NASA spacecraft zips past Earth on way to asteroid Bennu

An unmanned NASA spacecraft has successfully zoomed past Earth, using the planet's gravity to slingshot itself towards the Sun-orbiting asteroid Bennu for a rendezvous next year, the US space agency said today.
The OSIRIS-REx spacecraft received the gravity-boost yesterday, about a year after launching on a mission to Bennu.
The spacecraft is currently on a seven-year journey to study and return a sample of Bennu to Earth, NASA said.
This sample of a primitive asteroid will help scientists understand the formation of our solar system more than 4.5 billion years ago, it said.
The OSIRIS-REx spacecraft came within 17,237 kilometres of Antarctica, just south of Cape Horn, Chile, before following a route north over the Pacific Ocean, NASA said.

OSIRIS-REx launched from Cape Canaveral Air Force Station in Florida on September 8, last year on an Atlas V 411 rocket.

Although the rocket provided the spacecraft with the all the momentum required to propel it forward to Bennu, OSIRIS- REx needed an extra boost from the Earth's gravity to change its orbital plane, NASA said.
Bennu's orbit around the Sun is tilted six degrees from Earth's orbit, and this manoeuvre changed the spacecraft's direction to put it on the path towards Bennu.
As a result of the flyby, the velocity change to the spacecraft was 3,778 kilometres per second.

"The encounter with Earth is fundamental to our rendezvous with Bennu," said Rich Burns, OSIRIS-REx project manager at NASA's Goddard Space Flight Centre in the US.
"The total velocity change from Earth's gravity far exceeds the total fuel load of the OSIRIS-REx propulsion system, so we are really leveraging our Earth flyby to make a massive change to the OSIRIS-REx trajectory, specifically changing the tilt of the orbit to match Bennu," said Burns.
The mission team also is using OSIRIS-REx's Earth flyby as an opportunity to test and calibrate the spacecraft's instrument suite.
About four hours after the point of closest approach, and on three subsequent days over the next two weeks, the spacecraft's instruments will be turned on to scan Earth and the Moon.

These data will be used to calibrate the spacecraft's science instruments in preparation for OSIRIS-REx's arrival at Bennu in late 2018.
"The opportunity to collect science data over the next two weeks provides the OSIRIS-REx mission team with an excellent opportunity to practise for operations at Bennu," said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson in the US.