Planning for a new giant space telescope armed with an unfolding mirror with a diameter of 8-16 metres should begin now to provide the true successor to Hubble by the 2030s, according to the President of the Royal Astronomical Society, Professor Martin Barstow of the University of Leicester.

An artist's impression of ATLAST with a 16-metre segmented mirror. Image: Northrop Grumman Aerospace Systems/NASA/STScI.
 
Barstow presented the case for the Advanced Technology Large Aperture Space Telescope (ATLAST) at this week's National Astronomy Meeting (NAM) at the University of Portsmouth. ATLAST would operate at optical and ultraviolet wavelengths, just like the Hubble Space Telescope currently does. However, Hubble has been in space for 24 years and is not expected to outlast the decade, while the upcoming James Webb Space Telescope (JWST) set to launch in 2018 is an infrared telescope designed for probing dusty regions of the Universe and seeking the earliest galaxies, and not for taking the pretty pictures that Hubble excels at.

"ATLAST is the next logical step beyond the JWST," Barstow tells Astronomy Now. "It will be a multi-purpose telescope, so it will be able to study stars and galaxies, but one of the crucial things that it will be able to do is probe the habitable zones around stars like our own Sun and directly detect any Earth-like exoplanets that may be out there."

Existing only as a concept design study produced by the Space Telescope Science Institute in the United States -- the agency that manages the science operations of the Hubble Space Telescope -- ATLAST still has a long way to go before being approved and funded by any space agency. Given the exorbitant costs that JWST has racked up, those in charge of the purse strings may be reluctant to immediately fund another large space telescope. As such, the ATLAST project first has to recruit friends in the astronomical community, to which end Barstow presented ATLAST's case to an audience of exoplanet researchers at NAM. "The big question is, are we alone?" he says. "If we can detect Earth-like exoplanets and identify things in their atmospheres such as oxygen, methane and ozone, it would be a pretty clear signature that there is some kind of biological activity going on."

Hubble's mirror is 2.4 metres across, while the largest space telescope launched thus far has been the European Space Agency's Herschel Space Telescope, which was armed with a 3.5-metre wide mirror. JWST will beat that, with a 6.5-metre mirror that will be the first test of the technology that allows the segmented mirror to fold up during launch and then unfurl once in space. ATLAST will require the same technology -- its mirror would be so big that no currently-working launch vehicle is big enough to house it, although several are planned for the coming decades, including NASA's Space Launch System that will take the manned Orion capsule into space.

"Hopefully we will be able to build something where you can unfold the mirror from several segments and that allows you to build something bigger than if you create a single mirror," says Barstow. "We'll have tested that with the JWST so the actual step in technology isn't necessarily that big."

With such a large mirror, ATLAST's angular resolution will be five to ten times better than JWST's and 2,000 times more sensitive than Hubble. Although it will be much smaller than the next generation of ground-based observatories such as the Thirty Metre Telescope and the 39-metre European Extremely Large Telescope, ATLAST will have the advantage of being in space, away from the deleterious effects of our atmosphere.

Although expensive, Barstow is confident that ATLAST could be constructed for no more than JWST. For one, he says, some of the technology will have already been pioneered on JWST and two, cost does not scale with the size of the mirror, so a telescope with a mirror twice the size of JWST will not make it twice as expensive. Nevertheless, it will be a multi-billion pound project that will likely involve funding and cooperation from a number of different space agencies. Barstow reports that the European Space Agency have begun to show a glimmer of interest.

"We have to convince the space agencies, because it is not going to be a cheap mission, but it is worth doing," he says. It is now becoming a race against time, he points out. Planning for Hubble began in the late 1960s and for JWST since the mid-1990s. Even with a 2030 launch, it could leave us without a large optical space telescope for over a decade if Hubble fails and the gap will only widen the longer we delay.