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MESSENGER makes final move before impact

Jenny Winder, News Writer
Apr 27, 2015, 18:21 UTC

Sen—NASA's MESSENGER probe has made its final maneuver ahead of its impact on Mercury at the end of April.

During the final orbital correction maneuver (OCM) on April 24, gaseous helium, originally used to pressurize the hydrazine fuel, was expelled to raise the spacecraft's minimum altitude above the planet from about 8 to 19 km (5 to 12 miles). This was the last of six planned maneuvers designed to raise the orbit of the spacecraft, prolonging the mission, and the third maneuver using just helium gas as a propellant.

Launched in 2004, MESSENGER (short for MErcury Surface, Space ENvironment, GEochemistry and Ranging) travelled to our innermost planet via one flyby of Earth, two flybys of Venus, and three flybys of Mercury itself. It became the first spacecraft to enter the orbit of Mercury on March 18, 2011. Since then it has made the first detailed study of the planet.

Back in March, mission controllers initiated a "hover" observation campaign designed to gather scientific data from the planet at ultra-low altitudes until the last possible moment. This low altitude campaign has given MESSENGER's seven science instruments a unique opportunity to study surface, exosphere, and magnetic field up close and has produced higher-resolution imaging of Mercury than ever before.

Bobby Williams, who leads the KinetX Space Navigation and Flight Dynamics group, said in a statement: “Navigating a spacecraft so close to a planet’s surface had never been attempted before, but it was a risk worth taking given mission success had already been met, and the novel science observation opportunities available only at such very low altitudes.”

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At approximately 1.1 metres/pixel, this image, acquired on April 23, 2015, is among the highest-resolution views MESSENGER has ever taken of the surface of Mercury. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

MESSENGER Principal Investigator Sean Solomon said in a statement: “Operating a spacecraft in orbit about Mercury, where the probe is exposed to punishing heat from the Sun and the planet’s dayside surface as well as the harsh radiation environment of the inner heliosphere, would be challenge enough.

“But MESSENGER’s mission design, navigation, engineering, and spacecraft operations teams have done much more. They’ve fought off the relentless action of solar gravity, made the most of every usable gram of propellant, and devised novel ways to modify the spacecraft trajectory never before accomplished in deep space.

"They’ve extended the duration of MESSENGER’s orbital observations by more than a factor of four over the original plan, and an amazing set of scientific discoveries has been enabled by their creative efforts. This latest maneuver is icing on a multi-tiered cake of spectacular accomplishment. The MESSENGER mission will soon end, but its legacy of scientific knowledge and technical innovation will endure for as long as we study the planets and explore the Solar System.”

MESSENGER is expected to crash into the surface on the far side of Mercury from Earth on April 30, at approximately 3.91 km per second (8,750 miles per hour), producing a crater 16 metres (52 feet) wide. 

The next mission bound for Mercury is BepiColombo, due to launch in January 2017