Alien worlds? Far-off galaxies? Study sets US space priorities.

If the Perseid meteor shower has whetted your appetite for matters astronomical, a menu of projects has been drawn up that promise dramatic cosmic discoveries over the next decade.

From observing the universe's first galaxies and black holes, which are thought to have appeared some 13 billion years ago, to building a detailed tally of the number of habitable planets around nearby stars, astronomers in the United States have developed an ambitious set of projects for the next 10 years.

The once-a-decade report releases Friday represents a two-year effort of consultation and debate to set priorities for the US space-science community, after sorting through hundreds of suggestion regarding major projects and programs researchers would like to undertake.

The document historically has served the blueprint federal agencies such as the National Aeronautics and Space Administration, the National Science Foundation, and the US Department of Energy use for formulating their astronomy and astrophysics budget requests.

To achieve the goals it lays out, the plan includes new ground- and space-based telescopes. It recommends increased support for projects that can be fielded fairly quickly in response to serendipitous discoveries. And it includes calls for closer cooperation among astronomers and astrophysicists in countries worldwide.

"If you look toward the future, we're going to have to be doing more, not less, international coordination and collaboration," says panel member Michael Turner, an astrophysicist at the University of Chicago. "The projects that we're doing are very big, very bold, and very expensive. And the scientific visions that we have are converging."

What the plan wants

The report was released Friday by the National Research Council's Committee for a Decadal Survey of Astronomy and Astrophysics.

On the ground, the committee's highest priority is the Large-Scale Synoptic Telescope, or LSST. It's a 8.4-meter telescope that is designed to photograph the entire sky every three days. Objects in any single patch of sky will get their portraits taken roughly 1,000 times over 10 years. The aim is to detect more rapidly exotic explosions and other transient events that a less exhaustive sky survey might miss.

In space, the top priority is an orbiting infrared telescope, the Wide Field Infrared Survey Telescope, also designed for large, repeated images of the sky high above Earth's atmosphere, which hinders infrared observations from Earth.

In setting the research themes and picking the projects, "some very tough choices were made," says Roger Blandford, a Stanford University cosmologist who headed the committee.

Of the five decadal surveys, this is the first to try to rigorously estimate future science budgets, then weigh that against cost estimates for the projects they considered, as well as the level of technological development those projects still require, according to Neil deGrasse Tyson, who heads the Hayden Planetarium in New York and also served on the decadal committee.

"This may be the first decade where we have some hope that the [budget] targets estimated will be reached," he said. "In the previous decade, there was a lot of dreaming about: Wouldn't it be great if..."

A new realism

The LSST is a case in point. The LSST essentially swapped places with another major initiative – a giant segmented-mirror telescope – as the committee's top priority. The LSST is a smaller telescope than the two segmented-mirror candidates, the Thirty Meter Telescope and the Giant Magellan Telescope.

In looking at the three, the panel "was deeply impressed with the scientific potential" of the LSST and of the two segmented-mirror candidates, says Timothy Heckman, an astrophysicist at the Johns Hopkins University in Baltimore and a member of the decadal committee.

But "based on the judgment of the committee and the independent assessment we received" from the Aerospace Corporation – which also took part in the process of reorienting NASA's human spaceflight program – "LSST looked like it was ready to go," Dr. Heckman says.

The analysis showed that the project appeared to have no technological gotchas looming, and it matched well with the science themes the panel identified, he says.

Meanwhile, the committee recommended that the National Science Foundation take a 25 percent stake in one of the two the giant segmented-mirror telescope efforts.

That implies some intense politicking ahead as leaders from each try to convince the NSF that their project is the one to back.