NASA's Galileo spacecraft will pass within 600 miles of Earth at 12:35 p.m. PST Saturday, December 8, 1990, as it continues to work its way out to Jupiter.
During this flyby, Galileo will pick up some of the energy necessary to reach the giant planet in 1995. It will increase its speed in solar orbit by about 11,600 mph.
One more Earth gravity assist, in 1992, will pump up the flight path the rest of the way to Jupiter, for a 1995 encounter. An earlier gravity assist, at the planet Venus in February 1990, set the conditions for today's Earth flyby.
After the Venus flyby, six trajectory-correction maneuvers, designed and programmed by Galileo's flight team and executed on command by the spacecraft over the last 8 months, put Galileo on the precise flight path for the required gravity assist. Although the fifth maneuver was accurate within 1 percent, a very small sixth adjustment was made November 28 to remove remaining errors and save propellant after the Earth flyby.
The sole objective of the Earth and Venus flybys is to add energy to Galileo's orbit so it may reach Jupiter. As a bonus, however, the Project's scientists will Use these encounters to test the spacecraft's systems and sensors andadd to science's knowledge of these planets.
As Galileo approaches the dark side of Earth, it will be measuring the Earth's magnetic field and the surrounding solar plasma flows. It will also image and map the crescent Moon, which swells to half-moon as Galileo approaches. The first Earth images are scheduled about an hour after closest approach. They will continue, at various intervals, for about a week.
Galileo will leave Earth's magnetosphere about two hours after closest approach. The various instruments will continue to be active for some days.
Galileo will encounter the main-belt asteroid Gaspra in late October 1991 for a first and very brief scientific close-up of such a body. It will return to Earth's vicinity December 8, 1992 for a second, precisely engineered gravity assist.
A first look at preliminary analyses of the EarthMoon science observations will be presented in a press conference scheduled for 10 a.m. PST Wednesday, December 19, 1990, at JPL, and via NASA SELECT, Satcom F2R, Transponder 13, C-Band.
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