After almost two decades in space, NASA’s Cassini spacecraft is reaching the end of its life. Wednesday marks the very literal beginning of the end for Cassini, when it will enter the first phase of a series of orbits grazing the outer edges of Saturns main rings. Once that exploration is complete in April 2017, Cassini will enter its “grand finale”, eventually being allowed to fall into the planet’s atmosphere in September 2017.

Cassini launched all the way back in 1997 and arrived at Saturn in 2004, where it’s remained in orbit discovering cool shit like liquid methane. Essentially, it’s about to run out of gas. The ring-grazing orbits it will complete over its final five months leading up to the finale will provide NASA with data and imagery for a number of the moons that lie in near those rings, including Pandora, Atlas, Pan, and Daphnis. Cassini will also be sampling various particles and gas molecules from the rings themselves.

Once it gets a “gravitational nudge” from Titan on Wednesday, Cassini can begin a cycle of diving into the outer rings once every seven days, returning after each dive to circle Saturn’s poles. By spring, just before it begins the grand finale and effectively plunges to its death in the autumn, it will be exploring the F ring, the outermost feature of the main ring system, from a range of less than 5,000 miles — closer than NASA has ever come before.

The F ring is of particular interest to NASA, bursting with dynamic yet extremely transient, short-lived filaments and streamers. The A and B rings will also get their due, the former of which should reveal the presence of small, propeller-shaped moonlets.

Cassini will need to perform one final engine burn — its 183rd — in December before it’s clear to begin the grand finale in April. Once that phase begins, the spacecraft will perform a series of dives in between Saturn and its rings, just 1,000 or miles above the planet’s clouds.

Photos via Getty Images / NASA