Mercury MESSENGER

It’s been almost a year since I last posted about the MESSENGER mission to the planet Mercury. The long interlude isn’t from lack of interest — there just hasn’t been much happening. That’s because MESSENGER is one of the now-common missions that uses gravitational assists from planets to greatly lower the fuel requirements. In MESSENGER’s case, it will be getting a total of six such gravity assists from planetary flybys: one from Earth (last August), two from Venus (the first one on October 24, 2006), and three from Mercury. Not until 2011 will MESSENGER finally make its orbital insertion burn. Between now and then there’s not much happening, except for those planetary flybys, each of which is planned to generate much good science.

The picture at right was taking on the Earth flyby (click for a larger view).

The planned orbit around Mercury is interesting. From the MESSENGER official web site:

MESSENGER’s orbit about Mercury is 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 plane of the orbit is inclined 80° to Mercury’s equator, and the low point in the orbit is reached at a latitude of 60° north. The low-altitude orbit over the northern hemisphere allows MESSENGER to conduct a detailed investigation of the geology and composition of Mercury’s giant Caloris impact basin - the planet’s largest known surface feature.

About 33% 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 0.83 kilometers (0.52 miles) per second. As the spacecraft approaches Mercury, the largest thruster must be pointed close to the forward velocity direction of the spacecraft. The first maneuver (lasting about 15 minutes) places the spacecraft into a stable orbit; it also sets up a much shorter cleanup maneuver two to three days later near the orbit’s lowest point.

We’ll be keeping an eye on this mission. In the meanwhile, visit the MESSENGER site for more information.