The James Webb Telescope is delayed again. Here's why.

By Jon Kelvey

The bad news: The launch of the James Webb Space Telescope, the decades in the making, big-freaking-mirror-equipped successor to the Hubble, has been delayed yet again.

The good news: Webb is still launching by the end of 2021. Probably.

NASA announced Wednesday that the launch of the Webb telescope aboard an ESA Ariane 5 rocket is set for December 18, 2021, but prior to the announcement, the two space agencies were targeting late October to get the telescope off the ground.

It’s the latest of many delays in a project that has been underway since the late 1980s, but probably a small — and hopefully final bump — before the Webb telescope can finally take up its destined position far from the Earth and begin hunting alien worlds, and peering back into the earliest days of the universe.

Why was the launch of the James Webb Space Telescope delayed?

ESA is launching the Webb on an Ariane 5 from its facility near Kuoru in French Guiana, but the site only allows for the preparation of one rocket launch at a time, and a launch scheduled for the French Military, VA255, is in line ahead of NASA and the Webb and currently scheduled to launch on October 22.

“Arianespace has fine-tuned the sequence and support for VA255 (French Military) and the VA256 (JWST) launch support at CSG in French Guiana,” Mark Voyton, NASA’s launch site manager for the Webb telescope mission, tells Inverse. “This has resulted in a new targeted launch date of December 18 for JWST.”

Mark McCaughrean, an astronomer and member of the ESA science team for the telescope, had previously told Inverse that the launch of the Webb was dependent on the VA255 launch schedule and that the former could change if the latter were to slip.

The new launch date is “indeed due to the preceding Ariane 5 launch and the serial nature of launch prep — No technical or other issues on the side of the spacecraft,” McCaughrean tells Inverse. “Many of the components of JWST's Ariane 5 launcher have been arriving at Kourou from Europe in the past week, so that's all going well.”

Those rocket components are arriving by sea, as is the Webb telescope — while the exact timing of its arrival is being kept under wraps for security reasons, NASA is shipping the telescope to French Guiana through the Panama Canal.

After arrival, it takes 55 days to get the telescope ready and packaged for launch aboard the Ariane 5, according to Voyton.

How many times has The James Webb Space Telescope been delayed? —

The new December launch date makes the sixth NASA has scheduled for its often delayed flagship space telescope.

  1. Back in 2003, the plan was to launch the Webb telescope sometime in 2011
  2. In 2011, mounting problems forced an overhaul, budget increase, and readjustment to the mission schedule. The Webb launch was delayed until October 2018.
  3. In September 2017, NASA announced the launch date was being pushed a second time, to sometime in the spring of 2019
  4. By March 2018, the date was pushed a third time, with NASA now aiming to launch in the spring of 2020
  5. That date would also slip, with the fourth launch date set for October 31, 2021
  6. December 18 will be the fifth and final new launch date — assuming it holds

But a few weeks or months now may well be worth the wait for a space telescope that has been the focus of entire careers of many people involved, and will conduct science for years to come that will make the careers of many scientists more.


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