The Multi-Mission Satellite Operations at the NSPO Ground Segment

Transcription

1 P Road, Conference (Hosted and organized by ESA and EUMETSAT in association with AIAA) AIAA The Multi-Mission Satellite Operations at the NSPO Ground Segment NSPO, 8F, 9 Prosperity 1P Shin-Fa Lin, Tim Lin, John Wang, Marty Pong, Chia Soong st Science-Based Industrial Park, Hsin-Chu City, 30078, Taiwan, R.O.C. Shin-Fa Lin s address: sflin@nspo.org.tw, telephone: Ext. 1572, fax number: The National Space Organization (NSPO) of Taiwan had successfully launched a series of three (3) satellite missions since The first satellite mission was decommissioned in June 2004 after near 6 years of mission operations. The other two satellite missions are currently being controlled and operated from the Satellite Operations Control Center (SOCC) of NSPO Ground Segment (NGS). The under controlled and operated two missions include one remote sensing satellite mission and one satellite constellation mission with 6 micro-satellites for collecting the atmospheric data for weather prediction, atmospheric studies, and space weather monitoring. Since the operational diversity, the harmony of the multi-mission operations in all aspects is significant in one SOCC with one operations team. This paper describes how the ground system architecture and services designed for the multi-mission operations support. The trade off study on the database design for the constellation satellite is depicted. This paper also addresses how the ground system resources allocated for supporting different operational phases within two missions. The communication stations assignment, ground networking architecture, and data distribution routes for these two missions are all described. For supporting multi-mission, the operations tools are helpful for the operators with appropriate mission planning. How the supporting tools used in the SOCC and integrated with the mission planning software will be depicted. To operate 7 (1+6) satellites with one team while the satellite constellation is still in orbit deployment phase, the callout mechanism for the satellite safety is critical. To complete the efficient callout mechanism, the event triggering is implemented in the ground control system in the SOCC and will be described in this paper as well. This paper also addresses the difficulty encountered when the manpower need to be allocated to support two missions with different operational phases using the same operations team. The lesson learned from the multi-mission operations support will be delineated as a summary. Heidelberg, Germany May 12 16, of 15 Copyright 2008 by Shin-Fa Lin, NSPO. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

2 1. Introduction The National Space Organization (NSPO) of Taiwan had successfully launched a series of three (3) satellite missions since The first satellite mission, FORMOSAT-1 (also named as ROCSAT-1), is a low earth orbit (LEO) scientific satellite designed for a mission of conducting scientific and technological experiments. It was successfully launched in January 1999 and was de-commissioned in June 2004 after five and half years of mission operations. The other two satellite missions are currently being controlled and operated from the Satellite Operations Control Center (SOCC) of NSPO Ground Segment (NGS). The under controlled and operated two missions include one remote sensing satellite mission, FORMOSAT-2, and one meteorology satellite constellation mission, FORMOSAT-3. The FORMOSAT-2 satellite was successfully launched by Taurus XL from Vandenberg AFB at 17:47:03 UTC on May 20th, 2004 and had been on commission to take remote sensing images and perform experiments since entering into normal mission operations phase. It is a three-axis stabilized satellite and is being operated in a circular sun-synchronous orbit of 891km altitude with an inclination of over a five years mission lifetime. The primary goals of this mission are remote sensing applications for natural disaster evaluation, agriculture application, urban planning, environmental monitoring, and surveillance over Taiwan area and its surrounding oceans. The Remote Sensing Instrument on board the FORMOSAT-2 is an electrical-optical type of sensor with spectral bands in the visible (VIS) and near infrared (NIR). The spectral bands include panchromatic and four multi-spectral bands. The ground sampling distance (GSD) is 2 m and 8 m for panchromatic band and VIS/NIR bands, respectively. The swath is 24 km for all panchromatic and multi-spectral bands. In addition, the FORMOSAT-2 is carrying a scientific instrument, the Imager of Sprites Upper Atmospheric Lightning (ISUAL), to perform upper atmospheric lightning researches. The FORMOSAT-3 mission, a constellation of 6 micro-satellites, was designed to support the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) payload suite. The 6 micro-satellites constellation had been successfully launched by Orbital s Minotaur launch vehicle on April 15th, 2006 and had been continuously collecting atmospheric data and conducting the orbit deployment. The launch vehicle placed the constellation into a circular LEO with an altitude of 500 km at 72 degrees of inclination. Following checkout at the insertion parking orbit, the constellation satellites then were intermittently raised to an altitude of 800 km final mission orbit and deployed to six orbit planes with one satellite in each plane over a 13- month period. The orbit planes were phased around 24 apart in ascending node. The FORMOSAT-3 mission is to collect atmospheric sounding data for scientific research and operational testing. It is now aiding in the prediction and characterization Heidelberg, Germany May 12 16, of 15

3 of Earth s weather pattern using the collected data. The mission design lifetime is two years with a goal of five years. Each FORMOSAT-3 spacecraft supports a GPS Occultation Experiment (GOX) receiver, a Tiny Ionospheric Photometer (TIP), and a Tri- Band Beacon transmitter (TBB). The GOX payload collects rising and setting occultation soundings of GPS spacecraft that appear within its fore and aft limb antenna beams. The TIP counts ultraviolet photons emitted from the F2 layer of the atmosphere directly below the satellite. Baseline operations for the TIP mission occur during the eclipse portion of the orbit. The TBB transmits its UHF, VHF & L-Band signal to a string of ground-based receivers, where the science data is collected. Since a great diversity of operations, the harmony of the multi-mission operations in all aspects is significant in one Satellite Operations Control Center within NSPO Ground Segment with only one operations team. 2. Ground System Architecture for Multi-Mission Operations The NGS consists of one SOCC, three S-Band TT&C stations (TS1, TS2 and TS3), one X-Band Antenna System (XAS) and one Image Processing System/Center (IPS/IPC). The SOCC is the central node of the ground system from which all mission operations and data handling functions are conducted. It functions for real-time operations, planning & scheduling, orbit navigation, science data pre-processing, satellite performance monitoring, and trend analysis. The S-Band TT&C stations perform TT&C functions for FORMOSAT-series satellites. The TT&C functions include tracking the satellite, uplinking command and data to satellite, and receiving telemetry and science data from the satellite. The XAS and IPS/IPC perform X-Band image data reception and image data processing, respectively, for earth observation satellites. Figure 1 and 2 illustrate the NGS Configuration and its associated Facility, respectively. The ground system architecture and services designed not only can support single satellite mission, it can also fulfill the needs for the multi-mission operations support Figure 1. NGS Configuration Heidelberg, Germany May 12 16, of 15

4 Figure 2. Facility of NGS The following paragraphs delineate the communication stations assignment, ground networking architecture, and data distribution routes of the ground system for supporting one remote sensing satellite mission, and one meteorology satellite constellation mission: To support remote sensing satellite mission, the baseline ground configuration includes SOCC, domestic TT&C stations, XAS and IPS/IPC in the NGS. However, in order to fulfill the international market need and to maximize the on-board SSR memory usage, the polar receiving stations and other direct receiving stations are all integrated into the FORMOSAT-2 operational system. Figure 3 shows the FORMOSAT-2 System Architecture and its Operational Data Flow. Since the FORMOSAT-2 is a remote sensing satellite with one science instrument onboard, the SOCC will combine the tasking request from the NSPO IPS as well as the science activity request from ISUAL Science Data Distribution Center (ISUAL SDDC) to generate the command loads after completing the satellite and ground resources check. The command loads are then uplinked to the satellite through domestic TT&C stations during the satellite contact time. In case the emergency situation, the Remote TT&C Station in Kiruna will be requested for the backup support via ISDN link. The imaged data can be either directly downlink when imaging taken or stored in the on-board SSR until the visibility of the receiving ground stations. Currently in addition to NSPO XAS, there are two Polar Stations and other Direct Receiving Stations are scheduled for the image data reception. Each receiving station are integrated with one IR2T (International ROCSAT-2 Terminal, ROCSAT-2 is original name of FORMOSAT-2) for the Level 0 processing after acquiring the image data dump from FORMOSAT-2. Heidelberg, Germany May 12 16, of 15

5 Figure 3. FORMOSAT-2 System Architecture and Operational Data Flow The FORMOSAT-3 System Architecture is shown in Figure 4. The SOCC of NGS monitors and commands the satellite using real-time health and status data. Command files are generated by the SOCC, forwarded to the TT&C site, and transmitted to intended satellite on an uplink data stream. There are on average two contacts per satellite with the TT&C sites in Taiwan per day. That is statistically, the ground station will communicate with one of the satellite every 100 minutes. Each contact lasts 5 to 12 minutes at a ground station elevation angle of 10 degrees or better. The satellite is designed with the capability of autonomous operations and will enter automatically into a safe mode when experiencing any kind of contingency. The operational orbits allow the satellite to collect soundings data worldwide with a statistically uniform coverage spatially and temporally. The state-of-health (SOH) data of the entire satellite bus and the science data collected by the payloads are stored and downlinked at a maximum rate of 2.0 Mbps via an S- Band TT&C channel at either northern latitude ground stations when in view of the ground station. Real-time and stored SOH data is multiplexed with the payload data stream, and this SOH data will be supplied to the SOCC during each and every downlink event at the northern latitude sites. The real-time and stored SOH data is also downlinked each day via the same S-Band T&C channel at all Taiwan contacts. Two science data processing centers will be established for scientific data receiving, processing, and distribution to users: the COSMIC Data Analysis and Archival Center (CDAAC) in Boulder and the Taiwan Analysis Center for COSMIC (TACC) in Taiwan. The data from worldwide TBB stations and RT Fiducial Network will be sent to CDAAC for further processing. Heidelberg, Germany May 12 16, of 15

6 Figure 4. FORMOSAT-3 System Architecture 3. Database Design for the Constellation Satellite In nominal situations, each satellite has its own dedicated Satellite Stream and also a dedicated database. Prior to a real-time pass of a specific satellite, the operator invokes the dedicated Satellite Stream, which then automatically ingests in the dedicated database flat file to complete the initiation process. After the initiation process completes, the operator sets up the directories and files for the storage of various satellite-related data. Normally, once the directories are set, they need not be changed again during the runtime of the Satellite Stream. But typically the data storage files will need to be reset again each time before a new real-time pass is coming. As a result, different satellite-related data will be stored into different directories and different files. In other words, data from different satellite will by no means be wrongly stored in the same file. If two or more real-time passes of different satellites are coming in tightly close to each other, the operator will bring up the correspondent Satellite Streams and set up the appropriate data storage directories and files prior to those passes. Then, during each pass of different satellite, the operator only needs to switch to the relevant Satellite Stream to control the now-passing satellite, and data belonging to different satellite will be separated automatically into different files. Since the six (6) micro-satellites of constellation mission FORMOSAT-3 are identical in their telemetry and command except for the Spacecraft ID, it is theoretically feasible to establish only one dedicated Satellite Stream and only one dedicated database flat file for all the six (6) satellites of the constellation. In this one-for-all configuration, control Heidelberg, Germany May 12 16, of 15

7 system software sees all the six (6) satellites as one and the only satellite. Database maintenance jobs are therefore simplified. Computer system loading is reduced since only one Satellite Stream is needed when different satellite passes of the same constellation are coming in closely. However, if all the satellites of the constellation share one Satellite Stream and one database flat file, Spacecraft ID needs to be set correctly by directives each time the operator switches to operate a different satellite of the same constellation to make sure the Satellite Stream generates correct commands, or else the satellite will not accept any command. Besides, before the telemetry of a different satellite of the same constellation comes in, the original data storage files for the previous satellite of the constellation need to be closed, and directories and files need to be set up again to make sure that data belonging to the upcoming new satellite will be stored in the right place. Otherwise, data relating to different satellites will be wrongly stored in exactly the same files, which will cause incorrect data processing and data analysis results. In addition, if the two passes of different satellites of the constellation are tightly close to each other (which occurs frequently during L&EO phase) and the time span to close and reopen data storage files takes a relatively long time, it may result in loss of precious satellite-related data. Moreover, since each satellite of the constellation is a unique individual that experiences different aging process and has its own health conditions and issues, we cannot rule out the possibilities to adjust database (e.g. limits, transfer functions, etc.) to meet new requirements of mission operations of a specific satellite in the constellation. Therefore, it is more flexible in mission operations point of view to let each individual satellite of the constellation to have its own dedicated database. Furthermore, since computer technology has come a long way, it is not really an issue nowadays to reduce the computational loading of the system hardware, especially on the ground. After careful consideration to the above-mentioned trade off study, NSPO decided to adopt the traditional way, that is, to let individual satellite have its own dedicated Satellite Stream and its own dedicated database. From near two years of mission operations experiences, since each satellite of the constellation experiences different environmental aging process and result in its own health conditions and issues, it is very often to adjust the database (e.g. limits, transfer functions, etc.) to fulfill the needs of the mission operations. If it is not the case to use the database design with each satellite in the constellation has a dedicated Satellite Stream and a dedicated database for the FORMOSAT-3, the mission operations may not be so smoothly. Table 1. Database Tradeoff Each satellite in the constellation has a dedicated Satellite Stream and a dedicated database Pros Spacecraft ID is automatically set Data relating to different satellite will be separated automatically into All satellites in the constellation share one Satellite Stream and one database Database maintenance jobs are simplified Computer system loading is reduced Heidelberg, Germany May 12 16, of 15

8 different files Satellite-related data won t be lost in the case of tightly close passes More flexible in mission operations point of view Cons Database maintenance jobs cannot be simplified Computer system loading is higher 4. Mission Planning Tools Spacecraft ID needs to be set manually by operator, which increases the risk of operator error Data relating to different satellites may be wrongly stored in the same files due to operator error Satellite-related data might be lost in the case of tightly close passes Less flexible in mission operations point of view For supporting multi-mission, the operations tools are helpful for the operators with appropriate mission planning. The main issue in the mission planning system is how to keep track of satellite on-board resources and allocate ground recourses. For the single mission operations, the mission planning system only needs to allocate available ground recourses without temporal and manpower constraints for the mission operations team. However, for the multi-mission operations, the mission planning requires allocating conflict-free ground resources for multi-missions based on the finite time and manpower. For allocating ground resources of two missions with 7 (1+6) satellites together, the Satellite Contact Auto Selection Utility is designed, implemented and integrated with the current mission planning software. Figure 5 shows the Satellite Contact Auto Selection Utility and its production of conflict-free ground resources allocation used for the requests to all the S-Band TT&C stations and X-Band receiving stations. The design of the utility will be depicted in the following and the integration between the planning utility and the current mission planning software will be described as well. Heidelberg, Germany May 12 16, of 15

9 Figure 5. Satellite Contact Auto Selection Utility Concept The Satellite Contact Auto Selection Utility can be divided into two phases. One is the constraint build-up phase and another one is the contact selection phase. The former collects the operational criteria, such as ground station turnaround time and ground station unavailable time, and transfers them into the constraints. The latter picks the available ground stations based on the constraints. After completing these two phases of processing, the conflict-free allocation for ground resources of two missions will be generated and the ground resources will be transferred into the activities for the latter scheduling processing. UConstraint Build-up PhaseU: (1) Define ground station turnaround time (See Figure 6) The ground station turnaround time is enforced to set between two satellite contacts. The criterion is used for the mission operations team to handle two consecutive satellite contacts. The team requires sufficient time to prepare operational commands and procedures before satellite contact and to archive the dump data and log information after satellite contact. There are two cases for the ground station turnaround time as described below: (a) Time between two telemetry (only) contacts or between one telemetry (only) contact and one commanding contact (b) Time between two commanding contact (2) Define the upper limit of SSR capacity (See Figure 6) The utility measures the usage of solid-state recorder (SSR) by time for each satellite of the constellation mission. To achieve optimization, the data in the SSR shall be downlink within the upper limit time. (3) Define the ground stations (See Figure 6) Heidelberg, Germany May 12 16, of 15

10 The utility provides the available lists to define the ground stations that are to be used during the ground station selection phase. Figure 6. Constraint Build-up GUI (4) Define the ground station unavailable time (see Figure 7) Unavailable time indicates a time period where the ground station is unavailable for supporting mission operations. The utility provides the unavailable timetable for the ground station by entering the time values. The unavailable time could be divided into two types: (a) Commanding Operations unavailable time Commanding unavailable time means during a time period the ground station cannot support command uplink operations but can still have telemetry downlink. (b) Telemetry Only Operations unavailable time Telemetry only unavailable time reveals during a time period the ground station supports neither command uplink nor telemetry downlink operations. In brief, the ground station is unavailable for usage during a period. Heidelberg, Germany May 12 16, of 15

11 Figure 7. Ground Station Unavailable Time Settings (5) Define the mission priority Definition of priority between multi-missions is required for measuring resources allocation if there has conflict. UContact Selection PhaseU: (1) Define the satellite sequence of constellation mission The definition of satellite sequence is essential and given as the entry point for the firstround picks of contact selection. For example, if the sequence of satellites is [FM2 FM4 FM5 FM3 FM6 FM1], in the first-round the utility always picks FM2 first and then searches FM4 subsequently. The next several rounds the utility picks contacts based on the remaining SSR capacity of each satellite. (2) Check constraints The utility lists all available satellite contacts during the given period of time. All of satellite contacts are examined by the constraints defined in the Constraint Build-up Phase and the violated one will be eliminated. (a) Ground station turnaround time The time constraint will be verified in the each contact selection. (b) Upper limit of SSR capacity After the first-round pick of contact selection, the utility uses upper limit of SSR capacity to evaluate the remaining SSR capacity of each satellite. The least capacity the satellite has the most possible to be selected. (c) Ground station unavailable time The time constraint will be validated to filter out the restricted contacts. Until now, the selected contacts are all available for the telemetry (only) operations of mission operations. (3) Select the applicable commanding contacts Due to the complicated operations of satellite command uplink, it needs more time for mission operations team to prepare the commands load and procedures before the contact and to archive dump data and telemetry after the contact. All of telemetry (only) contacts are examined by the constraints and the violated one will be eliminated. (a) Ground station turnaround time The time constraint will be verified to be sure the time between two commanding contacts is sufficient to prepare the operations. (b) Ground station unavailable time The time constraint will be validated to filter out the restricted contacts. After the successful processing of two phases in the Satellite Contact Auto Selection utility, the planning satellite contacts are generated and will be used for the subsequent scheduling processes. Heidelberg, Germany May 12 16, of 15

12 UIntegration The Satellite Contact Auto Selection Utility is integrated into the current mission planning system successfully. The utility uses the same developing tools as the current mission planning system. The design architecture of the utility is compatible with the current mission planning system as well. Therefore, the data between the new utility and the current mission planning system could be shared to each other. The output of the Satellite Contact Auto Selection Utility is the scheduled contact activities. The activities could be scheduled and verified for the scheduling processes in the mission planning system. The advantages of the Satellite Contact Auto Selection Utility are to facilitate the mission operations team to select domestic/and Remote TT&C stations for contacts automatically and efficiently, as well as to make sure it s conflict-free for contacts to support multi-mission operations. The utility integrates all related constraints of the contact selection, converts the constraints into quantification parameters, and provides graphics user interface (GUI) for users to adjust the parameter values. The utility makes the operations processes easier and reduces the mistakes without manual interference. 5. Callout Mechanism and Triggering System To operate 7 (1+6) satellites with one team while the satellite constellation is still in orbit deployment phase, the callout mechanism for the satellite safety is critical. To complete the efficient callout mechanism, the event triggering is implemented in the ground control system in the SOCC. The event triggering, Auto-Trigger Process, is achieved by using the EPOCH STOL (Satellite Test and Operations Language) to establish a set of STOL procedures that will be initiated once the relevant EPOCH Satellite Stream has started. The key directive used in the STOL is the TRIGGER directive, which will check the specified telemetry point against its limit, and automatically execute the specified STOL procedure when the telemetry point is out of limits. Auto-Trigger Process will send s and cell phone message to engineers for status reporting. In case of contingency, the whole mission operations team and satellite engineers will be called back to SOCC to take actions for the satellite recovery. Figure 8 illustrates the callout mechanism and triggering system used in NGS for supporting the multi-mission operations. With the combination of the Callout Mechanism and Triggering System, the operators can concentrate their attention on the continuous satellite control and operations. The workload and operator error are reduced significantly as well. Heidelberg, Germany May 12 16, of 15

13 Figure 8. NGS Triggering System 6. Operations Conflict during the L&EO Phase The impact to single operations team to operate and control multi-mission satellites during the Launch and Early Orbit (L&EO) phase is very serious. It is especially critical to the real time operations position such as Operations Controller (OC, who is responsible for operating the ground stations) and Satellite Analyst (SA, who is responsible for monitoring and control the satellite directly). For example, during the L&EO phase of FORMOSAT-3, both the FORMOSAT-2 and FORMOSAT-3 are in contact very often. Therefore, it is necessary to allocate the ground resources depends on the satellite priority. To make sure there is no confusion and conflict in antenna stations, the team had developed automation scripts and display pages to distinguish the FORMOSAT-2 from FORMOSAT-3. In addition to the ground resources, the manpower allocation rule and coordination mechanism for the FORMOSAT-2 and FORMOSAT-3 operations also need to be clearly defined and followed during to the FORMOSAT-3 L&EO phase. To define the manpower allocation rule, the FORMOSAT-2 and FORMOSAT-3 operations are divided into three levels: Normal, Major and Critical. The latter two are belong to contingency situations. If there is any manpower conflict between FORMOSAT-2 and FORMOSAT-3, the shift rule listed in the table are followed. FORMOSAT-2 Manpower Shift FORMOSAT-3 Normal Normal Normal Major Heidelberg, Germany May 12 16, of 15

14 Normal Major Major Major Critical Critical Critical Normal Major Critical Normal Major Coordinate Critical Critical The arrow shows the manpower shift direction, if there is any conflict. The coordinate symbol means that the direction of manpower shift needs to be determined by Coordinate Team. Since the manpower allocation rule and the associated ground resources priority are followed, the impact of L&EO phase of FORMOSAT-3 to FORMOSAT-2 normal operations is minimized and the team successfully completes the L&EO operations of FORMOSAT-3 without HjeopardizingH the operations of FORMOSAT Summary Coordinate By using one SOCC with only one operations team, the harmony of the multi-mission operations mainly depends on the efficiency of the centralization of the management. Especially it is very serious to operate and control multi-mission satellites during the L&EO phase with single operations team. It is recommended that the ground resources, the manpower allocation rule and coordination mechanism for different missions need to be clearly defined and followed during to the L&EO phase, so as to minimize the operations impact and avoid jeopardizing the operations of either mission. Currently, both FORMOSAT-2 and FORMOSAT-3 missions are in the normal operations phase. They are being controlled and operated simultaneously from the SOCC of NGS with one operations team. The single operations team can easily handle the multi-mission satellites operations due to the more stable activities of satellites planning. However, thanks to the higher maintenance of operating FORMOSAT-3 constellation satellites, the operations team has developed many procedures, Heidelberg, Germany May 12 16, of 15

15 operations tools, and has combined the callout mechanism with the event triggering system, which are not fully available at the beginning. In general, the satellite operations environment is evolving as a living organism and has to grow as new mission needs and constraints arise. In a multi-mission environment, the growth and necessary upgrade are usually difficult to integrate with the existing system structure. Therefore the deliberate tradeoff study in advance is necessary. The constellation database design is a good example. After the experiences of operating 7 (1+6) satellites simultaneously with one team, the NGS has build up the confidence and know-how to meet the future challenge of multimission operations. Heidelberg, Germany May 12 16, of 15