Studies of space transportation in recent years have spanned a wide range of issues, from the pressing problems of recovering from specific failures and meeting budget limits to how the U.S. space program might develop over the next 50 years. However, there have been few studies that compare both means and ends. This report evaluates launch vehicle combinations capable of meeting a range of U.S. space traffic needs between 1990 and 2010. The evaluation aims to clarify alternatives available to the United States in pursuing potential national goals and to increase understanding of the implications of those alternatives. The study methodology involved six steps: (1) review the space transportation planning process, current issues, and political factors; (2) define alternative levels of U.S. space traffic demand for 1990-2010; (3) create various combinations of existing and proposed launch vehicles to fulfill each demand level; (4) calculate costs and uncertainties; (5) interview space transportation planners on institutional criteria for evaluating launch vehicle mixes; and (6) evaluate launch vehicle options and recommend preferred U.S. actions in space transportation planning and procurement.