This way up: James Webb Space Telescope gets ready for shipment after final tests

It's been a big week for the much-delayed James Webb Space Telescope (JWST) as testing of the observatory was completed and operations to ship the spacecraft to the Kourou launchpad began.

It has been a long time coming – the best part of 25 years since development started – but it looks very much the JWST will finally head to space this year.

A poster child for cost overruns, the JWST is a joint NASA, ESA and CSA project and will make observations in a lower frequency range than the veteran Hubble Space Telescope (HST). Scientists expect the observatory to be able peer at objects too distant for the HST from its L2 location.

The spacecraft is an impressive beast: "100 times more powerful than Hubble," according to NASA. Its primary mirror consists of 18 hexagonal shaped segments, each 1.32m in diameter. Six actuators are attached to the back of each segment for focusing (with an extra one at the centre of the primary mirror segments for adjusting the curvature) and each mirror is aligned to 1/10,000th the thickness of a human hair.

The mirror must also be kept very cold – down to -220°C – and use a sunshield to shade the mirrors and instruments from the Sun as well as the heat coming off the spacecraft's bus itself.

It's all added to up to a hellishly complicated spacecraft that must unfurl itself in space while controllers monitor things from Earth.

Preparations for shipping are expected to be completed in September and once the JWST arrives at the spaceport, the processing for launch will begin in earnest. The spacecraft will be checked for damage incurred in transit, fuelled and mated to its Ariane 5 launch vehicle before rolling out to the launch pad in late November or early December, two days before launch.

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• NASA delays James Webb Space Telescope launch date by at least seven months

Once off the pad, scientists face a nerve-wracking 26-minutes as the telescope rides the Ariane 5 to space, followed by a six-month commissioning period. The sunshield will deploy soon after launch and, during the month it will take the observatory to reach its intended orbital location, the instruments will be powered up, the telescope cooled and the mirrors unfolded.

Assuming the launch goes well. NASA's GAO noted [PDF] "launch vehicle anomalies" back in May. The Ariane 5 has an enviable track record for reliability – its last total failure occurred in 2002, although a repeat of 2018's whoopsie, where satellites were placed in the wrong orbit, would be less than ideal for the JWST. A hiatus of nearly a year occurred between the last Ariane 5 launch, in July, and its predecessor, in August 2020.

Still, the completion of testing and kicking off of the shipment process is a moment to savour for scientists, many of whom have dedicated substantial chunks of careers to the observatory. ®

I've been involved with this project for 23 years. This is a huge moment 😳

Congratulations to all at @nasa, @esa, @csa_asc, @northropgrumman, & the industrial, government, & academic teams who have made this mighty machine.

Next stops: Kourou, L2, & science 🚀 https://t.co/vkw51fO7dw

— Mark McCaughrean (@markmccaughrean) August 26, 2021