12 The Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) is a multispectral imaging radiometer with 14 spectral bands of VNIR, SWIR and TIR, 60 km imaging swath, and 15-90 m spatial resolution. It was launched on NASA's Terra (EOS AM-1) on December 18, 1999. The ASTER scheduling algorithm and the ASTER Scheduler software was developed in order to maximize the scientific content of each schedule. The Scheduler divides each day into a series of short timesteps (several seconds), for the purpose of prioritization. Prioritization is the process of ranking possible observations, so that the observation opportunities with higher scientific or programmatic value are given higher probabilities of being scheduled. The Scheduler uses the prioritization function to calculate a priority for each potential observation. The prioritization function uses information from all data acquisition request parameters requesting a possible observation. After calculating all the priority, the Scheduler generates 24 hour schedule, namely One Day Schedule (ODS). At each point in this process, the Scheduler checks to make sure that no operating constraints are being violated. Finally, the ODS is transmitted to EOS Operation Center (EOC) every day.