TORONTO -- It鈥檚 taken 25 years to build, has faced long delays, and cost many billions of dollars more than expected, but the countdown is finally on to launch the James Webb telescope, the successor to the Hubble Space Telescope.

In just six weeks, a powerful rocket is expected to carry into space the most ambitious space telescope ever built, one promising to revolutionize how we see the universe.

At a news conference this week, scientists said that after more than a decade of delays, the James Webb telescope is finally ready to fly.

Recently transported from California by boat and then trucked to a launch facility in French Guiana, the telescope will be loaded onto a European rocket and then launched on Dec. 18.

鈥淚 find it an amazing journey to see we鈥檙e almost there, and I look forward to the realization of our work,鈥 said Begona Vila, a mission instrument systems engineer.

That work started 25 years ago. The Hubble telescope had been in orbit for just six years when scientists began developing an instrument with a much bigger mirror and 100 times more powerful than the Hubble. The Hubble鈥檚 mirror is 2.4 metres in diameter, while Webb鈥檚 is 5.6 metres in diameter.

Scientists say the James Webb is not a replacement for Hubble, but a successor, because its goals were inspired by some of the incredible results Hubble has given astronomers across the years.

James Webb also will be using different eyes to look at the universe than Hubble. Webb uses primarily infrared to image the stars, which will allow for it to gaze deeper into the universe, where distant objects are more 鈥渞edshifted,鈥 a term referring to how the wavelength of light from objects moving farther away from us is more red. Infrared can also see through large star-forming dust clouds that absorb light on the visible spectrum.

Hubble can only observe a small part of the infrared spectrum.

The project to construct James Webb was supposed to cost $500 million, but that ballooned to more than $10 billion, in part because the James Webb needs a sun shield the size of a tennis court, which has to perfectly unfurl in space to protect it.

鈥淛ames Webb has to perform some of the most complex sequence of deployments ever attempted,鈥 said Mike Menzel, a JWST mission systems engineer.

To fit inside the rocket, the telescope has to fold up, and then, as it reaches its destination, four times further away from Earth than the Moon orbits, it has to unpack itself.

This is a process that will take nearly a month and there are plenty of ways it could fail.

"This will be 20 to 30 days of terror, so we will not sleep well at that time,鈥 said Gunther Hasinger, science director for the European Space Agency.

If all goes well, the James Webb will be able to look much further into the universe than the Hubble, able to see the first galaxies that lit up after the Big Bang, and thus deepen our understanding of planets that orbit distant stars.

The project, led by NASA, includes the European and Canada Space Agencies.

鈥淭he contribution by Canada is quite critical,鈥 Martin Bergeron with the Canadian Space Agency told CTV News.

Canada鈥檚 contribution clocks in at around $200 million, and includes a pair of instruments, one of which will help the James Webb stay locked on its distant targets.

The other instrument will help examine the composition of exoplanets鈥 atmospheres, among other observations.

According to the Canadian Space Agency, Canadian astronomers will be some of the first to study data collected by James Webb as we will receive 鈥渁 guaranteed share of Webb鈥檚 observation time鈥 due to our contribution.