by Syed
You may have seen the James Webb Space Telescope (JWST) launch on Christmas Day 2021. It was the joint effort of NASA, the ESA (European Space Agency) and the CSA (Canadian Space Agency). It has cost $10 billion, taken over 25 years, and suffered severe delays due to budget overruns, the covid pandemic, a ripped sunshield, issues with the Ariane 5 rocket, and a major redesign in 2005. It was originally planned to launch in 2007, it is almost 15 years late, but the progress we will make compensates this.
It is named after the NASA administrator James E. Webb, who played a significant role in the Apollo program. This telescope will be the successor to Hubble and the “Great Observatories”, a group of 4 space telescopes that observe throughout the electromagnetic spectrum:
- The Spitzer Space Telescope observes the infrared spectrum
- The Hubble Space Telescope views visible light and near ultraviolet
- The Chandra X-Ray Observatory views soft x-rays (x-rays that are of lower energy and of longer wavelength)
- Compton Gamma Ray Observatory observes gamma rays and hard x-rays
When someone views an object, they are seeing it as it was in the past because of the time it takes the light to travel to the observer. Whenever you talk to someone, you can see what they were like nanoseconds in the past. Therefore, if a telescope is viewing objects many millions of lightyears away, they are like observational time machines. JWST can exploit its use of the infrared spectrum and look further into the past, and the early moments of the Universe, than Hubble ever could.
However, even after a successful launch, there are still many precarious measures and steps that need to be taken before it can start observing. So far, the solar array has opened, and the telescope does not have power failure, but the next crucial step is unfolding the sun shield so the mirrors can start working. Because the observatory is so big, the shield had to be folded into the nosecone of the Ariane launcher. The hair-thickness membranes in the shield are held together by the electrical insulator Kapton and silicon, and the shield needs to be pulled so its five sheets make a smooth, rigid surface. This will be achieved with lots of restraint mechanisms.
The sun shield is essential, as JWST will view the faintest and furthest stars with its infrared detector. It needs to be shaded from bright, hot sources, so the mirrors and instruments on the cold side of the telescope are designed to work at -230°C. Once the sunshield is sorted, the primary mirror (Optical Telescope Element) will start to combine its 18 hexagonal, adjustable, gold-plated beryllium segments to create a 6.5m diameter mirror (much larger than Hubble’s 2.4m mirror). This will have to be to nanometre precision. Then, the secondary mirror will be positioned roughly 7 metres from the primary to focus the light, creating immaculate precision in the viewing of objects. After the second week, the telescope and instruments will take several weeks to cool down to stable temperature, which will be carefully monitored through strategically placed electric heater strips that will evaporate trapped water stopping it freezing on instruments and damaging them. All the mirrors will be verified for movement, the scientific instrument systems powered-up, and JWST will be inserted into its orbit around L2 (Lagrange Point 2).
The Lagrange points are the solution to the “three-body problem”, by 18th century mathematician Joseph-Louis Lagrange. The problem asks whether there is any stable configuration in which three bodies could orbit each other but stay in the same position relative to each other. The five solutions to this problem are the five Lagrange points, where the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them. L1, L2 and L3 are all in line with each other, and L4 and L5 are at the points of equilateral triangles. L4 and L5 are completely stable, with objects orbiting around them. L1, L2 and L3 are metastable, and objects will slowly drift away into their own orbits unless acted upon by another force (like small periodic rocket thrust). The combine gravitational pull of the Sun and the Earth will keep Webb at roughly the same speed as Earth when going around the Sun, and the benefit of Webb orbiting L2 in this way is that it is always outside of the shadows of the Earth and Moon, but not facing the exposure of the Sun, unlike Hubble, which dips in and out of Earth shadow every 90 minutes. Its orbit around L2 takes roughly 6 months, and science operations can operate 24/7. Since Webb will always be in the same position relative to Earth in the sky 1.5 million km away, it can communicate constantly with the 3 Deep Space Network antennae located in Australia, Spain and California. Webb will take roughly 30 days to reach the start of its orbit around L2, and its temperature, distance from Earth, cruising speed, and time elapsed can all be monitored through this website while you wait. Of course, I have linked to the metric units version!
In the months following, the observatory will use its Fine Guidance Sensor and point at a single bright star using its NIRCam (near infra-red camera). There will be 18 distorted images of the same star as the segments would not have been aligned yet, and the telescope will be adjusted and refined until both its mirrors are in optimal position. More infrared instruments will start taking data. The instruments will all be meticulously calibrated, and objects such as comets, asteroids, moons, and planets will be tracked. These “Early Release Observations” will showcase Webb’s potential. By six months, there will hopefully be some first-light pictures. All the steps I have mentioned will have to be perfect, as any problems could be catastrophic. It would be almost impossible to solve problems, as the telescope would be incredibly hard to be reached through a manned expedition.
More detailed information into all the observatory elements can be found by visiting the NASA website.
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