The Common Core Booster (CCB) is an American rocket stage, which is used as the first stage of the Atlas V rocket as part of its modular design. It was also intended that two additional CCBs would be used as boosters on the Atlas V Heavy, however this configuration has not been developed. Use of a Common Core Booster as the first stage of the Japanese GX was also planned; however, this programme was cancelled in late 2009.