LIKE A BEACH UMBRELLA protects people from the Sun’s heat and ultraviolet radiation, the James Webb Space Telescope’s sunshield will protect the telescope and the sensitive infrared instruments from the Sun’s heat and light.
“Each of the five layers of the shield is less than half the thickness of a piece of paper. The five work together to create an effective SPF (or Sun Protection Factor) of 1,000,000,” said John Durning, Deputy Project Manager for the James Webb Space Telescope Project, at NASA’s Goddard Space Flight Centre.
The large sunshield is 20 metres by 12 metres and made of a material called Kapton that can be folded like a blanket. Kapton is a film developed by DuPont which can remain stable and strong over the wide range of temperatures, from 36K to 650 Kelvin (K) (-237 to 377°C), the sunshield will experience during its launch and deployment.
Once on orbit, the sunshield creates a 330 K (117°C to -212°C) temperature differential between the hottest and coldest layers. Using multiple separated layers allows most of a layer’s heat to radiate to space before it reaches the next one, forming a substantial temperature drop from one layer to the next.
The James Webb Space Telescope will observe primarily the infrared light from faint and very distant objects. But all objects, including telescopes, also emit infrared light in the form of heat energy. To avoid swamping the very faint astronomical signals with radiation from the telescope and the telescope from seeing its own thermal signature, the telescope and its instruments must be very cold, at an operating temperature of under -223°C.
The observatory will be pointed so that the Sun, Earth and Moon are always on one side, and the sunshield will act like a beach umbrella, keeping the Optical Telescope Element and the Integrated Science Instrument Module on the telescope’s topside cool by keeping them in the shade and protecting them from the heat of the Sun and warm spacecraft electronics.
The Webb telescope will orbit 1,513,000 km from Earth at the L2 Lagrange point and will be the first deployable optical telescope in space. It will undergo a complex post-launch sequence of deployments including the sunshield, before it becomes fully operational.
For more information on the sunshield, visit http://www.jwst.nasa.gov/sunshield.html
For more information on the James Webb Space Telescope, visit http://jwst.nasa.gov/
Adapted from information issued by Rob Gutro, NASA’s Goddard Space Flight Centre.
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