James Webb Telescope

On 18 December a Ariane 5 rocket will take off from the  Guiana Space Centre in French Guiana, aboard it is going to be the $12 billion James Webb Space Telescope (JWST) – the costliest scientific instrument ever launched into space. In this publish I’ll speak about this exceptional telescope and the mission to deploy it.

Who was James Webb?

The telescope is known as after James E. Webb (1906-1992). Interestingly, though many  telescopes are named after well-known scientists,  Webb wasn’t a scientist. He was the NASA administrator (in impact its CEO) from February 1961 to October 1968.  This was a really thrilling time for the organisation. Webb oversaw the event of the crewed space programme from the primary American human space flight, Alan B. Shepard’s quick suborbital 15-minute hop into space in a Mercury capsule in May 1961, till the daybreak of the Apollo programme. He left NASA 9 months earlier than Apollo 11’s historic touchdown on the floor of the Moon.

Webb’s tenure in workplace was an necessary time for unmanned space exploration as effectively. In 1962, Mariner 2 turned the primary space probe to move one other planet when it went previous Venus. In 1965, Mariner 4 took the well-known photographs of Mars which confirmed its cratered floor.

Image of Mars taken in 1965 by Mariner 4

Why do we have to put a telescope in space?

One query typically requested is:

why is it essential to spend an enormous sum of money to place a big telescope into space when it’s far easier and cheaper to construct the telescope on the bottom?

There are various causes for this. One is that if we have a look at your entire electromagnetic spectrum which runs from gamma rays, which have wavelengths lower than 10-11 metres, by way of to the longest radio waves, which have wavelengths measured in kilometres, most areas of the spectrum are blocked by the Earth’s ambiance.

How the atmospheric opacity varies with wavelength. For a lot of the electromagnetic spectrum the opacity is 100% – that means that no radiation reaches the Earth’s floor. For these unfamiliar with these items: one nanometre (nm) = one billionth of a metre and one micron (μm) = one millionth of a metre

The two home windows, the place electromagnetic radiation will get by way of to the Earth’s floor with comparatively little attenuation are as follows.

  1. Visible mild which has a slim vary of wavelengths between 380 and 750 nanometres and a small vary of UV and infrared both facet of this. However,  if we contemplate the infrared area of the spectrum the place the JWST will probably be working, which has wavelengths as much as 28 microns, there’s vital attenuation by the Earth’s ambiance
  2. Radio waves  having  wavelengths between 2 cm and 10 m. This is a subset of your entire radio wave spectrum and most Earth-based radio astronomy takes place inside this vary.

Another good cause for placing a telescope into space is that every one astronomical photographs taken by ground-based telescopes are affected to some extent by turbulence within the Earth’s ambiance. This is named seeing and causes a blurring of the picture even on the biggest and most costly telescopes. .

An extra issue is that if we wish to have a look at  emissions at a single wavelength, i.e. a spectral line  attributable to the presence of compounds corresponding to water, methane or carbon dioxide in planets’ atmospheres, these compounds additionally exist within the Earth’s ambiance which complicates the analysi

Why is the JWST an infrared telescope? Rather than seen mild?

Astronomers will use the JWST to watch over a wavelength vary from 0.6 microns, on the red finish of the seen mild vary, as much as 28 microns which is effectively into the infrared. There are three primary causes for this. Firstly, very distant objects corresponding to galaxies are shifting away from us at a really excessive speed. This means the wavelength of the seen mild emitted from these objects is elevated (or red-shifted) as a result of growth of the Universe into the infrared area of the spectrum. Secondly, objects that are a lot cooler than stars corresponding to: particles discs, planets, clouds of gas and  objects referred to as brown dwarfs (that are intermediate in mass between the heaviest gas large planets and the good stars) emit primarily within the infrared. Thirdly, taking infrared spectra and observing by way of infrared filters (which solely enable a small vary of wavelengths to get by way of) can inform us an important deal in regards to the chemical composition of astronomical objects. As talked about earlier than, it’s tougher to check infrared spectral line emissions with ground-based astronomy  due to contamination  by emissions from Earth.

The JWST is usually described as a successor to the well-known Hubble Space Telescope (proven beneath) which has been operational since 1990. This isn’t fairly true. The major capabilities of the Hubble Space Telescope are to take observations at wavelengths between  0.1 microns and 0.8 microns, which implies that it really works on the close to ultraviolet and visual wavelength ranges, with solely a slight overlap into the infrared ( supply https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html). Also, when the JWST begins scientific operations the Hubble Space Telescope won’t be switched off. It may effectively proceed working for an additional ten years.

Costs of the JWST

One topic for which the JWST has acquired a lot damaging publicity is its monumental prices. Like many massive science tasks (and certainly massive tasks which don’t have a lot to do with science ) constructed on modern expertise, the prices have turned out to be a lot bigger than the unique estimates and the timescales lots longer.  When the JWST was first thought of again in 1996 the unique ball park estimates have been that it will cost around $1 billion and would launch in 2007 .  When the event of the telescope began there have been quite a few slippages and the estimated prices saved escalating. At one stage it seemed like that the JWST could be cancelled altogether. However, NASA have been dedicated to finishing the mission as a result of the scientific worth of such a novel instrument was so excessive. The present prices of the telescope are given beneath. They additionally embody the primary 5 years of operation.

All expenditure from earlier years has been adjusted upwards for inflation to be  in 2021 {dollars}.

These prices make it the costliest astronomical intruments ever constructed. One apparent truth is that, though the JWST is usually cited for instance of worldwide cooperation, 92% of the fee is borne by the US taxpayer.

Deployment of the JWST

The diagram beneath reveals how the JWST will seem when it’s in operation.

The ISIM is the Integrated Science Model, which incorporates the scientific gear hooked up to the telescope

The most noticeable element of the construction (aside from the telescope itself) is the sunshield. This measures 22 metres by 10 metres. It can be extra exact to name it “the five sunshields” as a result of it has 5 separate layers to maximise cooling. Each layer is made out of a really skinny movie of Kapton E (a high-performance polymer) coated with aluminium. Because of its sheer dimension the sunshield must be folded up earlier than launch and, through a posh set of manoeuvres, unfolded in space.

The cumulative impact of the 5 layers of sunshield is to maintain the telescope and the devices hooked up to it cooled all the way down to a temperature of -233 oC. This cooling is  important as a result of objects round room temperature emit quite a lot of infrared radiation on the wavelengths which the JWST will probably be observing.

The telescope itself has three mirrors in a design referred to as a three-mirror anastigmat. This is identical design because the LSST being built at the Vera Rubin observatory in Chile .The major mirror is 6.5 metres in diameter however, due to its sheer dimension, it consists of 18 separate mirrors. A single 6.5 metre diameter mirror can be tough to assemble and, in any case, can be too massive to place into the Ariane launcher. The major mirrors are manufactured from beryllium, which is likely one of the lightest metals, and are coated in a skinny movie of gold, which supplies them a yellowish color. The secondary mirror is 0.74 metres in diameter. To save weight and simplify deployment, not like the Hubble Space telescope, the JWST has no “telescope tube”. The secondary mirror is held in place by three poles. The telescope will probably be deployed in a halo orbit across the Earth- Sun L2 Lagrange level. At this location the sunshield will protect it from radiation from each the Sun and the Earth.

An object positioned precisely on the L2 level will at all times stay on the other facet of the Earth to the Sun.

In idea, if the Earth and the Sun have been the one our bodies within the Solar System, an object positioned precisely on the L2 Lagrange level would take exactly  one year to orbit the Sun and would at all times stay on the other facet of the Earth from the Sun on an imaginary straight line becoming a member of the centre of the Earth and the centre of the Sun.

However,  the L2 Lagrange level  isn’t a steady equilibrium. If an object is positioned there any  slight perturbation of the thing’s place (for instance by the method of one other planet) will trigger  it to float away into a unique orbit. So, moderately than being positioned in orbit across the Sun on the L2 Lagrange level,  the JWST is positioned in  moderately advanced trajectory wherein the JWST  is in orbit across the Sun, but in addition seems to be an orbit across the L2. For extra particulars see the easy video beneath.

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This trajectory (referred to as a halo orbit) is comparatively steady. Even so, a small quantity of gasoline will probably be  wanted to regulate the JWST’s place in order that it stays within the halo orbit. This propellant will probably be a limiting issue of the JWST lifetime. The quantity must be adequate to present the spacecraft a lifetime of greater than ten years. When the gasoline has been used up the JWST will drift into an elliptical orbit across the Sun and the sunshield will not protect the spacecraft from infrared radiation from Earth .

And Finally…

Fingers crossed that the telescope launch is profitable on 18 December and that deployment of the telescope goes to plan. It will probably be a nervous few months for a lot of astronomers! Hopefully, we’ll see some nice science from observations taken by the JWST over the approaching decade. The picture beneath reveals a  Hubble ultradeep failed lengthy publicity {photograph} taken with 22 days of statement. It will probably be fascinating to see what the infrared photographs taken by the JWST seem like!

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