One Year Until Mercury Orbit Insertion
18 Mar 2010
(Source: Johns Hopkins Applied Physics Laboaratory)
One year from today - starting at 12:45 a.m. UTC - MESSENGER will transition from orbiting the Sun to being the first spacecraft ever to orbit the planet Mercury.
"We are finally closing in on the most intense phase of the mission," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "MESSENGER's six and a half years of interplanetary flight are a long warm-up for the main event, when we are in orbit about Mercury. The final year of that flight will be a busy time for the team, as we review orbital operation plans for all spacecraft subsystems."
Entering orbit about Mercury will require the probe to perform the largest propulsive maneuver of the entire mission. For Mercury orbit insertion (MOI), MESSENGER will point its largest thruster very close to the direction of travel and fire that thruster for nearly 14 minutes as well as other thrusters for an additional minute, slowing the spacecraft by 862 meters per second (1,929 miles per hour) and consuming 31% of the propellant that the spacecraft carried at launch.
For an animation of the orbit insertion maneuver and initial orbit of Mercury, see http://messenger.jhuapl.edu/the_mission/gallery.html. Two animations and various view perspectives of the orbit insertion maneuver and initial orbit of Mercury are available at http://messenger.jhuapl.edu/the_mission/MESSENGERTimeline/MercuryOrbitInsertion.html.
"Less than 9.5% 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 future orbit correction maneuvers," says MESSENGER Mission Design Engineer Jim McAdams of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.
MESSENGER engineers recently tweaked the strategy for entering into orbit about Mercury. "MESSENGER's propulsion system has consistently performed with high accuracy," McAdams explains. "We replaced an MOI clean-up maneuver with a placeholder for a contingency clean-up maneuver, which reduces risk by simplifying the orbit insertion process."
Another change affecting the orbit insertion is a shift in the spacecraft orbit's tilt relative to Mercury's equator plane, from 80.0° to 82.5°, "a carefully studied change that will improve overall science data returned during the Mercury orbital phase," McAdams says.
The orbit insertion will place the spacecraft into an initial orbit about Mercury that has a 200 kilometer (124 mile) minimum altitude and a period of 12 hours. At the time of orbit insertion, MESSENGER will be 46.14 million kilometers (28.67 million miles) from the Sun and 155.06 million kilometers (96.35 million miles) from Earth.
MESSENGER Team Delivers Mercury Flyby 3 Data to Planetary Data System
The Planetary Data System (PDS) has released data to the public from MESSENGER's third flyby of Mercury. PDS has the responsibility to archive and distribute all of NASA's planetary mission data. This, the fifth release from the MESSENGER mission, includes both raw and calibrated data from all of the instruments. In addition, calibrated data from the Energetic Particle and Plasma Spectrometer, Gamma-Ray and Neutron Spectrometer, Mercury Laser Altimeter, and X-Ray Spectrometer instruments from the previous flybys are also included in this release.
Since the mid-1990s, NASA has required all of its planetary missions to archive data in the PDS, an active archive that makes available well-documented, peer-reviewed data to the research community. The PDS includes eight university/research-center science teams, called discipline nodes, each of which specializes in a specific area of planetary data. The data libraries at these nodes provide rich sources of information for scientists, educators, and the interested public.
According to MESSENGER Project Manager Peter Bedini, of APL, a substantial amount of effort on the part of a large number of people was required to prepare these mission data for release to the public. In addition to developing - or updating, in the case of the Mercury Dual Imaging System, Mercury Atmospheric and Surface Composition Spectrometer, and Magnetometer instruments - the algorithms needed to transform the raw data into calibrated files, instrument teams were called upon to validate all data.
"Members of the MESSENGER science operations center generated the multitude of descriptive documentation required to accompany the data in order to facilitate its use by the public," Bedini says. "Guidelines for the creation of these files and for the structure of the archives are very stringent, and representatives from each PDS node reviewed every delivery for compliance with these formats."
Such strict procedures are critical, says Marilyn Lindstrom, NASA Program Scientist for MESSENGER. "It's important to maintain a planetary data archive that will withstand the test of time so future generations of scientists can access, understand, and use the data."
"The release of calibrated data from the entire mission cruise phase through the third Mercury flyby for the full MESSENGER payload represents a critical milestone for the project," says MESSENGER Principal Investigator Sean Solomon. "The methodologies for archiving calibrated records from every instrument have now been established by the MESSENGER team and validated by the PDS, clearing the path to begin archiving data from Mercury orbit in 2011."
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 launched on August 3, 2004, and after flybys of Earth, Venus, and Mercury will start a yearlong study of its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, 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.