force NASA to purchase additional seats on Russian Soyuz flights to and from the International Space Station, the cost of which has grown significantly over the last decade.

The report argued that while previous delays in the overall commercial crew development program could be blamed on funding shortfalls, more recent delays have their roots in technical problems both Boeing and SpaceX are experiencing in the development of the respective vehicles, the CST-100 Starliner and Crew Dragon.

“While past funding shortfalls have contributed to the delay, technical challenges are now driving schedule slippages,” the report stated. “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.”

As of June, Boeing had completed 15 of 34 milestones in its Commercial Crew Transportation Capability (CCtCap) contract with NASA, valued at $1.067 billion, according to the report. The company has experienced problems, though, with the CST-100’s development, including mass growth and aeroacoustical loads on its Atlas 5 rocket during launch. Earlier this year, Boeing delayed an uncrewed test flight of the spacecraft to December 2017 and a crewed test flight — likely to carry one NASA astronaut and one Boeing test pilot — until February 2018.

SpaceX, according to the report, has completed eight of 21 milestones under its CCtCap contract and received $469 million. Its issues with Crew Dragon stem in large part from a design change from a spacecraft that would land on dry land to one that will splash down. “This resulted in significant challenges, including complications with vendor components and the effectiveness of the integrated landing system designed to ensure parachutes work and the capsule does not take on excessive water after landing in the ocean,” the report stated.

The report added that SpaceX, which was planning uncrewed and crewed test flights in mid-2017, was encountering issues with several other vehicle subsystems, including the spacecraft’s parachutes and the tunnel allowing the crew to move between the Dragon and the ISS. SpaceX also hadn’t completed all the milestones associated with a critical design review. “Accordingly, we anticipate additional schedule slippage and do not expect certified flights by SpaceX earlier than late 2018,” the report stated.

That assessment came before the Sept. 1 pad accident at Space Launch Complex 40 at Cape Canaveral that destroyed a Falcon 9 and its satellite payload and damaged pad infrastructure. While commercial crew missions will launch from Launch Complex 39A here, the investigation into the failure could delay upcoming launches, including commercial crew test flights.

SpaceX argued in the report that a prior Falcon 9 launch failure in June 2015 did not have a major effect on its commercial crew work. “Although SpaceX officials told us that the [2015] mishap has not delayed its crew development efforts because it had built sufficient margin into the schedule,” the OIG report stated, “they also noted the lack of margin remaining to accommodate any additional unexpected issues that may arise.”

A delay to late 2018, and the possibility of additional delays, could require NASA to purchase additional Soyuz flight services, which currently run through 2018. The report noted that the price of Soyuz seats charged to NASA by Roscosmos has increased by 384 percent since NASA first acquired seats in 2006, to nearly $82 million for six seats in 2018.

The NASA Advisory Council, meeting in Cleveland in July, expressed similar concerns about needing to buy additional Soyuz seats, adding that NASA would likely need to make a decision soon.

“Due to the long lead time to procure Soyuz seats, a decision must be made really very shortly — before the end of 2016 — to guarantee access to the ISS in 2019,” said Wayne Hale, interim chairman of the council’s human exploration and operations committee, at the July 28 meeting, “or we may be forced to reduce or possibly eliminate its crew complement.”

NASA had planned to hold a commercial crew update here Sept. 6 in advance of the Sept. 8 launch of the agency’s OSIRIS-REx asteroid sample return mission. Media arriving at the center for the event were told the event was canceled, without explanation.