Just Passing By Earth
Cassini has completed another flawless gravity assist
maneuver en route to the ringed planet Saturn
August 18, 1999: Earthlings bid farewell to the Cassini spacecraft last night as the Saturn-bound mission successfully completed a highly accurate pass of Earth at 8:28 p.m. Pacific Daylight Time (03:28 Universal Time August 18). The flyby gave Cassini a 5.5-kilometer-per- second (about 12,000-mile-per-hour) boost in speed, sending the spacecraft on toward the ringed planet more than 1 billion kilometers (almost one billion miles) away.
Right: These images of Earth were captured by the Galileo spacecraft in 1990 as it flew by our planet on its way to Jupiter. [more information]
Engineers at NASA's Jet Propulsion Laboratory confirmed that
the spacecraft flew past Earth at an altitude of about 1,171
kilometers (727 miles), passing most closely above the eastern
South Pacific at -23.5 degrees latitude and 231.5 degrees longitude.
Cassini may have been visible from small islands in that area,
such as Pitcairn Island or Easter Island.
The spacecraft remains in excellent health as it continues along its seven-year-long journey to Saturn. Having completed its cruise among the inner planets, Cassini's future now resides in the cold, dark realm of the outer planets. The spacecraft will pass by Jupiter on December 30, 2000; the giant planet's gravity will bend Cassini's flight path to put it on course for arrival into orbit around Saturn on July 1, 2004.
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The Cassini/Huygens program is a joint endeavor of NASA, the
European Space Agency and the Italian Space Agency. The Cassini
orbiter, built by NASA, and the Huygens probe, provided by the
European Space Agency (ESA), were mated together and launched
as a single package from Cape Canaveral, Florida, on October
15, 1997. Cassini's dish-shaped high-gain antenna was provided
for the mission by the Italian Space Agency. At Saturn, the Huygens
probe will detach from Cassini to parachute to the surface of
Titan on November 30, 2004.
Nine of Cassini's 12 science instruments were turned on to make observations of the Earth/Moon system. Scientific and engineering data from the Earth flyby will be transmitted by Cassini to receiving stations of NASA's Deep Space Network over coming days.
The Cassini mission is a joint effort of NASA, the European Space Agency and the Italian Space Agency. The mission is managed and the Cassini spacecraft built and operated by NASA's Jet Propulsion Laboratory, Pasadena, CA. JPL is a division of the California Institute of Technology.
Gravity Assist Maneuvers
or... What happens when a ping-pong ball hits an electric
You say tomato, I say tomato...
Gravity assists are well-grounded in classical Newtonian physics,
but they can appear paradoxical, as illustrated by this thought
experiment posed by JPL's Dave Doody in the May/June 1995 issue
of The Planetary Report:
Cassini: Voyage to Saturn -- Cassini Mission home page
The Basics of Spaceflight -- from JPL. Includes basic information about gravity assist maneuvers.
Venus: Just Passing By -- Astronomy Picture of the Day, May 1, 1998
Venus's Once Molten Surface -- Astronomy Picture of the Day, Jan. 10, 1999
The Nine Planets: Venus -- from SEDS
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For more information, please contact:
Dr. John M. Horack , Director of Science Communications
Curator: Bryan Walls
NASA Official: John M. Horack