cassette recorders intended to allow them to make observations during the mission. The Apollo9 crew was the first to be allowed to bring music mixtapes, one each, that could be played in that device. McDivitt and Scott preferred easy listening and country music; Schweickart's cassette tape of classical music went missing until the ninth day of the ten-day mission, when it was presented to him by Scott. After the Gemini 3 craft was dubbed Molly Brown by Grissom, NASA forbade naming spacecraft. The fact that during the Apollo9 mission, the CSM and LM would separate and need different call signs caused the Apollo9 astronauts to push for a change. In simulations, they began to refer to the CSM as "Gumdrop", a name inspired by the CM's appearance while in the blue protective wrapping in which it was transported from the manufacturer, and the LM as "Spider", inspired by the LM's appearance with landing legs deployed. Personnel in NASA public relations thought the names were too informal, but the call signs ultimately gained official sanction. NASA required more formal call signs for future missions, starting with Apollo 11. Life Support System backpack The Extravehicular Mobility Unit (EMU) backpack flew for the first time on Apollo9, used by Schweickart during his EVA. This included the Portable Life Support System (PLSS), providing oxygen to the astronaut and water for the Liquid Cooling Garment (LCG), which helped prevent overheating during extravehicular activity. Also present was the Oxygen Purge System (OPS), the "bedroll" atop the backpack, which could provide oxygen for up to roughly an hour if the PLSS failed. A more advanced version of the EMU was used for the lunar landing on Apollo 11. During his stand-up EVA, Scott did not wear a PLSS, but was connected to the CM's life support systems through an umbilical, utilizing a Pressure Control Valve (PCV). This device had been created in 1967 to allow for stand-up EVAs from the hatches of the LM or CM, or for brief ventures outside. It was later used by Scott for his lunar surface stand-up EVA on Apollo 15, and for the deep-space EVAs by the command module pilots of the final three Apollo flights. Mission highlights First through fifth days (March 3–7) Originally scheduled to launch on February 28, 1969, the liftoff of Apollo9 was postponed because all three astronauts had colds, and NASA did not want to risk