Spacecraft call signs are radio call signs used for communication in crewed spaceflight. These are not formalized or regulated to the same degree as other equivalent forms of transportation, like aircraft. The three nations currently launching crewed space missions use different methods to identify the ground and space radio stations; the United States uses either the names given to the space vehicles or else the project name and mission number. Russia traditionally assigns code names as call signs to individual cosmonauts, more in the manner of aviator call signs, rather than to the spacecraft. The only continuity in call signs for spacecraft has been the issuance of "ISS"-suffixed (or "-1SS", for its visual similarity) call signs by various countries in the Amateur Radio service as a citizen of their country has been assigned there. The first Amateur Radio call sign assigned to the International Space Station was NA1SS by the United States. OR4ISS (Belgium), GB1SS (UK), DP0ISS (Germany), and RS0ISS (Russia) are examples of others, but are not all-inclusive of others also issued. United States In America's first crewed space program Project Mercury, the astronauts named their individual spacecraft. These names each consisted of a significant word followed by the number 7 (representing the seven original astronauts) and were used as the call signs by the capsule communicators (CAPCOMs). In Project Gemini, the astronauts were not officially permitted to name their two-man spacecraft, which was identified by "Gemini" followed by the mission number (3 through 12). A notable exception was that Gus Grissom named his Gemini 3 spacecraft Molly Brown after the Titanic survivor, as a joke based on his experience with his Liberty Bell 7 capsule sinking. This name was used as a call sign by CAPCOM L. Gordon Cooper, without NASA's approval. Starting with the second Gemini flight, Gemini 4, NASA used the Lyndon B. Johnson Space Center (JSC) to house the flight control center. The call sign for this facility was Houston. The Christopher C. Kraft Jr. Mission Control Center, the current flight control facility at JSC, also uses Houston as its call sign. The practice of using the mission number continued through the first two flights of the Project Apollo crewed lunar landing program, Apollo 7 and Apollo 8. But all remaining Apollo missions included two crewed spacecraft (Command/Service Module (CSM) and Lunar Module (LM)) on each flight, which required the use of separate call signs