Five things to know about the James Webb Space Telescope


Washington (AFP) – The James Webb Space Telescope, the most powerful space observatory ever built, is now tentatively ready for launch on Christmas Day, after decades of waiting.

A marvel of engineering, it will help answer fundamental questions about the Universe, going back 13 billion years. Here are five things to know.

Giant gold mirror

The centerpiece of the telescope is its enormous primary mirror, a concave structure 21.5 feet (6.5 meters) wide and made up of 18 smaller hexagonal mirrors. They are made from gold coated beryllium, optimized to reflect infrared light from the far reaches of the universe.

The observatory also has four scientific instruments, which together serve two main purposes: imaging of cosmic objects and spectroscopy – breaking down light into distinct wavelengths to study the physical and chemical properties of cosmic matter.

The mirror and instruments are protected by a five-layer, kite-shaped sun visor designed to deploy to the size of a tennis court.

Its membranes are made from kapton, a material known for its high heat resistance and stability over a wide temperature range – two vital elements, as the side of the shield facing the sun will get as hot as 230 degrees Fahrenheit (110 degrees Celsius), while the other side will hit lows of -394F.

The telescope also has a “spaceship bus” containing its subsystems for power, propulsion, communications, orientation, heating, and data processing; all in all, Webb weighs as much as a school bus.

– Trip of a million kilometers –

The telescope will be placed in orbit about a million kilometers from Earth, about four times the distance from our planet to the Moon.

James Webb Telescope Jonathan WALTER AFP

Unlike Hubble, the current first space telescope to revolve around the planet, Webb will orbit the Sun.

It will stay directly behind the Earth, from the Sun’s point of view, allowing it to stay on the night side of our planet. Webb’s lens hood will always be between the mirror and our star.

It will take about a month to reach this region in space, known as the second Lagrange point, or L2. While astronauts were dispatched to repair Hubble, no human has ever traveled as far as Webb’s intended orbit.

High-tech origami

Because the telescope is too large to fit into a rocket’s nose cone in its operational configuration, it must be transported folded, origami-style. Deployment is a complex and difficult task, the most intimidating deployment NASA has ever attempted.

About 30 minutes after take-off, the communications antenna and the solar panels that supply it with energy will be deployed.

Then comes the deployment of the sun visor, hitherto folded like an accordion, from the sixth day, well after having passed the Moon. Its thin membranes will be guided by a complex mechanism involving 400 pulleys and 1312 feet of cable.


Because the telescope is too large to fit in the nose cone of a rocket in its operational form, it must be transported folded, origami style
Because the telescope is too large to fit in the nose cone of a rocket in its operational form, it must be transported folded, origami style jody amiet AFP / File

During the second week, it will finally be the turn of the mirror to open. Once in its final configuration, the instruments will have to cool and be calibrated, and the mirrors adjusted very precisely.

After six months the telescope will be ready for use.

Life, universe and everything

Webb has two main science missions, which together will account for over 50 percent of his observation time. First, explore the early phases of cosmic history, going back in time just a few hundred million years after the Big Bang.

Astronomers want to see how the very first stars and galaxies formed and how they change over time.

Its second major objective is the discovery of exoplanets, that is to say planets outside the solar system. He will also study the potential for life on these worlds by studying their atmospheres.

The great promise of Webb is its infrared capability.

Unlike the ultraviolet and visible light in which Hubble primarily operates, the longer wavelengths of infrared penetrate dust more easily, allowing the cloud-shrouded early universe to appear more clearly.

Infrared also allows scientists to travel further back in time through a phenomenon called redshifting. Light from more distant objects is stretched as the universe expands, toward the infrared end of the spectrum.

Also planned are closer observations, in our solar system, of Mars and Europe, the frozen moon of Jupiter.

Decades in the making

Astronomers began debating which telescope should succeed Hubble in the 1990s, with construction on Webb starting in 2004.


The Hubble and James Webb Space Telescopes
The Hubble and James Webb Space Telescopes Valentin RAKOVSKY AFP

The launch has been postponed several times, initially scheduled for 2007, then 2018 … mainly due to the complexities associated with development.

The observatory is the result of immense international collaboration and integrates Canadian and European instruments.

Over 10,000 people worked on the project, the budget eventually snowballing to around $ 10 billion.

The mission is expected to last at least five years, but hopefully 10 or more.


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