NASA's New Horizons Spacecraft Is Studying Our Solar System in Its Sleep

New Horizons, the spacecraft currently on its way to Pluto, is putting all productive, Earth-bound scientists to shame. As it approaches the dwarf planet, the spacecraft is doing science in its sleep. Or, more specifically, it's gathering data while in hibernation.

The mission launched in January 2006, made a flyby of Jupiter for a gravity assist to set its course for Pluto in February 2007, and has since been crossing the interplanetary space to our solar system's controversial little planet. During this cruise, most of the spacecraft's subsystems were meant to shut down in an effort to preserve its power and extend its useful lifetime. The only instrument designed to be left on is the Student Dust Counter (SDC) that allows the spacecraft to collect data on dust in interplanetary space by measuring impacts as it flies through the solar system's dust disk.

But New Horizons is in too rare a position to let it sleep the whole way to Pluto. It's only the fifth spacecraft to fly this far from home, preceded by Pioneers 10 and 11 and Voyagers 1 and 2. Those missions launched in the 1970s and the spacecraft were equipped with instruments that are antiquated by New Horizons' standard. Not only that, it's the first spacecraft in three decades to fly beyond Saturn and the first time a spacecraft has been returning data from such a distant point in space when scientists have benchmark data from other missions.

The project's Principal Investigator Alan Stern recognized the rare interplanetary opportunity, and that it could be decades before another spacecraft retraces New Horizons' trajectory. With this in mind, mission scientists decided to investigate operating two solar science instruments during the cruise along side the SDC: the Solar Wind Around Pluto (SWAP) and Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI).

Both SWAP and PEPSSI measure the charged particle radiation environment along New Horizons' trajectory. They sample solar wind protons that travel away from the sun at about a million miles per hour, pickup ions that are created by solar wind protons and solar photons interacting with neutral hydrogen from the interstellar medium, ions heavier than helium, suprathermal ions that travel faster than the solar wind, and other particles.

"Events associated with solar flares and coronal mass ejections that propagate through the solar wind plasma can now be observed throughout the heliosphere as never before," Says Matthew Hill, PEPSSI instrument scientist from Johns Hopkins University Applied Physics Laboratory. "With solar activity on the rise, the timing is great to have these state-of-the-art New Horizons instruments observing the heliosphere."

The only problem with the proposal to keep these instruments running is the demand on the spacecraft to maintain sufficient power, data storage, and on-board fuel margins during hibernation. The team also had to make sure that the three instruments wouldn't interfere with each other or the spacecraft if they operated simultaneously. After all, the idea was more science, not sacrificing one instrument for another.

To address all these issues, the mission team ran a battery of ground tests and analyses, a 10 day three-instrument test on the hibernating spacecraft in October 2011, and an 80 day enhanced hibernation cruise science test between January and April 2012. The results confirmed that SDC, SWAP, and PEPSSI could all collect excellent data while operating together during hibernation.

In early June, enhanced science was officially added to the docket for New Horizons' mission. When the New Horizons operations team placed the spacecraft back into hibernation on July 6 after a 10-week annual systems and instrument payload checkout, all three instruments remained operational.

"This is a real success story for a low-cost outer planets mission," Stern said of the teams successful certification of Hibernation Cruise Science as an added mission objective. "Now let's see what heliospheric discoveries we can make on the road to planet Pluto." New Horizons will begin its encounter with Pluto in January 2015; its closest approach will come on July 14, 2015.