[meteorite-list] Third of Four Planned Maneuvers Extends MESSENGER Orbital Operations

[Ron Baalke]

http://messenger.jhuapl.edu/news_room/details.php?id=267

MESSENGER Mission News
October 24, 2014

Third of Four Planned Maneuvers Extends MESSENGER Orbital Operations

MESSENGER mission controllers at the Johns Hopkins University Applied 
Physics Laboratory in Laurel, Md., conducted the third of four maneuvers 
today to raise the spacecraft's minimum altitude sufficiently to extend 
orbital operations and delay the probe's inevitable impact onto Mercury's 
surface until early next spring.

The first of the four maneuvers, completed on June 17, raised MESSENGER's 
altitude at closest approach from 115 kilometers (71.4 miles) to 156.4 
kilometers (97.2 miles) above the planet's surface. The second of the 
four maneuvers, completed on September 12, raised MESSENGER's altitude 
at closest approach from 25.2 kilometers (15.7 miles) to 93.7 kilometers 
(58.2 miles) above the planet's surface. Because of progressive changes 
to the orbit over time, the spacecraft's minimum altitude has continued 
to decrease since September.

At the time of this most recent maneuver, MESSENGER was in an orbit with 
an altitude at closest approach of 26 kilometers (16.1 miles) above the 
surface of Mercury. With a velocity change of 19.37 meters per second 
(43.33 miles per hour), the spacecraft's four largest monopropellant thrusters 
(with a small contribution from four of the 12 smallest monopropellant 
thrusters) nudged the spacecraft to an orbit with a closest approach altitude 
of 185.2 kilometers (115.1 miles). This maneuver also increased the spacecraft's 
speed relative to Mercury at the maximum distance from Mercury, adding 
about 7.4 minutes to the spacecraft's eight-hour, five-minute orbit period.

This view shows MESSENGER's orientation shortly after the start of the 
maneuver.
http://messenger.jhuapl.edu/the_mission/maneuvers.html

MESSENGER was 116.9 million kilometers (72.64 million miles) from Earth 
when the 2 minute, 29 second maneuver began at 2:58 p.m. EDT. Mission 
controllers at APL verified the start of the maneuver 6.5 minutes later, 
after the first signals indicating spacecraft thruster activity reached 
NASA's Deep Space Network tracking station outside of Goldstone, California.

One more maneuver, on January 21, 2015, will again raise the spacecraft's 
minimum altitude, allowing the MESSENGER science team to continue to collect 
images and other data from the spacecraft's instruments.
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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 17, 2011 (March 18, 2011 UTC), 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.