MOIS Scheduler
The MOIS Toolset
MOIS is an integrated set of tools for spacecraft mission preparation and execution. The system has been adopted by satellite manufacturers as well as flight operators. MOIS is already in use in a variety of programs. Developed in close collaboration with operations engineers, AIV engineers and ground and space segment developers, MOIS addresses the real issues that are key to successful mission preparation.
The MOIS Scheduler
The MOIS Scheduler is a constraints checking tool based on a generic planning model. It provides a resource and constraints modelling capability and can be tailored for specific applications:
Planning of On-Board Schedules – The scheduler planning engine uses constraints such as ground station availabilities, or flight dynamics and orbital events or User Operations Requests. The MOIS Scheduler then establishes a conflict-free schedule that can be exported into mission specific executable schedules, or a time-tagged list of commands.
Planning of Station Allocation – In its tailoring for the ESTRACK Scheduling Office at ESOC, the MOIS Scheduler imports ground station allocation prediction schedules from various stakeholders and information sources such as the ESTRACK Management & Scheduling System (EMS). It allows the editing and saving of the compiled schedules into a coherent dataset for all ESA missions and all ESA stations and commits these changes back to the EMS. The scheduler is customised to produce and distribute the conflict-free stations allocations to the missions and to the ground controllers for their daily activities and activity reporting. The scheduler is also capable of collecting the tracking activity for evaluation and statistics to generate operations reports containing information such as downtimes, anomalies, station usage and mission recharges.
Planning and Execution of Ground Operations Automation – The Scheduler does not only establish a schedule of activities in an off-line preparation mode, but it can also act as a real-time execution system by linking to the MOIS Automation components. The Scheduler runs its schedule requesting procedure executions and receiving execution statuses and then visualises the overall status of all running procedures in a high-level Gantt view. The procedure execution details can be viewed with MOIS Validator, which can be called up for a specific procedure from the scheduler MMI if needed.
Figure 1 shows the integration of the Scheduler into the 3 groups of MOIS components Preparation, Library and Automation. In order to establish the plan, the scheduler references the dataset prepared by the Preparation tools; these are the procedures established by the Writer & Flowcharter and, for the generation of On-Board Schedules, it accesses the Spacecraft Database that is maintained by the DB Editor. In its execution mode, the Scheduler links to the Automation environment with which it schedules and controls the procedure execution.
The MOIS Scheduler Resource Model
The generic scheduler resource model plans User Operations Requests containing timing and resource constraints.
The timing constraints can be expressed against an absolute time or events. For both timing constraint types, the User Operations Requests can specify a number of repetitions with a delta time. The event constraint can be specified against a specific instance of an event or against an event type.
The resource constraints model the tailored target system. Resources can be of type unique, status or capacity. Constraints on unique resources attempt to reserve the resource for the duration of the procedure (example: a ground station for a spacecraft). Constraints on status resources check that a given resource is in the specified state for the duration of the procedure (example: an instrument in a specific mode) and finally constraints on a capacity resource set a consumption of a capacity limit in terms of a consumption rate (example: bits/sec on storage) or a fixed value (example: volts on power).
Scheduler Pictures
Figure 2 – The MOIS Scheduler Planning MMI showing 2 sub-windows of its main display. The topmost window contains a Gantt view of the planned activities together with a list of the resource constraints and their check status individually for each procedure. The second window visualises the overall resource consumption calculated from all procedures in the plan.
Figure 3 – The MOIS Scheduler Execution MMI is an animated Gantt view and shows (from top): Events (FDE), scheduled procedures (SORs) & their links to the events and pass information. The tabular view is a time ordered list of the same procedures showing (from left): scheduled time, procedure name, current execution status & executing step and execution result when the procedure has finished execution. The MMI has a supervising role, where procedures can be paused, resumed, aborted, viewed or manually inserted & started.
