The Interstellar Boundary Explorer, or IBEX, spacecraft will launch Oct. 19 from Kwajalein Atoll on a mission to study the heliopause boundary between the solar system and open galactic space, NASA officials said today.

A Pegasus rocket will provide the first-leg boost for IBEX, in what will be the heaviest payload ever lofted by a Pegasus, with most of that weight being propellant. That will get the spacecraft to 127,000 miles, where separation will occur.

Then a solid rocket booster will ignite. Finally, IBEX will be moved into final position with hydrazine propellant.

IBEX will soar at the high point of its orbit some 200,000 miles from Earth, so that it can gain a clear view of the collision between solar wind radiation particles (forming the heliosphere) moving outward at 1 million mph in all directions from the sun. Those particles reach a point 8 billion to 9 billion miles away (130 to 150 times the distance from the Earth to the sun), where the particles collide with galactic radiation, briefers said.

The pressure between the heliosphere particles rushing outward in the solar system — at that boundary point — are in equilibrium with the force of galactic radiation aimed toward the solar system.

That 200,000 miles altitude is needed because IBEX must be clear of the magnetosphere surrounding Earth, so as to gain that clear view of the heliosphere limit.

The pressure of solar wind radiation from the sun balances the pressure of the galactic radiation outside the solar system.

The collision is much like a supersonic bow wave, or sonic boom.

In a teleconference with journalists, several NASA briefers outlined the IBEX mission. They are Willis S. Jenkins, IBEX program executive; Gregory V. Frazier, IBEX mission manager; David J. McComas, IBEX principal investigator and senior executive director of the Space Science and Engineering Division at the Southwest Research Institute in San Antonio; and Eric R. Christian, IBEX program scientist.

The $169 million program will see the IBEX spacecraft in position in something like three weeks after launch, with data beginning to flow five to six weeks post-launch.

In half a year, NASA should have in hand its first all-sky panoramic image of the heliopause.

One factor here is that the solar system isn’t still, but rather is moving at great speed in the galaxy. That may be a reason the boundary between the heliosphere, the sun- generated radiation moving out from the sun, and galactic radiation isn’t neatly round, but rather is asymmetric.

The heliosphere shields Earth and the other planets from strong galactic radiation.

If it weren’t for the heliosphere, wicked galactic radiation would move through the solar system to strike the atmosphere around Earth.

NASA already has explored the interstellar boundary between the solar wind heliopshere and galactic radiation, with the Voyager I and Voyager II spacecraft that crossed the boundary. After 30 years, the spacecraft still work.

While the IBEX spacecraft has a two-year mission capability, there is no reason to believe it won’t be working after that, briefers said.

Goddard Space Flight Center plays a major role in the program. The spacecraft was designed and built by Orbital Sciences Corp. [ORB].

Others in the program include Lockheed Martin Corp. [LMT], the Applied Physics Laboratory, Los Alamos National Laboratory, Alliant Techsystems Inc. [ATK], University of New Hampshire, and the Adler Planetarium and Astronomy Museum.