WEBB TELESCOPE
Looking back in time
How the James Webb Space Telescope will unlock secrets of the universe
It was finished years late at a cost far higher than planned, but NASA’s James Webb Space Telescope due for launch plans to usher in a new era in astronomy as it gathers information on the universe’s earliest stages, star formation and whether planets beyond our solar system may be habitable.
In 1990, NASA launched the Hubble Space Telescope that gave scientists a window into deep space. The Webb launch seeks to succeed the Hubble showing a different side of space.
Valuable payload
The orbiting infrared observatory, designed to be about 100 times more sensitive than its Hubble predecessor, will blast off Dec. 25 at the earliest from a site in French Guiana on South America’s northeastern coast. (Weather and other factors could delay the launch date.)
The telescope will be tightly folded inside the payload bay of an Ariane 5 rocket. The launch vehicle is part of the European Space Agency’s (ESA) contribution to the mission, along with launch services for the U.S. National Aeronautics and Space Administration (NASA) for Webb.
Once in space it will separate from the launch vehicle and begin its journey towards the orbit point.
Folded
James Webb
telescope
Folded
James Webb
telescope
Folded
James Webb
telescope
The long deployment
After being released from the rocket, Webb will gradually unfurl as it travels to its destination beyond the Moon, executing one of the most complex deployment sequences ever attempted.
Solar array deployment
The first step is to power up the Webb by deploying the solar array.
Sunshield pallet deployment
Two special pallets holding Webb’s essential sun shields deploy.
Tower assembly
A tower holding the instrument package is lifted to its operational location.
Momentum flap deployment
As the sun’s solar pressure pushes against the large sun shield this flap helps stabilize the telescope.
Sunshine membrane cover release
On the same day, special covers that hold the tennis court-sized sun shield are released.
Membrane tensioning
Sun shield mid-booms are deployed and the sun shield is slowly tensioned, separating the five layers.
Secondary mirror
The support structure for the smaller, secondary mirror is deployed.
Primary mirror wings
The side panels of the main mirror are extended, completing the instrument deployment.
One of the goals of the telescope is to look back through time to when galaxies were young. Webb will do this by observing distant galaxies that are over 13 billion light years away from Earth.
When a telescope looks further away, it is also looking back in time. It takes time for the light the telescope is receiving to travel through space. Therefore, we see objects not as they are now but as they were at the time when they released the light that has travelled for billions of years across the universe to reach us.
To see objects so faint and far away, the telescope needs a giant mirror to collect the light.
The size of a telescope’s mirror area determines its sensitivity, or how much detail it can see. Since the Webb telescope has a much bigger mirror than Hubble, it can look further back in time.
Webb’s primary mirror intercepts red and infrared light traveling through space and reflects it onto a smaller secondary mirror. The secondary mirror then directs the light into the scientific instruments where it is recorded.
Because the telescope will be observing very faint infrared signals, it needs to be shielded from any bright, hot sources such as the sun. There is a huge temperature difference between the hot and cold sides of the telescope, separated by a sun shield.
First reflected off
primary mirror
First reflected off
primary mirror
First reflected off
primary mirror
First reflected off
primary mirror
First reflected off
primary mirror
Webb will primarily observe the universe in infrared, while Hubble studies it mostly at optical and ultraviolet wavelengths, although it does have some infrared capability.
Infrared observations are important to astronomy because recently formed stars and planets are often hidden behind masses of dust that absorb visible light. Infrared light can penetrate these obstacles.
“Infrared light will go around the dust grains instead of bouncing off, so we can see that with the Webb telescope. And that’s one of our top goals - to see how stars grow, with their young planets,” said John Mather, Webb senior project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Images: NASA, ESA and the Hubble Heritage Team (STScI/AURA)
Images: NASA, ESA and the Hubble Heritage Team (STScI/AURA)
The instruments
The telescope has four science instruments contained within the Integrated Science Instrument Module (ISIM). This section is considered the heart of the telescope and located just behind the primary mirror.
An instrument called a spectrometer can study the atmospheres of exoplanets. Mather said finding one with lots of water - thought to be one of the key ingredients for life - would be “really interesting.” As he put it: “a wet little planet out there that might be a little bit like home.”
An orbit beyond the moon
Unlike Hubble, the telescope will not orbit the Earth. Instead it will orbit the Sun, around 1.5 million kilometers (1 million miles) away from the Earth at what is called the second Lagrange point, also known as L2.
Lagrange points, named after their discoverer, Joseph-Louis Lagrange, an 18th century mathematician, allow the gravitational pull of two large masses (the Earth and Sun) to equal the force required for a small object, such as a satellite, to move with them.
It will take roughly 30 days for Webb to reach the start of its orbit at the L2 position.
“We’re going to look at everything there is in the universe that we can see. We want to know: how did we get here from the Big Bang, how did that work? So, we’ll look,” Mather said.
Video credits
Opening video: Goddard Media Lab, NASA
Deployment sequence video: Conceptual Image Lab, NASA (Animations by Adriana Manrique Gutierrez Released on December 15, 2021)
Instruments video: Goddard Media Lab, NASA
Orbit video: Goddard Media Lab, NASA
Sources
Goddard Space Flight Center, NASA;
Edited by
Christian Schmollinger