Mirror, Mirror

The James Webb Space Telescope's "eyes" will be a wonder of complex, precisely coordinated technology. An elaborate system of mirrors, support trusses and instrument apertures will collect light and direct it into the telescope's instruments for analysis and recording.

The system's most innovative component is the telescope's primary mirror. The mirror consists of 18 extremely lightweight  but rigid segments. The segments are made of beryllium, a material capable of handling the extreme cold the Webb telescope will face: -233.3 Celsius (40 Kelvin, -388 degrees Fahrenheit). Beryllium contracts and deforms less than glass at this cold temperature, and thus remains more uniform.

The Webb mirror will also be coated with a fine layer of 24-karat gold. This gold coating is used in infrared telescopes because it reflects red light extremely well. Using gold will make the mirror 98 percent reflective; ordinary mirrors are only 85 percent reflective.

Packing Light

The mirror will be folded up to fit inside the rocket that launches it. Once the telescope is placed in its orbit, ground controllers will send a message telling the telescope to unfurl its mirror segments — like a butterfly opening its wings.

Once the mirror is open, its segments will be looking at different points in the sky. Webb's operators will order the telescope to reposition its mirrors so they all focus on the same point. Each segment has three attachment points around its edge, which are connected to two variable-length legs and a pressure pad in the center. Through adjustments in the six legs, each mirror segment can tilt, twist, and shift to face the correct direction and position. In addition, the pressure pad can be moved like a piston, allowing Webb's operators to warp the very shape of the segment to perfectly match the others. The mirror segments will be repositioned at least once a month.

At 21.3 feet (6.5 m), Webb's mirror has about seven times the area of Hubble's. The resolution of the new observatory will be three times more powerful than Hubble in the infrared. Hubble can see to about 800 million years after the Big Bang, while Webb will be able to see to about 200 million years after the Big Bang.

It may not sound like big difference, but like any newborn, the universe changed drastically and quickly in its early life. Looking at the early universe at different stages is like the difference between viewing pictures of a baby and pictures of a teen. The infant pictures will change swiftly, within days, while the teen pictures will hardly differ at all from week to week.