NASA MESSENGER spacecraft’s planned orbit about Mercury will be highly elliptical (egg-shaped), 200 kilometers (124 miles) above the surface at the lowest point and more than 15,193 kilometers (9,420 miles) at the highest. The spacecraft will enter orbit on March 18, 2011.
At the outset of the orbital phase of the mission, the plane of the spacecraft’s orbit is inclined 82.5° to Mercury’s equator, and the low point in the orbit is reached at a latitude of 60° North.
About 31% of the spacecraft’s propellant is required for Mercury orbit insertion — the process of placing the spacecraft into its primary science orbit around Mercury. MESSENGER’s thrusters must slow the spacecraft by just over 0.86 kilometers (0.53 miles) per second. As the spacecraft approaches Mercury, the largest thruster must be pointed close to the forward velocity direction of the spacecraft.