It’s never a good thing when an anomaly is detected in your scientific instrument during pre-operational testing. When that instrument is the James Webb Space Telescope—which is expected to cost about $8.8 billion, cannot be fixed after launch, and is counted upon to provide insights about the earliest days of the Universe—it’s cause for significant concern.

The anomaly occurred earlier this month, on Dec. 3, during vibration testing at Goddard Space Flight Center in Maryland. As part of the run-up to a launch in late 2018, the telescope will be subjected to all manner of conditions, from extreme temperatures to a hard vacuum, to ensure that it will survive during its five- to 10-year mission in deep space. The telescope must also withstand its launch aboard an Ariane 5 rocket, and the vibration test mimicked the shaking and gravitational forces of launch. After the test began, accelerometers detected “anomalous readings,”  but so far cause of the anomaly has yet to be determined.