Additional telescope mirror reflects new possibilities in astronomy

NASA engineers install the JWST's secondary mirror

NASA engineers install the JWST's secondary mirror (Credit: NASA/Chris Gunn)

On March 3rd, a team of engineers at NASA's Goddard Space Flight Center succeeded in installing the secondary mirror onto the frame of the future James Webb Space Telescope (JWST). Once operational, the JWST will represent the most powerful space telescope ever launched, heralding an exciting new period in the exploration of our Universe.

The recently completed primary mirror of the JWST boasts a diameter almost three times greater than that of the Hubble's Space Telescope, allowing for superior light collection. Unlike Hubble, JWST's primary mirror is comprised of 18 smaller segments that work together to create a single 21.3-ft (6.5-m) surface.

The purpose of the secondary mirror is to reflect light collected by the primary mirror, into the sophisticated suite of scientific instruments housed behind the mirror surface. As with the primary mirror, the newly installed convex secondary mirror is constructed from a material known as beryllium and coated in a thin layer of gold to improve its infrared light reflecting capabilities.

The telescope's primary and secondary mirrors are constructed in such a way that, even in the frigid and generally inhospitable conditions of outer space, the mirrors will only deviate by one ten-thousandth the diameter of a human hair.

The attachment method chosen by engineers when selecting how to secure the secondary mirror to the main body of the JWST represents a dramatic divergence from Hubble's more traditional design. Hubble's primary and secondary mirrors were both housed inside a 44-ft (13-m) cylindrical spacecraft capable of fitting snugly inside the fairing of a Space Shuttle.

The sheer size of the JWST made it impossible for the telescope's enormous primary mirror or its 70-ft (22-m) long sunshield to fit inside even the largest rocket fairing, forcing engineers to come up with an ambitious new approach for the design of the telescope.

To work around the issue, the 18 mirror segments of the primary mirror and the sunshield were designed to fold inward to fit inside the constrictive fairings of the Ariane 5 launch vehicle slated to blast the telescope into orbit in 2018.

En-route to its operational orbit at the L2 lagrangian point, the spacecraft's enormous sunshield will (hopefully) unfurl, followed by the JWST's primary mirror. Finally, the secondary mirror is lifted into place by three 25 ft (7.6 m)-long struts.

The 1 mm-thick composite material used to construct the hollow struts is incredibly lightweight, and like the rest of the telescope, is designed to cope with the dramatically diverse temperatures they will be subjected to during launch and the subsequent extended stay in deep space.

Source: NASA

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