JWST Sunscreen Offers SPF 1,000,000

By Nancy Atkinson - March 21, 2011 at 2:17 PM UTC | Telescopes

The James Webb Space Telescope will have a sunshield that is about the size of a tennis court, and mission managers say it will offer the best "SPF" (Sun Protection Factor) in the Universe.

"Each of the five layers of the shield is less than half the thickness of a piece of paper," said John Durning, Deputy Project Manager for JWST. "The five work together to create an effective SPF of 1,000,000."

This sunshield protects the observatory from unwanted light, keeping it cool and allowing it to detect heat from faraway objects in the universe. So, how do you get something that large into orbit?

The sunshield will be folded up during launch, and then deployed in a special process that will take seven hours once the telescope reaches its destination at about 1.5 million km (1 million miles) from Earth. Two deployable towers, or Mid Boom Assemblies (MBA), will stretch the sunshield open.

The completion of this hour-long process triggers another mechanism that separates the sunshield's five layers, readying the sunshield for work.

The video above shows how the special mechanisms for deploying the sunshield will work.

The sunshield will protect the telescope's sensitive infrared instruments from the heat and ultraviolet radiation from the Sun.

The sunshield measures 20 meters (65.6 ft.) by 12 meters (39.3 ft.). It is made of a film-like material called Kapton, which is pliable enough that can be folded like a blanket, but strong enough to remain stable in wide range of temperatures, from 36K to 650 Kelvin (-395°F to 710°F or -237 to 377°C).

But JWST will observe primarily the infrared light from faint and very distant objects, so the telescope and its instrument must be very cold, at an operating temperature of under 50 K (-370F/-223C). If the sunshield does its job, the Optical Telescope Element and the Integrated Science Instrument Module on the telescope's topside will stay cool enough by staying in the shade of the sunshield.

The Webb telescope will orbit 1,513,000 km (940,000 miles) from Earth at the L2 Lagrange point and is the first deployable optical telescope in space.

Source:

Goddard Space Flight Center

Nancy Atkinson

Nancy Atkinson

Nancy Atkinson is a space journalist and author with a passion for telling the stories of people involved in space exploration and astronomy. She is currently retired from daily writing, but worked at Universe Today for 20 years as a writer and editor. She also contributed articles to The Planetary Society, Ad Astra (National Space Society), New Scientist and many other online outlets.

Her 2019 book, "Eight Years to the Moon: The History of the Apollo Missions,” shares the untold stories of engineers and scientists who worked behind the scenes to make the Apollo program so successful, despite the daunting odds against it. Her first book “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos” (2016) tells the stories of 37 scientists and engineers that work on several current NASA robotic missions to explore the solar system and beyond.

Nancy is also a NASA/JPL Solar System Ambassador, and through this program, she has the opportunity to share her passion of space and astronomy with children and adults through presentations and programs. Nancy's personal website is nancyatkinson.com