[meteorite-list] MESSENGER Primed for Mercury Orbit

[Ron Baalke]

The Johns Hopkins University Applied Physics Laboratory
Office of Communications and Public Affairs
Laurel, Maryland
Media Contact: Paulette W. Campbell
(240) 228-6792
Paulette.campbell at jhuapl.edu

March 15, 2011

FOR IMMEDIATE RELEASE

MESSENGER PRIMED FOR MERCURY ORBIT

After more than a dozen laps through the inner solar system and six 
planetary flybys, NASA's MESSENGER spacecraft will move into orbit 
around Mercury on at around 9 p.m. EDT on Thursday, March 17.

The durable spacecraft -- carrying seven science instruments and 
fortified against the blistering environs near the sun -- will be the 
first to orbit the innermost planet.

"From the outset of this mission, our goal has been to gather the 
first global observations of Mercury from orbit," says MESSENGER 
principal investigator Sean Solomon of the Carnegie Institution of 
Washington. "At the time of our launch more than six and a half years 
ago, that goal seemed but a distant dream. MESSENGER is now poised to 
turn that dream into reality."

Just over 33 hours before the main Mercury orbit insertion maneuver, 
two antennas from NASA's Deep Space Network -- one main antenna and 
one backup -- will begin to track the MESSENGER spacecraft 
continuously. At 6:30 p.m. EDT on March 17, the number of antennas 
tracking MESSENGER will increase to five; four of these will be 
arrayed together to enhance the signal from the spacecraft and a 
fifth will be used for backup.

At about 8 p.m., the solar arrays, telecommunications, attitude 
control, and autonomy systems will be configured for the main 
thruster firing (known as a "burn"), and the spacecraft, operating on 
commands transmitted last week from Earth, will be turned to the 
correct orientation for MESSENGER's Mercury orbit insertion maneuver.

To slow the spacecraft down sufficiently to be "captured" by Mercury, 
MESSENGER's main thruster will fire for about 15 minutes beginning at 
8:45 p.m. This burn will slow the spacecraft by 1,929 miles per hour 
(862 meters per second) and consume 31 percent of the propellant that 
the spacecraft carried at launch. Less than 9.5 percent of the usable 
propellant at the start of the mission will remain after completing 
the orbit insertion maneuver, but the spacecraft will still have 
plenty of propellant for orbit adjustments during its yearlong 
science campaign.

After the burn, the spacecraft will turn toward Earth and resume 
normal operations. Data will be collected by Deep Space Network 
antennas and transferred to the Mission Operations Center at the 
Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, 
Md., to be analyzed. It is expected that by 10 p.m. EDT, mission 
operators will be able to confirm that MESSENGER has been 
successfully captured into orbit around Mercury.

The maneuver -- which will be completed at a time that MESSENGER is 
more than 96 million miles from Earth -- will place the probe into an 
orbit that brings it as close as 124 miles to Mercury's surface. At 
2:47 a.m. EDT on March 18, the spacecraft will begin its first full 
orbit around Mercury, and the probe will continue to orbit Mercury 
once every 12 hours for the duration of its primary mission.

"For the first two weeks of orbit, we'll be focused on ensuring that 
the spacecraft systems are all working well in Mercury's harsh 
thermal environment," says APL's Eric Finnegan, the MESSENGER mission 
systems engineer. "Starting on March 23, the instruments will be 
turned on and checked out, and on April 4 the science phase of the 
mission will begin and the first orbital science data from Mercury 
will be returned."

While in orbit, MESSENGER's instruments will perform the first 
complete reconnaissance of the cratered planet's geochemistry, 
geophysics, geological history, atmosphere, magnetosphere, and plasma 
environment.

"The marathon cruise phase of the MESSENGER mission is nearing the 
finish line," says Solomon. "Like a seasoned runner, the MESSENGER 
team is positioned to break through the tape. We are extremely 
excited by the prospect that orbital operations will soon begin."

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