[meteorite-list] Maneuver Successfully Delays MESSENGER's Impact, Extends Orbital Operations

[Ron Baalke]

http://messenger.jhuapl.edu/news_room/details.php?id=271

MESSENGER Mission News
January 21, 2015

Maneuver Successfully Delays MESSENGER's Impact, Extends Orbital Operations

MESSENGER mission controllers at the Johns Hopkins University Applied 
Physics Laboratory (APL) in Laurel, Md., successfully conducted a maneuver 
today designed 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 immediately previous maneuver, completed on October 24, 2014, raised 
MESSENGER to an altitude at closest approach from 25.4 kilometers (15.8 
miles) to 184.4 kilometers (114.6 miles) above the planet's surface. Because 
of progressive changes to the orbit over time, the spacecraft's minimum 
altitude continued to decrease.

At the time of this most recent maneuver, MESSENGER was in an orbit with 
a closest approach of 25.7 kilometers (16.0 miles) above the surface of 
Mercury. With a velocity change of 9.67 meters per second (21.62 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 
105.1 km (65.3 miles).

This maneuver also increased the spacecraft's speed relative to Mercury 
at the maximum distance from Mercury, adding about 3.7 minutes to the 
spacecraft's eight-hour, 12.9-minute orbit period. This maneuver was the 
first during the mission to intentionally use both fuel and gaseous helium 
pressurant to impart the desired velocity change. The propellant was drawn 
from a small auxiliary fuel tank, and the gaseous helium was drawn from 
the main fuel tanks.

"This maneuver has demonstrated the safety of this concept and will allow 
us to characterize system performance during the use of cold gas propellant,"
said MESSENGER Mission Systems Engineer Dan O’Shaughnessy, of APL. "Such 
characterization will be necessary to forecast accurately the timing of 
the spacecraft's surface impact and to plan low-altitude maneuvers for 
the remainder of the mission."

This view<http://messenger.jhuapl.edu/the_mission/maneuvers.html> shows 
MESSENGER's orientation soon after the start of the maneuver. The spacecraft 
was 118.9 million kilometers (73.9 million miles) from Earth when the 
1-minute, 49-second maneuver began at 1:27 p.m. EDT. Mission controllers 
at APL verified the start of the maneuver 6.6 minutes later, after the 
first signals indicating spacecraft thruster activity reached NASA's Deep 
Space Network tracking station in Goldstone, California.

The next maneuver, on March 18, will again raise the spacecraft's minimum 
altitude, allowing scientists to continue to collect images and data from 
MESSENGER's instruments.
________________________________

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 (UTC), to begin its primary mission -
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 this spring. 
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.