But officials said they hope to resume testing at the Greenbelt center later this month and keep the $8.7 billion project on track for a launch that is less than two years away.
Engineers began exposing the telescope's mirrors and instruments to intense vibrations in November — part of testing to ensure it can survive its ride into space.
They stopped those tests Dec. 3 when sensors indicated parts of the telescope were shaking more than expected.
Officials said Tuesday they are closer to figuring out why that is, and have successfully exposed the telescope to lower levels of vibrations as they sort out the problem.
"Currently, the team is continuing their analyses with the goal of having a review of their findings, conclusions and plans for resuming vibration testing in January," Eric Smith, the telescope's program director, said in a statement.
The telescope is considered the successor to the Hubble Space Telescope, and is designed to see parts of the universe that Hubble cannot. It could spot galaxies just a few hundred million years old, instead of the billion-year-old galaxies Hubble can see.
The Goddard center in Greenbelt has led development of the Webb telescope since its inception in the late 1990s. Once the telescope reaches space and begins observing, Baltimore's Space Telescope Science Institute will oversee its scientific mission and operations.
After years of development and construction at Goddard, the telescope with its honeycomb-shaped mirrors was scheduled to be shipped to NASA's Johnson Space Center in Houston in February.
But first, the telescope has to complete tests in Greenbelt that expose it to the violent vibrations and booming sounds it will face when it launches from a European spaceport in French Guiana in October 2018.
During vibration testing last month, sensors attached to the telescope measuring its movement "detected unexpected responses and consequently the test shut itself down to protect the hardware," NASA officials said. Since then, a team of engineers and scientists has been analyzing what could be responsible.
Visual inspections of the telescope structure and examinations using sound waves show it to be unharmed, officials said.
The project remains on schedule and on budget, NASA spokeswoman Felicia Chou said. Before the problem was detected, there was a six-month cushion built into the 22 months to launch to account for delays, she said.
Some of that cushion is currently being used up, "but the precise amount will be determined once the team decides how it will proceed through the remainder of the test program," Chou said.
After undergoing testing in a massive cryogenic chamber in Houston, the telescope is slated to arrive at Northrop Grumman facilities in California in July or August, where it will be integrated with its tennis-court-sized sun shield.
The Hubble telescope was infamously launched into orbit around Earth in 1990 with a faulty mirror that had been ground into the wrong shape, producing images of poorer quality than expected. It was repaired in 1994 in the first of several servicing missions.
The Webb telescope, on the other hand, cannot be serviced in space because it is headed for a point in space a million miles from Earth.