Unless significant new hazards are found, expect NASA's New Horizons spacecraft to stay on its original course past Pluto and its moons, after mission managers concluded that the danger posed by dust and debris in the Pluto system is less than they once feared.

The New Horizons team recently completed an 18-month study of potential impact hazards - mostly dust created by objects hitting Pluto's small satellites - the spacecraft would face as it speeds some 30,000 miles per hour (more than 48,000 kilometers per hour) past Pluto in July 2015.

The team estimated that the probability of a mission-ending dust impact was less than 0.3 percent if the spacecraft followed the current baseline plan, far below some early, more conservative estimates. So, with the concurrence of an independent review panel and NASA, the project team expects to keep New Horizons on this baseline course, which includes a close approach of about 12,500 kilometers (nearly 7,800 miles) from the surface of Pluto.

"We found that loss of the New Horizons mission by dust impacting the spacecraft is very unlikely, and we expect to follow the nominal, or baseline, mission timeline that we've been refining over the past few years," says New Horizons Project Scientist Hal Weaver, of the Johns Hopkins University Applied Physics Laboratory. "Still, we'll be ready with two alternative timelines, in the event that the impact risk turns out to be greater than we think."

Those alternate plans (called SHBOTs, short for Safe Haven by Other Trajectories) are being developed should new information - gathered from New Horizons camera observations during the approach to Pluto, for example, or new dust-dynamics analyses - indicate less-than-smooth sailing for New Horizons.

One plan, the Generic Inner SHBOT, is essentially the same as baseline trajectory, but with the spacecraft turned so that its 7-foot dish antenna faces the incoming dust particles; this "Antenna-to-Ram" (or ATR) configuration would protect the spacecraft underneath.

The Deep Inner SHBOT also employs ATR protection, but would additionally dip the trajectory to within just 3,000 kilometers (nearly 1,900 miles) of Pluto's surface, where atmospheric drag tends to sweep out lingering dust.

New Horizons managers recently presented their impact-hazard outlook and if-necessary mitigation plans to an independent NASA review panel and to the NASA Science Mission Directorate Program Management Council - receiving endorsements from both.

New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, says the mission team is now finalizing plans for the Pluto encounter. In early July, the team will rehearse the most critical nine-day segment of the baseline encounter plan, putting itself and the spacecraft through the paces of the flight toward and just past Pluto and its moons.

Stern adds that the spacecraft remains on target for a close approach to Pluto in 2015, all subsystems are performing nominally, and "the anticipated science observations will revolutionize our understanding of dwarf planets and the Kuiper belt, and excite a whole new generation of the public to the first reconnaissance of a planet on the very frontier of our solar system."

Read more about the New Horizons impact-hazard study and SHBOTs