Ground Segment Scheduling System - Design and Implementation

Transcription

1 SpaceOps 2006 Conference AIAA SYSTEMS ENGINEERING SUPPORT SERVICES MUNICH PARIS MONTREAL LITTLE ROCK Ground Segment Scheduling System - Design and Implementation Simona Turco SESS GbR; Muenchener Str. 20; Wessling 1. Abstract Ground resource usage is a key issue in operational environments and a parameter for evaluating mission success. Today, Ground Segment (GS) concepts are expanding to include multi-mission environments and configurations with distributed ground stations and user centers. Typical GS physical resources include communications (e.g. network, data, voice and video services), infrastructure and personnel. Although the scheduling problems for onboard resources and their optimization are a very common topic in the operational world, it is our opinion that not enough attention is dedicated to the scheduling and optimization of ground segment resources. A (SESS) team has: defined a ground segment scheduling concept; implemented a process to drive ground segment scheduling activities; implemented procedures to detail operator/planner actions; designed and developed tools to support detailed resource scheduling. The basic goals are to create applications in line with the operational concept to support the users implementation of it, and to introduce the maximum level of modularity in the tool design to allow customization, future upgrading and support of mission specific configurations. The concept and process definition, while in line with already existing and consolidated concepts for ground segment operations and scheduling, considers aspects of a central ground segment, operating on diverse parallel missions and with distributed data and resource users. This paper presents the development phases of the overall ground scheduling system, from concept and processes to design, implementation and utilization. We concentrate mainly on user requirements collection and on resource conflict/constraint detection. Furthermore, attention was dedicated in the design phase to: importing and exporting capabilities, in order to keep the interface functions of the applications as flexible as possible; resource usage optimization possibilities. The latter is, possibly, the focal point in ground operation environments. It is clear that there are costs associated with resource usage (e.g. communications costs) and that there are trade-offs between costs and optimal allocation of the resources amongst users. These and other aspects are presented in the paper as part of the present and foreseeable future of ground segment scheduling capabilities. The implementation of the complete Ground Segment scheduling function has been put in place for DLR in GSOC (German Space Operations Center) in the context of the development of the Ground Segment function for the Columbus Control Center infrastructure. The scheduling functions for the ground segment are active in GSOC since a couple of years while the tools development is at the final testing stages before full usage in support to the ground segment scheduling and operations. SpaceOps 2006, Rome 1 6/1/2006 Copyright 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

2 1 Ground Segment Scheduling Concept To define the conceptual approach to a Ground Segment planning environment, we started with putting into context the planning functions. The definition of the high level capability needed to execute the Ground Segment (GS) planning tasks, of their interfaces and associated products is part of the concept description. We think about Ground Segment Scheduling as the daily schedule of all activities using ground communication resources. The scope can be enlarged to take into consideration the ground personnel as a resource; personnel availability needs also to be verified and scheduled. The position identified to lead and carry on the GS scheduling activities is the Ground Operations Planner. An approval entity is identified to review the plans and provide guidance for conflict resolution. A list of ground segment scheduling products, with their template and format, has been defined. As a natural correspondence to the flight scheduling concept, also for ground we assumed that the two operational timeframes (long and short term) had to be treated differently since the level of details associated to each ground activity is getting higher the closest it gets to the execution. The scheduling products therefore are updated in each scheduling phase, taking into account the constraints and requirements as they are available. We will address the products and their development in a dedicated paragraph of this paper. We decided to group the ground segment activities in three main categories: Testing and Validation Activities, Operational Activities and Maintenance Activities. They have different attributes and are treated with a different priority in the scheduling processes. In any case, each activity to be scheduled derives from a user request of a ground segment service or from a flight planning activities which has an associated ground distribution task. We started from the analysis of the Ground Segment services, e.g. analysing the details of the ground segment configuration and of its services and communication systems. To each service we associated the subsystems involved in the service provision and distribution. For each subsystem we identified constraints and resource limits that could be quantified and embedded as rules in the software application. Rules are mainly designed in order to support planning conflict detection and scheduling feasibility. The high level categories of ground services are: - video - voice - data The resources (typically all ground subsystems, networks and personnel) associated to each of the above services are the ones to be scheduled for usage and configured for the execution of a ground activity. The processes are defining the interactions between the entities involved in the scheduling activities and the high level functions to be carried on in the ground segment in order to develop a conflict-free schedule of the ground tasks. The following processes are used to define the high level ground segment scheduling functions: - Service Request Collection - Conflict Resolution - Cost assessment - Service Request Scheduling The ground scheduling procedures are defined to detail the processes and, therefore, are derived from them. The procedures are detailing the steps executed in each process and the tools used for the development of the ground scheduling products. The products are distributed to the users, updated in real time and made available to the Ground Controllers that, on console, are responsible for the real time implementation of requirements and execution of the tasks according to schedule. 1.1 Processes and Procedures The ground segment planning processes clarify the flow of activities envisaged in the development of the ground schedules. They are the starting point to define the requirements for the tools designed to support the ground planners in the generation of the relevant ground scheduling products. The focus was put on the definition of scheduling products that would provide: - Communication Service Request - Ground Segment activities overviews Mainly designed for management purposes and long term planning information, publishing and coordination SpaceOps 2006, Rome 2 6/1/2006

3 - Ground Segment Maintenance schedule (Facility Work Plan) To provide a view of all the maintenance activities scheduled on the different facilities of the Ground Segment and affecting the availability of the resources and, as a result, the feasibility of some activities - Ground Communication Schedule The short term schedule of the Ground Segment activities where a more accurate resource check and conflict assessment algorithms need to be applied in order to provide a very detailed view of the scheduled tasks to be used by the operators to configure and run the Ground Segment subsystems in support of operational activities. The tool requirements and design could be done in parallel with the procedure definition. The procedures are listing the step by step operator activities up to the lowest level of detail. They have to consider the interaction between all entities involved in the ground planning execution and the tools usage. Therefore, the definition of the procedures contributes to the assessment/validation of the processes and the refinement of requirements, while the associated operational activities become clearer. The scheduling procedures details are not presented in this paper, while the main processes and the ground scheduling tools are described hereafter Service Requests Collection This process describes the development and management of Communication Service Requests (CSRs). CSRs can be submitted anytime during the operation preparation and real-time operations to request the use of GS communication services in the operational and simulation context. Communication Services requests for the ongoing execution day, are submitted via voice loops and handled by the GCs in real time. The CSR are related to Ground Communication Services only. Nominally, for flight activities no CSR is needed because it is foreseen the generation of an operational input to the Ground Communication Schedule from the STP (Short Term Plan) including the ground resources already scheduled as part of a flight activity. An interaction between the Flight Planning the Ground Planning ensures that coordination and feedback are provided directly, if needed. All the GS authorized users can submit a ground service request. The ground team is in charge of collecting, reviewing, checking the feasibility and submitting a CSR to the Ground Operations Manager for approval. Once a CSR is approved, the Ground Operations Planner schedules it as part of the Ground Communication Schedule (GCS). CSRs requesting non available ground resources are nominally rejected unless their allocated priority outweighs the priority of the conflicting activities. Such a conflict resolution is handled, case by case, by the GOP and closed with approval of the Ground Ops Manager and with a communication of the CSR status to the relevant user/s. The approved CSR are all stored in a Database and archived as operational product. GS users can monitor the status of their requests once submitted and receive notification of comments, approvals for implementation. All approved CSRs are input for the development of the Ground Communication Schedule (GCS). The Ground Communication Schedule is one of the ground scheduling products. The following flow chart presents the nominal CSR process. The process flow can be read in phases associated to the status of the CSR product. The CSR statuses are: - Draft CSR - Submitted CSR the CSR author sends the CSR to the Ground Team to request GS communication resources associated to a certain operational activities. - CSR under Review the submitted CSR content is reviewed and, after first assessment on the completeness and formal correctness of the request, it is provided to the GOP for conflicts assessment. The CSR is sent back to the author when a clarification/update is considered necessary. - CSR for Approval after the GOP has evaluated the possible ground resource conflicts and the impact of the CSR on the future plans, the CSR is sent to relevant authority for approval/rejection. - CSR Approved the CSR signed by the ground manager is officially ready for implementation. The approved CSR is archived and used as input to the development of the Ground Communication Schedule SpaceOps 2006, Rome 3 6/1/2006

4 The process participants are the following: - GS Users all the users located in a center which is connected via Network to the Ground Segment - GCs the Ground Controllers responsible for the configuration and monitoring of all the GS communication resources - GOP the Ground Operation Planner is responsible for the development of the Ground Communication Schedule which is the timeline of the activities using GS communication resources to fulfill the GS operational needs and the user s requests. - Ops Manager - CSR Approval Authority is the GS authority signing the CSR before implementation. Figure 1 CSR Process flow Conflict Resolution The processing of the ground service requests includes a resource usage and availability assessment. During this phase the planners, supported by the planning tools, detect eventual conflicts. This process describes the steps performed in case a conflict arises, from its detection to its resolution. The description of the process is presented in the form of Flow Diagram. SpaceOps 2006, Rome 4 6/1/2006

5 Each block represents a set of steps to be performed, the entity responsible for the execution of the steps is displayed with assigned color code, the association color-position is in the diagram box Legenda. Figure 2 Conflict Resolution Flow Diagram Costs Assessment Input to the scheduling of the Ground Resources is: - CSR (Communication Service Request) request for operations and simulation activities - Test Request request for testing activities - Maintenance Request request for maintenance related activities The above input is submitted, as previously said, to the planners for processing and scheduling. The processing of the input includes a resource usage and availability assessment. From the Ground Segment resources point of view, it is very important also to assess the costs associated to the usage of the communication resources for the activity execution. During this phase, the GOP verifies which communication connections are needed in order to support the requested activity and includes these requirements in the list of resources associated to the service request. The cost assessment is done by the relevant communication engineer on the basis of the requirements included in the ground SpaceOps 2006, Rome 5 6/1/2006

6 schedule. The communication engineer informs the planner about the service requirement for the foreseen network configuration and budget. He/she provides a problem/cost assessment which is submitted to Management for evaluation. The management decision on the implementation of the communication service is used by the planner in the final assessment of the request feasibility. The budget factor is very important in a large ground segment configuration as it is the Columbus Ground Segment. The analysis of the communication requirements and of the associated costs conducted together with the optimization of the scheduling is one of the main challenges of the ground scheduling implementation. An optimized scheduling function should include: - resource configuration and resource limits information; - rules and algorithms to detect errors occurring when a limit is exceeded or a requested configuration is not available These factors were highly driving the scheduling tools development. Once these capabilities are correctly designed and implemented in the scheduling tools, they become a precious help in conducting the cost/feasibility analysis. Nevertheless, the interaction between the entities of the Ground Segment that can assess the various aspects of the problem is still absolutely necessary Service Request Scheduling The Service Request Scheduling is the last process of the overall chain of ground scheduling activities. It is encompassing the generation of a timeline to be used by all entities involved in the ground segment operations. The ground timeline should only show activities that are using available resources, are not exceeding the ground system limits and are requiring non conflicting resource configurations. Due to the fact that a ground timeline is needed to different operators and managers for different purposes in the context of the ground segment handling, more than one timeline product needs to be developed at any given time. To do so without loosing consistency, the activities, grouped into categories, are archived into a common ground scheduling database with their attributes and status information. The scheduling functions act all on the same archive, the content of which is updated according to new submitted requirements, change of activity statuses, change of activity attributes and data elaboration algorithms used for conflict analysis and resource usage assessment. Different views of the timelines are produced to serve different purposes: - long term schedules; - schedule overviews; - daily timelines; - as flown timelines. The level of detail used at different stages of the scheduling process is higher closer to the execution time, when the configuration for the activities is well known and the last check on the resource availability can be performed for the real time allocation. The ground scheduling functions in the following diagram give a view of the high level design for the scheduling tool, which is the first step to translate into software functions the required planning capabilities. SpaceOps 2006, Rome 6 6/1/2006

7 Figure 3 Ground schedule functions overview 2 Ground Segment Scheduling Tools A large Ground Segment entity, with distributed facilities and a number of parallel missions to be handled, requires that the schedule of the activities is based on several factors at once: - complete set of GS requirements; - clearly defined configuration of the ground resources; - identified set of priorities amongst the missions and amongst the activities; - knowledge of the resource limitations; - capability of assessing conflicts; - assessment of alternative plans and re-scheduling rules; - clear information to the operators and users related to the status and to the attributes of the activities; - complete product definition; - easy product update and distribution. SpaceOps 2006, Rome 7 6/1/2006

8 A set of tools to support the Ground Planners in the overall scheduling process is conceived in order to automatically factoring the above scheduling characteristics and to develop scheduling products in an efficient, and optimized, fashion. The tools are used to implement two main ground planning tasks; therefore they can be represented as two high level components: - Request Collection tools; - Ground Scheduling tools. The ground segment scheduling tool has been designed to import and export data in XML format so that we could have flexibility in importing data provided by different and non proprietary applications and in further expanding the elaboration of data with new modules. Tools and Interfaces Flight Planning Ground Segment Service Requests Collection XML Interface DB Interface Ground Scheduling XML Interface Ground Segment Resource Utilization Figure 4 Tools overview The flight planning and the ground segment resource utilization are systems outside of the scope of the ground planning functions but are representing their main external interfaces. The service request collection tools and the ground scheduling tools (including their interface capabilities) have been already implemented and tested. 2.1 Tools - User Interfaces As far as tool user interfaces, the following main functions are implemented: - service requirements collection interfaces providing all external users an interface for submitting their requests for the usage of the ground segment resources in an easy and clear way and providing the ground planners with a unique source of input to a common database where all requests are archived and used for the necessary processing activities before becoming scheduled tasks on the ground timeline; - publishing of status providing all external users with feedback on the status of their requests so that they are allowed to follow the scheduling process and, in predefined circumstances, intervene; - publishing of ground scheduling products. A few snapshots are presenting, in the remaining of this paragraph, the above mentioned user interfaces. The tools interfaces presented hereafter are the ones customized and currently in use at the Columbus Control Center in Germany. SpaceOps 2006, Rome 8 6/1/2006

9 Figure 5 Ground Segment Service Request Collection 1 Figure 6 Ground Segment Service Request Collection 2 SpaceOps 2006, Rome 9 6/1/2006

10 Figure 7 Ground Segment Service Request Status Figure 8 Timeline view SpaceOps 2006, Rome 10 6/1/2006

11 Figure 9 Activity view 2.2 Configuration Capabilities The Ground Segment configuration module allows the Ground Planners to save the Ground Segment Configuration as part as the tool setting and, when the scheduling checks are performed, the algorithms are using these data in the rules to verify the possibility of scheduling an activity in terms of conflict detection and resource availability. The fact that the configuration is not hard coded gives an extra degree of flexibility in the usage of the tool ensuring that changes in the ground segment configuration can be taken into account in the scheduling activities and that the tool can be easily configured to support ground scheduling of facilities designed differently, with different systems and resources, therefore with different scheduling constraints. SpaceOps 2006, Rome 11 6/1/2006

12 Figure 10 Ground Segment Schedule Configuration 2.3 Resource Usage Optimization Resource optimization is possible with the support of the ground scheduling tools. It helps reducing communication costs and makes the schedule of activity more efficient. Our approach is to assess the activity requirements, carefully modeling the level of resource usage over time and aim at scheduling, especially for what concerns the usage of communication links, parallel activities that maximize the network utilization. The tools are supporting this task with the automatic assessment of the resource availability and feasibility of parallel activities with respect to the ground segment configuration constraints, which can be easily represented in the tool configuration tables. The remaining optimization work is left to the ground planner, who is coordinating with the external entities responsible for the activities and to the communication engineer, who is placing the orders to the service providers and assessing the communication costs associated to the activities. We are currently working on the possibilities to include communication cost calculation in the scheduling tool and to develop interfaces for the automatic generation of relevant service requests to be sent to external providers. 3 Conclusions The complexity of the Columbus Ground Segment has provided the perfect environment to design a ground scheduling system that encompasses the issues relevant for the configuration and usage of resources common to many other ground segment entities. The deriving scheduling capabilities (processes, procedures and tools) are therefore easy to adapt and use in different contexts, where similar scheduling problems need to be addressed and solved. SpaceOps 2006, Rome 12 6/1/2006

13 There is a wide margin for further development of the currently existing modules composing our system. We plan to continue the effort of improving our ground scheduling system focusing, in the next future, on identified specific areas: - completion of the software functions under development; - development and/or integration of algorithms to improve the automatic placement of activities in a timeline; - development and/or integration of algorithms to improve the resource conflict assessment. The goal is also to reduce the number of manual tasks in the ground scheduling process, hence making the scheduling activities less time consuming and error prone. SpaceOps 2006, Rome 13 6/1/2006