James Webb: A Cosmic Time Machine

Introduction

On December 25th, 2021, at 7:20 AM, the James Webb space telescope was launched aboard the Ariane 5 rocket from Arianespace’s ELA-3 launch complex in French Guiana. The telescope began its million-mile journey to the second Lagrange point (L2), a point in space where gravity from the Sun and Earth balance the orbital motion of a satellite. There are five known Lagrange points, and each makes a perfect viewing location for space telescopes. After launch, over the following 30 days, Webb will begin and continue to unfold and prepare itself for use, as it was previously folded up in the Ariane 5 rocket for launch. You can check the current progress of Webb’s unfolding and voyage here: Where Is Webb? NASA/Webb

The development and construction of Webb officially began in 1996, and the telescope was named after James E. Webb, NASA’s second administrator who served between 1961 and 1968. The telescope was originally expected to launch in 2018, but complications led to its delay to May 2020. However, further complications due to the Covid-19 pandemic and technical issues led to another delay for launch. The launch was rescheduled to September, then November, then finally December 25th, 2021. The telescope is one of world’s most powerful space telescopes and will revolutionize current scientific knowledge regarding the universe.

Overview Purpose The James Webb space telescope has many purposes, including:

• To search for light from the first stars and galaxies that formed in the Universe after the Big Bang.

• To study the formation and evolution of galaxies.

• To understand the formation of stars and planetary systems.

• To understand planetary systems and the origins of life.

Unlike the Hubble Space Telescope, which studies the visible light portion of the electromagnetic spectrum, the James Webb space telescope is designed to study the infrared, or heat portion of the electromagnetic spectrum. Infrared radiation has less energy than visible light and therefore requires both sensitive and precise instruments to measure. Design The James Webb space telescope’s design consists of many intricate parts, including:

• Optical Telescope Element (OTE).

• Integrated Science Instrument Module (ISIM).

• Sunshield.

• Spacecraft Bus.

The ability for each part to work correctly and coordinated with the others is crucial to the mission. Below, we will examine each part and the role it plays for Webb.

Optical Telescope Element (OTE)

This portion of Webb includes the telescope’s 18 hexagonal-shaped mirrors, which help reflect light into the telescope. They are made from beryllium, a strong yet light element. The mirrors are so large they must be folded up during launch to fit into the rocket. The OTE also consists of a secondary mirror and a backplane, which is a large structure that holds and supports the hexagonal mirrors of the telescope. It also carries the entire module of scientific instruments, A.K.A. the Integrated Science Instrument Module (see below).

Integrated Science Instrument Module (ISIM)

Also referred to as the “main payload” of the James Webb Space Telescope, this module houses the four main instruments that will detect light from distant stars and galaxies, and planets orbiting other stars.

The first instrument is a Near-Infrared Camera, provided by the University of Arizona. It can detect light in the near and mid-infrared wavelengths of the electromagnetic spectrum and can see light from the earliest stars and galaxies in the process of formation, the population of stars in nearby galaxies, and young stars in the Milky Way and Kuiper Belt objects. Furthermore, it is equipped with coronagraphs, which, according to NASA, are instruments that allow astronomers to take pictures of very faint objects around a central bright object, such as stellar systems or planets orbiting stars.

The second instrument is a Near-Infrared Spectrograph, provided by the European Space Agency, NASA, and the Georgia Student Finance Commission. This device is used to disperse light from an object into a spectrum. Scientists can use the spectrum of an object to learn more about its physical properties, including its mass, temperature, and chemical composition.

The third instrument is a Mid-Infrared Instrument, also known as a MIRI, provided by the European Consortium with the European Space Agency and the NASA Jet Propulsion Laboratory (JPL). It has both a camera and spectrograph that sees light in the mid-infrared range of the electromagnetic spectrum, which includes wavelengths longer than our eyes can see. It will be able to see the redshifted light of distant galaxies, newly forming stars, faintly visible comets, and objects in the Kuiper Belt.

The final instrument is a Fine Guidance Sensor / Near InfraRed Imager and Slitless Spectrograph, provided by the Canadian Space Agency. This combination of smaller instruments allows Webb to point at specific regions in space precisely so it can obtain high-quality images. It has a wavelength of 0.8 to 5.0 microns.

Sunshield

Webb’s sunshield has the purpose of protecting the telescope from external sources of light and heat so it can detect the faint light and heat of distant stars and planets. It is conveniently positioned between the Sun, Earth, Moon, and the telescope. It will allow the telescope to cool down to a temperature below 50 Kelvin Degrees by also passively radiating the spacecraft’s heat into space. It also contains five layers of sun-shielding, with space in between each one, to radiate out the heat between the layers and use the vacuum of space as an insulator. The sunshield is made with Kapton, which is a lightweight material with special thermal properties.

Spacecraft Bus Webb’s spacecraft bus provides the necessary support functions for the operation of Webb and houses six major subsystems: the electrical power subsystem, attitude control subsystem, communication subsystem, command and data handling subsystem, propulsion subsystem, and the thermal control subsystem. Other Parts Other parts of Webb that enable it to function include:

• The momentum flap, which balances the solar pressure on the sunshield.

• The Earth-pointing antenna, which sends scientific data back to Earth and receives commands from NASA’s Deep Space Network.

• The solar array, which is always facing the sun and converts sunlight to electricity to power the telescope.

• The star trackers, which are small telescopes that use star patterns to target the observatory.

Why Analyze Infrared Light? As you can tell from both Webb’s description and its elements, the observatory is designed to study infrared light. But why infrared light, and not any other part of the electromagnetic spectrum? And how will analyzing light tell scientists about the past?

Light, like everything else in our universe, has a speed limit, and it is arguably the speed limit of the universe since nothing can travel faster than light. Its speed is 3.00 * 10^8 meters per second. Since even light takes time to reach Earth, light that is farther away will take longer to reach our eyes than light closer. Scientists measure this distance in light-years, or the distance light can travel in a year, which is about 6 trillion miles. So, light from a star four light-years away, for example, would take four years to reach our eyes, and if we were looking at that star currently, we would see it four years in the past.

This explains how Webb can see into the past by analyzing light from distant stars, but why infrared light? Because light from the Big Bang and the beginning of the universe is so old (13.8 billion years old to be exact), and because the universe is ever-expanding, the light has lost energy and its wavelength shifted from the visible part of the electromagnetic spectrum to the infrared part of the electromagnetic spectrum, which is what Webb is looking for. So, by searching for infrared radiation from distant stars, Webb can theoretically see up to 13.8 billion years into the past and study the origins of the universe. How cool!

Webb and the Future of Astronomy

With the James Webb Space Telescope, scientists will be able to better understand the origins of the universe and of distant stars and galaxies by studying the infrared portion of the electromagnetic spectrum. With such information, astronomy is bound to change forever. Be sure to stay connected with NASA when Webb’s first images roll out in February 2022!