LONG BEACH, Calif. -- NASA leaders are shelving their planned mission to Pluto because of increasing spacecraft costs, NASA officials say. The chief delay comes from growing costs of the Outer Planets Program, says Ed Weiler, NASA's associate administrator for space science.

Four years ago when space agency officials conceived a mission to Pluto, they assumed that many of the necessary technologies would be simple to evolve, Weiler said Sept. 21. Many of these did not come to fruition, he says.

NASA leaders are focusing on launching an orbiter to Europa, Jupiter's fourth-largest moon, in January 2006. Experts projected costs of the Pluto and Europa missions at about $800 million combined. Today that cost is projected at $1.3 billion. NASA officials had to choose one or the other, and they are choosing Europa.

Work continues on the Europa Orbiter and a solar probe, which is to be launched in 2007 or 2008, says Doug Stetson, manager of solar system exploration at the Jet Propulsion Laboratory in Pasadena, Calif.

Weiler says he has told engineers to develop an inexpensive spacecraft design that could explore Pluto by 2020. Engineers have a basic design for a Pluto probe. The biggest change in a new design will likely be in propulsion, with a futuristic ion engine replacing the costly chemical engines used in most previous spacecraft, he says.