The Mighty James Webb: Not Just a Mirror

While the giant mirror and infrared primary camera are the most impressive design elements of James Webb Space Telescope, the on-board equipment is limited to these alone. There’s also a spectrograph that can see alien life, and a mid-infrared camera capable of detecting the universe’s most obscure objects.

James Webb is not just a giant mirror. Source:

The NIRSpec spectrograph and the search for extraterrestrials

Although the NIC camera may act as a spectrograph, there is an instrument on board the James Webb Space Observatory that has much more reason to be called that. This is the Near-Infrared Spectrograph (NIRSpec). In order to grasp what this engineering miracle is, it is necessary to understand how the spectra of astronomical objects are usually obtained.

For this, starlight is passed through a narrow slit to form a beam. Then this beam is passed through a prism and a “rainbow” is obtained, in which the lines are seen. But for this, each singular light source must somehow be separated from the rest. The field of vision encompasses hundreds of stars at the same time, and there is no time to focus on each of them one by one.

Engineers managed it as follows. NIRSpec consists of hundreds of individual shutters, each of which can be opened independently of the others. Thanks to this, it is possible to receive hundreds of high-quality visual spectra almost simultaneously.

Spectra of multiple objects obtained with NIRSpec. Source:

Scientists have found an equally wonderful application for NIRSpec. It is this device that will look for signs of life in space, viewing the spectra of stars having exoplanets around them. If one of those planets comes between the star and us, we will be able to see the spectrum of rays passing through the atmosphere. And in this spectrum, scientists can discern lines that are characteristic of certain substances.

These substances are called biomarkers, because they either indicate the planet’s suitability for Earth-like life, or they themselves are products of life. The former group includes oxygen, nitrogen and water. As for the latter one, there are disagreements, because, for example, methane and phosphine, although they are considered biomarkers, can be formed without the participation of living organisms.

There are also more complex biomarkers, such as amino acids or peptides. They are much more reliable evidence of the presence of life on the planet, because they are usually not formed in abiotic processes. And James Webb will hunt for them especially carefully. After all, almost 10,000 planets have already been discovered, and observing them with NIRSpec, the observatory will find traces of primitive life on at least one. And maybe there are hundreds of such planets, and then we will be able to say with much more certainty how widespread this phenomenon is in the universe.

Biomarkers. Source:

Mid-Infrared Instrument

Another instrument on board the orbiting observatory is the Mid-Infrared Instrument, or MIRI. Mid-infrared is the shorter wavelengths. Their images are not as clear as NIC, but they allow you to see objects whose radiation is weaker.

Otherwise, this camera works similarly to the NIC. It can take pictures of objects through filters, conduct spectroscopy and use coronagraphs. The tasks of this instrument are to determine the redshift of distant galaxies, to study the formation of distant stars, Kuiper belt objects and comets. Interestingly, the technical solutions for this device were originally developed by Raytheon Company for the Javelin anti-tank complex.

Device for work in the mid-infrared range. Source:

James Webb telescope’s precision targeting system

But in order to see something, you must first know where to look. This task in the design of the telescope is assigned to the FGS precision pointing sensor. Basically, it is a separate small telescope with a computer attached to it. Its memory contains the spectra of various stars.

The FGS looks at the surrounding stars, compares their spectra with those stored in its memory, and determines which way the telescope is currently pointed. In accordance with this, a decision is made as to what objects should be studied by its main tools at the moment.

James Webb’s Heat Shield

The operation of the telescope in the infrared spectrum means that it can only work at very low temperatures. MIRI generally needs 7 degrees Kelvin to work. Sure, the telescope has a cooling system, but the primary way to protects it from solar glare is the sun shield.

Heat shield of the telescope. Source:

It consists of five large sheets of polymer covered with a mirror layer. Each of them has a size of 21.1 x 14.6 m. The polymer layers are stretched on the frame one by one and due to this, they completely cover the entire giant James Webb’s mirror from the sunrays.

Conceiving the telescope and commencement of its operation

In 1997, when the James Webb project was just getting started, its launch was planned for 2007. The price of the project was then estimated 500 million dollars. However, the technical challenges turned out to be much more complex than originally thought, and by 2000 the price had more than tripled.

But even this did not help to save the project from stalling. As early as 2005, at the cost of three billion dollars, it became clear that the device would not be launched into orbit before 2013. Then the terms were repeatedly shifted, and the price increased.

James Webb starts moving to the Lagrange point. Source:

When James Webb was sent into space in 2021, its price was already 10 billion dollars, which is about 20 times more than originally planned. Nevertheless, the project was completed successfully. After the launch into orbit, the telescope headed to the L2 point, where it will work.

Lagrange points are the points where the gravitational forces of two bodies — for example, the Earth and the Sun — balance each other. Due to this, the device does not need to spend fuel for orbit correction. Point L2 is located behind our planet and is always covered by it from the Sun.

In early 2022, James Webb reached its destination and began testing its systems. On February 3, the NIC camera received its first test image. The next few months were devoted to preparing all the devices for work.

The first image received from the telescope. Source: NASA

James Webb has become one of the coldest objects in the universe. It successfully tested all its cameras and spectrographs and even managed to track a small asteroid. Even a meteorite hitting its mirror did not prevent it from continuing preparations. And now it is finally ready for scientific discoveries.