NASA's asteroid sampling spacecraft has caught its first glimpse of its target Bennu last week and begun the final approach towards it after an almost two-year journey.
The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) obtained the image of the asteroid from a distance of 2.1 million kilometre on August 17 using its PolyCam camera.
OSIRIS-REx is NASA's first mission to visit a near-Earth asteroid, survey the surface, collect a sample and deliver it safely back to Earth.
The spacecraft has travelled approximately 1.8 billion kilometre since its 2016 launch and is scheduled to arrive at Bennu on December 3 this year.
"Now that OSIRIS-REx is close enough to observe Bennu, the mission team will spend the next few months learning as much as possible about Bennu's size, shape, surface features, and surroundings before the spacecraft arrives at the asteroid," said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona in the US.
"After spending so long planning for this moment, I can't wait to see what Bennu reveals to us," said Lauretta.
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As OSIRIS-REx approaches the asteroid, the spacecraft will use its science instruments to gather information about Bennu and prepare for arrival.
During the mission's approach phase, OSIRIS-REx will regularly observe the area around the asteroid to search for dust plumes and natural satellites, and study Bennu's light and spectral properties.
It will execute a series of four asteroid approach maneuvers, beginning on October 1, slowing the spacecraft to match Bennu's orbit around the Sun.
The OCAMS will reveal the asteroid's overall shape in late-October and begin detecting Bennu's surface features in mid-November.
After arrival at Bennu, the spacecraft will spend the first month performing flybys of Bennu's north pole, equator and south pole, at distances ranging between 19 and 7 kilometres from the asteroid.
These manoeuvres will allow for the first direct measurement of Bennu's mass as well as close-up observations of the surface. These trajectories will also provide the mission's navigation team with experience navigating near the asteroid.
"Bennu's low gravity provides a unique challenge for the mission," said Rich Burns, OSIRIS-REx project manager at NASA's Goddard Space Flight Center in the US.
"At roughly 500 metres in diameter, Bennu will be the smallest object that any spacecraft has ever orbited," said Burns.
The spacecraft will extensively survey the asteroid before the mission team identifies two possible sample sites.
Close examination of these sites will allow the team to pick one for sample collection, scheduled for early July 2020.
After sample collection, the spacecraft will head back toward Earth before ejecting the Sample Return Capsule for landing in the Utah desert in September 2023.