When the Mars Pathfinder probe and its Sojourner rover landed on the Red Planet in 1997, NASA was overwhelmed by 17.3 million Web visits during the first month of the mission. Next month, two NASA rovers are scheduled to hit Mars, and the Web traffic is sure to be even heavier. But this time around, the space agency is benefiting from what’s been learned about managing Internet data in the past six and a half years.