Update (December 22, 2016) – NASA has responded to our request for more information. In an email, a NASA spokesperson said: 

Engineers observed unexpected data from devices attached to the telescope that measure how much and fast parts are moving. Engineers are currently running diagnostics to determine the source of these anomalies, and whether this has impacted the telescope. The test aborted safely, like it was designed to do. Initial inspections of all telescope systems did not show any damage to the telescope. We will have more information available once the engineers have methodically run through the tests and determine the cause.

We will have to determine the source of the anomaly before we can determine whether there is an impact to the testing schedule. We will provide updates as they are available. The test-schedule and budgets have built-in reserves precisely to account for such issues.

Our original story is below.

Uh oh.

The $8.8 billion James Webb Space Telescope (JWST) has had a tough time of things so far, being seven years delayed and billions of dollars over budget. So finding a fault in the telescope isn’t going to do anything good to its reputation.

That’s what seems to have happened though. In a brief update, NASA said that an anomaly had been found during vibration testing, which simulates the forces the telescope will experience during its launch on an Ariane 5 rocket in 2018.

“During the vibration testing on December 3, at Goddard Space Flight Center in Greenbelt, Maryland, accelerometers attached to the telescope detected anomalous readings during a particular test,” the statement read.

The cause isn't known yet, with NASA saying they were performing further tests to identify the source of the anomaly. On the plus side, NASA said the engineering team could see no signs of visible damage. We’ve asked for further information, but haven’t heard back yet. (edit: response above)

And, well, everyone will be hoping beyond hope that this is just something minor. There is huge pressure on the JWST to be successful, not least because of the delays and budget overruns, but also because it is billed as the successor to the Hubble Space Telescope. Once launched, it will be positioned 1.5 million kilometers (1 million miles) from Earth, where – unlike Hubble in Earth orbit – it cannot be repaired by any future missions. So it has to work perfectly first time.

Hubble, of course, infamously launched in 1990 with a design flaw in its primary mirror, and had to wait until 1993 until it was fixed via a Space Shuttle servicing mission. Four more servicing missions were carried out up to 2009, and today Hubble works flawlessly, giving us astonishing views of the universe.

This problem comes just a month after JWST’s huge primary mirror, made of 18 hexagonal gold-plated segments, was revealed to the public for the first time. This milestone meant that JWST is effectively complete, beginning preparations for the launch in October 2018.

If everything does go to plan, then we’re in for a treat. Observing the cosmos in infrared, JWST will be unmatched in its power, studying distant stars, galaxies, exoplanets, and more. It’s arguably the greatest space observatory we’ve ever built – so here’s hoping things play out a bit more smoothly from here on.