James Webb: One Small Step for Man

James Webb: One Small Step for Man

Cedric Bruges '22

This Christmas, viewers around the globe were gifted an impressive display from tropical French Guiana as the European Space Agency’s Ariane 5 rocket pierced through dense cloud cover and thundered into orbit. Its payload, the James Webb telescope, is the culmination of 10 billion dollars, two decades of preparation, and extensive international cooperation; named after its respective NASA administrator who played an integral role in the Apollo program, Webb is the most powerful telescope ever built, succeeding Hubble to become NASA’s flagship mission in the domain of astrophysics.

Webb’s key goals are centered around peering back in time to discover more about the origins and formation of the Universe; its planets, stars, and galaxies; and life itself. To do this, Webb carries with it a few pieces of revolutionary engineering. Its primary mirror has around 5.6 times the light-collecting area of Hubble, measuring in at an impressive 21 feet diameter; this will allow the telescope to view fainter objects more effectively. Along with this, Webb is equipped with an impressive array of instruments and attachments for observation. Imagers such as the instrument NIRCam (Near InfraRed Camera) are combined with spectrometers, like NIRSpec (Near InfraRed Spectrograph), which are used to perform spectroscopy and determine the chemical makeup of objects. Spectroscopy has many uses, such as observing the atmospheres of planets to determine if they appear habitable, or the elements in stars to learn more about their life cycles. 

Webb’s instruments focus on the infrared spectrum for multiple reasons, including most importantly redshift—a phenomenon that results from the constant expansion of the universe. Over time, as light waves from extremely distant sources travel through space, the distance between the light source and its recipient (in this case, the Webb telescope) also increases. Because of this, the wavelength of this light is stretched, pushing it from the visible spectrum into infrared. The farther away a star is, the more noticeable redshift is; and for many stars, their spectrums have been shifted so much that we can no longer view their light from Earth. Thus, by focusing on the infrared spectrum, Webb can observe extremely faint signatures from stars and galaxies that are not otherwise visible, even with Hubble.

But this is only half of the reason why Webb can “peer back in time.” Since light can only travel so fast, looking at distant objects is effectively the same as looking into their past. Take, for example, the light traveling from the sun to Earth. It takes around eight minutes for this light to reach our eyes. So, if the sun hypothetically exploded right now, we would not be able to tell for eight minutes. This time discrepancy grows as distance increases. So, the light that we observe coming from the most distant stars and galaxies possible is actually showing us what those galaxies and stars were like around 14 billion years ago, right after (relatively speaking) the Big Bang. Taking both these phenomena into account, by observing the faintest, oldest, most distant infrared signatures, Webb will be able to look at the first stars and galaxies, effectively traveling to the edge of time.

Another defining feature of Webb is its characteristic five-layer sunshield which rests below the primary mirror. To make observations in the infrared spectrum, the telescope must be kept under 50K (-369.7 ℉), lest infrared radiation from the telescope itself interfere with its instruments. Even in the vacuum of space, without the proper cooling, light rays and the functioning of the telescope’s instruments can provide enough heat to overcome this margin. Thus, Webb employs these five massive layers, each as thin as a human hair, to effectively disperse heat. However, one of Webb’s instruments, MIRI (Mid-InfraRed Instrument) measures even fainter infrared signatures; in order to prevent interference on such a precise and sensitive instrument, MIRI’s systems must not exceed 6K (-449 ℉), a mere six degrees from absolute zero. This has been counteracted by a helium gas cooler, which spirals through the telescope.

Unlike Hubble, which orbits around the Earth, Webb is taking a more daring approach.  Having successfully deployed in space, it is now traveling towards its destination, a relatively stable orbit around a point in the solar system where gravitational forces from the Earth and sun counteract each other. This location, known as Lagrange point two (L2), is around 930,000 miles “behind” Earth, in its shadow; here, the best conditions for observation are provided, as light and heat from the sun, Earth, and moon are not excessive and can be dispersed by Webb’s extensive cooling systems. But since Webb is so far from Earth, maintenance is impossible. This means that if another error such as the flaw (an aberration one-fiftieth the thickness of a human hair) that previously plagued Hubble’s mirror and led to blurry images is present in Webb, nothing can be done to resolve it.

The marvel of engineering Webb still has challenges facing it, but it seems that the worst is over. Webb’s primary mirror’s 18 hexagonal, gold-plated segments, which were originally folded during launch, have successfully unfolded and deployed; within the next few days, Webb will hopefully reach L2 and begin calibration and testing. In around five months, the telescope should be fully operational for its primary mission. NASA expects Webb to last for around 20 years; because Webb’s orbit is not perfect, it will decay over time, and reserve fuel must be spent to temporarily realign the telescope. Since Webb cannot receive service or refueling, eventually Webb will run out of fuel, fall out of its orbit, and be retired. But what we learn from this telescope will help us build the next—we are on the cusp of a new space age. Humans have always been driven by exploration, curiosity, and expansion; and for the next two decades, we have the incredible opportunity to learn more about the nature of the universe, to uncover and explore what has never been seen before, and to attempt to solve the unanswered, enduring question—how did we get here?