In the simplest terms, spacecraft navigation entails determining where a spacecraft is and keeping it on course to the desired destination, with the added difficulty that point A (Earth) and point B (a planet or other body in our solar system) are not fixed positions in space. Trajectory designers and navigators are faced with challenges like calculating the exact speeds and orientations of a rotating Earth, a rotating target destination, and a moving spacecraft, while all are simultaneously traveling in their own orbits around the Sun. Dr. Mar Vaquero will describe the theory and techniques currently used in trajectory design and spacecraft flight path control at the Jet Propulsion Laboratory, specifically applied to the Cassini mission -- arguably the most complex gravity-assist trajectory ever flown. Dr. Mar Vaquero is a Mission Design and Navigation Engineer at the NASA Jet Propulsion Laboratory in Pasadena, CA, where she has worked on different projects ranging from developing early mission concepts to navigating the Cassini spacecraft through its Grand Finale. Her research interests include spacecraft trajectory design, optimal control theory, and mission design optimization techniques. Dr. Vaquero is specifically interested in finding ways to fly spacecraft through the solar system using little to no fuel.