September 23, 2016 – On Tuesday, September 20, 2016, the Cassini spacecraft took its final optical navigation, or Opnav, image of the mission. Throughout its journey Cassini has used its narrow angle camera to capture images of Saturn’s moons against backgrounds of known stars to precisely determine the spacecraft’s course, as well as the moon’s. Without Opnav images, the Cassini team would not have attempted such daring feats as flying through the plume of the icy moon Enceladus just 16 miles (25 kilometers) from its surface.
In all, the spacecraft has taken 2,817 images solely for navigation purposes since launching in 1997. But for Cassini’s final 11 months before diving into Saturn’s atmosphere, it will navigate using only the Doppler shift and timing of radio signals to and from Earth. Cassini will, however, continue collecting images for scientific purposes.
In the above image, the yellow squares identify the positions of known stars, and the yellow half-circle shows where the moon Rhea was expected to be. The difference between the expected and observed position of Rhea can be used to refine our understanding of the moon’s precise orbit around Saturn.
After more than 12 years studying Saturn, its rings and moons, the Cassini spacecraft has entered the final year of its mission. The conclusion is planned for September 2017, at which time the spacecraft will experience a “controlled burn out” in Saturn’s atmosphere.
Beginning on November 30, Cassini’s orbit will send the spacecraft just past the outer edge of the main rings. These orbits, a series of 20, are called the F-ring orbits. During these weekly orbits, Cassini will approach to within 4,850 miles (7,800 kilometers) of the center of the narrow F ring, with its peculiar kinked and braided structure.
Cassini’s final phase, the Grand Finale, begins in April 2017. A close flyby of Saturn’s giant moon Titan will reshape the spacecraft’s orbit so that it passes through the gap between Saturn and the rings – an unexplored space only about 1,500 miles (2,400 kilometers) wide. The spacecraft is expected to make 22 plunges through this gap, beginning with its first dive on April 27.
During the Grand Finale, Cassini will make the closest-ever observations of Saturn, mapping the planet’s magnetic and gravity fields with exquisite precision and returning ultra-close views of the atmosphere.
The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.