The European Space Agency (ESA) has postponed the deployment of the James Webb Space Telescope on the Ariane 5 launcher for December 24 after a communications issue was rectified. While a formal statement from NASA and the European Space Agency was still due as of late December 17, numerous sources, such as the Space Telescope Science Institute, claimed that the launch had been rescheduled for December 24 at 7:20 a.m. The launch was delayed due to a communication failure between the spacecraft and base equipment. After the encapsulation of the JWST within Ariane 5 payload fairing was completed, the agencies formally confirmed the new launch date on December 18th.

NASA reported on December 14 that the launch, which had been slated for December 22, had been pushed back to no earlier than December 24. The postponement was due to a “communication difficulty between the observatory as well as the launch vehicle system,” according to the agency, which did not provide any other information.

NASA and ESA authorities discussed the matter at an ESA launch briefing on December 16, which was scheduled before the new delay. “It’s an issue with the electrical network that connects the observatory to the ground support equipment.”  Or, to be more exact, it’s a cable placed in the launch table that is experiencing sporadic data losses,” ESA director in charge of the space transportation Daniel Neuenschwander stated.

According to Thomas Zurbuchen, who works as the NASA associate administrator in charge of science, the cable problem caused a delay in a final “aliveness test” of spacecraft systems, which lasts several hours. The spacecraft is enclosed within the payload fairing after the test is completed. “From that point on, it’s all rocket stuff on the critical path.”

He stated he thought the issue, which he characterized as “finicky,” had been solved at the time. “Those of us who work in the launch industry is aware that this happens from time to time. It’s just that when it’s Webb, there aren’t any minor issues.” Zurbuchen tweeted a few hours later that the issue had been rectified and that the aliveness test had begun.

However, completing the test allows the remainder of the launch operations to proceed in the same manner as a conventional Ariane 5 launch. “From now on, it’ll be more of a conventional approach,” Neuenschwander added. “Of course, because Webb is such a unique payload, we’ve enhanced several components,” such as more oversight.

“There’s nothing routine about Webb,” Zurbuchen said of the aliveness test. “But it’s a lot more conventional after that.” The cable problem was not the only issue with communication. NASA offered no detailed details regarding what went wrong at the moment of the incident notice. Josef Aschbacher, who is the ESA Director General tweeted on December 17 that the launch had been delayed for December 24, but then removed the tweet without explanation a short time later. The launch was rescheduled for December 24, according to NASA Administrator Bill Nelson, and the Space Telescope Science Institute notified both staff and the media of the new launch date. However, as of December 17, neither NASA nor the European Space Agency had issued a formal update.