The 2001 Mars Odyssey mission—so named, in part, to honor the classic science fiction novel 2001: A Space Odyssey by Arthur C. Clarke—was launched by NASA on April 7, 2001, on a Delta II rocket, and successfully inserted into orbit on October 24, 2001. Equipped with three main scientific instruments—THEMIS (Thermal Emission Imaging System), GRS (Gamma Ray Spectrometer), and MAREE (Mars Radiation Environment Experiment)—2001 Mars Odyssey successfully completed its primary scientific mission between February 2002 and August 2004. It began its extended mission on August 24, 2004.