In 2001, the National Aeronautics and Space Administration (NASA) began undertaking a new effort--the Space Launch Initiative (SLI)--to develop a new generation of space transportation vehicles. SLI is expected to result in development of the second generation of reusable launch vehicles, the space shuttle being the first generation. NASA plans to define basic requirements for its second-generation reusable launch vehicle--that is, what the crew size will be, what the payload capacity will be, and what designs or architectures are worth pursuing--by November 2002. However, considerable challenges must be addressed before NASA can accomplish this. First, NASA has to complete a reassessment of its overall space transportation plans. Second, NASA is currently reassessing the future of the International Space Station. The decisions it will make as part of this evaluation, such as how many crew will operate the station, will have a dramatic impact on NASA's requirements for a second-generation vehicle. Third, NASA needs to decide whether the SLI program will be developed jointly with the Department of Defense (DOD) and, if so, how can it accommodate DOD's requirements for a reusable launch vehicle. Until NASA finalizes its basic requirements for SLI, it cannot implement management controls that are essential to predicting what the total costs of the program will be and to minimizing the risks with NASA's planned initial investment of $4.8 billion. It is important for NASA to implement management controls for SLI as soon as possible, so that it can provide its managers and Congress with the information needed to ensure that the program is on track and able to meet expectations.