The James Webb space telescope is a landmark observatory built to peer back through space and time to the first stars and galaxies that lit up the universe.
The Ariane 5 rocket is scheduled to blast off at 12.20pm UK time on Christmas Eve from the European spaceport in French Guiana. The telescope will be parked in space 1m from Earth for more than 30 years.
The $10 billion observatory is 100 times more powerful than Hubble and will be able to detect the faint glow from stars that ended the dark ages after the big bang. It will look for signs of methane and water in the atmospheres of planets around distant stars.
Prof Beth Biller, an astronomer at the University of Edinburgh who is due to use Webb to observe planets outside the solar solar system, said that it has incredible potential for expanding our knowledge of the universe. Many more scientific discoveries are going to come from this.
The observatory will look for conditions that could sustain life on distant planets.
It will be early summer before mission staff can relax and take data, as the launch itself will be nerve-racking. The six months after launch will be critical because of the size and complexity of the telescope.
The sun will be in the same position as Hubble. The second lagrange point is known as L2. The Earth and sun will be lined up behind the position that is being held here. It will take a month for him to reach L2.
It will take several more months to prepare for at least five years of operation. The telescope needs to deploy a sun shield the size of a tennis court to keep it cool and then unfold 18 hexagonal segments that form its primary mirror. It must make sure its systems and instruments are working correctly.
If there is a problem, it must be solved by commands from Earth. A repair mission of the kind needed to correct Hubble's faulty vision in 1993 is out of the question for a telescope four times more distant than the moon.
The deputy senior project scientist on the telescope has been working on it for more than 20 years. He said he didn't know if he would be excited or terrified for the launch. It has to work.
The mirror of the James Webb space telescope is being lifted by a crane. Laura Betz/AP
The size of the primary mirror and the sensitivity of the detectors will allow it to see some of the faintest objects in the universe. The light emitted by stars and galaxies is stretched as it travels because of the expansion of the universe. The oldest objects are the ones that formed first, and they are the ones that have been built to observe.
The light from the distant galaxies has traveled for most of the age of the universe to get to where we are. The telescope allows us to use it as a time machine. We look back in time to when the universe was younger, hoping to see the first galaxies that formed.
The telescope can look inside the dust clouds where stars are born to see their formation.
More than a quarter of the projects awarded time will observe exoplanets, alien worlds that circle stars beyond our solar system. Thousands of such planets, ranging from giant, hot Jupiters to water worlds and rocky planets like Earth, have been detected by the astronomer.
Some of these planets will cross in front of their parents. They can use the telescope to analyse how light from a star is absorbed by a planet's atmosphere. The conditions for life is what the man is focused on. Earth, Venus and Mars are small rocky planets. What are their temperatures, what do their atmospheres look like, and what kind of organic chemistry is going on in those atmospheres?
The telescope needs to reach its destination before it can unfold. That is enough to keep many scientists busy. Biller said that this was going to be a real nail-biter. Launching is just the beginning.
