The James Webb Space Telescope, scheduled for launch in 2007, was "unsurprisingly" delayed again. Since its development in 1996, people have been looking forward to the early launch and role of this infrared telescope, which is known as "the largest, most capable and most complex structure".
On November 2, local time, the National Aeronautics and Space Administration (NASA) held a press conference saying that the Weber Space Telescope, which has been preparing for more than 20 years and costs $10 billion, will replace the Hubble Space Telescope and is scheduled to enter space on December 18.
The launch was interrupted due to "vibrations caused by the accidental shedding of a fixed belt that could affect the telescope" and the launch date was changed to "no earlier than December 22". On December 14, local time, NASA issued a statement that the James Webb Space Telescope team is solving the communication problem between the telescope and the launch vehicle system, which led to another 2-day delay in launch, which will be launched no earlier than December 24.
Technicians used cranes to lift the Webb Space Telescope and move it to the clean room of NASA's Goddard Space Flight Center. Image source: NASA official website
Development began in 1996, and the Weber Space Telescope has not yet lifted off
In 1996, early in the course of the project, the James Webb Space Telescope was scheduled to launch in 2007 with a budget of $500 million. At that time, the famous Hubble Space Telescope had been in space for 6 years.
As the next generation of space telescopes, the Webb Space Telescope absorbs the benefits of Hubble and the decommissioned Spitzer Space Telescope. Equipped with a 6.5-meter diameter mirror and a tennis court-sized visor, the telescope is the most powerful and complex space telescope ever built. The telescope will operate in an orbit of 1.6 million kilometers from Earth, and the telescope will be 4500 times farther from Earth than the International Space Station, and also four times farther than the Earth-Moon distance.
"Changes in the design are perhaps the most important reason for the delay in launch." Jiao Weixin, a professor at Peking University's School of Earth and Space Sciences, told reporters.
In 2005, the design of the Weber Space Telescope was greatly adjusted, and the launch time was forced to be delayed. The staff carried out a lot of research on environmental testing, visor testing, mirror testing, etc., and the launch was repeatedly postponed as technology improved and new problems continued to emerge. According to NASA's previous news, they have planned to launch the Weber Space Telescope at different time nodes in 2014, 2018, 2019, 2020 and other years.
Technicians examine the mirror. Image source: NASA official website
At present, the complexity of the process and the difficulty of research and development are also the crux of the problem.
According to NASA officials, the James Webb Space Telescope will be a large infrared telescope with a disc made up of 18 small lenses made of ultra-lightweight metal element beryllium, which will be shaped according to demand after the telescope is launched.
Publicly available materials show that the Webb Space Telescope's 18 mirrors had to dock at 14 stops in 11 locations in the United States to be manufactured, and that the mirrors needed to remain cool. After the mirror is made, it is also necessary to carry out polishing, gold plating and other processes, and the finished lenses need to be kept in a special protective tank in the clean room.
According to two recent NASA releases, the Weber Space Telescope was scheduled to launch from Kourou, French Guiana, on December 18 aboard the French company Arianespace's Arianespace Rocket. At this point, the technicians will connect the Webb telescope to the rocket adapter and then install it on the upper stage of the rocket. But during launch preparations, the entrainment that secures the telescope to the adapter "suddenly and unexpectedly releases," causing the entire unit to vibrate. Since then, the launch has been postponed again due to communication problems between the telescope and the launch vehicle system.
The Webb Space Telescope was placed on top of Ariane 5. Source: Official website of the European Space Agency
The Webb Space Telescope is the "successor" of the Hubble Space Telescope
The main goal of the Weber Space Telescope is to study distant galaxies at the edge of the observable universe, and thanks to its outstanding infrared observation capabilities, the telescope can look for water vapor characteristics of exoplanets, thereby improving NASA's ability to find and study extraterrestrial planets.
"Weber is often referred to as Hubble's replacement, but we prefer to be called 'heir.'" Jiao Weixin said that the difference between the two is first reflected in the wavelength.
The Weber Space Telescope is observed primarily through infrared light, with four scientific instruments to capture images and spectra of astronomical objects. These instruments provide wavelength coverage between 0.6-28 microns, and the infrared part of the electromagnetic spectrum ranges from about 0.7 microns to hundreds of microns, which also means that the Weber Space Telescope is equipped with instruments that will mainly work in the infrared range of the electromagnetic spectrum and have a certain ability in the visible light range. Hubble is equipped with instruments that can only observe a small part of the infrared spectrum from the 0.8-2.5 micron range, mainly monitoring the ultraviolet and visible parts from the 0.1-0.8 micron range.
Secondly, there is also a difference in size between the two. The main mirror diameter of the Weber telescope is about 6.5 meters, which makes it have a larger collection area in the mirror than the current generation of space telescopes. Hubble is only 2.4 meters in diameter, and its corresponding collection area is 4.5 square meters, resulting in a collection area of 6.25 times more than Hubble, and The Weber telescope has a larger field of view than Hubble, covering more than 15 times.
The orbits of the two space telescopes are also different. According to reports, the Hubble Space Telescope is in low Earth orbit, orbiting the Earth at an altitude of about 570 kilometers above the Earth. The Weber Space Telescope does not orbit the Earth, but is located at the second Lagrange point, and if the Sun is connected to it in a straight line, then the Earth is in the middle, and it has been hiding 1.5 million kilometers away from the outside of the Earth and orbiting the Sun.
How far can the Webb Space Telescope see? Jiao Weixin believes that the Weber Space Telescope can see "juvenile galaxies".
"The Webb Space Telescope can see galaxies in the universe that have just formed for about 11 years. Einstein's general theory of relativity actually comes into play when the universe is expanding and we talk about the most distant objects, telling us that the expansion of the universe means that space between objects is stretching, causing objects or galaxies to move away from each other. In addition, any light in space will also be stretched, making the wavelength longer, which makes distant objects appear very dim or invisible under the light of the visible wavelength, because this light appears in the form of infrared light. So infrared telescopes like Webb's are ideal telescopes to observe these early galaxies. Jiao Weixin said.
■ Extension
Why send a telescope to the sky?
The Webb Space Telescope is more than 20 years old and costs $10 billion, so why do we have to launch telescopes into the sky?
Jiao Weixin introduced that the main reason is that space telescopes are not limited by the atmospheric window. "Earth has a rich atmosphere that completely blocks the passage of gamma rays, X-rays and electromagnetic waves in the ultraviolet band. That is to say, under the shroud of the atmosphere, short-wave electromagnetic radiation cannot pass through. Infrared can only pass through a limited number of wavelengths, although it can pass through visible light, but due to scattering and other factors, it will also cause distortion of the signal, affecting the resolution, which seriously affects the observation effect of the ground telescope, and the space telescope can avoid this effect. ”
Secondly, there is no light pollution in space, which also provides conditions for telescopes to play a role. "City lights, for example, make the sky brighter and it harder for people to see the stars, which explains why advanced modern observatories are built in remote areas far from light pollution." Taking China as an example, the National Astronomical Observatory, Nanjing Purple Mountain Observatory, Xinjiang Observatory and other places to avoid man-made light and atmospheric pollution are also stationed in places where man-made light and atmospheric pollution are serious, and large foreign observatories are almost all built on high mountains. ”
There is no atmosphere in space, and the sunlight is brighter, will that not affect the use of space telescopes? Jiao Weixin explained, "Because light needs to be reflected on the captured object, when the light is too strong, we can operate through instructions to point the telescope in the other direction, so in space, light pollution is not a problem." If we want to study the contents behind the sun, we can also wait for a period of time to change the trajectory of the telescope at an angle and then observe. ”
Third, there is no day and night in space, and space telescopes are not limited by night, which increases the effective time of telescopes and helps astronomers to carry out more research.
In addition, there is no bad weather in space. Generally speaking, weather changes on the ground directly affect the observation effect, but there will be no weather problems such as rainy days and fog days in space.
There are many benefits to sending a telescope into space, but there are also some obvious problems. Jiao Weixin said that the first is the high cost, a few tons of heavy objects are transported to outer space, and other costs such as launch vehicles and launch sites are very expensive. At the same time, problems found on the ground can be repaired at any time, but it is very difficult to repair in space.
Beijing News reporter Zhang Jianlin
Edited by Bai Shuang Proofreader Wang Xin