CBO Evaluates Launch Options

CBO Report: Alternatives for Future U.S. Space-Launch Capabilities, Congressional Budget Office

“In considering manned lunar missions, the Congressional Budget Office (CBO) explored alternatives that would use existing launch vehicles; those that would require minor modifications to the designs of existing launchers (termed “close derivatives”); as well as those that would call for major modifications to existing vehicle designs to develop essentially new and much more capable launchers.”