The James Webb Space Telescope Is Ready For Launch: Here’s Everything You Need To Know
After many years of research and development, NASA has announced that the James Webb Space Telescope (JWST) is officially making its way into outer space. The launch date is December 18th, 2021. This telescope is capable of operating at much longer infrared wavelengths than the Hubble Space Telescope, allowing JWST to peer farther back in time and gather imagery from the early years of the universe that would be impossible from ground-based telescopes due to the atmosphere.
FRED optical engineering software was used during the development of the JWST to assess its performance against the stringent straylight specifications that were needed.
Originally known as the Next Generation Space Telescope (NGST), development of the JWST started in 1996 and was intended as a replacement for the Hubble telescope that had launched into space some six years earlier. The initial launch date was expected for 2007 but due to a necessary redesign of testing plans to mitigate cost overruns, the launch date was postponed.
In 2013 scientists entered the building process of the JWST in Maryland, and in 2017 the build was completed and was transported to Texas for cryogenic testing. In 2018, the telescope was shipped to Space Park in California where it received three additional years of testing to ensure that it can survive the climate and turbulence of space.
The telescope was initially set to be launched into outer space in October of 2018 but it was postponed to June of 2019 when the telescope was deemed not ready. It later received a few more delays and was postponed three more times, announcing its launch for May 2020, March 2021, and finally December 2021.
On September 26, 2021, the telescope was shipped from California to the launch site in French Guiana by boat. It was transported on the MN Colibri which has previously been used to transport space gadgets such as satellites. The trip consisted of a 16-day voyage with a total of 2,400 kilometers traveled. It reached its destination of French Guiana on October 12, 2021. Currently, the telescope is preparing for its launch in two months.
The JWST will provide a deeper understanding of the universe with its advanced scientific capabilities. Scientists will now have more insight into the mysteries of the universe that were previously unachievable. According to NASA, “Webb will reveal insights about all phases of cosmic history – back to just after the big bang – and will help search for signs of potential habitability among the thousands of exoplanets scientists have discovered in recent years.” These discoveries can provide scientific breakthroughs about the origins of the universe including early star and galaxy formations and aid in the search for Earth-like planets.
The JWST will be observing space primarily in the infrared wavelength, allowing for more detailed images of deep space. According to NASA, “more distant objects are more highly redshifted, and their light is pushed from the UV and optical into the near-infrared.” This means that to see the objects in the distance, it would require an infrared telescope. The Hubble telescope is only able to observe a small portion of the infrared spectrum, missing out on distant objects.
Since the JWST has the ability to see farther, it will expand how much of the universe is observable. Since it takes time for light to reach Earth, this means the telescope will be observing some of the earliest forming celestial objects in the universe. The technology in the JWST will be able to see back to shortly after the big bang to what is called ‘baby galaxies’ providing insightful information reaching back 700 million years further than the Hubble telescope could.
The JWST will follow a halo orbit around the second Lagrange point, approximately 1.5 million kilometers from Earth. This is best described as an interaction between the gravitational pull of two large bodies (The Sun and the Earth). The 6-month orbit keeps the telescope out of the shadows of both the Earth and Moon. This allows for a clear view of deep space that will provide 24/7 observations for astronomers. This also allows the sun shields on the JWST to always face the Sun, thus ensuring a constant temperature below 50 Kelvin, which is necessary for infrared observations.
Video Courtesy: Animation: The James Webb Space Telescope's Orbit
Once the JWST has been launched, It will take around a month to reach the second Lagrange point. When the telescope has reached its desired orbit point, it will be controlled through a radio link. Since the telescope is located very far away, it will take six seconds for the commands to reach the telescope and six seconds for the command to be sent back to Earth.
The extent of testing that the JWST has gone through includes simulating the conditions of the rocket launch to ensure that the telescope can survive the trip, simulating the harsh conditions of space and ensuring the smooth deployment of the Sun shields. Scientists have also completed many tests on simulators to detect any potential incidents in space that may occur. They are continuing to practice on these simulators up until the telescope is launched so they are prepared for anything.
Even after the telescope has arrived at its destination, there is a waiting period of 35 days where the telescope needs to cool off before it can start to unfold. Once it starts to unfold, the telescope will take pictures of its positioning and send them back to Earth so adjustments can be made since the positioning must be precise for functionality.
The process of traveling to the second Lagrange point, unfolding itself, deploying the solar arrays, and positioning itself correctly will take a total of six months before it will be fully operational.
During the launch, and positioning of the telescope, a lot can go wrong. Using optical engineering software such as FRED can help reduce the problems to ensure that the telescope will be fully operational during the desired timeframe.
By re-creating the JWST in FRED, it provides the ability to test the performance of each of the optical components to simulate the advanced imaging without needing to spend billions of dollars.
Building The James Webb Space Telescope in FRED
JWST is a Three Mirror Anastigmat (TMA), allowing for correction of spherical aberration, astigmatism, and coma. The TMA consists of a concave near parabolic primary mirror, convex hyperbolic secondary mirror, and a concave elliptical tertiary mirror.
Image Courtesy: JWST
The light reflected from the tertiary mirror is then incident on a flat fine steering mirror which is used to direct the light to the various instruments.
To ensure the highest reflection efficiency in the infrared spectrum, each mirror is assigned a gold coating which gives high reflectivity from 0.6 to 28 microns.
Image Courtesy: EOPortal
Assembling the Primary Mirror
JWST’s Primary Mirror is made up of 18 hexagonal mirrors with a vertex to vertex distance of 1.5 meters, giving a total radius of 6.5 meters.
Image Courtesy: JWST
Each mirror is labeled A, B, or C to denote the differing optical prescription of placement. To assemble this in FRED, a hexagonal curve was drawn and was set to trim a surface that matched the curvature of the JWST ( Radius of curvature = 15879.7: Conic Constant = -0.9967).
Afterwards, an embedded script was used to generate the hexagonal curves and populate 18 segments to build the primary mirror.
FRED’s Digitizer Function was then used to create an accurate gold coating which was applied to the surface of the primary mirror. The secondary, tertiary and fine steering mirrors were placed with respect to the primary mirror, and a field bias 0.18 degrees was applied to the entire JWST. Rendering a plane wave shows the path light travels through the telescope in the 3D view.
Building the Frame
The “Frame” that houses the optical components can be entirely done using native FRED objects by taking advantage of the boolean object function and user defined curves.
The centerpiece that houses the fine steering mirror was built using 3 solid objects. An N-Sided Pyramid was trimmed by a Block Element in order to form the outer shape. Then another block was used to create the aperture that allows the desired rays to pass through.
By taking full advantage of user defined curvatures as well as FRED’s vast library of Element Primitive Shapes, it’s possible to construct a working model of the James Webb Space Telescope.
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