On September 22, NASA's OSIRIS-REx spacecraft successfully completed a gravity assist flyby with Earth, which has set the probe on a course to rendezvous with the asteroid Bennu next year. At its closest point, OSIRIS-REx flew within 10,711 miles (17,237 km) of Earth's surface, and has captured some stunning imagery in the days following its vital pass.
OSIRIS-Rex was launched in September 2016 on an ambitious seven-year mission to return an asteroid sample to Earth for detailed analysis. While the Atlas V 411 rocket was powerful enough to lift the 2.3 ton (2 tonne) spacecraft out of Earth's atmosphere and send it on its way, the probe still needed a little extra help from Earth's gravity if it hoped to rendezvous with its target.
Bennu's orbit around the Sun is roughly six degrees divergent from the orbital tilt traversed by Earth. The spacecraft simply didn't carry enough fuel to effect so massive a change to its tilt on its own, and so the team had to use Earth's gravity to manipulate OSIRIS-REx's orbit to match that of Bennu.
By the time OSIRIS-REx had completed the gravity assist, the probe was roughly 106,000 miles (170,000 km) from Earth, and had altered its velocity by 8,451 miles per hour (3,778 km per second). In the two weeks following the pass, mission operators will calibrate OSIRIS-Rex' instruments by having them scan Earth.
NASA has released three images taken by the spacecraft's cameras during this testing phase. Images in black and white were captured by the spacecraft's NavCams. Three of these imagers make up the Touch-and-Go Camera System (TAGCAMS), which help the probe to determine its position by tracking starfields and, eventually, features on the asteroid Bennu.
A color mosaic of the Earth was also created from images taken by the probe's MapCam mere hours after completing the flyby, showing Earth's blue marble swathed in cloud against the pitch black of space (see lead image). Featured in the top right of this image are the hurricanes Maria and Jose, which at the time of the pass were lurking off the coast of America.
If all goes to plan, OSIRIS-REx is expected to rendezvous with Bennu in August 2018. Should the mission be successful, scientists may be able to use the asteroid sample to unravel the processes that molded our solar system 4.5 billion years ago.
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