[meteorite-list] Planned Maneuver Further Extends MESSENGER Orbital Operations

[Ron Baalke]

http://messenger.jhuapl.edu/news_room/details.php?id=278

MESSENGER Mission News
April 3, 2015

Planned Maneuver Further Extends MESSENGER Orbital Operations

MESSENGER mission controllers at the Johns Hopkins University Applied 
Physics Laboratory (APL) in Laurel, Md., conducted a maneuver yesterday 
to raise the spacecraft's minimum altitude sufficiently to extend orbital 
operations and further delay the probe's inevitable impact onto Mercury's 
surface.

The previous maneuver, completed on March 18, raised MESSENGER to an altitude 
at closest approach from 11.6 kilometers (7.2 miles) to 34.4 kilometers 
(21.4 miles) above the planet's surface. Because of progressive changes 
to the orbit over time in response to the gravitational pull of the Sun, 
the spacecraft's minimum altitude continued to decrease.

At the time of yesterday's maneuver, MESSENGER was in an orbit with a 
closest approach of 5.5 kilometers (3.4 miles) above the surface of Mercury. 
With a velocity change of 2.96 meters per second (6.63 miles per hour), 
four of the spacecraft's 12 smallest monopropellant thrusters nudged the 
spacecraft to an orbit with a closest approach altitude of 27.5 kilometers 
(17.1 miles). This maneuver also increased the spacecraft's speed relative 
to Mercury at the maximum distance from Mercury, adding about 1.2 minutes 
to the spacecraft's eight-hour, 17.6-minute orbit period.

The second orbit-correction maneuver (OCM) in MESSENGER's low-altitude 
hover campaign, also called the extension of the second extended mission, 
OCM-14 is the first propulsive course correction since December 2006 to 
use the two small thrusters that point sunward from the sunshade center 
panel. This view shows MESSENGER's orientation at the start of the maneuver.

MESSENGER was 200.6 million kilometers (124.6 million miles) from Earth 
when the 6.7-minute maneuver began at about 4:30 p.m. EDT. Mission controllers 
at APL verified the start of the maneuver 11.2 minutes later, after the 
first signals indicating spacecraft thruster activity reached NASA's Deep 
Space Network tracking station in Goldstone, Calif. The next maneuver, 
on April 6, will again raise the spacecraft's minimum altitude, allowing 
scientists to continue to collect images and data from MESSENGER's instruments. 
The 3.8 days between OCM-14 and OCM-15 will be the shortest time between 
any two MESSENGER maneuvers.

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MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) 
is a NASA-sponsored scientific investigation of the planet Mercury and 
the first space mission designed to orbit the planet closest to the Sun. 
The MESSENGER spacecraft was launched on August 3, 2004, and entered orbit 
about Mercury on March 18, 2011, to begin a yearlong study of its target 
planet. MESSENGER's first extended mission began on March 18, 2012, and 
ended one year later. MESSENGER is now in a second extended mission, which 
is scheduled to conclude in March 2015. Dr. Sean C. Solomon, the Director 
of Columbia University's Lamont-Doherty Earth Observatory, leads the mission 
as Principal Investigator. The Johns Hopkins University Applied Physics 
Laboratory built and operates the MESSENGER spacecraft and manages this 
Discovery-class mission for NASA.