Trajectory optimization and 4D guidance algorithms can find place in the cockpit of advanced general aviation aircraft. The output of these algorithms could be directed as advisories to the electronic flight display systems. A side effect of this project is the development of advanced large scale, mixed-integer, robust, nonlinear optimization algorithms that are amenable to fast-time computation. High-complexity large-scale optimization problems arise frequently in the industry in the following areas: (1) floor planning, (2) network optimization, (3) allocation problems, (4) supply chain management, (5) transportation, (6) and scheduling applications. 4D trajectories and 4D guidance algorithms have enormous potential to solve several problems in the NAS in an integrated manner resulting in optimal performance. These two can affect improvements in throughput, efficiency and safety. Along, with GPS based navigation and datalink capability, 4D trajectories and 4D guidance systems can define the core of the vastly transformed and improved NextGen air-traffic management system. 4D trajectories and 4D guidance is an inexpensive option to extract the best performance out of the resource constrained NAS in view of projected multi-fold future demand increase. Both these concepts are expected to directly contribute to NASA efforts in designing NextGen concepts both on the ground side and the flight deck side. Trajectory optimization is an area that is of interest to NASA even outside the scope of air traffic management. All flight vehicles sub-sonic commercial aircraft, supersonic and hypersonic space access vehicles, orbiting spacecraft, planetary reentry vehicles, and even planetary surface rovers can benefit from improvements and advancements in optimal trajectory computation technology.