The James Webb Space Telescope (JWST) is a marvel of modern engineering, and one of its most impressive components is MIRI, the mid-infrared camera. This camera allows us to see stars and galaxies that are incredibly distant and invisible to the naked eye. But how does it achieve this? Let’s explore the fascinating technology behind MIRI and how it has revolutionized our understanding of the universe.
All the cameras on the James Webb Telescope are designed to detect infrared light, which is beyond the visible spectrum for humans. As light travels through space, it stretches, and if an object is far enough away, its light stretches into the infrared range by the time it reaches us. This stretching limits how far we can see with visible light, but MIRI’s sensors, made from arsenic and silicon, can detect this stretched infrared light, allowing us to peer deeper into space.
To capture faint infrared signals, MIRI’s sensors must be extremely sensitive. However, increasing sensitivity also increases noise, which can obscure the faint signals we want to detect. This noise comes from various sources, including the heat emitted by the telescope itself. To minimize this noise, MIRI must be cooled to a frigid temperature of negative 267 degrees Celsius, just 6 degrees above absolute zero.
Cooling MIRI to such low temperatures is no small feat. The telescope is equipped with a massive five-layer sun shield that reflects heat and initially cools the cameras to around negative 234 degrees Celsius. However, MIRI requires even lower temperatures to reduce a phenomenon known as dark current, where atoms in the sensor vibrate and create noise.
The cooling process begins with a device called a pulse tube, which uses pistons to compress helium gas. This compression creates sound waves that travel through the tube, forming areas of high and low pressure. By carefully managing these waves, engineers create a standing wave with distinct hot and cold regions. Heat exchangers then extract the heat from these regions, cooling the helium gas further.
After initial cooling, the helium travels through a long tube to the cold head assembly, where it undergoes the Joule-Thomson effect. This effect occurs when the gas is forced through a tiny hole, causing it to expand rapidly and cool down even more. The cooled helium then flows over copper plates attached to MIRI’s sensors, bringing them to the necessary low temperature.
When NASA began designing the James Webb Telescope, no existing cryocooler could achieve the required level of cooling. Engineers had to innovate and push the boundaries of physics to create a system that could fit within the constraints of a space telescope. This achievement not only allows us to see further into the universe but also demonstrates the incredible ingenuity of human engineering.
The James Webb Space Telescope, with its advanced infrared capabilities, has opened up new frontiers in astronomy. By detecting light from the most distant objects in the universe, it provides insights into the early stages of cosmic evolution. The technology behind MIRI and its cooling system is a testament to human creativity and determination, paving the way for future discoveries in space exploration.
Engage in a hands-on experiment to understand infrared light. Use infrared cameras or sensors to observe everyday objects. Document how different materials appear under infrared light compared to visible light. Discuss how this relates to the capabilities of the James Webb Space Telescope.
Work in groups to design a model cooling system for a hypothetical space telescope. Consider the principles of the pulse tube and Joule-Thomson effect. Present your design and explain how it minimizes noise and maintains the necessary low temperatures for infrared detection.
Take a virtual tour of the James Webb Space Telescope. Explore its components, focusing on MIRI and its cooling system. Reflect on how each part contributes to the telescope’s mission and discuss the engineering challenges overcome during its development.
Analyze a case study of a significant astronomical discovery made possible by the James Webb Space Telescope. Discuss the role of MIRI in this discovery and how infrared technology provided insights that were previously unattainable.
Participate in a workshop focused on engineering innovation. Examine the technological advancements required to build the James Webb Space Telescope. Discuss the importance of pushing technological boundaries and how these innovations can be applied to other fields.
Here’s a sanitized version of the provided YouTube transcript:
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This is MIRI, the mid-infrared camera on board the James Webb Telescope. Watch what happens when light enters the camera. A complex series of mirrors and filters direct and split the light into different wavelengths, which are then resized and directed onto the sensors. With this camera, Webb can see extremely distant stars and galaxies that are completely invisible to the human eye. This is only possible by cooling the camera down to just 6 degrees above absolute zero.
But why does it need to be so cold? In this video, we’re going to look at how Webb captures infrared light and how a simple sound is used to cool its camera down to a very low temperature. We’ll also be giving away a Lego ISS model, so stick around to the end of the video to see how you could win.
All of the cameras on board James Webb detect infrared light, which is invisible to the human eye. As light travels through space, its wavelength is constantly being stretched. If something is far enough away, the light will be stretched so much that it is no longer visible by the time it reaches us. This means there is a physical limit on how far we can see into space. Since MIRI’s sensors are made from arsenic and silicon, it can detect this super-stretched infrared light and see beyond that limit.
These sensors work like regular camera sensors by converting photons of light into an electrical signal, but in order to detect the faint signals of infrared light, the sensors on MIRI have to be extremely sensitive. Increasing the sensitivity, however, introduces a lot of noise. Whenever we point a camera at something, its sensor isn’t just detecting what we want it to see. There is so much more light bouncing around that our eyes simply can’t detect. This can trick the pixels in the sensor into registering random levels of light, creating a layer of noise in the image.
If the object you are looking at has a bright enough signal, it will stand out much more compared to the noise. However, if the object you are trying to image is faint, like the infrared light from a galaxy, you’ll need to increase the sensitivity of the sensor, which in turn will drastically increase the noise. Since Webb is detecting infrared light, the problem gets even worse. Every object in our universe emits heat energy, some of which is in the form of light. Most objects aren’t quite hot enough to emit visible light, but they do emit a lot of infrared light. The hotter the object, the more infrared light it will emit, which is essentially how thermal imaging cameras work.
Because of this, James Webb itself would emit so much infrared light that its sensors would be completely overwhelmed. To limit the amount of infrared light produced by the telescope, its cameras need to be kept at a temperature of negative 234 degrees, which is extremely cool.
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In order for MIRI to operate at negative 267 degrees, it’s located behind the massive five-layer sun shield. This alone reflects so much heat and cools Webb’s cameras down to around negative 234 degrees. However, since MIRI is much more sensitive than the other cameras, it faces an even bigger problem: dark current. This is where the atoms inside the sensor itself vibrate and mistakenly register a photon of light, creating more noise. Since temperature is just a measure of how fast an atom vibrates, lowering the temperature will lower the vibration and therefore reduce the amount of dark current. Even at negative 234 degrees, the vibration of these atoms would be too much for MIRI’s sensor, so they have to be cooled all the way down to negative 267 degrees, just 6 degrees above absolute zero.
At this temperature, the atoms in the sensor are almost completely still, drastically reducing the noise and allowing the faint infrared signals to shine through. But how did NASA take these sensors all the way down to negative 267? The cooling process starts at the bottom of the telescope with a device called a pulse tube. Inside these tubes are two pistons that move back and forth to compress helium into the pulse tube. Since this movement would create a lot of unwanted vibration, these pistons have to move in the exact opposite direction with precision timing to cancel out each other’s movement.
These pistons move very quickly, just like a speaker, to create a low-frequency sound wave with a frequency of 30 Hz. This sound wave travels down the tube and gets compressed once it reaches the end, creating an area of higher pressure. Then, as it bounces back in the opposite direction, it expands, creating an area of low pressure before being compressed once again. If the next wave is sent out exactly as the previous one returns, it means the frequency perfectly matches that of the tube. This creates a standing wave where the areas of high and low pressure remain in the same place. By tripling the frequency, it causes the waves to combine and create a stationary wave with multiple areas of high and low pressure. Since temperature and pressure are related, this also leads to areas of high and low temperature.
This alone wouldn’t change the overall temperature because the hot and cold parts simply cancel each other out, but if there was a way to extract the hot parts, then the temperature would start to drop. Three heat exchangers made of thin metal sheets are placed at the points where the hot and cold gas meet, allowing the gas to pass through while also absorbing some of its temperature, causing a heat gradient to form. The heat from the hot side is pulled out and sent to the radiators via a heat exchanger, and the cold temperatures on the other side are also drawn out. This causes the temperature to drop from 27 degrees all the way down to negative 256 degrees at the final heat exchanger.
But how is this used to cool the sensors located at the opposite end of the telescope? Next to the pulse tube is another set of pistons that compress helium in a completely separate line of tubing. This line passes through the cold parts of the pulse tube’s heat exchangers, cooling the helium down to around negative 256 degrees. But still, the helium isn’t quite cold enough. From there, the helium goes on a long journey winding its way up through 10 meters of thin tubing until it reaches the cold head assembly. Inside, there is another heat exchanger and a tiny hole less than one millimeter in diameter. The helium is pushed through the hole and undergoes something called the Joule-Thomson effect. As the gas moves through the hole, it gets compressed before quickly expanding on the other side. This rapid expansion causes the pressure to drop, cooling the gas very quickly.
This is why blowing air through our mouth is colder if we make a smaller hole with our lips. On James Webb, this cools the helium all the way down to just negative 267 degrees. From here, the helium flows onto copper plates attached to the back of MIRI’s sensors, cooling them down to the required temperature. After that, the helium has done its job and flows back down the telescope, where the entire process begins again.
When NASA began designing James Webb, no cryocooler with this level of cooling existed, so engineers had to really push the boundaries of physics while conforming to the limits of fitting it into a space telescope.
And now, time for something really special. The winner of the previous giveaway is Daniel Weinman. Congratulations! But, as always, we’ll be giving away another awesome space prize in the next video. To win this amazing Lego space station model, sign up at the link below and leave a comment saying how long you think James Webb will operate for. Thank you very much for watching, and I’ll see you in the next video.
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This version maintains the informative content while removing any promotional or potentially distracting elements.
Infrared – Infrared refers to electromagnetic radiation with wavelengths longer than those of visible light, typically from about 700 nanometers to 1 millimeter, often used in thermal imaging and astronomy. – The astronomers used infrared telescopes to observe the heat emitted by distant stars and galaxies.
Light – Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum, perceived by the human eye as visible light, and is crucial for various astronomical observations. – The study of light from distant galaxies allows astronomers to understand the composition and movement of celestial bodies.
Cooling – Cooling in physics refers to the process of lowering the temperature of a system, often necessary for reducing thermal noise in sensitive astronomical instruments. – The cooling of the telescope’s detectors was essential to minimize interference from thermal noise during the observation of faint astronomical objects.
Sensors – Sensors in physics and astronomy are devices that detect and respond to physical stimuli, such as light, heat, or motion, and convert them into signals for measurement and analysis. – Advanced sensors on the spacecraft were able to capture high-resolution images of the planet’s surface.
Noise – Noise in physics refers to random fluctuations that obscure or interfere with the desired signal, often a challenge in astronomical data collection and analysis. – Reducing noise in the data was crucial for accurately measuring the cosmic microwave background radiation.
Temperature – Temperature is a measure of the average kinetic energy of the particles in a system, and it plays a significant role in determining the physical properties and behavior of astronomical objects. – The temperature of the star was calculated based on the spectrum of light it emitted.
Universe – The universe encompasses all of space, time, matter, and energy, including galaxies, stars, planets, and all forms of radiation and physical laws. – The study of the universe’s expansion provides insights into the origins and future of cosmic structures.
Technology – Technology in astronomy refers to the application of scientific knowledge for practical purposes, particularly in the development of instruments and methods for observing celestial phenomena. – Advances in telescope technology have significantly enhanced our ability to explore distant galaxies.
Astronomy – Astronomy is the scientific study of celestial objects, space, and the universe as a whole, involving the observation and analysis of stars, planets, and other cosmic phenomena. – Astronomy has revealed the existence of exoplanets orbiting distant stars, expanding our understanding of potential life-supporting environments.
Signals – Signals in physics and astronomy refer to the transmission of information through electromagnetic waves or other means, often used to convey data from astronomical observations. – The radio telescope detected signals from a pulsar, providing valuable data on its rotation and magnetic field.
