Using Earth as a gravitational slingshot is a common trick since there isn't a rocket that's powerful enough to catapult a spacecraft directly to the outer solar system. (Agencies)
Launched in 2011, the Juno spacecraft zipped past the orbit of Mars and fired its engines to put it on course for a momentum-gathering flyby of Earth. During the manoeuvre, Juno will briefly pass into Earth's shadow and emerge over India's east coast.
At closest approach, Juno will fly within 350 563 kilometres of the Earth's surface, passing over the ocean off the coast of South Africa shortly before 12:30 pm local time.
The rendezvous was designed to bump Juno's speed from 78,000 mph (125,500 kph) relative to the sun to 87,000 mph (140,000 kph) enough power to cruise beyond the asteroid belt toward its destination.
During the gravity assist, the spacecraft's JunoCam, a wide-angle colour camera, will snap pictures of the Earth and moon. Weather permitting, skywatchers in India and South Africa with binoculars or a small telescope may see Juno streak across the sky.
Ham radio operators around the globe were encouraged to say "hi" in Morse code a message that may be detected by one of the spacecraft's instruments.
By space mission standards, Juno's flyby was expected to be low-key compared with the Curiosity rover's nail-biting landing on Mars last year.
"Our expectation is we will come through nice and clean," said today project manager Rick Nybakken of the NASA Jet Propulsion Laboratory, which manages the USD 1.1 billion mission.
Despite a government shutdown that has prevented NASA from updating its website or tweeting, the space agency's missions continue to operate. Earlier this week, NASA's newest spacecraft, LADEE, slipped into orbit around the moon.
Since the 1970s, spacecraft have visited or flown past Jupiter including the Voyagers, Pioneers, Galileo, Ulysses, Cassini and, most recently, the Pluto-bound New Horizons. Juno promises to venture closer than previous spacecraft for an in-depth study of Jupiter's cloud-socked atmosphere and mysterious interior to better understand how the gas giant formed.
Juno was scheduled to arrive at Jupiter on July 4, 2016 after journeying 2.74 billion kilometres. Chief scientist, Scott Bolton of the Southwest Research Institute, said he's pleased with Juno's performance so far. "The mission is going great and after this flyby of Earth, our next stop is Jupiter," he said.
Using Earth as a gravitational slingshot is a common trick since there isn't a rocket that's powerful enough to catapult a spacecraft directly to the outer solar system.