This paper addresses the application of an autonomous guidance concept to the ascent flight of the reusable launch vehicle Hopper, and to the reentry mission of the space plane X-38. Presently, the guidance requirements with respect to autonomy, accuracy and mission flexibility have been increased steadily for RLV applications. Nonlinear Programming (NLP)-based guidance strategies have been proposed that offer the potential to meet these demands. The autonomous guidance is achieved by combining onboard flight path prediction and NLP methods for flight optimization. Such guidance strategies hold promise for reduced pre-mission analyses for trajectory planning, and for improved adaptability to non-nominal mission conditions. Its applicability, autonomy and performance will be discussed showing numerical results obtained with a flight-simulation environment.