[meteorite-list] Maneuver Successfully Delays MESSENGER's Impact, Extends Orbital Operations
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 22 Jan 2015 17:26:09 -0800 (PST)
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 (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.
Received on Thu 22 Jan 2015 08:26:09 PM PST