As renowned cosmologist and author Lawrence Krauss says, “Gravity sucks.” He says that because the gravitational force between two masses attracts rather than repels. And for NASA’s rocket scientists, battling against gravity is an everyday task.
In addition to capturing a boulder, an ion drive could be used to deflect an asteroid that is headed toward Earth. Given enough time to prepare, there’s no need to send Bruce Willis into space with an atomic bomb. Just send a robotic ion-drive rocket to push the asteroid off course.