Graham writes ...
After 25 years in development, and a 10 billion dollar spend, the JWST was finally launched on Christmas Day 2021 (much to the delight, I’m sure, of the families of the army of engineers who had to attend the launch!) as I described in my January 2022 blog post. You might like to have a look back at that post, which discussed the launch and looked forward to the spacecraft deployment and orbit insertion.
A second brief post in January 2022, announced the news of the completed configuration deployment just 17 days after launch, while the spacecraft was still on its way to its operational orbit around the second Lagrange point. The deployment sequence required the successful actuation of over one hundred mechanisms which is unprecedented in the brief history of the space age. In the context of spacecraft engineering, ‘mechanisms’ are essentially moving parts which allow the deployment of things like solar arrays and antennae, which usually need to be stowed in a compact configuration for launch. I remember a time, in the 1980s, and to some degree the 1990s, when it was considered good practise to minimise the number of mechanisms, as each one represented a potential single-point failure that could terminate the mission of a very expensive spacecraft. I think it’s fair to say that the complex deployment sequence of the JWST has finally put that philosophy of ‘mechanism-phobia’ to bed. If you haven’t seen this remarkable sequence there is a link to an excellent video in my first January 2022 post.
After the deployment, the spacecraft continued its journey outwards towards its final operational orbit, which it reached about 30 days after launch. Three mid-course corrections (thruster firings) placed it into a large, sweeping halo orbit around the L2 point about 1.5 million km from Earth. L2 is an equilibrium point in the Sun-Earth-spacecraft three-body system (see January post and (1) for details). However, it is a point of unstable equilibrium, which means that the spacecraft will have to continue to execute course corrections during its operational lifetime to keep it on-station around L2.
The main features of the spacecraft configuration are a 6.5 m (21 feet) primary mirror, consisting of 18 hexagonal, gold coated elements and a tennis court-sized sun shield. The latter is required to passively cool the payload instruments to a temperature of around -230 degrees Celsius, as the telescope is optimised to operate in the infra-red (heat radiation) part of the spectrum – see diagrams. The temperature had already decreased to about -200 degrees C by early January. Since the instruments must be kept on the dark side of the observatory, the telescope can access only 40% of the sky on any specific day of the year, and it will take about 6 months to access the whole sky.
Each hexagonal element of the mirror has 7 actuators (mechanisms again!) to tilt, translate, rotate and deform each mirror surface to ensure they all operate as one ‘perfect’ parabolic surface. Prior to the alignment process, the telescope imaged a single bright star in the constellation of Ursa Major (aka ‘The Plough’ in the UK) called HD84406. The resulting image shows the star in 18 different positions. To undertake the alignment process of the individual elements, a test star in the constellation of Draco (the Dragon) called 2MASS J17554042+6551277 (2) was chosen because it is effectively an easily identifiable ‘lonely star’ with few nearby neighbouring stars. Using this star, each hexagonal element was adjusted so that the 18 separate images were amalgamated into a single point at the telescope’s focus to an accuracy of around 50 nm (1 nm = 1 nanometre = 1 thousand-millionth of a metre). This was a landmark process in the commissioning of the telescope, which was completed successfully in early May 2022.
As I write, the process of collimating each of the observatory’s instruments is underway. The spacecraft has a number of primary instruments (spacecraft engineers love their acronyms!):
Returning to the picture of the test star in Draco, which was acquired using the NIRCam instrument, the alignment team noticed a scattering of galaxies in the background of the image, many of which were estimated to be billions of light years distant. One scientific bonus derived from this commissioning activity is the image of a galaxy which appears to be in the process of ejecting its once-central super-massive black hole (see picture). As described in (3), such super-massive back holes (with masses typically of the order of millions of solar masses) are ubiquitous at the centres of galaxies throughout the cosmos. About 8 billion light-years distant, the galaxy 3C186 is home to an extremely bright galactic nucleus — the signature of an active super-massive black hole. But this one is about 35,000 light-years from the centre of its home galaxy, suggesting it is in the process of being ejected. This object had already been imaged by the Hubble Space Telescope, and this new data from the JWST has reignited debate about what may be causing the ejection of this extremely massive object.
So, when can we expect the first operational images from the new observatory? Best guess at the moment is probably late June or early July. And what can the JWST do in furthering our understanding of the Universe? The answer to this question is related to the characteristic that the observatory is optimised to observe in the infra-red part of the spectrum, as we mentioned earlier. This is effectively heat radiation, which is why the telescope and the payload instruments need to be cooled to very low temperatures. If the JWST operated at the same temperature as the Hubble Space Telescope – around room temperature – the telescope and instruments themselves would produce thermal radiation which would swamp the incoming data from the sky.
So why is infra-red good? First off, it is less prone to scattering from dust and debris (compared to visible light) so the JWST will be able to observe ‘local’ events such as the formation of stars and the development of embryonic planetary systems beyond our own. The infra-red optimisation will also enable the observation of very distant objects, such as the first stars and galaxies. When these were forming, around 13 billion years ago, the light that they emitted in the visible part of the spectrum will have been stretched in wavelength by the subsequent expansion of the fabric of space-time. The JWST will now ‘see’ this radiation in the near and mid infra-red parts of the spectrum. Also, as mentioned above, one of the payload elements has been enabled to observe exoplanets to look for signatures of habitability in their atmospheres – such as water vapour and oxygen.
The JWST is part of a long heritage of astronomical instruments designed to answer the deep questions about the cosmos in which we live, such as
Clearly big questions, and of course no one project such as the JWST can be expected to provide all the answers. Clearly, the quest for understanding is an incremental process. However, we have great expectations that, like its predecessors, the JWST will reveal new findings beyond our hopes and imagination. However, it is also important to realise that all observatories that utilise the electromagnetic spectrum to probe the cosmos are ultimately limited by a fundamental barrier. As described in the book (4), immediately after the Big Bang, and for some 380,000 years afterwards, the energy and matter content of the Universe comprised a dense and very hot soup of charged particles and photons. Because the photons (particles of light) were continually interacting with the particles, the radiation was unable to propagate freely so the Universe was effectively opaque. This state of affairs continued until the temperature of the Universe was low enough for the charged particles to form neutral atoms, at which point the Universe became transparent to light. Consequently, direct observation of the events of the Big Bang using the electromagnetic spectrum are veiled by this early era of universal fog.
Rather than finish on this rather negative note, it should also be pointed out that we have other avenues of investigation to discover the secrets of the Big Bang, the main one currently being the emulation of the physical conditions just a fraction of a second after the Bang using particle accelerators. Another pathway is the utilisation of the new technology of gravitational wave detectors. The era of universal fog presents no barrier to the propagation of gravitational waves, and consequently the cosmos is probably awash with gravitational radiation containing information about the genesis event. However, the science of gravitational wave detectors is very much in its infancy, and nobody quite knows where it’s going and what a gravitational wave observatory of the future might look like. That is a revolution that has yet to unfold.
At the end of the day, after all the talk of science and engineering, our amazing God has given us a rational and creative intellect to envisage and build incredible machines like the James Webb Space Telescope (and the Large Hadron Collider, comes to that). The motivation that drives us to these heights of ingenuity and creativity comes from a God-given curiosity to uncover the secrets of His beautiful creation!
I hope to be showing some JWST images of this in the July blog post.
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