Ever since a 16th-century eyeglass manufacturer in the Netherlands named Hans Lippershey invented the first telescope, the instruments have been getting bigger. In fact, according to Rebecca Bernstein of the University of Sant Cruz, who kicked off the opening session of IPF08, the diameter of the largest operating telescopes has doubled every 30 years.
There’s a reason for that: a telescope must gather large amounts of light from dim, distant objects in order to achieve decent resolution of features. The best way to accomplish this is with a large concave (objective) lens to gather as much light as possible — with smaller lenses and, these days, other advanced optics to bring the gathered light into focus.
The payoffs in terms of scientific advancement of knowledge have been huge. Consider this: at the start of the 20th century, we didn’t even know if there were other galaxies other than our Milky Way, never mind that our universe was still expanding. There’s been an explosion of discovery over the last 150 years, and better telescopes played a critical role in those advancements.
Astronomy in the 21st century will require even bigger “eyes.” The most recent generation of telescopes currently in operation boast aperture diameters of between of between 6 and 10 meters, according to Bernstein, and the next generation of Extremely Large Telescopes (ELTs) — really, they constitute an entirely new class — will have apertures ranging between 25.5 meters and 42 meters. She provided a handy overview of three major planned telescopes: the Giant Magellan Telescope (42 meters), the European Extremely Large Telescope (25.5 meters), and the Thirty-Meter Telescope (TMT), which is the furthest along in terms of design and development.
Of course, scaling up what has worked for smaller telescopes in the past is no easy feat. Fortunately, the scientists developing the TMT were able to build on past experience with segmented-mirror designs, most notably the famed KECK telescope in Hawaii, which boasts 36 segmented mirrors. In contrast, the TMT will employ 492 hexagonal mirrors, each about 1.44 meters (57 inches) across its corners, arrayed together into a 30-meter-wide primary mirror. The individual segments aren’t necessarily much larger, but there are more of them, and they are more aspherical and highly curved, thanks to advances in lens manufacturing techniques.
Other practical considerations: the optics must be finely calibrated, and huge, but also thin and lightweight. Adaptive optics will be needed to correct aberrations caused by turbulence in the atmosphere, so the TMT scientists must figure out how to scale up existing AO technologies sufficiently, and implement active controls.
Furthermore, the entire structure must be stable, able to withstand high winds in particular. That’s because location matters: the best sites for this next generation of telescopes are high, dry, and generally pretty remote — which can substantially increase construction costs. Site selection is still underway for the TMT, but Bernstein said that they are looking at areas in Chile, among other regions.
Ultimately, though, the biggest obstacle is that all these technical challenges must be balanced against a corresponding need to control costs. We’re talking about capital costs of around $1 billion, amassed from a combination of private and federal funding. Once it’s up and running, Bernstein estimates that the TMT will cost around $100 million annually to operate. That’s not exactly chump change, and it will need to be squeezed out of federal funding agencies.
And that, says Bernstein, means the astronomy community will need to present a solid consensus to funding agencies on the necessity of what she describes as both “a new technical and cultural frontier for astronomy.” Make a convincing case, and scientists will be able to explore when the first sources of light and the first heavy elements in the universe formed, along with galaxies an large-scale structure in the young universe. We will learn more about the massive black holes believed to be at the center of most galaxies, and about the process of planet formation and the properties of extra-solar planets.
Offhand, I’d say that’d be worth a cool $100 million a year.