James Webb Space Telescope Working Artistic Imagination Diagram. (NASA website/photo)
The James Webb Space Telescope, known as the "strongest space telescope in history", has attracted great attention from the astronomical community and the public after its successful launch on December 25, 2021, Beijing time. On January 25, 2022, Beijing time, the National Aeronautics and Space Administration (NASA) announced that the James Webb Space Telescope successfully implemented orbit capture control at about 3 a.m. on the same day, and successfully entered the halo orbit orbit of the second Lagrange point (L2) around the Sun and Earth, drawing a perfect end to the crucial first stage after launch. The project team has already started testing the telescope and is actively preparing for the first official observations in the summer of 2022.
In the month since launch, the James Webb Space Telescope flew to the second Lagrange point of the Sun and Earth, about 1.5 million kilometers from Earth, while completing what is arguably the most complex space unfolding ever made, and these unfolding actions directly determined the success or failure of the mission. During the unfolding, there are 344 nodes called "single point failures", which is equivalent to 344 tests for telescopes. If one step goes wrong, the telescope, worth more than $10 billion, is at risk of being scrapped. Fortunately, this highly anticipated space telescope successfully completed all the scheduled operations, laying a solid foundation for the next exploration work.
After launch, the James Webb Space Telescope first opened the solar panels to obtain an energy supply. After that, the first key operation performed by the telescope was to open the 5-layer film of the umbrella. The role of the parasol is to help the telescope insulate the heat radiation from the Sun, earth and moon. Of the five films, four are used to cool the telescope, and the remaining one is used as a backup to complement the damage to the other four films. The thermal insulation effect of these specially designed films is very obvious: the telescope will operate at an extremely low temperature of -233 ° C, while the heating surface temperature of the telescope reaches about 85 ° C.
The James Webb Space Telescope then begins the development of the secondary and primary mirrors, which is the most complex and challenging task of the whole process. The epoch-making detection capabilities of this space telescope are due to a significant increase in the main mirror area compared to previous telescopes such as the Hubble Space Telescope and the Spitzer Space Telescope, but this also poses a challenge to rocket launches.
James Webb Space Telescope. (NASA website/photo)
The telescope mirror consists of 18 hexagonal mirrors with a diameter of 6.5 meters and needs to be folded to fit into the rocket. The folding method is that the three hexagonal mirrors on each wing fold backwards at launch and unfold after the telescope enters space. 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 completing the unfolding in space, the entire telescope is 8 meters high, 21.2 meters long and 14.2 meters wide.
On the evening of January 5, 2022, Beijing time, the telescope secondary mirror was first successfully unfolded and locked. The mirror of the secondary mirror is gilded, and the role is to reflect the light reflected and focused by the main mirror into a small hole in the middle of the main mirror, in which the light passes through a series of optical paths and finally enters the detection equipment. On the evening of January 8, Beijing time, the main mirror of the telescope was spliced. The 18 hexagonal mirrors are spliced together to form a near-circular main mirror, which is conducive to focusing to form a clear image. A miniature motor is installed behind each main mirror to precisely adjust the position of the lens.
After the main mirror unfolded, the James Webb Space Telescope was officially formed. After that, the telescope flew for more than half a month to the predetermined position, near the second Lagrange point of the same day and earth. Spacecraft working in this position can 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 relative to Earth. Prior to that, probes such as the Wilkinson Microwave Anisotropy Probe, the Herschel Space Telescope and the Planck Satellite had all stopped near this location.
The orbit of the James Webb Space Telescope is an elliptical orbit with a semi-major axis of 832,000 kilometers, a semi-minor axis of 250,000 kilometers, an orbital period of about 6 months, and a maximum distance of about 1.8 million kilometers from Earth. Because telescopes need to be powered by solar panels, telescopes will never be in the shadows of the Earth or the Moon.
The expensive telescope is designed for a service life of 10 years, which is largely determined by the amount of fuel the telescope carries. But given that both the launch into orbit and the mid-course correction have reached extremely high accuracy, saving a lot of fuel, the mission team believes that the telescope's working cycle will be much more than 10 years, and the plan can reach about 20 years.
After the James Webb Space Telescope reached the second Lagrange point of the Sun-Earth, the project team began a three-month testing exercise to calibrate the 18 lenses of the main mirror so that they truly integrated into one to exert powerful observation capabilities. The 18 lenses must be tightly seamed, and the height undulation between the different lenses cannot exceed 50 nanometers. If the size of the telescope is compared to the size of the United States, then the size of each main lens is equivalent to a Texas, and the telescope project team needs to ensure that the height difference between the different "Texas" when spliced together does not exceed 3.8 centimeters, which shows its precision.
Over the next 3 months, the work of calibrating the primary mirror will be divided into 7 stages. Previously, the project team had developed an algorithm for calibrating the telescope's main mirror and conducted extensive ground tests on a 1/6 size telescope model, and now they were going to operate on a real telescope. On Feb. 2, a near-infrared camera (NIRCam) on the telescope completed a photograph of a star numbered HD84406, the first ray of star the telescope detected, and the photos will be used to help calibrate the telescope's main mirror.
While calibrating the main mirror, the telescope instruments will continue to cool to reach the low temperatures required for work. After about 4 months, the telescope will officially begin to probe and get the first results. In the summer before, we are expected to look deep into the universe with unprecedented precision, gaining insight into what the universe would look like just a few hundred million years after the Big Bang.
Southern Weekend contributed to Ju Qiang