Additional telescope mirror reflects new possibilities in astronomy
On March 3rd,a team of engineers at NASA's Goddard Space Flight Center succeededin installing the secondary mirror onto the frame of the future James Webb Space Telescope (JWST). Once operational, the JWST willrepresent the most powerful space telescope ever launched, heraldingan exciting new period in the exploration of our Universe.
The recently completed primary mirror of the JWST boasts a diameter almost threetimes greater than that of the Hubble's Space Telescope, allowing forsuperior light collection. Unlike Hubble, JWST's primary mirror iscomprised of 18 smaller segments that work together to create asingle 21.3-ft (6.5-m) surface.
The purpose of thesecondary mirror is to reflect light collected by the primary mirror,into the sophisticated suite of scientific instrumentshoused behind the mirror surface. As with the primary mirror, thenewly installed convex secondary mirror is constructed from amaterial known as beryllium and coated in a thin layer of gold toimprove its infrared light reflecting capabilities.
The telescope's primaryand secondary mirrors are constructed in such a way that, even in thefrigid and generally inhospitable conditions of outer space, themirrors will only deviate by one ten-thousandth the diameter of ahuman hair.
The attachment methodchosen by engineers when selecting how to secure the secondary mirrorto the main body of the JWST represents a dramatic divergence fromHubble's more traditional design. Hubble's primary and secondarymirrors were both housed inside a 44-ft (13-m) cylindrical spacecraftcapable of fitting snugly inside the fairing of a Space Shuttle.
The sheer size of theJWST made it impossible for the telescope's enormous primary mirroror its 70-ft (22-m) long sunshield to fit inside even the largestrocket fairing, forcing engineers to come up with an ambitious newapproach for the design of the telescope.
To work around theissue, the 18 mirror segments of the primary mirror and the sunshieldwere designed to fold inward to fit inside the constrictive fairingsof the Ariane 5 launch vehicle slated to blast the telescope intoorbit in 2018.
En-route to itsoperational orbit at the L2 lagrangian point, thespacecraft's enormous sunshield will (hopefully) unfurl, followed bythe JWST's primary mirror. Finally, the secondary mirror is liftedinto place by three 25 ft (7.6 m)-long struts.
The 1 mm-thick composite material used to construct the hollow struts isincredibly lightweight, and like the rest of the telescope, isdesigned to cope with the dramatically diverse temperatures they willbe subjected to during launch and the subsequent extended stay indeep space.
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I have great sympathy for those working on it because, even if I were capable of such towering feats, I doubt that I could withstand the stress that every design decision carries nor, especially, when it comes time to launch!