The primary objective of “WebPlan” proposal is to provide observers and observatories with novel tools (web-based with backend services) necessary for efficient scheduling of targets for heterogenous, nonuniform sensors (telescopes, radars, laser ranging stations) in the context of ESA’s SST. Efficient scheduling is a complex process dependent on the observers’ objectives and external factors (for example weather conditions, technical problems). The objectives may vary significantly depending on the observing strategy (for example survey, tracking, stare-chase), targets’ general properties (for example orbital elements, size and albedo), cadence (for example orbit or tumbling monitoring), additional instruments used (for example spectrograph or filter wheel), scenario (contingency, re-entry, mission support, launch and early operation, etc.) and many more. Numerous combinations of requirements and external factors are possible, some of them with fluctuations happening over minutes, some over months.