astronomy

James Webb Space Telescope sunshield

James Webb Space Telescope sunshield is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand James Webb Space Telescope sunshield rather than just read about it. In short: The James Webb Space Telescope (JWST) sunshield is a passive thermal control system deployed post-launch to shield the telescope and instrumentation from the light and heat of the Sun, Earth, and Moon. By keeping the telescope and instruments in permanent shadow, it allows them to cool to their design temperature of 40 kelvins (−233 °C; −388 °F).

Key takeaways

James Webb Space Telescope sunshield belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect James Webb Space Telescope sunshield to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of James Webb Space Telescope sunshield from memory before moving on to harder problems.

Reference excerpt

The James Webb Space Telescope (JWST) sunshield is a passive thermal control system deployed post-launch to shield the telescope and instrumentation from the light and heat of the Sun, Earth, and Moon. By keeping the telescope and instruments in permanent shadow, it allows them to cool to their design temperature of 40 kelvins (−233 °C; −388 °F). Its intricate deployment was successfully completed on January 4, 2022, ten days after launch, when it was more than 0.8 million kilometers (500,000 mi) away from Earth. The JWST sunshield is about 21 m × 14 m (69 ft × 46 ft), roughly the size of a tennis court, and is too big to fit in any existing rocket. Therefore, it was folded up to fit within the fairing of the launch rocket and was deployed post-launch, unfolding five layers of metal-coated plastic. The first layer is the largest, and each consecutive layer decreases in size. Each layer is made of a thin (50 microns for the first layer, 25 microns for the others) Kapton membrane coated with aluminum for reflectivity. The outermost Sun-facing layers have a doped-silicon coating which gives it a purple color, toughens the shield, and helps it reflect heat. The thickness of the aluminum coating is approximately 100 nanometers, and the silicon coating is even thinner at approximately 50 nanometers. The sunshield segment includes the layers and its deployment mechanisms, which also includes the trim flap.

Overview

To make observations in the near and mid infrared spectrum, the JWST must be kept very cold (under 50 K (−223 °C; −370 °F), some parts under 40K), otherwise infrared radiation from the telescope itself would overwhelm its instruments. Therefore, it uses a large sunshield to block light and heat from the Sun, Earth, and Moon, and its position near the Sun-Earth L2 Lagrange point keeps all three bodies on the same side of the spacecraft at all times. Its halo orbit around L2 avoids the shadow of the Earth and Moon, maintaining a constant environment for the sunshield and solar arrays.

Infrared is heat radiation. In order to see the faint glow of infrared heat from distant stars and galaxies, the telescope has to be very cold. If sunlight or the warm glow of the Earth heated the telescope, the infrared light emitted by the telescope would outshine its targets, and it wouldn't be able to see anything.

The sunshield acts as large parasol allowing the main mirror, optics, and instruments to passively cool to 40 kelvins (−233 °C; −388 °F) or cooler, and is one of the enabling technologies that will allow the JWST to operate. The kite-shaped sunshield is about 21 by 14 metres (69 by 46 ft) in size, big enough to shade the main mirror and secondary mirror, leaving only one instrument, the MIRI (Mid-Infrared Instrument), in need of extra cooling. The sunshield acts as a V-groove radiator and causes a temperature drop of 318 K (318 °C, 604 °F) from front to back. In operation the shield will receive about 200 kilowatts of solar radiation, but only pass 23 milliwatts to the other side. The sunshield has five layers to mitigate the conduction of heat. These layers are made of the polyimide film Kapton E, which is stable from −269 to 400 °C (−450 to 750 °F). However the thin films are delicate – accidental tears during testing in 2018 were among the factors delaying the JWST project, and Kapton is known to degrade after long term exposure to Earth conditions. The sun-facing layer is .05 mm (0.002 in) thick, and the other layers are .025 mm (0.001 in) thick. All layers are coated on both sides with 100 nm of aluminum, and the Sun-facing sides of the outermost two layers are also coated with 50 nm of silicon "doped" with other elements. This helps the material survive in space, radiate excess heat, and to conduct electricity, so a static charge does not build up on the layers.

Each layer has a slightly different shape and size. Layer 5 is the closest to the primary mirror and is the smallest. Layer 1 is closest to the Sun and is bigger and flatter. The first layer blocks 90% of the heat, and each successive layer blocks more heat, which is reflected out the sides. The sunshield allows the optics to stay in shadow for pitch angles of +5° to −45° and roll angles of +5° to −5°. The layers are designed with Thermal Spot Bond (TSB), with a grid pattern bonded to each layer at intervals. This helps stop a rip or hole from increasing in size should one occur.

Design and manufacture

Northrop Grumman designed the sunshield for NASA. The sunshield is designed to be folded twelve times so it can fit within the Ariane 5 rocket's 4.57 m (15.0 ft) diameter by 16.19 m (53.1 ft) shroud. When it deployed at the L2 point, it unfolded to 21.197 m × 14.162 m (69.54 ft × 46.46 ft). The sunshield was hand-assembled at ManTech (NeXolve) in Huntsville, Alabama before it was delivered to Northrop Grumman in Redondo Beach, California for testing. During launch it was wrapped around the Optical Telescope Element and then later unfolded. The sunshield was planned to be unfolded approximately one week after launch. During development the sunshield layer material was tested with heat, cold, radiation, and high-velocity micro impacts. Components of the sunshield include:

Core Front and aft four-bar linkage Aft structure assembly Momentum trim tab (the tab is attached to the aft structure assembly) Aft spreader bars (spreads layers in the rear) Forward structure assembly Forward spreader bars Mid-booms (one on each side) Mid-spreader bars (spreads the 5 layers apart) Two forward and two aft bipod launch lock assemblies The bipod launch lock assemblies are where the sunshield segment connected to the OTE when it was folded up during launch. There are six spreader bars that expanded to separate the layers of the sunshield, which has roughly six sides.

Trim flap/momentum trim tab

… excerpt ends here. Continue reading the full article.

Illustrations

James Webb Space Telescope sunshield: The temperature differences between the hot and cold sides of the James Webb Space Telescope five-layer sunshield — The temperature differences between the hot and cold sides of the James Webb Space Telescope five-layer sunshield

Worked examples

Example 1 — a first encounter with James Webb Space Telescope sunshield

Start with the simplest possible case. Write down what James Webb Space Telescope sunshield claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to James Webb Space Telescope sunshield before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about James Webb Space Telescope sunshield ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of James Webb Space Telescope sunshield

In research: James Webb Space Telescope sunshield appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses James Webb Space Telescope sunshield in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: James Webb Space Telescope sunshield is common in secondary-school and first-year university syllabi. It links to neighbouring topics James Webb Space Telescope, so understanding it makes those chapters shorter.
In everyday life: Look for James Webb Space Telescope sunshield outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study James Webb Space Telescope sunshield in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what James Webb Space Telescope sunshield means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain James Webb Space Telescope sunshield out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is James Webb Space Telescope sunshield in simple terms?

Why does James Webb Space Telescope sunshield matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study James Webb Space Telescope sunshield?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on James Webb Space Telescope sunshield.