Tomorrow is the 10th anniversary of one of the worst tragedies in America's history. We remember and we mourn, but it's a pleasant thought to know that the memories of those who perished are part of the machinery that is exploring the Martian surface even now.
Honeybee Robotics, collaborating with NASA, were working on the Mars Explorations Rovers Spirit and Opportunity when the towers fell on 9/11. Their offices were located in Lower Manhattan, so they were especially affected. However, in the wake of the disaster, they decided to incorporate some of the rubble into their design as a way of honoring those who died that day.
The American flag you see on the Spirit Rover? That's made of the aluminum salvaged from the destroyed towers. It serves as a cable shield for the rock abrasions tools the rovers use on the Martian soil for their research. And both rovers have worked hard to increase our knowledge of Mars, despite Spirit's demise.