1\12 More Galileo Amazing Facts
Date: 12 Jan 1996 09:30:16 -0800

More Galileo Amazing Facts

A new amazing fact about the Galileo mission appears daily on the
Galileo home page: http://www.jpl.nasa.gov/galileo/ .  Here are some
facts that have appeared recently.

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On Christmas Day in 1642, Galileo Galilei passed away. On the same day
in Woolsthorpe, England, Isaac Newton was born.
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Galileo passed about 100 km closer to Io than planned. This meant that
the gravity assist from Io slowed Galileo's speed more than was
planned, putting the spacecraft into a shorter orbit around Jupiter
than expected. Rather than use up over 10 kilograms of propellant to
"fix" this, Galileo's navigators realized that they could just let the
spacecraft continue on its way...where it would arrive at its first
encounter with the moon Ganymede a week early!  Amazingly, going
slower means we're getting where we're going sooner! (The Ganymede
flyby was originally scheduled to occur on July 4, 1996. Since it
takes a little over one week for Ganymede to go around its orbit, it
would be in about the same location one week earlier on June 27. Since
Galileo's orbit was one week shorter than originally planned, the
first satellite encounter could simply be moved earlier by one week)
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January 7 was the 386th anniversary of Galileo Galilei's discovery of
Jupiter's moons Io, Europa, and Callisto. Galileo spotted the moon
Callisto a few days later. The four moons--the largest in the Jovian
system--are now called the Galilean satellites, in honor of their
discoverer.
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Because the asteroid Gaspra is so small (about 19 x 12 x 11
kilometers, or 12 x 7.5 x 7 miles), its surface gravitational force is
two thousand times smaller than that of the Earth's, yielding an
escape speed of only 10 meters per second (22 miles per hour); an
Olympic-caliber sprinter could run himself into orbit!  A 200 pound
person would weigh 0.1 pounds!
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The Gaspra asteroid flyby was yet another example of outstanding
navigation: at closest approach, Galileo was just 1.5 seonds and 1
kilometer (0.6 miles) from the aim point. Even so, taking the picture
was a dramatic achievement. One of Galileo's scientists said "It was
like taking a picture of a large house in San Francisco from Los
Angeles."
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Most of Galileo's actions are controlled by commands that have been
stored on board the spacecraft in advance, but there are still many
occasions when the spacecraft's commands have to be sent up in "real
time." How many times have we had to do this? As of December 14, 1995,
a total of 275,586 real-time commands have been transmitted to Galileo
since launch. In the past week alone, 169 real-time commands were
transmitted.
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When the Galileo Photopolarimeter Radiometer detected the flashes of
light caused by Comet Shoemaker-Levy 9 crashing into Jupiter in July
1994, it was using a 4 inch telescope, and it was as far away from
Jupiter as Mars is from the Sun.
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Galileo's second Earth flyby brought the spacecraft within 303
kilometers (182 miles) of the Earth's surface. The gravity assist
added 3.7 kilometers per second (7,992 miles per hour) to the
spacecraft's speed in its solar orbit. As always, Galileo's navigation
was impeccable: the spacecraft was within a kilometer of its intended
path, and was just 0.1 second early.
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Galileo Galilei didn't always want to study mathematics. As a young
boy, he wanted to be a monk.
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Galileo's first earth flyby, delta v was 5.2 kilometers per second, or
11,600 mph, with closest approach at 960 km, or 597 miles, above the
Earth's surface.
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Galileo's cameras will capture pictures that can detect objects as
small as 12 meters (39 feet). That's an improvement on Galileo
Galilei's original telescopic observations by factors up to 100,000 to
1,000,000.
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Although Galileo Galilei was a college dropout, he went on to become a
respected professor.

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