A new report on the James Webb Space Telescope has found that ongoing technical issues with final testing and assembly of the $8.8 billion project will probably cause the launch date of the oft-delayed instrument to slip again to the right. Presently, NASA is targeting June 2019 for launch aboard an Ariane 5 rocket.

The US Government Accountability Office published the report on Wednesday. It concluded, "Given several ongoing technical issues, and the work remaining to test the spacecraft element and complete integration of the telescope and spacecraft, combined with continuing slower-than-planned work at Northrop Grumman, we believe that the rescheduled launch window is likely unachievable."

The report catalogs a number of issues that Northrop Grumman has dealt with during the integration process, particularly the technical challenges and workforce issues needed to meet them. For example, the report cites a worrying problem that cropped up during one of the tests to deploy the telescope's essential sunshield—one of its six membrane tensioning systems experienced a potentially crippling "snag."

Moreover, last year the contractor found that eight of 16 valves in the spacecraft's thrusters were leaking beyond acceptable levels. Although it could not conclusively determine the cause of the leak, Northrop Grumman ultimately determined that this was most likely caused by technician handling errors. The thruster modules had to be individually investigated, refurbished, and re-attached, which contributed months of delays to the schedule.

All of this has left the telescope project with just 1.5 months of schedule reserve. In recognition of this urgency, Northrop Grumman has, according to the report, increased its daily work shifts from two to three, and teams are now working 24 hours per day on spacecraft integration.

This 24-hour-a-day work means that it will not be possible for Northrop Grumman to pour more people into the telescope should further technical issues arise, which the GAO report suggests is likely due to the nature of such a complex project. Moreover, Northrop Grumman had intended to begin to scale back its workforce last year, but due to the problems, it has yet to significantly cut back.

As a result, the James Webb Space Telescope is now perilously short on schedule margin, and with further delays likely and contractor workforce costs still high, it may very well exceed its Congressionally mandated cost cap. The telescope's managing board will soon meet, the report says, and will determine whether the June 2019 launch date can still be met.