The idea of ​​developing a telescope to replace Hubble was proposed between 1989 and 1994. This infrared conceptual telescope with a 4-meter aperture was called Hi-Z and orbited the Sun at a distance of 3 AU (three times the distance of the Earth from the Sun). This circuit was very far away, But it also had advantages. The telescope remained an idea until other designs gave it new life. The scientists gave the initial name of this project NEXUS, which was very innovative at the time; But NASA had a different opinion. In the mid-1990s, the US space agency announced that it would invest in a project that would be done quickly, be the best, and have the lowest cost; So NASA’s top managers focused on building a low-cost space telescope. The result of this decision was the NGST concept telescope with an 8-meter aperture that orbits the Sun in Lagrangian 2 (L2) orbit, But it only cost 500 million dollars.

Early proposed designs for the James Webb Space Telescope.

NASA accepted the project and immediately signed a contract with Goddard Space Flight Center, Bal Aerospace, and TRW to conduct studies on the technical requirements of the project as well as its various costs. In 1999, NASA contracted Lockheed Martin and TRW to build an early version of its concept telescope. In 2002, a conceptual telescope was built and TRW agreed to fully build the NGST, now known as James Webb, and deliver it to NASA by 2010 in exchange for $824.8 million. At the end of 2002, TRW was acquired by Northrop Grumman, and the James Webb project was also assigned to this aerospace company.

NASA later announced in 2005 that there were changes in the program and some of the telescope’s equipment had to be changed, which caused the telescope’s launch to be delayed by 22 months and the launch date was postponed from 2011 to 2013. NASA also announced that it will no longer test systems at wavelengths shorter than 1.7 micrometers to focus on other areas. In 2006, the program had to be revised again; But this time the matter was not only in the technical field, but NASA also had to make a series of changes in the financial field so that the budget it had was distributed correctly.

That same year, NASA estimated that the cost of building and supporting the James Webb Telescope over its life cycle would be about $4.5 billion. Of this amount, $3.5 billion will be spent on design, manufacturing, launch and placement into orbit, and $1 billion will be the cost of supporting the telescope over the decades of the mission. The European Space Agency announced that it will provide 300 million dollars of this funding and will also accept the cost of the launch. On the other hand, the Canadian Space Agency also provided 39 million Canadian dollars from this budget. According to this information, the main cost of the project fell on NASA.

A full-scale model of the James Webb Space Telescope in Battery Park in Manhattan in 2010.

In January 2007, engineers announced that nine of the telescope’s 10 science instruments had successfully passed unshielded tests. In March 2008, the telescope successfully passed the initial design review test. By 2011, the telescope had successfully passed all tests and inspections and entered the final stage of structural design and body design. Since it was not possible to change the design and structure after the project was finalized and the launch time was approaching, the engineers had to use their utmost precision and examine the structure and tools with complete delicacy. From the 90s, when the idea of ​​the telescope was proposed, until 2011, new scientific achievements were achieved that were used in the telescope. For example, in the 1990s, scientists did not know how to design a large telescope with lightweight.

James Edwin Webb (right), former NASA administrator, with former US President Harry Truman in 1961. In 2002, in an unprecedented move, NASA chose the name of a non-scientist for one of its scientific missions.

In 2017, NASA again changed the launch date and postponed it to 2019; Because some instruments needed more testing and the simulation of the placement of the telescope in the rocket had to be done accurately. At the same time, Eric Smith, director of the James Webb project, said:

The biggest challenge in designing space telescopes is their size. A space telescope is launched into space by a rocket; Therefore, the designers had to do the design in such a way that it is possible to assemble and place the James Webb telescope in the upper part of the rocket. Also, this design should be in such a way that it can be opened in the space as easily as possible.

The James Webb Space Telescope is huge. The main mirror of this telescope has a diameter of 6.5 meters, and none of the current launch devices have the ability to accommodate a device with these dimensions. For example, the main mirror of the Hubble Space Telescope has a diameter of 2.5 meters, which made the process of transferring it to space easier. The dimensions proposed for the James Webb telescope made it impossible to transport it into space; But engineers and designers had to think of a solution for this problem. The main mirror of the Hubble telescope, due to its small diameter, was one piece and circular in shape; But since the main mirror of the James Webb telescope has a diameter of 6.5 meters, it could not be designed in one piece.

In this way, the engineers divided the telescope’s main mirror into three parts, which, when opened, are placed next to each other and form a single mirror; But this single mirror could not be any shape because it would cause optical aberration. The task of designing the shape of the mirrors was entrusted to the optical engineers. According to the simulations, the best case for the mirrors was to design them as a set of smaller, hexagonal mirrors. The main mirror of the James Webb telescope is made of a total of 18 smaller hexagonal mirrors that are placed next to each other in a special way, and there is a hole in the center of this mirror.

The James Webb telescope is also of the Casgreen type, and the center of its main mirror is perforated so that the secondary mirror sends the reflected light to the eye placed behind the central hole. Casgrain design has many advantages, including the compactness of telescopes that use this design. In Cassegrain telescopes, the focal length is long and the image distortion is reduced. The Hubble telescope uses this type of design; In fact, many research telescopes have a similar design.

Another challenge faced by the designers was the telescope’s solar shield. The James Webb Telescope can observe infrared and near-infrared lights. In order to receive and observe these thermal signals, the temperature of the telescope must be extremely low. To protect the telescope from light and heat sources (such as the Sun, Earth, Moon and the body of the observatory itself), engineers designed a 5-layer solar shield made of a very thin material called Kapton, which is the size of a tennis court. This solar shield acts like an umbrella or shade to prevent heat and light from reaching the telescope. This shield has a length of 21.197 meters and a width of 14.62 meters, which is large enough to completely cover the telescope. This layer causes the telescope to be placed in an environment with an average temperature of -223 degrees Celsius.

The interesting point in the design of the solar shield is its multi-layered nature. Scientists could produce this shield as a thick layer, But being 5 layers has its advantages. In this solar shield, each layer is cooler than the outer layers. There is a space between these layers that is a very good insulator; Therefore, the heat is spread between the layers and out. If the solar shield was made of a thick layer, the heat would cover the shield from the top to the bottom and it would be difficult to get it out.

The design of the layers of this solar shield could be any shape, But the engineers found that the best case is the kite-shaped design. This particular design as well as the number of solar shield layers play a key role in the telescope. The distance of these kite-shaped layers has also been determined with high precision and delicacy to have the best performance in the field of cooling. The kite-shaped design of the layers causes the heat to be directed to the sides and the remaining part is transferred between the layers until it finally exits between the layers. This unique design ensures that the heat from the satellite bus is instantly transferred by the layers so that it does not reach the optical equipment.

The third area is actually located in the satellite bus. In this area, the command and data processing unit of the telescope is located; Also, integrated flight software and control electronics are located in this area. As it was said, 4 of the scientific instruments of the telescope are placed in this section, which we will introduce and examine in the following.

NIRCAM is a highly accurate and advanced imager developed by the University of Arizona, which is installed on the ISIM module. This very important piece has two main tasks: first, it must image light in the 0.6-5 micron spectrum, and second, it acts as a coordinating sensor to adjust all 18 mirrors so that they can act as a single mirror. Nirkam is an infrared camera that has 10 detector arrays of mercury-cadmium-telluride or HgCdTe (one of the cadmium telluride alloys used in fast and sensitive detectors in the infrared sensor) and each of these arrays has a resolution of 2048×2048. The infrared camera itself also has a field of view of 2.2 x 2.2 arc minutes, which has an angular resolution of 0.07 arc seconds at a wavelength of 2 microns, and for this reason, it is known as the best camera currently.

Next to Nirkam is a chronograph (imager of the star crown) that works seamlessly with it. A chronograph can help gather data on exoplanets, and can image anything near a very luminous body; Because it can completely remove the light of the objects so that the objects around them are defined. The Nirkam camera only works at -236 degrees Celsius.

The Nirkam camera can capture objects with an apparent magnitude of +29 in high resolution during a single exposure of 10,000 seconds (2.8 hours). This camera can view and record at the same time and control the mirrors. All observations of this camera are made between wavelengths of 600 nm to 5000 nm. The precision of the sensors that align the telescope mirrors is so high that they can move the mirrors by less than a human hair. In other words, the movement accuracy of these sensors is at least 93 nm; But during the tests, this accuracy reached 52 and 32 nm, which is very surprising.

Nirkam sensors generally consist of the following parts:

• Separate Hartmann sensor (wavefront meter)
• GRISM (combination of prism and diffraction grating )
• Poor lenses

The Nirkam section is also composed of the following sections:

• The killer of mirrors
• Chronograph
• The first reflective mirror
• collimator lenses
• Dichroic beam splitter
• Long wavelength filter wheels (frequency less than 300 kHz)
• A group of long-wavelength imaging camera lenses
• Long wavelength focal plane
• Short wavelength filter wheels
• A group of short-wavelength imaging camera lenses
• Mirror reflecting short wavelengths
• Pupillary lens
• Short wavelength focal plane

Nirkam camera has two separate and complete optical systems that are used for accuracy in imaging. These two systems, known as sections A and B, can work simultaneously and observe two different paths of the sky. The lenses used in the inner parts of these parts are triple refractive lenses. These lenses are made of lithium fluoride, barium fluoride and zinc selenide respectively. These three lenses are parallel and the largest of them has an aperture of 90 mm.

Nirkam has important tasks that are very valuable for science. By exploring the early universe, this camera will examine how the universe’s first luminous objects formed and evolved to tell the history of the reionization of the universe. This camera can predict what the galaxies and galaxy clusters that we see directly look like in today’s universe; Because the sky we see does not belong to the present, but to the past. For example, if you see a star in the sky that is a thousand light years away from Earth, you are actually seeing an image of the star from a thousand years ago; Not the present time! The Nirkam camera can accurately predict the shape of objects near and far. Another important task of this camera is to examine the physical and chemical structure of objects in the solar system. With this work, James Webb can help scientists in understanding the origin of life on Earth.

Niraspec is a multi-mass spectrometer built by the European Space Agency and installed on ISIM. This advanced spectrometer can simultaneously measure the infrared spectrum of nearly 100 objects (such as galaxies, stars, etc.) with low, medium, and high resolution. The field of view of this spectrometer is 3 arcmin by 3 arcmin and it sees wavelengths between 0.6 µm and 5 µm. This spectrometer has a series of unique apertures that can spectrograph objects individually. It also has an integrated field unit called IFU, which is used for 3D spectroscopy. The European Space Agency has been responsible for installing this part on the ISIM chassis.

Scientists intend to observe the first light of the universe and the period of reionization with the help of Niraspec. Investigating the formation of galaxies and the birth of stars and non-planetary systems is also one of the goals of this piece. Scientists want to use telescopes to examine planetary systems to find signs of the origin of life.

Niraspec spectrometer has four main mechanisms, which are:

• Spectrum filter wheel
• Refocusing mechanism on the subject (RMA) which has two mirrors
• Microshutter (MSA) equipment used for multiple mass spectrometry
• Diffraction grating wheel (GWA) which has 8 positions. Also, 6 diffraction gratings, a prism, and a mirror are also located in this part.

As mentioned, this spectrometer is responsible for observing the first light of the universe after the end of the dark period as well as the reionization period. Near-infrared spectrometry (NIRS) investigates the earliest light sources in the universe (such as stars, galaxies, and active nebulae) at a spectral resolution between 100 and 1000. These lights indicate the beginning of the reionization period of the world. With the help of a multi-mass spectrometer (objects with a redshift between 1 and 7) at a spectral resolution of 1000, observations of a large number of galaxies are made in order to provide scientists with more information about smaller objects in the early universe.

One of Niraspec’s spectrographs takes high-contrast images and can observe objects with a spectral resolution of 100 to several thousand in order to provide scientists with a complete and accurate picture of the formation and evolution of stars and star systems. Another task of this spectrographer is to examine the objects of the solar system in high contrast and medium spectral resolution. Planets, moons, comets, and objects in the Kuiper Asteroid Belt are examined by this spectrograph so that scientists can learn more about the origins of life.

Miri is an advanced spectrometer built by the European Space Agency and NASA’s Jet Propulsion Laboratory. Miri actually consists of a camera and a spectrometer that observes mid-infrared between 5 microns and 28 microns. Miri also has a chronograph, which is specially used for observing exoplanets. Most of the James Webb telescope’s instruments observe the near-infrared spectrum or some wavelengths of visible light; But Miri, through other equipment, can observe longer wavelengths of light. The instrument uses arsenic-doped silicon arrays to observe at long wavelengths. Miri’s imager is designed to have a wide field of view, But Miri’s spectrometer is not like this and has a limited field of view.

As you go, you see longer wavelengths; So it needs to be cooler than other equipment. For this purpose, engineers have considered a special cooling system for this part, which includes a pre-cooling pulse tube and a Joule-Thomson ring as a heat exchanger. This equipment causes the temperature of Miri to drop to 7 degrees Kelvin or -266 degrees Celsius when working in space.

In fact, the spectrograph installed in Miri can observe wavelengths between 4.6 and 28.6 microns and has four separate channels, each with its own diffraction grating and image-cropping tool. The field of view of this spectrograph is 3.5 arc seconds by 3.5 arc seconds. In early 2014, sensors were installed on the ISIM module and their integrity was tested. Miri is mounted by a plastic hexapod structure and carbon fiber mounts on the ISIM and next to the satellite bus; But it is isolated so that it has a certain and constant temperature and is not affected by the temperature of the surrounding environment and the bass, which heats up a lot.

The main parts of Miri are:

• spectroscopic optical equipment (including main spectrographs and prerequisites)
• Arrays of focal planes
• Input light calibration module (including mirrors, imager calibration source and pollution control cover)
• Plastic hexapod and carbon fiber legs
• The main cameraman
• Image cropping tools
• The main page where the equipment is located

Most of Miri’s parts are placed in the main structure of ISIM; But the cooler is located in zone 3, which is near the satellite bass. Miri’s main imager has a special low-resolution spectrograph that can perform cut-free spectroscopy between wavelengths of 5 to 12 microns. The prisms of this spectrometer are made of germanium metal and zinc sulfide to cause more light scattering.

Dysfunction detectors can detect the redshift of distant galaxies, newborn stars, faint comets, and objects in the Kuiper Belt. The spectrometer can also image with medium resolution, which provides scientists with new information about distant objects; Information that Hubble is unable to collect.

FGS/Nyris is another scientific instrument installed on the Canadian Space Agency’s ISIM module. These instruments are actually a combination of a full-conductivity sensor and a near-infrared imager and spectrometer. FGS/Nyris can observe wavelengths between 0.8 and 5 microns. These instruments can perform observations in four different modes. Physically, the FGS and Neris are combined and housed in one enclosure; But the reality is that they do two completely different things. Neris uses the FGS to keep the telescope fixed on the subject and make the observations, which is why it’s called the FGS (Precise Guided Sensor). The near-infrared spectrometer has a special spectroscopic mode that is used only for observing exoplanets. The Neris detector has a mercury-cadmium-telluride or HgCdTe detector array and has a resolution of 2048 x 2048 pixels and a field of view of 2.2 arc minutes by 2.2 arc minutes. The precision guidance sensor helps to keep the telescope fixed on the desired subject; The FGS also sends the necessary data to the position control unit so that the telescope can more easily focus on subjects or rotate around.

In general, Neris is designed to do the following:

• Near infrared imaging
• Wide-field slit-free spectroscopy
• Slitless spectroscopy of a particular object
• Aperture coating interferometry

The aperture cover interferometry mode uses a seven-hole aperture cover plate and can help identify exoplanets orbiting known stars that are in the main light spectra. The FGS unit is designed to focus the telescope on predetermined stars, which makes the targets always worth studying. The action of changing the direction of the telescope is done by other parts, such as the systems in the satellite bus and the telescope mirrors.

The fully assembled James Webb Space Telescope at the Northrop Grumman facility.

The satellite bass along with a series of other important equipment is placed inside a carbon fiber box. Before launch, solar panels are also placed in this box to open in space. The MIRI cooler and some ISIM electronics are also inside this box. As mentioned, in the computer processing part, there is a solid-state memory. The capacity of this memory is 59.9 GB, which is known as SSR. A small satellite dish is also placed under the bass, which is responsible for sending and receiving information. The telescope is designed to be able to communicate with NASA’s deep space communication network. The telescope’s main communications center is located in Maryland, USA.

Installation of 18 parts of the main mirror of the James Webb Space Telescope.

In the first stage, the mirrors had to be polished well through different levels and stages; Because the earth’s gravity causes them to bend and they have different performances at different temperatures. First, a polishing step had to be done, and then the mirrors were sent to the freezer room, stayed there for a while, came out again, and the polishing process was repeated. The surface of the mirrors should remain shiny when exposed to low temperatures in order to have maximum efficiency; Therefore, the mirrors should be polished many times and at different temperatures to achieve an acceptable gloss and to be able to maintain their original state at low temperatures. When the beryllium was completely polished and polished, then the gold coating was added.

The reason for using gold is its high percentage of reflectivity and it can have the maximum reflectivity when the telescope is in infrared light. This gold coating must be thick enough to cover the entire surface of the mirror; But at the same time, it should be thin enough not to damage the original beryllium mirrors. The process of placing the gold coating on the mirrors is known as ” vacuum heater coating “. During this process, the mirrors were placed in a vacuum chamber and then all the air in the chamber was evacuated to create a vacuum. Then, a very small amount of gold was vaporized under certain conditions and injected into the chamber. The back layers of the mirror, which are not going to be covered with gold, are protected by layers so they don’t get damaged. After injecting evaporated gold into the chamber, the gold atoms slowly settled on the shiny surfaces of the beryllium mirrors and this process continued until the thickness of the gold coating layer reached 100 nm.

Gold is very soft and flexible, and a very thin coating of it acts like transparent glass to protect the very delicate beryllium surface and provide a highly reflective surface.

A NASA technician works on the mirrors of the James Webb Telescope at the Marshall Space Flight Center.

As mentioned in the beginning, the launch of the telescope was postponed many times and the final date was finally set for December 25, 2021. As a very sensitive telescope, James Webb had to be launched by a reliable rocket. The European Space Agency announced that it will finance the launch of James Webb and launch it into space on an Ariane 5 rocket. Ariane 5 is one of the most successful and reliable rockets in the world today, and various companies use it to transport their space cargo to Earth orbit. NASA also agreed to launch its new space telescope using this rocket from the French Guiana space base.

Ariane 5, with 108 successful launches out of 113 launches, was considered a suitable and safe option for launching James Webb. The ELA-3 telescope launch pad is located in French Guiana (located in South America) and takes advantage of its proximity to the equator. Near the equator, the rotation of the Earth can create more propulsive force and launch the rocket faster and easier. The rotation speed of the earth at the equator is 1670 km/h. In order for the telescope to fit in the upper part of the rocket, it must be folded. In the picture below, you can see how the telescope is placed in the upper part of the rocket.

After launching and leaving Earth, the telescope began a 30-day journey to reach a distance of 1.5 million kilometers from Earth. This point is known as Lagrangian point 2. Lagrangian points are five points between two masses where the gravitational force between the two masses is neutralized. The Earth and the Sun also have 5 Lagrangian points that place satellites and space telescopes at these points. Lagrangian point 2 has an interesting feature. If any mass is located at this point, it will be in line with the earth and it will go around the sun together with the Earth. James Webb’s placement at this point makes the solar shield able to repel the heat and light of the sun, earth, and moon at the same time.

From the point of view of communication, being at the L2 point has advantages. Since the telescope revolves around the sun at the same time as the earth; Communication with it will be simple and it will never leave the radar point. There are three terrestrial antennas in Australia, California and Spain that communicate with James Webb. The Hubble telescope is not like that and every 90 minutes, it is placed in the shadow of the earth and it is not possible to communicate with it permanently; But the James Webb telescope is always available. The timeline of post-launch events is as follows.

More than a month after launch, the Precision Guidance Sensor, or FGS, was activated, followed by NIRCAM and NIRSPEC. The first image that Nirkam captured was of very bright stars so that scientists could be sure that the light was properly passing through the telescope and reaching the instruments. Since the main mirrors were not yet aligned with each other, this image was out of focus and blurry. The sixth week after the launch, the process of aligning the main mirror began and they tested it by recording an image of a bright star.

As mentioned many times, James Webb is going to replace Hubble; So everything we’ve seen from Hubble so far, plus countless more, we should expect from James Webb. James Webb is a very powerful telescope that can observe the lights of the early universe and help us understand this important period. Scientists have already set goals for James Webb that take precedence over others. These targets include exoplanets, supermassive black holes, protogalaxies (old galaxies that gave birth to newer galaxies), quasars, watery terrestrial planets, the early universe and the reionization period of the universe, Jupiter and its important moons, comets, extragalactic planets. and Kuiper belt objects.

One of the targets that scientists have already begun to observe is the Trappist 1 system. This system has several Earth-like planets, and the James Webb telescope can clearly observe it and provide useful information to scientists. This system is particularly important; Even if none of its planets are habitable, scientists can gain valuable information from them that will help us find other planets.

Investigating the planets of the solar system is also on the agenda of scientists. By studying these planets, scientists can possibly obtain valuable information about the origin of life. James Webb also observes in infrared light; Therefore, we should expect it to discover new exoplanets and extragalactic planets. Due to the high power and the large size of the telescope’s main mirror, in the next few years we will see the release of unique images of galaxies and celestial bodies that we have not seen before.