Planning and scheduling systems organize “tasks” into a timeline or schedule. Tasks are logically grouped into containers called models. Models are a collection of related tasks, along with their dependencies and requirements, that when met will produce the desired result. One challenging domain for a planning and scheduling system is the operation of on-board experiments for the International Space Station. Another domain is planning and scheduling the tasks to be done by humans on the surface of the Moon, on Mars, or in a trans-Mars spacecraft. In these domains, the equipment used will be among the most complex hardware ever developed; the information sought will be at the cutting edge of scientific endeavor; and the procedures will be intricate and exacting. Scheduling will be made more difficult by a scarcity of resources. The models to be fed into the scheduler must describe both the complexity of the tasks and procedures (to ensure a valid schedule) and the flexibilities of the procedures and the equipment (to effectively utilize available resources). Ideally, remote platforms should be autonomous — the crew should schedule their own tasks. The great distance from earth, the long-duration of the mission, the need to cut cost, and the desire for autonomy call for an operations concept that is based on an automatic scheduler and a modeling schema that captures all the requirements.