Mercury Orbit Insertion

After more than a dozen laps through the inner solar system, NASA's MESSENGER spacecraft will move into orbit around Mercury on March 17, 2011. The durable spacecraft--carrying seven science instruments and fortified against the blistering environs near the sun--will be the first to orbit the innermost planet.

At 8:45 p.m. EDT, MESSENGER--having pointed its largest thruster very close to the direction of travel--will fire that thruster for nearly 14 minutes, with other thrusters firing for an additional minute, slowing the spacecraft by 862 meters per second (1,929 mph) and consuming 31 percent of the propellant that the spacecraft carried at launch. Less than 9.5 percent 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.

The orbit insertion will place the spacecraft into a 12-hour orbit about Mercury with a 200 kilometer (124 mile) minimum altitude. 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.