Giant Telescopes of the Future

Some 15 years from now, the 10-meter Keck telescopes on Mauna Kea, Hawaii, may look downright small. By then American astronomers should have access to a 30-meter behemoth, and construction of an even larger European telescope may be well underway (Sky & Telescope: August 2000, page 52). At a recent international workshop on extremely large telescopes ("ELTs") in Bäckaskog, Sweden, various giant-telescope teams discussed their plans and projects. Says Gerry Gilmore (Cambridge University), "In 2015 almost certainly one ELT will be nearing completion; possibly two."

Admittedly, the plans are just that: plans, or maybe dreams. Canadian, French, and Hawaiian astronomers have drawn up three possible designs for a 20-meter next-generation Canada-France-Hawaii Telescope, dubbed the ngCFHT. The National Astronomical Observatory of Japan (NAOJ) hopes to build a 20-meter "Super-Subaru." In Texas, a scaled-up, 25-meter version of the Hobby-Eberly Telescope is on the drawing board. But these projects are a long way from being realized, if they will ever be.

A bit more mature is the plan for a Giant Magellan Telescope, to be built by the same five institutions that operate the twin 6.5-meter Magellan telescopes in Chile. GMT's 20-meter aperture would consist of seven 8.4-meter mirrors to be spin-cast, ground, and figured by the University of Arizona's Mirror Lab. At the Sweden workshop, Roger Angel, the lab's scientific director, even suggested building two identical GMTs, either close together to work as an interferometer or at two different locations, one of which might be in Antarctica.

Meanwhile, two somewhat farther-along ELT projects recently merged into one. Caltech and the University of California were planning the 30-meter California Extremely Large Telescope (CELT), while the Association of Universities for Research in Astronomy considered building a very similar Giant Segmented Mirror Telescope (GSMT). Last March they decided to join forces in a four-year design and development study for what is now called the Thirty Meter Telescope (TMT). Last summer, a Canadian group of universities joined the collaboration as a fourth partner. Part of the $80 million study is already secured by a grant from the Gordon and Betty Moore Foundation.

On the other side of the Atlantic, the European Commission is funding a similar study through the Opticon project (the name stands for Optical Infrared Coordination Network). According to Opticon principal investigator Gilmore, no decision has yet been made on the size or design of a European ELT. Currently there are two serious contenders: the Swedish-led Euro50 project (a 50-meter segmented-mirror telescope to be built at La Palma in the Canary Islands) and the 100-meter Overwhelmingly Large (OWL) telescope designed by the European Southern Observatory.

Most American astronomers think that OWL is too ambitious to risk, at least until an intermediate generation of telescopes are built and working. For one thing, any ELT, but especially so large a one, will need to incorporate very complex new adaptive optics. But ESO’s Philippe Dierickx says, "We feel we have a concept that's already at an advanced stage of design. ESO doesn't want [just] to show it is possible; we want to build it."

Credit: European Southern Observatory / OWL Project

With an aperture of 100 meters (4,000 inches), the OWL, or Overwhelmingly Large Telescope, is the largest optical telescope ever seriously conceived. Astronomers with the European Southern Observatory hope to build it for less than the 2.4-meter Hubble Space Telescope cost.

Credit: Association of Universities for Research in Astronomy (AURA)
The first of the new giants? This is one design for the 30-meter (1,200-inch) Giant Segmented Mirror Telescope, which was recently incorporated into the US-Canadian Thirty Meter Telescope (TMT) project.