The Ariane 5 rocket is a workhorse for delivering satellites and other payloads into orbit, but fitting the James Webb Space Telescope (JWST) inside one is pushing the boundaries of the Ariane 5’s capabilities, and advancing our design of space observatories at the same time.
The Ariane 5 is the most modern design in the ESA’s Ariane rocket series. It’s responsible for delivering things like Rosetta, the Herschel Space Observatory, and the Planck Observatory into space. The ESA is supplying an Ariane 5 to the JWST mission, and with the planned launch date for that mission less than three years away, it’s a good time to check in with the Ariane 5 and the JWST.
The Ariane 5 has a long track record of success, often carrying multiple satellites into orbit in a single launch. Here’s its most recent launch, on January 27th from the ESA’s spaceport in French Guiana. This is Ariane 5’s 70th successful launch in a row.
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But launching satellites into orbit, though still an amazing achievement, is becoming old hat for rockets. 70 successful launches in a row tells us that. The Ariane 5 can even launch multiple satellites in one mission. But launching the James Webb will be Ariane’s biggest challenge.
The thing about satellites is, they’re actually getting smaller, in many cases. But the JWST is huge, at least in terms of dimensions. The mass of the JWST—6,500 kg (14,300 lb)—is just within the limits of the Ariane 5. The real trick was designing and building the JWST so that it could fit into the cylindrical space atop an Ariane 5, and then “unfold” into its final shape after separation from the rocket. This video shows how the JWST will deploy itself.
The JWST is like a big, weird looking beetle. Its gold-coated, segmented mirror system looks like multi-faceted insect eyes. Its tennis-court sized heat shield is like an insect’s shell. Or something. Cramming all those pieces, folded up, into the nose of the Ariane 5 rocket is a real challenge.
Because the JWST will live out its 10-year (hopefully) mission at L2, rather than in orbit around Earth, it requires this huge shield to protect itself from the sun. The instruments on the James Webb have to be kept cool in order to function properly. The only way to achieve this is to have its heat shield folded up inside the rocket for launch, then unfolded later. That’s a very tricky maneuver.
But there’s more.
The heart of the James Webb is its segmented mirror system. This group of 18 gold-coated, beryllium mirrors also has to be folded up to fit into the Ariane 5, and then unfolded once it’s separated from the rocket. This is a lot trickier than launching things like the Hubble, which was deployed from the space shuttle.
Something else makes all this folding and unfolding very tricky. The Hubble, which was James Webb’s predecessor, is in orbit around Earth. That means that astronauts on Shuttle missions have been able to repair and service the Hubble. But the James Webb will be way out there at L2, so it can’t be serviced in any way. We have one chance to get it right.
Right now, the James Webb is still under construction in the “Clean Room” at NASA’s Goddard Space Flight Centre. A precision robotic arm system is carefully mounting Webb’s 18 mirrors.
There’s still over two years until the October 2018 launch date, and there’s a lot of testing and assembly work going on until then. We’ll be paying close attention not only to see if the launch goes as planned, but also to see if the James Webb—the weird looking beetle—can successfully complete its metamorphosis.