All Systems Go For The James Webb

All Systems Go for the James Webb Space Telescope

By Jodie Sims

With its original launch date set for 2007, the JWST has been plagued with its fair share of delays. The original budget was set at $500million USD however with all the delays, by the time of the launch, this had blown out to $10billion USD. Delays took many forms ranging from funding to technical issues. Starting with the threat of project cancellation in 2011.

Then design challenges with the propulsion system and a discovery that the sunshield may snag on other components in 2018. The COVID pandemic added further delays in 2020 followed by issues with the readiness of the Ariane 5 launch vehicle and site in 2021. During the final phase of preparation, a clamp unexpectedly released during attachment to the rocket causing potentially damaging vibrations.

This was followed by the discovery of an electrical fault in early December 2021. Finally, unfavourable weather predictions pushed back the launch to no earlier than 12:20 UCT on the 25th December. Finally, years of research, designing and testing culminated in the successful launch on Christmas Day 2021.

31 minutes into the mission the solar array was deployed allowing the JWST to power up ready for instrument operation and communication. This was the first crucial step in the 50 major deployments required to fully unfurl into an operational observatory.

10 days after launch on the 4th January 2022 another of JWST’s innovative critical features completed deployment. A tennis court sized sunshield unfurled successfully. This process employed 139 of Webb’s 178 release mechanisms, 70 hinge assemblies, eight deployment motors, 400 pulleys, and 90 individual cables totaling roughly one quarter of a mile (0.4km) in length. Made up of 5 layers each as thin as a human hair this sunshield is designed to protect the scientific instruments on board from heat that would disrupt its ability to view and collect clear low noise images and data.

Image Credit: ESA-CNES-ARIANESPACE Each layer is made of aluminium coated Kapton, a special highly durable polyimide flexible film developed by DuPont. This material remains stable at temperatures as low as -269 C and up to 260 C. The 2 layers closest to the sunward side are also coated in treated silicon to help reflect the suns heat back into space. This design will allow the instruments on board to operate at a chilly -223 C.

Measuring at a total of 20.197 m x 14.162 m, once fully unfurled this celestial trail blazer is also comprised of a 6.5m diameter primary mirror made out of 18 x 1.32 m individual hexagonal mirrors weighing 20 kg each. These mirrors can be angled and focused independently of each other by actuators to give a final combined image. Made from gold coated beryllium this design is both lightweight, strong and perfect for viewing the infrared part of the spectrum.

With gold having high reflectivity of infrared light and also having low reactivity to changes in temperature it was the perfect choice of mirror material. Comparatively the JWST mirror is six times larger than Hubble’s and 100 times more powerful. The light gathered by the primary mirror will be concentrated by a secondary mirror held out by a supporting tripod. This concentrated light will then pass through an opening in the main mirror to a third mirror, which will reflect the light to the sensors of the telescope’s various instruments.

Positioning for this telescope is everything. On the 24th January 2022 delivery of the JWST to Lagrange Point 2 was complete. Along with the sunshield and onboard cooling system this position in space would aid in shading JWST’s instruments from as much heat as possible. The L2 Earth -Sun Lagrange Point 1.5 million kilometres from Earth was perfectly chosen as the final operational destination. This point allows earth to shield the telescope from the sun’s rays as they move in tandem around the sun with the telescope always keeping it’s back sunward looking out into the depths of space whilst staying cool.

This tailored configuration will allow the JWST to easily see unhindered the stretched redder wavelengths of light emanating from faraway galaxies as they move further away due to the expansion of the universe. Using a suite of four instruments, NIRSpec (Near Infrared Spectrograph), MIRI (Mid - Infrared Instrument), NIRCam (Near- Infrared Camera and FGS/NIRISS (Fine Guidance System / Near- Infrared Imager and Slitless Spectrograph) the capabilities of this telescope will allow astronomers to probe back to approximately 400,000 years after the Big

Bang. Enabling scientists to examine some of the earliest formed stars to illuminate the universe. Using the on-board instruments this telescope has the ability to analyse the spectra within atmospheres of exoplanets in the search for signatures of biological life. Once the 5-month calibration period is completed this orbiting infrared observatory will start collecting data that will expand and help verify our current knowledge about the origins to the universe, the birth of galaxies and galactic evolution.

Excitingly, on the 11th February 2022 NASA rereleased the first images. A mosaic of 18 images of the same star. Verifying that that all 18 mirrors had survived the journey and were working. Over the next few months these mirrors will be optimally calibrated ready to start gathering data. In order to maintain the observatories orbit and altitude JWST is powered by a hydrazine fuel with dinitrogen tetroxide oxidiser propulsion system. Enough fuel is on-board to keep the observatory running for approximately 10 years. This is predicted to be an exhilarating 10 years of ground-breaking discoveries that will accelerate our understanding of how the cosmos works.