Aerospace giants are already prepared to compete for lucrative contracts in NASA’s next big step toward the moon and Mars but they aren’t eager to start from scratch on a new rocket to take it there. Rather than a crash program to produce a new super-rocket, like the Saturn 5 moon rocket in the 1960s, this new initiative — which NASA is a year or more away from detailing — is more likely to use existing technology from space shuttles and expendable rockets.