James Webb Space Telescope Working Imaginary Diagram. (Image from NASA website)
At 20:20 Beijing time on December 25, 2021, the James Webb Space Telescope of the National Aeronautics and Space Administration (NASA) was carried by the European Space Agency's (ESA) Ariane 5 rocket and successfully launched at the Space Launch Center in Kourou, French Guiana, and then successfully launched the solar panels and began to fly autonomously. The most expensive space telescope ever built and carrying the anticipated eyes of all people has finally ushered in the day of liftoff after countless twists and turns. The day that the astronomical community has been waiting for has finally arrived, and the history of human exploration of the universe will enter a new era.
The responsibility lies on your shoulders
Since human beings entered the era of space telescopes, space telescopes have continuously refreshed our understanding of the universe with the advantage of not being limited by ground observation conditions and powerful observation capabilities. From 1990 to 2003, NASA implemented the Great Observatories program, launching four large space telescopes, including the Compton Gamma-ray Observatory, chandra X-ray Observatory, and Spitzer Space Telescope in addition to the famous Hubble Space Telescope. These four space telescopes observe the universe in different wavelength bands of electromagnetic waves, giving us a more complete picture of the universe.
Launched in April 1990, the Hubble Space Telescope has been in orbit for more than 31 years and has received massive observations, making it the most successful space telescope to date. We often refer to the James Webb Space Telescope as the "successor" of the Hubble Space Telescope, which shows what expectations are placed on the James Webb Space Telescope. The words of Thomas Zurbuchen, vice president of NASA's Science Mission Directorate, are typical: "The more we know about our universe, the more we realize how important this telescope is to answering questions that we didn't even know how to ask when we designed the telescope." ”
However, in a strict sense, the Hubble Space Telescope and the James Webb Space Telescope are not the same type of telescope: the Hubble Space Telescope works primarily in the optical band, while the James Webb Space Telescope works primarily in the infrared band with wavelengths of 0.6 microns to 28.5 microns. In terms of working principle, it is more appropriate to position the James Webb space telescope as the "successor" of the Spitzer space telescope, and such a "succession" is more urgent. The Spitzer Space Telescope was launched in August 2003 and has been in service for more than 16 years, and NASA announced on January 30, 2020 that the Spitzer Space Telescope was officially retired on the same day. The Spitzer Space Telescope allowed us to see a different picture of the universe in the infrared band, helped us discover exoplanets, and conducted research that paved the way for the James Webb Space Telescope. Now, we need the James Webb Space Telescope to better reveal the secrets of the universe in the infrared band.
After launch, the James Webb Space Telescope will take 29 days to reach the second Lagrange point (L2) of the Sun-Earth, 1.5 million kilometers from Earth. Spacecraft operating in L2 are able to remain largely stable relative to the Sun and Earth, so it is an ideal location for spacecraft that need to work for a long time in a relatively stable position on Earth. Prior to that, probes such as the Wilkinson Microwave Anisotropy Probe, the Herschel Space Telescope and the Planck Satellite had all stopped near L2. After reaching L2, the James Webb Space Telescope will take 1-2 months to open the instrument and then take about 3 months to test the instrument. About half a year after launch, the telescope can officially carry out scientific observations.
James Webb Space Telescope (Credit: NASA website)
Celestial weapon
The reason why the astronomical community has great expectations for the James Webb Space Telescope is that it has unprecedented detection capabilities. Astrophysicist john Mather, winner of the 2006 Nobel Prize in Physics, once described the telescope's detection capabilities at a meeting of the American Association for the Advancement of Science (AAAS): "It has the ability to detect the heat emitted by a bumblebee 250,000 miles away, and this is the distance between Earth and Moon." ”
As a powerful "time machine," the James Webb Space Telescope has the ability to look back at what the universe looked like 200 million years after the Big Bang, or about 13.5 billion years ago, and observe the formation of early stars and galaxies. At the same time, its ultra-high infrared sensitivity will help astronomers compare the earliest and smallest galaxies with today's massive spiral and elliptical galaxies, helping us understand how galaxies have converged over billions of years. The James Webb Space Telescope can observe interstellar dust, which is especially important for studying the birth of stars, because young stars are often born in huge clouds of dust. In addition, the James Webb Space Telescope will also study the atmospheric composition of exoplanets, potentially finding clues to the existence of life in other corners of the universe.
Mirror area is a key indicator of a telescope, in general, the larger the mirror, the stronger the ability to collect signals. However, due to factors such as rocket carrying space and launch weight, the mirror area of space telescopes is much smaller than that of ground-based telescopes. Although the Hubble Space Telescope has achieved great results, its main mirror size is only 2.4 meters, which also limits its detection capabilities. In terms of mirror area, the James Webb Space Telescope has made a revolutionary improvement. Its main mirror consists of 18 hexagonal mirrors with a diameter of 6.5 meters, and the mirror area is 50 times that of the Spitzer Space Telescope, which is also an infrared telescope.
However, even a size as inconspicuous as 6.5 meters in diameter for ground-based telescopes is still too large for rockets, so the mirror of the James Webb Space Telescope needs to be folded up to fit into the rocket. The telescope, when folded, is 10.66 meters high and 4.5 meters wide, and is placed in a fairing with a height of 17 meters and a diameter of 5.4 meters. After unfolding in space, the telescope has a height of 8 meters, a length of 21.2 meters and a width of 14.2 meters. The expansion of the James Webb Space Telescope in space will also be the most complex space unfolding process ever made, which is another challenge for the telescope after a successful launch.
The James Webb Space Telescope will observe the universe with unprecedented accuracy, so it is necessary to be equipped with unprecedented advanced technology, and technical research is also one of the important reasons for the repeated delays in the launch time of the telescope. For example, the telescope needs to operate at extremely low temperatures, so cooling technology must be innovated. The tennis court-sized structure on the telescope is used to shield the heat emitted by the sun and the earth. The internal body of the sunscreen is a vacuum, which takes advantage of the excellent thermal properties of the vacuum. The part outside the vacuum is the thermal insulation layer, with a total of 5 layers, of which 4 layers are used to meet the requirements of telescope cooling, while the remaining 1 layer is mainly used to supplement the damage caused by tiny objects in space to the other 4 layers of insulation. The effect of the insulation layer is very obvious: the telescope will operate at a temperature of -233 ° C, while the temperature of the heating surface of the telescope is about 85 ° C.
Another issue for the James Webb Space Telescope is weight. In the case of a significant increase in the mirror area compared to the Hubble Space Telescope, if the same material is used, it is bound to exceed the take-off weight of the rocket. So the researchers used beryllium to make mirrors. This metal is very light and can not be deformed at extremely low temperatures. At the same time, the mirror is gilded, which can obtain high infrared reflectivity, which is why the photos we see with the James Webb Space Telescope are all golden.
Good things grind more
The successful launch of the James Webb Space Telescope is both exciting and gratifying to the astronomical community and the public concerned about space exploration, but also somewhat "unexpected", because throughout the telescope's development cycle, it is unknown how many launch delays have occurred.
In the mid-1990s, shortly after the Hubble Space Telescope entered service, NASA established the concept of the Next Generation Space Telescope (NGST). In 2002, NASA officially established a project and renamed the telescope the James Webb Space Telescope. James Webb was NASA's second director from 1961 to 1968. It was under his direct leadership that the United States began its lunar program and ushered in a golden age of space science.
When NASA proposed the concept of the next generation of space telescopes, the launch time of the telescope was set for 2007. When the project is officially approved, the estimated launch time is 2010. However, the development process since then can be described as a twist and turn, and the launch schedule has been updated repeatedly. In March 2015, NASA informed the U.S. Congress that the Launch of the James Webb Space Telescope was October 2018. But in September of the same year, NASA postponed the launch until the spring of 2019. By March 2019, NASA gave the launch date no earlier than May 2020. Not long after, on June 28, 2019, NASA directly postponed the launch time by another 10 months, scheduled for March 30, 2021.
When NASA announced that the James Webb Space Telescope will launch in December 2021, many onlookers may be skeptical, after all, there are many "previous convictions" for the delay in launch. Sure enough, the December launch date was postponed several more times: from December 18 to December 22 to December 24. However, due to the weather forecast showing poor weather conditions at the launch site on December 24, the launch time was postponed to Christmas Day. It wasn't until the rocket ignited and the James Webb Space Telescope actually embarked on a journey of exploration that the long wait finally came to an end.
It is normal for the space exploration program to postpone the launch, because in the process of designing and manufacturing probes, there will be many uncontrollable situations, including the adjustment of scientific goals, the research and development of manufacturing processes, and so on. However, the number of delays and delays of the James Webb Space Telescope is a record. There are both political reasons, such as negotiating with the U.S. Congress for funding; social reasons, such as the delay in telescope manufacturing caused by the COVID-19 pandemic since 2020; and accidents, such as the project contractor using the wrong solvent to clean the installed propulsion valve, resulting in the propulsion valve needing to be dismantled and cleaned before reinstalling, and the telescope causing unexpected shaking due to mistakes, and so on. When the launch is approaching, the launch is postponed due to weather reasons.
The series of delays resulted in the james Webb space telescope finally launching 14 years later than originally planned, and spending soared from $500 million when the project was first established to $10.8 billion, making it the most expensive scientific project ever supported by the U.S. government. NASA wants to share the costs to some extent while strengthening international cooperation, because the James Webb Space Telescope was made into an international cooperation project, in which the European Space Agency and the Canadian Space Agency (CSA) were also involved, each sharing a small share. In addition to providing some of the telescope's equipment, one of the main tasks of the European Space Agency is to provide the Ariane 5 rocket carrying the telescope and related supporting launch services, which is why the telescope is launched at the launch site of the European Space Agency.
The James Webb Space Telescope was designed for a service life of 10 years. At the same time, NASA is also developing new technologies, hoping to add propellant to the telescope through robots to extend the use of the telescope. Given the previous situation of space telescopes, if the deployment is successfully completed and reaches the predetermined position, we have reason to believe that the James Webb space telescope will be able to serve longer. We also have reason to believe that this space telescope, which brings together the wisdom of tens of thousands of scientists and engineers, will completely change our understanding of the universe in the future.
Southern Weekend contributed to Ju Qiang