Like many of us, New Horizons is starting the new year with a workout regimen. After six months of cruising quietly through the outer solar system, NASA's Pluto-bound spacecraft came out of hibernation last weekend for three weeks of activity that include system checks, a new flight software upload and science data downloads.

The mission operations team at the Johns Hopkins University Applied Physics Laboratory (APL) in Maryland "woke" New Horizons from electronic slumber on Jan. 6.

First tasks included evaluating real-time spacecraft data (which indicated New Horizons was in good health), sending operating commands to the spacecraft's main computer, and gathering tracking data that will help the navigation team keep New Horizons on course toward the Pluto system.

Operators are communicating with New Horizons through NASA's largest Deep Space Network antennas in Spain, Australia and the U.S. (California).

If you can't wait mere minutes to download a new app, this will make you cringe: With radio signals needing nearly 3 hours and 40 minutes to reach the spacecraft - which is about 2.4 billion miles (3.9 billion kilometers) from Earth, between the orbits of Uranus and Neptune - the full software upload will take about 44 continuous hours, says New Horizons Mission Operations Manager Alice Bowman, of APL.

"The Mission Operations Center must remain in constant contact with New Horizons in case the unexpected happens, despite the numerous preparations and precautions the team has taken," Bowman says.

"I think of the C and DH system software update as a 'tune-up' at the 2.4 billion-mile marker," says APL's Glen Fountain, New Horizons project manager.

Other activities planned over the next 20 days include radio frequency system and Radio Science Experiment checkouts, and a download of cruise science data from New Horizons' space plasma instruments - SWAP and PEPSSI - which have been studying the charged-particle populations of the outer solar system.

Additionally, New Horizons' solid-state digital recorders (filled with data from last summer's near-Pluto encounter rehearsal) will be erased in preparation for this summer's rehearsal of the nine days surrounding Pluto close approach. The spacecraft will be put back into hibernation on Jan 30.

C and DH: The Brains 'Inside' New Horizons
The command and data handling system - a radiation-hardened 12-megahertz Mongoose V processor guided by intricate flight software - is the spacecraft's "brain."

The processor distributes operating commands to each subsystem, collects and processes instrument data, and sequences information sent back to Earth. It also runs the advanced "autonomy" algorithms that allow the spacecraft to check the status of each system and, if necessary, correct any problems, switch to backup systems or contact operators on Earth for help.

Hibernating Spacecraft:
New Horizons has spent about 80 percent of the past five years in hibernation, a low-power mode that reduces operation costs, frees up Deep Space Network tracking resources for other missions and lessens wear and tear on spacecraft electronics. During the past two years, this hibernation mode has been enhanced to enable New Horizons to collect plasma science data in interplanetary space.

The team wakes New Horizons two or three times a year to check systems and run tests, but after May 2014 the spacecraft will remain "on" without hibernating through the 2015 Pluto encounter.