What’s after Webb? Maybe a 12-meter space telescope

NEW YORK—On Monday, a group of astronomers revealed a new report that lays the groundwork for space-based astronomy after the James Webb Space Telescope ends its time as a functional observatory. The report calls for a next-generation telescope that covers the same wavelengths as the Hubble—UV to near infrared—while carrying specialized planet-imaging hardware. But the real jaw-dropper is the size of the primary mirror: 12 meters, or larger than some of the biggest of the current generation of Earth-bound telescopes.

The telescope, currently going by High Definition Space Telescope (HDST), wouldn't launch until the late 2030s at the earliest, which seems like a lot of lead time. But Matt Mountain, president of the Association of Universities for Research in Astronomy, said that the first report to look beyond the Hubble was produced in 1996. The James Webb won't be sent to orbit before 2018. Thus, there's a lot of lead time required for projects of this nature.

While the project might seem audacious, it's relatively conservative. All of the technologies required to get it to work are already under development or working at a smaller scale. For example, the HDST will use the same segmented mirror design as the Webb, but the segments will each be larger, and there will be an extra ring of them. The 12-meter size is set by the internal diameter of the fairings of a Delta IV Heavy; any bigger and, in the words of the University of Washington's Julianne Dalcanton, "it's like that last suitcase in the overhead bin—you just can't get it in."