A decade ago, NASA’s Cassini spacecraft flew past Earth at a distance of 1,171 kilometers (727 miles) on its way to an appointment with the solar system’s second largest occupant – Saturn.
Launched in October of 1997, Cassini required a grand total of four planetary flybys to provide the gravity boost it needed to get to the ringed world.
A gravity boost uses a planet’s mass and orbital speed to “boost” a spacecraft’s velocity as it flies past. Prior to its Earth encounter, Cassini had flown past Venus on two occasions (April 26, 1998 and June 24, 1999).
The Earth flyby on Aug. 18, 1999 gave Cassini a 5.5-kilometer-per-second (about 12,000-mile-per-hour) boost in velocity, speeding Cassini toward its final gravity boost target of Jupiter in December of the following year.
The total effect of the probe’s four planetary flybys – two Venus, one Earth and one Jupiter – was an extra 21.44 kilometers (13.64 miles) per second of velocity for the spacecraft.
Cassini arrived at Saturn and was captured into orbit on June 30, 2004. Since then, it has been returning a wealth of data about the planet, its rings and its moons.
