for each vehicle when they flew independently of each other. For this reason, NASA permitted the three-man crews to name both crafts for each of their missions, and these names were used as the call signs. A temporary exception to this was on the first Moon landing, Apollo 11: since the first Moon landing site was in the Sea of Tranquillity, the call sign Tranquillity Base was used while the LM was on the lunar surface. Before and after the independent flight of the LM, the mission number was used as the call sign. The Apollo call signs were: For project Skylab, the practice returned to using the mission name as the spacecraft call sign, since the Skylab station was left uncrewed while the shuttle vehicle (an Apollo CSM) carried a crew to it or back to Earth. The six Space Shuttle orbiters were given individual names (they also had letter-and-number callsigns) by NASA, which were used as the call signs: Enterprise (OV-101, which was not fitted for spaceflight), Columbia (OV-102), Challenger (OV-099), Discovery (OV-103), Atlantis (OV-104), and Endeavour (OV-105). Of these, Columbia, Challenger, and Endeavour had previously served as call-signs of Apollo spacecraft. SpaceX Crew Dragon capsules use two calls signs. Dragon is used as a generic call sign, particularly if the capsule has not been named. The name of the spacecraft is also used as a call sign. The name and call sign of each Crew Dragon, as given by the crew of the spacecraft's initial mission, is: Endeavour, which was named for the space shuttle Endeavour, had previously served as call signs for both an Apollo spacecraft and the spacecraft's namesake shuttle. The name Freedom honors Freedom 7, the space capsule used by Alan Shepard's Mercury Redstone 3, the first United States human spaceflight mission. The call sign SpaceX is used by the Crew Operations and Resources Engineer (CORE) (the SpaceX equivalent of the CAPCOM in Houston) at SpaceX Mission Control (MCCX) in Hawthorne, California. Russia (including the former Soviet Union) The spacecraft of the Soviet Union were not individually named, nor are those of Russia today. Only the general type of spacecraft, for example, "Vostok," "Soyuz," or "Soyuz-T" is publicly announced after launch, usually followed by the number of the flight of that type of spacecraft. The Soviet and now Russian call signs are more nearly code words, and so are not disclosed before launch. Each