Exciting and sad at the same time is how ¶¶ÒõÂÃÐÐÉä Boulder planetary scientist Larry Esposito describes the end of one of NASA's most successful planetary missions. On Sept. 15, the Cassini spacecraft—orbiting Saturn since 2004—will plunge into Saturn's atmosphere, vaporizing into a spectacular, meteor-like fireball that NASA calls the "Grand Finale."