Hubble has been a boon to deep space exploration, gifting us iconic pictures of the skies and revealing new insights into the history of the early universe. For the next big step in space astronomy, NASA, ESA and the Canadian Space Agency (CSA) are raising the stakes even higher with one of their most ambitious projects in decades: building the largest space telescope ever ... the James Webb Space Telescope.

The James Webb Space Telescope, JWST for short, will have seven times the light-collecting capability of Hubble, span the size of a tennis court, and be so sensitive it could spot a single firefly a million kilometers away.

This "absolutely impressive piece of engineering," as NASA administrator Charles Bolden put it, includes technologies that make this spacecraft unlike any other and will allow us to learn about Earth-like exoplanets, help us understand how life began on Earth, and image the cosmos as it was only millions of years after the Big Bang, further back in time than ever before.

The contemplation of celestial things will make a man both speak and think more sublimely and magnificently when he descends to human affairs. Marcus Tullius Cicero, c. 30 BCE

Space telescopes can be extremely expensive. Hubbles total operating costs (including a Shuttle visit to repair its main mirror) have long passed the 10 billion US dollar mark, and similarly the budget for JWST, originally set at $2 billion, is now closer to nine after a bump-up of its mirror size. Projects such as these can not only have a meaningful scientific output, but also produce iconic images that can inspire a generation. But why go through the hassle of operating a telescope in space, when we could build much larger ones on the ground at a fraction of the cost?

One reason why Hubbles images became such a powerful part of the collective imagery is that, during its first years of operation, no telescope on the ground could remotely compete with Hubbles capabilities at imaging faint and distant celestial objects, due to the way our atmosphere distorts incoming light before it reaches the ground. But in recent years, the advent of adaptive optics a technique that can correct for atmospheric distortions in real time has meant ground telescopes have caught up in many respects. With that being the case, is there still a point to space telescopes?

"[Adaptive optics] is pretty good, not perfect," Physics Nobel laureate and JWST senior project scientist John Mather told Gizmag. "Instead of a star looking like a big blur an arcsecond across, it now looks like a smaller blur with a sharp core. We are finally getting some real discoveries made with this technique. It can show fainter stars and galaxies, and it can show better maps of extended objects. But theres still a bit of haze around things."

Space telescopes can image distant celestial objects without the haze typical of ground telescopes (Image: HST/NASA)

Both NASA and ESA already have definite plans for building a series of very large ground telescopes in the near future, including the $1.4 billion aptly-named Thirty Meter Telescope and the $1.3 billion, 42-m (138-ft) European Extremely Large Telescope (E-ELT). The latter would see first light as soon as 2018, the same year the Webb is scheduled to launch.

These and other upcoming ground-based behemoths will employ the latest in adaptive optics to try and image celestial objects as clearly as possible. However, these telescopes were never designed to replace a space telescope. Rather, it is more likely that these giant ground telescopes will be used to find targets for a space telescope to study in more detail. In fact, despite having to make do with a much smaller mirror, space telescopes can often see more clearly than their ground-based counterparts, no matter their size.

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Searching for the origins of life with the James Webb Space Telescope