August 28, 2009
New Horizons Checks Out, Enters Hibernation

The New Horizons mission team has closed out a successful summer workout, putting its Pluto-bound spacecraft back into hibernation Aug. 27 after seven weeks of functional tests and system checks.

The mission’s third annual checkout (ACO-3), which started July 7, “went very well,” says Mission System Engineer Chris Hersman, of the Johns Hopkins University Applied Physics Laboratory. “New Horizons is in good shape.”

Principal Investigator Alan Stern, of the Southwest Research Institute, says ACO-3 was less “cluttered and complex” than previous ACOs, kept simple to let mission engineers and scientists focus on Pluto-encounter planning. But it was still productive: the team performed functional checkouts of all seven science instruments and every spacecraft subsystem, including the primary and backup hardware in each system; carefully tracked the spacecraft to refine its knowledge of New Horizons trajectory; and uploaded the instructions that will guide New Horizons through hibernation.
The author (center) goes over the New Horizons model with Smithsonian National Air and Space Museum staff.
“New Horizons is in good shape.”

-Chris Hersman, mission system engineer

The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) and Solar Wind at Pluto (SWAP) instruments also each accumulated about a day’s worth of data on the interplanetary gases and particles around the spacecraft – currently 1.33 billion miles (2.13 billion kilometers) from the Sun, nearly halfway between the orbits of Saturn and Uranus, more than 14 times the distance between Earth and the Sun.

The team will pull New Horizons out of hibernation for 10 days starting on Nov. 9, for a set of maneuvers that keep Earth in the beam of the spacecraft’s antenna. “It’s an adjustment we have to make as Earth moves around the Sun and New Horizons moves farther along on its path toward Pluto,” Hersman says.

For frequent mission updates, follow the New Horizons Twitter page at