WASHINGTON — NASA’s cost and performance on major programs has “deteriorated” significantly in the last year according to a report May 1 by the U.S. Government Accountability Office.

The report, its tenth annual assessment of the agency’s major human and robotic programs under development, found that those programs had an average launch delay of 12 months, the largest GAO had measured over the last decade, and cost growth of at least 18.8 percent.

That cost increase is much less than annual cost growth of more than 45 percent seen earlier in the decade. However, it marks the end of several years of declining cost growth. The report added it could not accurately gauge cost growth because of a lack of an updated cost estimate for the Orion spacecraft, which accounts for 22 percent of overall agency development costs.

“The cost and schedule performance of NASA’s portfolio of major projects has deteriorated since last year,” the report stated.

The GAO attributed most of the cost and schedule growth in the last year to four projects: the Space Launch System, Exploration Ground Systems, Mars 2020 and Space Network Ground Segment Sustainment (SGSS), an upgrade to ground systems used to communicate with NASA spacecraft. Those projects accounted for $638 million of a net cost increase of $646.7 million among NASA projects in development in 2017, and 59 of 91 months overall schedule delay.

All four of those programs suffered “technical challenges compounded by risky programmatic decisions,” according to the report. Examples of the programmatic decisions that contributed to the cost and schedule problems, particularly in the case of human spaceflight programs, include providing low cost and schedule reserves and use of “aggressive” internal schedules that “could exacerbate delays and lead to cost overruns.”

In the case of Mars 2020, its cost overruns are more modest — $12.9 million in the last year — and the mission remains on schedule for a mid-2020 launch. The report blamed issues with a technology demonstration instrument on the mission, as well as higher costs for integrating another instrument.

SGSS has suffered repeated problems, the GAO said, including “incomplete understanding of its requirements” by the contractor and project management issues. Those problems have continued, the report noted, even as the scope of the project decreased.

Steve Jurczyk, NASA acting associate administrator, acknowledged that there were “serious challenges” with SGSS in a May 1 presentation to a joint meeting of the Aeronautics and Space Engineering Board and Space Studies Board of the National Academies. “The good news is that they’ve turned it around,” he said, citing improved project management and contractor performance.

However, he added that the administration’s 2019 budget request to cancel SGSS and consider commercial alternatives. “That leaves us in a very challenging position,” he said, with only one of four antennas upgraded. He said the agency is performing an independent study of SGSS and alternatives.

Other delays and cost increases, the GAO report, are due to technical problems found during integration and testing of spacecraft. That includes the James Webb Space Telescope, whose launch has now been delayed to around May 2020, with a potential overrun of its $8 billion cost cap. NASA’s ICESat-2 spacecraft, an Earth science mission, has also suffered several months of delays because of problems with its main instrument, a laser altimeter.

Some problems, the GAO said, are not directly to blame on the projects themselves. That includes delays in the launch of the GRACE-Follow On and ICON missions because of launch vehicle problems, and a change in scope in a synthetic aperture radar mission being jointly developed by NASA and the Indian space agency ISRO as a result of discussions by an interagency working group.

Some of the schedule issues, the report said, may be due to workforce issues. The GAO cited several cases where projects have run into delays because of “experienced workforce shortages” and difficulty retaining key workers. NASA’s workforce, the report noted, is aging, with 56 percent of its employees age 50 or older, an increase of seven percentage points in five years.

The GAO said NASA was at risk of growing cost and schedule overruns because of those projects and others, citing previously-reported schedule risks for NASA’s commercial crew program. New programs, like Europa Clipper and a proposed follow-on lander, and the Wide-Field Infrared Survey Telescope (WFIRST), will also be ramping up.

“The composition of the portfolio in the coming years is expected to include similarly large and complex projects, putting NASA at risk of continued cost increases and schedule delays,” the GAO concluded. While NASA is taking steps to prevent similar problems, like a recent effort to reduce the scope and cost of WFIRST, the report argued those measures may not be sufficient.

“But even with these efforts, NASA’s cost and schedule performance may be further tested in upcoming years as some expensive, complex projects linger in the portfolio longer than expected,” the report stated.