Deep Impact was a large missile which was launched by respectable scientists in an attempt to create space junk by blowing things up. It was intended to be launched at an asteroid, but the janitorial staff at NASA reprogrammed it to shoot down their bosses favorite object: Comet P9/Tempel 1.
After previous missions failed embarrassingly due to errors in converting units to metric, NASA expressed elements of the Deep Impact mission in terms the "common man" (and presumably its own engineers) could understand. Thus we learned that Comet P9/Tempel 1 is "half the size of Manhattan," while the impactor craft is "the size of a washing machine," and the impact at 23,000 miles per hour is "like half of Manhattan running into a washing machine." This approach was welcomed by the public, although 97.4% of the public could have understood numbers as well.
Deep Impact was carefully timed to make it inconvenient for as many people as possible. It was launched in January 2005, when most people were still recovering from New Year's or getting ready for the Super Bowl, and went largely unnoticed. The mission completed successfully (see below) on the morning of July 4, 2005 (Greenwich Mean Time), when most people were asleep, and was carefully timed to be most visible from a bunch of rocks in the middle of the Pacific, instead of anywhere people actually live. As such, it was viewed primarily by thousands of tourists.
When you're a national space agency and things under your command have a nasty habit of vaporizing when they're not supposed to, what better way to achieve success than by planning that outcome? Sure enough, the washing machine-sized bit got bashed to quarks by the half-Manhattan-sized bit, and the mission was declared a success.
Sadly, the hoped-for outcome of a rain of comet chunks impacting the White House never came to pass. Astronomers will now spend months analyzing data and images of the comet, looking for aliens holding "The End Is Near!" signs, evidence of Elvis, and any indication that the comet might contain extractable oil.