The New Horizons probe is bearing down on Jupiter and a flyby that will swing the spacecraft out to Pluto.
The US mission was already the fastest ever launched, but the extra kick from the gas-giant's gravity will ensure it arrives at the dwarf planet by 2015.
So far, New Horizons has taken more than 20 images of Jupiter; hundreds more will have been obtained by the end of a late February flyby.
The encounter will be an important examination of the probe's systems.
"This is a big test for our mission," said Alan Stern, from the Southwest Research Institute, Boulder, Colorado, and the principal investigator on the US space agency (Nasa) mission.
"We specifically want to exercise the spacecraft hard enough so we turn up any small vulnerabilities or weaknesses, either in our ground planning or in the bird in flight.
"We are really looking forward to being the next mission to Jupiter and my team is rabid to work with the data as soon as we can get it on the ground."
Running the tail
The $700m (£350m) probe was launched in January last year to gather information on Pluto and its moons.
The Jupiter pass is needed to accelerate New Horizons away from the Sun by an additional 14,500km/h (9,000mph), pushing it past 84,000km/h (52,000 mph). This will shorten the journey time to Pluto by four years.
The probe will make more than 700 observations of the gas-giant and its four largest moons - Io, Europa, Ganymede, and Callisto. The observation campaign, which has already begun, will continue through to June.
Targets of interest include Jupiter's turbulent, stormy atmosphere and its ring system.
The spacecraft will also fly down the long "tail" of Jupiter's magnetosphere, a wide stream of charged particles that extends tens of millions of kilometres beyond the planet.
"All the plasma that is put out by the volcanoes on Io ultimately escapes down this tail, and no spacecraft has flown down this region before; it's real terra incognita," explained New Horizons science team member Dr John Spencer.
"There's not much to see there, but there is a great deal for the plasma instruments to sense."
Some of New Horizon's investigations will be supported by observations made by the Hubble Space Telescope.
On and on
Much of the data from the Jupiter flyby will not be sent back to Earth immediately. Some of it will be stored onboard the spacecraft and returned after the day of closest approach to the gas-giant on 28 February.
Scientists expect to announce initial results from their investigations in April.
For the next years following the Jupiter pass, New Horizons will cruise towards Pluto, being "woken" annually for technical checks and rehearsals for its encounter with the dwarf planet.
Long before it approaches Pluto, New Horizons will start collecting data. The first maps of Pluto and its biggest moon Charon will be made three months before the July 2015 rendezvous.
PLUTO IN 2015
Spacecraft will fly past Pluto and its biggest moon, Charon
Observations confirm Pluto has at least two other moons
Pluto recently downgraded to status of 'dwarf planet'
But interest is undiminished - if anything, it is getting stronger
Orbits Sun every 248 years; surface temperature -233 C
Rotates every 6.8 days; gravity about 6% of Earth's
During a day-long close flyby, ultraviolet emissions from Pluto's atmosphere will be measured and the best quality maps of Pluto and Charon, including surface detail, will be made.
New Horizons will go to about 10,000km (6,200 miles) from Pluto and about 27,000km (16,800 miles) from Charon, before pressing onwards.
The spacecraft will look back at the "far side" of the pair to spot haze, look for rings and examine the objects' surfaces.
With extra Nasa approval and funding, the probe will then be maintained to travel on to other objects in the Kuiper Belt, a region of space that contains many frozen leftovers from the construction of our Solar System.
"Going to Pluto and the Kuiper Belt is very new; it's the new frontier," said Dr Stern. "It's opening up both a window on the deep outer Solar System and a window back in time, 4.5 billion years to the birth of the planets."