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James Webb Space Telescope completes its voyage to French Guiana

Only a million or so miles to go

The multinational James Webb Space Telescope – named after a former NASA administrator – has arrived in French Guiana, home to Europe's Spaceport, with launch finally in sight.

An international collaboration (including contributions from NASA, ESA and the Canadian Space Agency), the long-in-gestation and eye-wateringly overbudget observatory is due for launch atop an Ariane 5 rocket on 18 December, just squeaking into 2021, if all goes well.

Aside from the 16-day, 5,800-mile trip at sea from California, it has been quite the journey for the space telescope, on which work began in 1996 ahead of a 2007 launch date. Back then the budget was around $500m. These days it's nearer $10bn after repeated delays and a redesign. To be fair, however, nothing quite like the James Webb Space Telescope (JWST) has ever been built before. Then again, that is still quite the overrun and delay.

Unlike the Hubble Space Telescope (HST), which lurks in a Space Shuttle-friendly Earth orbit, the JWST will be placed near the Earth-Sun L2 Lagrange point. A large sunshield will keep the payload cool to permit observations in the infrared using the iconic 6.5m mirror, which is itself made up of 18 hexagonal mirrors and considerably larger than the comparatively weedy 2.4m mirror of the ageing HST.

The focus on the infrared means that while the JWST won't work in the same wavelengths as the HST, its lower frequency range means it should be able to observe objects far older and more distant than the HST can. However, its location means that dealing with any spacecraft anomalies will present considerably more of a challenge than the Hubble servicing missions of old. Which, in turn, has caused some of the delays as engineers have tested and tested again the observatory while it is on the ground.

Construction was completed in 2016 (although integration of all the components took a few years longer). The intervening years before its shipment to French Guiana have seen multiple tests, including one that resulted in the sunshield tearing. Other issues included problems with the propulsion system and, in one report [PDF], "loose hardware was found in the lower area of the spacecraft."

While it might have seemed at times that the launch date would never stop slipping, the JWST is now closer to the launchpad than it has ever been. And, once in space, all will be forgiven once the data starts flowing from the science payload.

"We are going to see things in the universe beyond what we can even imagine today," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate in Washington, after paying tribute to the efforts of the multinational team responsible for the telescope.

Before it can trouble the top of an Ariane 5, engineers must extract the JWST from its shipping container (following a drive to the launch site) before performing some final checks and loading the spacecraft with fuel. It will then be enclosed in the Ariane fairing for launch.

The first few days of the JWST's journey to its final orbit will see the solar array, antennas and sunshield deployed, with the full mirror being unfolded at around the two-week mark.

The spacecraft is expected to arrive at the second Lagrange point 30 days after launch with the entire commissioning phase expected to take six months, followed by a five-year science mission. The goal is a lifetime greater than 10 years, although the limiting factor will be the fuel needed to keep the spacecraft in place around L2.

Not quite the prodigiously long life of the HST but, again, there isn't much on the JWST that can really be serviced by astronauts should things go wrong. Even getting a crewed spacecraft to the JWST's final location would be a challenge in itself. ®

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