NASA launches American robot explorer

A robotic U.S. explorer set sail today on a two-year mission to study the very edges of the solar system -- the boundary between the sun's atmosphere and the rest of the Milky Way galaxy.

NASA's Interstellar Boundary Explorer was propelled into a highly elliptical orbit after launch on a Pegasus XL rocket that was dropped from the belly of an Orbital Sciences Corp. L-1011 aircraft flying 39,000 feet above the Pacific Ocean near Kwajalein Atoll.

NASA Assistant Launch Director Omar Baez said the four-stage rocket appeared to perform just as expected. The explorer's own upper stage then successfully pushed the spacecraft into an orbit with high and low points of 200,000 and 4,400 miles, respectively.

NASA ground controllers were running health checks on the spacecraft after the upper stage and the explorer separated, and no problems were immediately reported.

Two sensors on the spacecraft are designed to gather high-speed atoms known as Energetic Neutral Atoms that travel toward Earth from regions beyond the orbit of Pluto. Subsequent analyses will enable scientists to map the region that separates the heliosphere -- the region influenced by the sun -- and interstellar space.

The boundary shields the solar system and its planets, moons and asteroids from potentially deadly galactic cosmic rays. Data from the explorer is expected to help scientists determine the nature and state of the protective boundary region.

The $169 million mission is the latest in a series of relatively inexpensive NASA science missions that date back to the launch of the nation's first man-made satellite -- Explorer 1 -- in January 1958.

The launch was managed by the Kennedy Space Center Launch Services Program.