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In 2016, NASA launched a spacecraft named Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer or OSIRIS-REx, and sent it on its way to a near-Earth asteroid named Bennu. And on September 22, the spacecraft, roughly the size of an SUV, slingshot around the Earth’s South Pole, altering its trajectory and so as to reach Bennu in the autumn of 2018.

The episode of NASA’s video podcast series ScienceCasts titled Riding the Slingshot to Bennu explains exactly how crucial the “slingshot” was for the mission to be successful. Describing gravity as “most efficient and powerful force of all”, the narrator explains how the earth-gravity assist or the slingshot effect was used to propel the spacecraft towards its destination.

Scientists hope that the mission will bring back a couple of ounces of the asteroid, so that they “can explore how planets formed and life began.” The asteroid is known to regularly cross the Earth’s orbit, with a 1-in-2,700 chance that it could crash to the surface of our planet between 2175 and 2196.

This is not NASA’s first rodeo. In 1974, they employed the slingshot effect when they used the gravity of Venus to help spacecraft Marin 10 to reach Mercury. The earth’s gravity assist (EGA) will help OSIRIS-REx reach Bennu even though their paths are not the same: Bennu’s orbit is tilted by about six degrees compared to Earth’s. The EGA thus serves two purposes: increasing its speed as well as altering its trajectory. OSIRIS-REx is scheduled to return to Earth in 2023.