The most powerful space observatory ever built is set to be launched in December after decades of waiting.
It will help answer fundamental questions about the Universe, peering back in time 13 billion years. There are five things to know.
The telescope's centerpiece is its enormous primary mirror, which is made of 18 smaller hexagonal mirrors.
The observatory has four scientific instruments that are used to study the physical and chemical properties of the universe.
A five-layer sun shield is built to unfurl to the size of a tennis court and protects the mirror and instruments.
The shield's membranes are made of kapton, a material known for its high heat resistance and stability under a wide temperature range, which is vital since the Sun-facing side of the shield will get as hot as 230 degrees Fahrenheit (100 degrees Celsius) while the other side will reach low
The telescope weighs around as much as a school bus and has subsystems for electrical power, propulsion, communications, orientation, heating, and data handling.
Four times the distance from the Moon to Earth, the telescope will be placed in a million miles from Earth.
The current premier space telescope that revolves around the planet is Hubble.
It will be able to remain on our planet's night side from the point of view of the Sun. The sun shield will always be between the mirror and the star.
It will take about a month to reach this region in space. No humans have ever traveled as far as the planned path of the space shuttle.
3. High-tech folding.
The telescope is too large to fit into a rocket's nose cone, so it has to be folded. Unfurling is the most difficult deployment NASA has ever attempted.
The communications antenna and solar panels will be put up about 30 minutes after take-off.
After having passed the Moon, the sun shield will be unfurled, folding like an accordion. A complex mechanism involving 400 pulleys and 1,312 feet of cable will guide it.
The mirror will finally open during the second week. The instruments will need to cool and be adjusted before they are in their final configuration.
The telescope will be ready after six months.
4. Everything, including the universe.
More than 50 percent of its observation time will be spent on two primary scientific missions. Look back in time to only a few hundred million years after the Big bang, to explore the early phases of the universe.
How the first stars and galaxies formed and how they evolve over time are what Astrologers want to see.
The discovery of planets outside the solar system is its second major goal. It will look at the potential for life on those worlds.
The promise of the Webb is in its ability to be seen in the sky.
The early universe can be seen more clearly thanks to the longer wavelength of IR that Hubble mostly uses.
Scientists can go further back in time because of redshifting. Light from objects farther away is stretched as the universe expands.
Closer observations of Mars and of Jupiter's icy moon, Europa, are planned.
5. It has been decades in the making.
The debate about the telescope that should succeed Hubble began in the 1990s.
The launch was originally penciled in for 2007, but was pushed back several times.
The observatory is the result of an international collaboration.
The budget ballooned to around $10 billion after more than 10,000 people worked on the project.
The mission is expected to last at least five years.
Agence France-Presse.
