A Telescopic Glimpse Into The Past

Astronomy Jan 24, 2022

By Ashwin Biju Nair

The Big Bang has boggled scientists for many decades. They have come up with many theories stating that the Big Bang is real and some theories contradict the others. What should we believe? Which theory points to the truth?

Well, the scientists at NASA have gone all the way and spent 10 billion USD on building a time machine, metaphorically, to finally settle this debate, and it is called the James Webb Space Telescope.

What is it? How is a telescope going to help us time travel? Or is it even an actual time machine? These are the questions that are going to be answered in this article.

The James Webb Space Telescope, named in honor of James Webb, is by far the biggest and the most ambitious project of NASA. It was launched on December 25, 2021. This telescope was built as an attempt to travel back in time, of sorts. Using this telescope, we can get a glimpse of what our universe was 13 billion years ago.

Basically, scientists can see how stars and galaxies formed after the Big Bang using the aid of this powerful telescope, as shown in the diagram below.

Image Courtesy: Washington Post

How exactly are we looking into the past?

Stars and galaxies are located millions of light-years away from us, and when we look at them through telescopes, we are actually seeing them as they were millions of light-years ago. The same concept applies here as well. The James Webb telescope aims to capture those photons that were emitted 13.5 billion years ago.

The telescope was launched on the Ariane 5 rocket. It will travel almost 1.5 million kilometers away from Earth to a special point called Lagrange point 2 or L2, from where it will continue observing the universe for the next ten years.

What is a Lagrange point?

Have a look at the image below. There are a total of 5 Lagrange points (They are more of orbits than points) located in the Sun-Earth-Moon system. These are points in space where small objects can stay in their position relative to the gravitational bodies they revolve with. Meaning the gravitational pull on the object will be equal to the centripetal force, causing it to be in a relatively stable position. Satellites or space stations would require minimum fuel to run if placed at these points.

Image Courtesy: Washington Post

Why did NASA choose L2 for their telescope?

One of the main reasons for this is to avoid sunlight. Why? Because it is an infrared telescope and the heat from the Sun would saturate its sensors, observation would not be possible. The physics for L2 is such that the telescope will always remain in the shadow of the Earth as it revolves around the Sun.


Parts of the Telescope:

Image Courtesy: webbtelescope.org

Golden mirror

The most striking feature of the telescope is its golden mirror. It contains 18 hexagonal segments with a total area of 25 m2, making this mirror much bigger than the Hubble Telescope's mirror.  

The material used for the mirror's subsurface is Beryllium. There were two main reasons for choosing Beryllium. One, it is exceptionally lightweight. Second, since the operational temperature of the telescope is -233 °C, it is much better at dealing with shallow temperatures than Silica glass.

Another reason could be its dimensional stability (Beryllium is much stiffer than Steel).

The mirror's surface is gold-plated with a thickness of 0.1 micrometers. Gold was used for its reflective properties mainly because it is highly unreactive.

The mirrors can also adjust their focal points according to their focus.

Sunshield

The sunshield was designed to completely block out the Sun to ensure that the telescope remains operational at its optimum temperature of -233°C.

The sun-facing side of the telescope receives around 200,000 Watts of power from the Sun, and only < 1 Watt is allowed to pass through to the other side. So it goes without question that this shield should be very efficient at redirecting the incoming heat.

The design of the sunshield was a significant factor in ensuring that this 10 billion dollar project did not fail. The first choice the scientists had to make was the choice of material. The sunshield has to be reflective, stable across a range of temperatures, strong, and resistant to degradation and space debris. The material chosen was a high-performance plastic called Kapton. A layer of Kapton, of thickness lesser than human hair, was coated on a 100 mm thick sheet of Aluminum (gives the shield its shiny appearance). The layers closer to the outside surface were also coated with Silicon (gives the shield a light pink appearance), which has high emissivity, i.e., it emits most of the energy absorbed as thermal radiation.

A simple design choice makes this sunshield so effective. Take a look at the image below.

Image Courtesy: webb.nasa.gov

A slight angle ensures that the heat is deflected out of the system and into space. Each layer reduces the temperature as it gets closer to the telescope. Also, the area of the layers decreases in the same direction.

Even after all these considerations, there were a few hiccups.

  • Unfolding the sunshield: Non-rigid objects like this are non-deterministic. Other examples of such objects are cables and wires. What it means is that determining the probability of how the shield will unfold is merely an impossible task. Therefore, the scientists had to fold this shield with utmost precision because if the sunshield did not unfold properly, the whole project would fail.
  • Wear and tear of the sunshield: Since the sunshield is under tension, space debris as small as a micro-meteor could cause a small tear leading to the whole shield being torn apart. The last thing we would want is the heat to pass through. To prevent this, the team incorporated rip-stop seams into the layers.

All of the above design and engineering choices ensure that the heat-sensitive equipment on the cold side stays at -233 °C.

Infrared detector

The James Webb Telescope will be able to detect infrared radiations. This detector works at approximately 7 Kelvin. The benefit of an infrared telescope is that infrared radiation can pass through clouds of dust and thick layers of gasses which allows us to see farther into space without any hindrance.

Here is a photo was taken by the James Webb Telescope (right). The image on the left is taken by the Hubble Telescope and senses only the visible light. One can see what difference the James Webb telescope makes just by capturing the same picture in infrared.

Image Courtesy: webb.nasa.gov

As of January 24, 2022, NASA has confirmed that the telescope mirrors have been fully deployed, and it has almost reached L2 (predicted to enter orbit on January 25, 2022).

This is what NASA had to say about what they expect from this mission - "Webb will reveal new and unexpected discoveries and help humanity understand the origins of the universe and our place in it." (Source: NASA)

Check out the official NASA website for more information and updates on what mysteries the James Webb Telescope helps unravel.


Tags

Mechanical Engineering Association (MEA) | BITS Pilani

MEA: The hub of professional activities of Mechanical Engineering students and staff. We conduct workshops, seminars, and many other things to enhance the core mechanical culture on campus and beyond.

Great! You've successfully subscribed.
Great! Next, complete checkout for full access.
Welcome back! You've successfully signed in.
Success! Your account is fully activated, you now have access to all content.