WASHINGTON — Northrop Grumman Space Technology is investing in what it says is a cheaper way to image Earth-size planets orbiting neighboring stars.

Dubbed New Worlds Observer, the planet-finding concept is the brainchild of Webster Cash, an astronomy professor at the University of Colorado at Boulder. Cash initially developed the idea under a grant from the NASA Institute for Advanced Concepts.

Cash, with Northrop Grumman’s backing, submitted a proposal to NASA this year to build and launch a free-flying star shade that would work in tandem with the James Webb Space Telescope to search out and image any Earth-sized planets that may be hiding in nearby solar systems. Star shades, or occulters, work by blocking out a star’s light to reveal dim objects hidden in their glow.

With an estimated price tag of around $425 million, the New Worlds Observer would cost a fraction of the Terrestrial Planet Finder, a multibillion-dollar pair of planet-hunting telescopes that NASA has been talking about for years. The agency recently decided to put that idea on indefinite hold while it finishes other major space telescope projects, like Webb, already in development.

When NASA selected its latest crop of Discovery-class mission candidates this fall, it passed on the New Worlds Observer proposal. NASA’s Discovery Program funds competitively selected deep space missions that can be accomplished for no more than $425 million.

Redondo Beach, Calif.-based Northrop Grumman Space Technology is continuing to refine the New Worlds Observer idea using an undisclosed amount of internal research and development funds.

Amy Lo, Northrop Grumman’s systems engineer on the New Worlds Observer, said the company is preparing experiments for the year ahead meant to show that the novel approach would work.

Lo said the concept entails a large flower-petal-shaped star shade that would be positioned thousands of kilometers away from Webb but directly in its line of sight to a nearby star system. The shade would, in effect, block out the light from the star so that Webb could pick up fainter objects in that general vicinity — planets.

Lo said the free-flying star shade would be tens of meters across and probably made out of Kapton, a strong but lightweight material similar to Mylar .

Lo said that while the New Worlds Observer approach works especially well with the James Webb Space Telescope, the idea can work with a much simpler telescope . A 2-meter or larger optical aperture, she said, should be sufficient.

The Hubble Space Telescope, which will have a new lease on life if NASA pulls off a successful servicing mission in 2008, is not well suited to work in tandem with the New Worlds Observer, Lo said.

“If Hubble was in the right orbit, it would work perfectly fine,” she said.

The problem with Hubble, Lo said, is that it is “whizzing by too fast for the occulter to line up.”

Hubble, located some 600 kilometers above the Earth , orbits about every 96 minutes. In its higher orbit , “the occulter would have to move even faster to stay lined up,” Lo said. “It’s really not feasible.”

“A better place would be someplace like the second Lagrange point where James Webb will be,” Lo said.

The Lagrange point 2, located 1.5 million kilometers from Earth, is considered a good location for an observatory like Webb because its unique gravitational properties will keep the telescope constantly on the night time side of the Earth as it circles the sun.

To put the New Worlds Observer concept to the test, Northrop Grumman is heading to the laboratory. Lo said the company is building very small, subscale occulters — about 50 millimeters across — and testing them out on an optics bench to make sure the approach works.

“The reason we have to make them so small is we’ve got this scale problem,” she said.

To simulate the vast distances that would be involved in planet searches using the New Worlds Observer, Northrop Grumman is building an optics bench on its Space Park campus that will be 20 to 30 meters long at minimum, Lo said.

At one end of the test bed will be a detector called a scanning photometer that will simulate the space telescope. At the other end will be a tiny light source representing the star. Somewhere in between the two Lo and her colleagues will place the miniature occulters.

Unlike previous experiments conducted to validate the New Worlds Observer approach, the tests Northrop Grumman has planned for 2007 will be carried out in a vacuum, Lo said. The subscale occulters will be manufactured with greater precision than those used in previous experiments, she added. That is important, she said, because it will tell Northrop Grumman whether it would need to be accurate to the micron or to the millimeter in building a full-size star shade. “Manufacturing accuracy translates directly into its viewing accuracy,” she said.

Northrop Grumman spokeswoman Sally Koris said the company hopes the work it is doing on the New Worlds Observer will point the way toward a cheaper approach to finding planets and make it possible for NASA to fund such a mission sooner rather than later.

Lo said the New Worlds Observer approach could still be cheaper than other planet-finding options even if NASA — by itself or with an international partner — had to build a dedicated telescope to go

“We think it is [cheaper] compared to having to develop new technology,” she said. “There’s fairly difficult engineering to do but no new technology.”