New Horizons has One Last Sleep til Pluto

On Aug. 25, New Horizons crossed the orbit of Neptune-the last planetary orbit crossing during cruise.

Now the spacecraft is outbound for Pluto.

On Aug. 29 the team put New Horizons into hibernation for the final time, prior to its encounter with Pluto.

This last hibernation lasts 99 days and ends on Dec. 6.

After seven-plus years of hibernating through most of the 2.5-billion mile journey from Jupiter to Pluto and the inner reaches of the Kuiper Belt, the spacecraft has reached the final, short leg of cruise.

New Horizons will be re-awakened for the last time in just 10 weeks. Once this has been done, 'encounter' preparations will begin, and six weeks later, the Pluto encounter itself will begin.

At that time, the New Horizons team will have good cause to celebrate. They will have reached the outer end of our Solar System, twenty-five years after first wondering if Pluto might someday be explored.

This summer's eighth and final "pre-Pluto" spacecraft and payload Active Check Out (ACO-8) lasted from June through late August. All spacecraft subsystems-both prime and backup-were checked out and were found to be operating successfully.

Additionally, the team performed their first course-correction since 2010, uploaded the final autonomy system software for the encounter, checked out all seven payload instruments, conducted some final instrument calibrations, and performed their first optical navigation campaign to home in on Pluto using New Horizons' Long Range Reconnaissance Imager (LORRI).

Those activities went well, and so did many others, including more sampling of the heliospheric plasma and dust environment with PEPSSI, SWAP and Student Dust Counter instruments.

The only real anomaly of the entire ACO-8 was a failed startup of a single Alice ultraviolet spectrometer observation.

That observation was to study the distribution of interplanetary hydrogen near Neptune's orbit; it failed because Alice was much colder than was planned, and onboard software "safed" (or turned off) Alice's high-voltage power supply when it took too long to get to its set point voltages.

The team have now learned that they need to adjust some timing settings for future power-ons when Alice will be as cold or even colder, On its approach to Pluto.

Additionally, ACO-8 was the subject of a recent news story from New Horizons: While testing the methods to be used to search for hazards in the Pluto system on approach, the spacecraft detected Pluto's little moon Hydra.

The team didn't think it would be possible to see Hydra until early in 2015, when the spacecraft was much closer, but science team members John Spencer and Hal Weaver found Hydra in the July hazard-sequence test.

The New Horizons team sees the early detection of Hydra as good news, because it anticipates their ability to detect currently unknown moons and rings close to Pluto.