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New Horizons to wake for final leg of journey to Pluto

Jenny Winder, News Writer
Nov 17, 2014, 18:46 UTC

Sen—Just as ESA's Philae lander has begun sleeping on comet 67P/Churyumov–Gerasimenko, another space probe is getting ready to wake up. NASA’s New Horizons Pluto-bound spacecraft will come out of hibernation for the last time next month. 

The wake-up call was preprogrammed into New Horizons’ on-board computer in August, commanding it come out of hibernation at 3pm EST on 6 December. About 90 minutes later New Horizons will transmit word to Earth that it is in “active” mode; those signals, even traveling at light speed, will need four hours and 25 minutes to reach home.

At the time New Horizons will be more than 2.9 billion miles from Earth, and just 162 million miles—less than twice the distance between Earth and the Sun—from Pluto

While the the probe enjoys three more weeks of electronic slumber, work on Earth is well under way to prepare the spacecraft for a six-month encounter with the dwarf planet that begins in January.

“New Horizons is healthy and cruising quietly through deep space—nearly three billion miles from home—but its rest is nearly over,” said Alice Bowman, New Horizons mission operations manager at the Johns Hopkins University Applied Physics Laboratory (APL). “It’s time for New Horizons to wake up, get to work, and start making history.”

Launched in January 2006, New Horizons has spent 1,873 days in hibernation, 66 per cent of its journey, spread over 18 separate hibernation periods from mid-2007 to late 2014 that ranged from 36 days to 202 days long.

New Horizons has pioneered routine cruise-flight hibernation for NASA. Hibernation reduces wear and tear on the spacecraft’s electronics, lowers operations costs and frees up NASA Deep Space Network tracking and communication resources for other missions.

On average, operators woke New Horizons just over twice each year to check out critical systems, calibrate instruments, gather science data, rehearse Pluto-encounter activities and perform course corrections when necessary.

In hibernation mode the onboard flight computer monitors system health and broadcasts a weekly beacon-status tone back to Earth while the rest of the space craft remains unpowered.


New Horizons will arive at Pluto in 2015. Image credit: JHUAPL/SwRI

Once the probe awakes the mission team will conduct final tests on the spacecraft’s science instruments and operating systems, and build and test the computer-command sequences to guide New Horizons through its flight to and reconnaissance of the Pluto system. 

Distant observations of the Pluto system begin on 15 January and continue until late July 2015. Closest approach to Pluto will be on 14 July.

“We’ve worked years to prepare for this moment,” said Mark Holdridge, New Horizons encounter mission manager at APL. “New Horizons might have spent most of its cruise time across nearly three billion miles of space sleeping, but our team has done anything but, conducting a flawless flight past Jupiter just a year after launch, putting the spacecraft through annual workouts, plotting out each step of the Pluto flyby and even practising the entire Pluto encounter on the spacecraft. We are ready to go.”

New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, said: “The final hibernation wake up 6 December signifies the end of an historic cruise across the entirety of our planetary system. We are almost on Pluto’s doorstep!”