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Thruster firing puts New Horizons back on track

Posted: July 2, 2010

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The New Horizons mission speeding toward a fleeting visit to Pluto fired its thruster system for 35.6 seconds Wednesday, correcting a small error in the probe's trajectory into the outer fringes of the solar system.

Artist's concept of New Horizons encountering Pluto in 2015. Credit: JHUAPL/SwRI
The thruster burn occurred as planned Wednesday at 3 p.m. EDT and accelerated the spacecraft by about one mile per hour, according to an update posted on the mission's website.

That doesn't seem like much when you factor in the robot's dazzling speed. New Horizons covers nearly a million miles per day, but with so much time between now and its 2015 flyby of Pluto, just one mile per hour is the difference between a scientific bonanza and a researcher's doomsday.

At the time of the burn, New Horizons was 1.49 billion miles away from Earth, near the orbit of Uranus. It takes more than two hours for radio signals to travel from the spacecraft to Earth from such distances.

It was the fourth time the piano-sized spacecraft has trimmed its flight path since launching Jan. 19, 2006. The last time New Horizons fired its propulsion system was October 2007.

Mission officials say the New Horizons navigation team discovered radiative thermal energy from the spacecraft's nuclear power source drove the probe slightly off course. Photons, or tiny particles of energy, reflecting off the craft's high-speed communications antenna slowly altered its trajectory.

Controllers sent orders for the maneuver from Earth to New Horizons last week amid a two-month checkout and testing campaign while the spacecraft is out of hibernation.

Engineers inside the New Horizons control center at the Johns Hopkins University Applied Physics Laboratory. Credit: JHUAPL
New Horizons spends most of its cruise from Earth to Pluto in a deep slumber, and engineers only occasionally wake up the spacecraft for annual check-ups, flyby rehearsals and science observations.

This year marks several halfway points on the trek to Pluto.

On Feb. 25, New Horizons soared past the halfway point in mileage traveled from Earth to Pluto. The spacecraft will mark half the days from launch to flyby on Oct. 17.

Managers plan more minor burns over the next few years to keep New Horizons on track for a flyby of Pluto and its three moons in 2015. Engineers have already nailed down the time of closest approach: 7:49 a.m. EDT on Wednesday, July 15, 2015.

The closest New Horizons will get to Pluto will be 7,767 miles, according to the latest projections.

The $700 million mission is the first to study a new class of bodies -- icy dwarf planets stranded on the frontier of the solar system. New Horizons will take pictures of Pluto and its three moons, analyze Pluto's atmosphere and measure the chemical composition of Pluto and its natural satellites.

New Horizons could target an even more distant object after careening past Pluto, extending its mission to 2020 or beyond.