Atlas V vehicles carry a three-digit designation indicating the diameter of the payload fairing, the number of solid rocket boosters, and the number of Centaur engines. Thus, the most basic vehicle—the 401—would have a 4-meter fairing, no solid motors, and a single-engine Centaur. A 552 vehicle would have a 5-meter fairing, five solid rocket boosters, and a dual-engine Centaur. The heavy-lift vehicle consists of three cores strapped together.