This is super cool. I recommend reading the article and then watching the animation. I'm no physicist, but it looks like the fundamental idea is to use elliptic

This is super cool. I recommend reading the article and then watching the animation. I'm no physicist, but it looks like the fundamental idea is to use elliptical orbits to slip in front of a planet along it's orbital track, and have the planet's gravity slow the probe, and then get out of the way fast as the planet passes. It's kind of the opposite of a cyclist drafting.