Popular Science USA – July-August 2019

FA

LL

2

01

9

• P

O

PS

C

I.

C

O

M

102

Although the surface of the mirror is

smooth, the underside features a

honeycomb pattern of 1,681 hexag-

onal spaces, seen here (opposite)

through the top of the reflector. This

results in a stiffer piece of glass that

is 80 percent lighter than a compa-

rable solid chunk. More important,

Once the glass cools, the team

lifts the slab from the furnace

using a temporary fixture they

secure to the surface with super-

sticky adhesive. The disc, which is

27.5 inches thick, gets a good

scrubbing top and bottom. Then

technicians flip the unwieldy mass

FRAMING SWEAT-PROOF

the design sheds heat much faster

come nightfall, minimizing thermal

distortion. Imagine hot air shim-

mering above a road, except it’s

coming off your billion-dollar tele-

scope, obscuring your view. The

resulting images will be sharper and

clearer come showtime.

upside down to install 157 brack-

ets called load spreaders that

distribute the mirror’s weight as

evenly as possible. That hardware,

which the crew is preparing to

install here (above), affixes the

finished product to its designated

spot within the telescope.