by Jim Nintzel
Robert Strom, professor emeritus in the UA's Lunar and Planetary Laboratory, said: "Once in orbit, MESSENGER will image the surface at 250 meters per pixel. At its closest approach, it will even get to a resolution of six meters per pixel. Of course, you can't image a whole planet at this fine resolution. This will be reserved for targets of opportunity — features that MESSENGER images during its surveys and that catch our attention."
Strom pointed out that the MESSENGER mission is unusual because its main payload is not the instruments, but the fuel needed to slow the spacecraft down.
"Because the journey from Earth to Mercury goes toward the sun, we need a lot of energy to counteract the sun's gravitational pull," he explained.
To save fuel, the engineers devised a carefully choreographed dance that MESSENGER performs around selected planets: the Earth, the moon and Mercury.
"By having the probe dance around planets, it can take advantage of their gravitational fields to slow its speed," Strom added. "Even once in orbit around Mercury, the spacecraft will need to burn fuel every few hours or so to prevent the sun's gravitational field from pulling it out of orbit."
Another great challenge MESSENGER has to cope with is the intense heat due to Mercury's proximity to the sun. At the equator, surface temperatures become hot enough to melt lead. The heat reflected from the planet's surface is so intense that the spacecraft's instruments need to be shielded against the glare.
"The spacecraft is going to go very fast, traveling around the planet every 12 hours," Sprague explained. "The orbit is highly elliptical to allow the spacecraft to cool down. We couldn't do this with a circular orbit, like around Mars. Everything would just overheat. MESSENGER must swoop in, keeping its sunshade pointed toward the sun, and then it has to swing out far into space so it can cool down."
Strom added: "The strategy is to have MESSENGER gather data during its close approach and then read the data out and send them back to Earth while the probe is at a safe distance from the scorching planet."