Where is the difference between old Hubble and young James Webb? Why is the James Webb telescope suddenly becoming the center of attention? Why is the James Webb Telescope called a milestone in the development of human technology?
The James Webb Space Telescope, a joint venture between the European Space Agency, the Canadian Space Agency and NASA, is a worthy successor to the previously launched Hubble Space Telescope. NASA has already been able to prove it and they have released some great photos by James Webb. Although Hubble and James Webb telescopes have many similarities in their goals and objectives, they differ greatly in terms of structure, operation and performance.
At least that is the expectation of space enthusiasts that the James Webb Hubble telescope will be many times over in terms of performance. Today we will try to understand the structural and functional differences between the old Hubble and the young James Webb Space Telescope.
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Who is located where from the world?
The Hubble telescope has already provided great images of space. But this does not mean that Hubble is very close to those cosmic objects. Hubble’s position is very close to Earth in low orbit just above the atmosphere. Hubble orbits the Earth at a height of only 550 kilometers (approx) above the Earth’s surface and travels at 27,000 km per hour. The speed completes an orbit once every 95 minutes.
James Webb is about 2800 times distant from Hubble. Like Hubble, James Webb does not orbit the Earth, but like Earth, James Webb also orbits the Sun. The place where James Webb is located is called Lagrange Point-2 or Lagrangian second point (L2). These points of interest are usually gravitationally fixed; Apart from this point, there are four other such points of interest in the Sun-Earth system.
Being behind the Sun, Earth and Moon at this Lagrangian-2 point, James Webb will be shielded from their light and heat. Thus it was possible to reduce the distance to some extent in the case of James Webb’s space observation.
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James Webb is located at a distance of 15 lakh kilometers from the Earth (more than four times the distance from the Moon). After all, James Webb will have an added advantage in space observation. The ability to observe cosmic objects will also be greater than Hubble’s.
What are their structural differences?
James Webb’s primary and main reflecting mirror is made of beryllium with a gold metal coating. The mirror, consisting of 18 hexagonal reflectors of 1.3 m diameter, does not change its shape at high and low temperatures. Their special feature is that each segment is able to move in a convenient way with the help of an automatic program.
If for some reason the primary mirror cannot properly reflect the light to the second reflecting mirror, the mirror segments will automatically reposition themselves to adjust the reflection of the light.
These small hexagonal mirror segments combine to form a large 6.5m honeycomb-like primary reflecting mirror. The mirror will allow the James Webb Telescope to collect light over an area of 25 square meters; Its area is more than 6 times larger than the area of the Hubble telescope’s 2.4 meter diameter mirror. So the amount of light collection of the web is also several times higher.
Because James Webb’s mirror is made of beryllium metal, it is light but strong and can hold its shape at extremely low temperatures—without shrinking. Also, the mirror is gold plated as gold is more chemically inert. Due to which the mirror will act as an excellent reflector for infrared radiation.
On the other hand, Hubble’s 7.8-foot-diameter main reflector mirror is coated with aluminum and magnesium fluoride, which enhances the reflection of ultraviolet rays but is not capable of working with mid- or high-wavelength infrared light.
Early Hubble images had problems with clarity. Small distortions remain in the mirrors due to mismeasurements by the mirror manufacturers, and Hubble images remain blurry. A number of instruments, including Hubble’s mirrors, were replaced by later service missions.
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James Webb has already overcome such problems and started sending great pictures. However, due to the use of relatively complex hinges, there is doubt as to whether its durability will be as long-lasting as Hubble’s. However, the duration of the James Webb Space Telescope mission is only 10 years.
Who is observing what kind of light?
Ultraviolet and near-infrared rays do not reach Earth much because of atmospheric blocking. Which is why Hubble was placed in a low orbit; So that cosmic objects can be observed easily. Hubble primarily observes visible light, ultraviolet light, and near-infrared (0.1 to 1 micrometer wavelength) light.
James Webb, on the other hand, is primarily designed to detect mid-infrared (with wavelengths of 0.6 to 28.3 micrometers) light. This high wavelength infrared light cannot be seen by humans with the naked eye or even with the Hubble telescope. James Webb is doing just that.
Disfracted light from distant primordial galaxies, old and newly formed stars, usually travels through space not as visible light but as invisible infrared or infrared (a type of heat) radiation. Infrared waves pass easily through the gas and dust clouds of space, which have not been clearly observed by any telescopes on Earth or the Hubble telescope.
But James Webb will be able to observe these highly red-emitting objects with extremely high resolution and sensitivity, which has never been possible before.
The image above shows that after processing in infrared light, cool stars and diffuse halos appear relatively bright. Each different wavelength has a different resolution.
The Hubble telescope uses red, blue, and infrared filters for the same image. At least 7 types of filters and sensors must be used to get the image from Hubble that James Webb published. The temperature sensitivity of the sensors is also difficult to maintain. James Webb easily overcomes these complications. Because it is able to work directly on high wavelength infrared light. These features make James Webb unique.
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Is the 5 layer sunshield keeping James Webb cool?
Infrared is emitted by every object. How much infrared light is emitted depends on the temperature of the object. If the temperature of the object is higher, more infrared will be emitted from that object, if the temperature is lower, the amount of infrared emitted will be less.
Infrared light can also determine the thermal state of objects. If we look at an object in visible light, it will look different if we look at the same object in infrared light. The most interesting thing is that hidden objects can be easily understood through infrared light. In this case, the TV remote in our house or the CC camera in the darkness of the night can be taken as an example.
The further away objects in space are from us, the further back we can go. Light traveling from a distant star or galaxy is no longer in the wavelength range of visible light (400 to 700 nanometers). As the universe expands (redshifts), this visible light becomes infrared light as its wavelength increases. That is why it is possible to observe distant objects by collecting infrared light. James Web is designed for infrared light. Through which he will look for distant objects and the past.
James Webb must be extremely cold to observe infrared light; Store at around -230°C. You will see that in winter we can feel the warmth of a little hot object very easily. This is because our body temperature is very low. James Webb will also be able to observe the very low temperature of infrared light emitted from stars in the Universe’s past if the Webb’s temperature is also very low.
James Webb must be very cool for that. Otherwise he will not be able to accurately observe the temperature of the infrared radiation. So keeping James Webb cool in space is one of the challenges. For this, three types of arrangements have to be adopted.
1. James Webb is kept at the coveted point-2 to hide from sunlight. Because these Lagrangian points are gravitationally fixed, the web’s distance from the Earth is always the same and the Sun is behind the Earth.
2. It uses a 5-layer sunshield to protect and cool James Webb from the reflected heat of the sun, earth and moon. Made of a special type of plastic called Kapton coated with aluminum and silicon, this sunshield is highly heat resistant, light in weight, strong and easy to fold.
This sunshield works great in high temperatures and low temperatures. Spaces are left between the five layers to allow heat to escape through any layer of the sunshield. The heat resistance of this sunshield is such that if the temperature on its hot side is 85 degrees Celsius, the temperature on the other side will be -233 degrees Celsius. This sunshield reflects all the heat as it faces the sun, keeping James Webb cool.
3. Controlling the temperature created by James Webb’s own faucet is also a challenge. The most important sensor on the web is the Mid Infrared Instrument or MIRI; This sensor can easily detect the transmitted mid-infrared light from distant galaxies. But it only works well at – 266.5°C. As a result, this sensor can easily absorb temperature from other parts of the web. That’s why crycooler with special cooling system of helium is used to protect this MIRI-sensor from very low temperature.
These complex processes are absent in Hubble’s case. Hubble’s primary mirror works like a normal mirror. Because Hubble operates with ultraviolet and visible light, no such system is needed.
Who is using which sensor?
In the James Web, the light is reflected by the mirror in several steps and finally the light enters the complex sensors. First is the Near Infrared Camera or NIRcam; Its job is to automatically collect light from less bright stars or galaxies by hiding the light from bright objects. However, the composition of cosmic objects cannot be determined with this sensor.
That is why there is a special sensor called NIRSPEC. which will deal with the properties of light and also analyze the mass, temperature and chemical composition of the objects from which the light is coming. The interesting function of this sensor is that it is able to analyze a specific object among many stars.
With the help of the Fine Guidance Sensor (FDS), James Webb can track several objects at the same time. There is also the Mid Infrared Instrument (MIRI). which can easily detect the migrating mid-infrared light from distant galaxies. Since these sensors are very heat sensitive, they are placed on the cool side of the sunshield.
Apart from this, various devices including radio communication antennas, solar panels and mechanisms for keeping them operating are on the warm side of the sunshield.
Like James Webb, Hubble also has the Fine Guidance Sensor (FDS), camera sensors include WFC3 and the Advanced Camera for Surveys (ACS), the Cosmic Origin Spectograph (COS) and the Space Telescope Image Spectograph (STIS) for analyzing ultraviolet radiation from unknown sources.
Works with camera and spectography. Besides, there is the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) for analyzing near-infrared light. Although this sensor is no longer working.
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Can JWST be maintained like Hubble?
Several major problems arose shortly after the Hubble Telescope was launched, including mirror distortion, thermal expansion problems with sensors and cameras. Hubble has been repaired five times so far by conducting servicing missions due to its proximity to Earth. If they were not possible, Hubble would not have survived for so long and all the complex astronomical researches would not have seen the light of day.
James Webb, on the other hand, will travel to a gravitationally stable location 1.5 million kilometers from Earth, known as the Sun-Earth Lagrange Point 2 (L2). It is not possible to conduct service missions like Hubble there. So it can be easily said that any error in James Web will remain unrepairable.
However, through long-term research and planning, James Webb has been made sufficiently durable and robust, and NASA claims that James Webb will not experience any malfunctions during the mission. However, due to a subtle error, the dust of this huge potential space telescope can be destroyed. Space debris may also pose a threat to it in the future.
11 July 2022 is undoubtedly a historic day. US President Joe Biden unveiled the first color image of this space telescope. In an instant, thousands of galaxies 13 billion years old can be seen in a single image of a small part of space. Since the launch, people all over the world have been eagerly waiting for this historic moment.
The James Webb Space Telescope launched on December 21, 2021, from the Ariana Space Center on an Ariana-5 rocket. The space telescope is named after James Edwin Webb, former administrator of the Gemini, Mercury and Apollo missions operated by NASA.
The James Webb Space Telescope is now championed around the world. The astonishing images of this telescope of the modern world are surprising people. The vast array of stars and galaxies in the distant sky is evident. It started with the Hubble Space Telescope.
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It is through Hubble that the true beauty of space begins to catch the eyes of people little by little. Hubble’s role in creating people’s space thinking and love for space is immense. New technology space telescope launches will continue in the future; But the love for the Hubble telescope will surely remain forever. After all, the hope is that Hubble, James Webb or any other device will reveal the beauty of the universe to the people of the world little by little.