What Is The Purpose Of Using Sunshield On James Webb Space Telescope?

The James Webb Space Telescope will primarily study the infrared light emitted by faint and faraway objects. The telescope itself must be kept exceedingly cold in order to detect those weak heat signals.

Webb includes a 5-layer, tennis court-sized sun shield [Actual dimensions: 69.5 ft x 46.5 ft, 21.197 m × 14.162 m] that works as a parasol giving shade to protect the telescope from external sources of light and heat (such as the Sun, Earth, and Moon) as well as heat emitted by the observatory itself.

This sunshield will always be between the telescope and the Sun/Earth/Moon. JWST will orbit the Sun 1.5 million kilometers away from (but almost in line with) the Earth, allowing it to be positioned in this manner.

Why Is Sunshiled So Important?

By passively venting its heat into space, the sunshield will allow the telescope to drop to a temperature below 50 Kelvin (-370°F, or -223°C).

Through a passive cooling system, the near-infrared instruments (NIRCam, NIRSpec, FGS/NIRISS) will operate at around 39 K (-389°F, -234°C). Using a helium refrigerator, or cryocooler system, the mid-infrared instrument (MIRI) will operate at a temperature of 7 K (-447°F, -266°C).

How Will The Sunshield CoolThe Webb Telescope?

The sunshield not only creates a cool atmosphere, but also one that is thermally stable. This is necessary to keep the primary mirror segments in good alignment while the telescope rotates around the Sun.

Why Does Sunshield Have Five Layers?

Why is the sunshield made up of five layers rather than a single thick one? Each layer of the sunshield below is colder than the one before it. The heat escapes through the gaps between the layers, and the vacuum between them acts as an excellent insulator. More than five layers separated by vacuum would transfer heat from the bottom to the top of a single large thick sunshield.

The five-layer sunshield’s gleaming silver substance is a complex and creative material science and engineering marvel. Each layer is built of a different composite material, has a different thickness and dimension, and must be spaced exactly to prevent meteorite damage. Specific seams and reinforcements have also been included.

In the material that makes up the sunshield, NASA and its industry partners devised a lightweight, strong way to protect the telescope and mirrors from the sun’s infrared radiation. The sunshield’s robust yet ultra-thin material, unusual kite-like design, and particular role of its layers are just a few of the features that set it apart.

What Material Is Used To Make The Sunshield?

The sunshield is constructed of Kapton, a lightweight polymer with excellent thermal qualities that has been specifically treated.

The sunshield is made up of five layers of Kapton material. Each layer is aluminum-coated, with a “doped-silicon” (or treated silicon) coating on the sun-facing side of the two hottest layers (named Layer 1 and Layer 2) to reflect the sun’s heat back into space. Because the infrared cameras and equipment aboard must be kept very cold and out of the sun’s heat and light to function correctly, the sunshield is an important feature of the Webb telescope.

What Is This Kapton?

Kapton is a polyimide film that DuPont invented in the late 1960s. It has a great heat resistance and can withstand temperatures ranging from minus 269 to + 400 degrees Celsius (minus 452 to plus 752 degrees Fahrenheit).

Even at these extreme temperatures, it does not melt or burn. Kapton polyimide film is utilized in a wide range of electrical and electronic insulating applications on Earth. For optical characteristics and lifespan in the space environment, the sunshield layers are also coated with aluminum and doped-silicon.

What Is Doping?

Doping is a procedure that involves mixing a small amount of another material into the Silicon coating process to make it electrically conductive. The coating must be electrically conductive in order for the Membranes to be electrically grounded to the rest of JWST and to prevent a static electric charge from accumulating on their surface.

Silicon has a high emissivity, which means it emits the greatest heat and light while also blocking the sun’s heat from reaching the infrared instruments beneath it. The highly reflective aluminum surfaces also reflect any remaining energy from the sunshield layer’s margins.

What Is The Reason For Kite Like Design In The Webbbs Sunshield?

On the telescope, the kite-like design and the number of layers of sun shield both play a significant role. To achieve their job, each of the layers is precisely positioned and separated.

“The form and architecture of the James Webb Space Telescope Sunshield also direct heat out the sides, along the perimeter, and between the layers,” said James Cooper, James Webb Space Telescope Sunshield Manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

“Heat generated by the Spacecraft bus in the “core,” or center, is pushed out between the membrane layers, preventing the optics from being heated.”

“The five layers are necessary to block and redirect enough heat to bring the telescope down to required temperatures with a margin of safety,” Cooper explained. “The fifth layer is primarily used as a buffer against flaws, micrometeoroids, and other hazards.” The space between the layers acts as an extra insulator.

Why Are The Layers So Thin?

The sunshield’s layers are extremely thin. The first layer, which will face the sun, is only 0.05 millimeters thick (0.002 inches), while the next four layers are 0.025 millimeters thick (0.001 inches). The aluminum and silicon coatings have even thinner layers. The silicon coating is 50 nanometers thick (1.9 microinches) while the aluminum coating is 100 nanometers thick (3.93 microinches).

The Different Sizes Of The Sunshield Layers

The layers are slightly diverse in size and shape. The smallest layer is Layer 5 (just beneath the primary mirror), and the largest layer is Layer 1. The first layer is rather flat, whereas the fifth layer is more curved. To direct heat from the center to the edges of the layers, the layers are closer together in the center and wider apart at the margins. The layers are often an inch or two apart in the center and roughly 10″ apart at the edges.

The maximum temperature of Layer 1 is 383K, according to thermal models. Layer 5 has a maximum temperature of 221K and a low temperature of 36K.

The optics of the telescope (such as the infrared camera and mirrors) must always be shielded from direct contact with any hot objects. As a result, the membranes are sized and placed in such a way that the mirrors only have a direct line of sight to the chilly Layer 5, whereas the sun only shines directly on Layer 1 regardless of which way the observatory is pointing.

Drawbacks Of The Sunshield

Although the membrane material is durable, a little tear or hole in it can quickly grow into a much larger hole. As a result, a specific procedure known as Thermal Spot Bond (TSB) – places where each layer is melted together – has been developed.

In addition, around every 6 feet or so, reinforcing strips of membrane material are Thermal Spot Bonded to the parent membrane, providing a grid pattern of “rip-stops.”

“This has been proved in testing to stop a tear from spreading beyond a certain grid area,” Cooper explained. As a result, if a hole in the sunshield arises as a result of a meteoroid or small meteor, the damage is reduced.

These aren’t meant to halt a meteoroid; rather, they’re meant to contain the damage.


The sunshield material shrinks as the temperature drops, while the hot layers expand. Cooper stated, ” “When compared to other materials, the Kapton type minimizes this. We’ve had the material tested to see how much it shrinks. We take this into account in both our production and our research of the shape we’ll take in space. To confirm our predictions, we tested a one-third-scale five-layer sunshield at temperature and vacuum.”

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