Friday, January 11, 2008


Friends of the Hudnall Planetarium,

Three Days to Mercury!

The MESSENGER spacecraft is scheduled to fly by Mercury soon. The
countdown to the first flyby of Mercury by the MESSENGER spacecraft has
begun. Sunday morning, MESSENGER will start recording the evidence of
this historic event. At 8 a.m. EST on January 13 - 30 hours before the
closest approach to Mercury - the spacecraft will turn its main antennas
away from Earth and automatically begin executing the 5,000 on-board
stored commands.

"The entire instrumentation suite will be operating during this
flyby, taking more than 1,200 images and gathering other scientific
observations, filling the on-board data recorder with more than 700
megabytes of history-making measurements, within a period of 55
hours," said MESSENGER Systems Engineer Eric Finnegan of the Johns
Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.
"Fifty minutes prior to closet approach, signals from the
spacecraft will go quiet as MESSENGER passes behind Mercury, out of
Earth's view. Forty-eight minutes later, engineers and scientists on
the ground will attempt to witness the gravitational pull of the planet
first-hand by re-acquiring the transmitted signal from the spacecraft
within minutes of the closet approach point."

On Tuesday, January 15, at noon EST, 22 hours after the flyby,
MESSENGER will take one last look at Mercury before turning back to
Earth to start returning the treasures stored on-board. "Complicating
this sequence of events is the demanding requirement to conduct all
observations by the spacecraft behind the safety of MESSENGER's
sunshade," Finnegan said. "Conducting this encounter at 30 million
miles from the Sun, almost two-thirds closer than the Earth, would have
been impossible in the era of Mariner 10. But thanks to advances in
material sciences, MESSENGER's electronics and sensitive instruments
can run at room temperature behind the sunshade, while the front surface
temperature rises to more than 600° F."

Notwithstanding the operational and scientific importance of this
flyby, MESSENGER is only slightly more than halfway along its
six-and-one-half year, 4.9 billion-mile journey between its launch in
August 2004 and orbit insertion around Mercury in March 2011. "Over
the next 12-month period, the MESSENGER team will engage in the most
grueling year of operations since launch, executing two planetary
encounters, two deep space maneuvers, and possibly six additional
maneuvers - using the smaller thrusters of the on-board propulsion
system - to keep the spacecraft on course," added Finnegan.

The primary goal of this flyby is to obtain a gravity assist from the
planet, which will reduce the arrival velocity of the spacecraft for
orbit insertion in March 2011. "Slowing the spacecraft by 5,000 miles
per hour, MESSENGER's orbital period around the Sun will be decreased
by 11 days, thus setting up a planetary car race with Mercury,"
Finnegan said. "Using its internal engine and future gravity assists,
the spacecraft, after being lapped by Mercury many times in this race
around the Sun, will ultimately match the 88-day orbital period of the
innermost planet."

To facilitate this change in velocity, the spacecraft will speed over
the uncharted surface of Mercury at a relative velocity of more than
16,000 miles per hour and pass within 124 miles of the surface, the
closest any man-made object has been to this planet. During this close
approach, the spacecraft will experience a period of 14 minutes without
solar power, where operations will rely only on the spacecraft's
internal batteries.

Don't miss Hudnall Planetarium's public presentation, "Larry, Cat in
Space" on Saturday and Sunday, January 12 and 13 at 2:00 p.m. Admission
costs to "Larry, Cat in Space" are $3.00 for adults and $2.00 for
students and seniors. Tickets are available at the door one-half hour
before each showing. No seating is allowed after the show begins. For
more information about the Hudnall Planetarium call 903-510-2312 or
visit the planetarium website at

planetarium is located on the main campus of Tyler Junior College near
the intersection of Mahon Avenue and Lake Street.

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