Mission Planning and Scheduling Software for /9

Nikita Gokhale, Kimberly Callis, Ella Herz, Ryan Bishop Orbit Logic, Inc., Greenbelt, MD, 20770, USA

Planning Element (CAPE) that was previously developed and

operated by USGS. Orbit Logic’s STK Scheduler will Abstract produce a deconflicted schedule for satellite communications This paper details the functionalities of the Mission between the Landsat satellites, U.S. and international ground Planning and Scheduling (MPS) software developed by Orbit Logic for the Landsat 8 and 9 missions. Orbit Logic stations, and TDRSS satellite communication nodes. Orbit will deliver their STK Scheduler software and Collection Logic's CPAW software will be used for Landsat 8 and 9 to Planning and Analysis Workstation (CPAW) software to generate validated optimized solutions, deconflicted General Dynamics Mission Systems for use by the Landsat schedules, and optimized high fidelity imagery collection Multi-Satellite Operations Center (LMOC). STK Scheduler plans. Only the mission planning and collection planning will generate a deconflicted schedule for satellite communications between the Landsat satellites, U.S. and software is being redesigned using Orbit Logic’s CPAW international ground stations, and Tracking Data Relay system. All other subsystems such as flight dynamics, Satellite System (TDRSS) satellite communication nodes. command and control, & image processing will focus mostly CPAW will generate validated, deconflicted, and optimized on heritage capabilities with minor updates. high fidelity imagery collection plans.

LMOC Planning System Driving Introduction Requirements The consists of satellites providing a Both Landsat 8 and Landsat 9 include a low earth orbiting continuous global record of the Earth’s surface via satellite (LEO) satellite with 2 instruments – the Operational Land imaging. The Landsat program has been collecting and Imager (OLI) and the Thermal Infrared Sensor (TIRS). archiving images of the earth’s surface continuously since Observations for Landsat are based on the Worldwide the early 1970’s. The U.S. Geological Survey (USGS) Reference System (WRS), specifically the extension of this awarded the Landsat Multi-satellite Operations Center system referred to as WRS-2. The WRS divides the earth’s (LMOC) contract to the General Dynamics Mission Systems surface into overlapping grid squares identified by a PATH team to maintain Landsat-8 heritage operations and and ROW. The spacecraft is in a sun-synchronous orbit with capabilities, develop, and integrate, the Landsat 9 Multi- a 16-day revisit for any point on earth. Imaging is typically Mission Operations Center as well as assuming operations performed at nadir in sunlight, but off-nadir or night-time of the on-orbit Landsat 9 observatory. collects can be scheduled. There are multiple calibrations As technology has evolved and the spacecraft subsystems that the Landsat observatory can perform. have matured, NASA and USGS have updated their fleet of imaging satellites as well as their ground operations The primary requirements for the mission planning and software. In the latest round of upgrades, Orbit Logic has collection planning software are to plan image collections, delivered their STK Scheduler software and Collection calibrations, housekeeping activities, solid state recorder Planning & Analysis Workstation (CPAW) software to management, as well as communications for the General Dynamics Mission Systems for mission planning observatory. This will require a constellation planning and scheduling for the Landsat Mission Operations Center system using high fidelity spacecraft models in order to (LMOC) for Landsat 8 and 9. Orbit Logic is now in the reliably plan the satellite’s courses. As mentioned in the process of integrating the software into the Landsat ground Planning and Scheduling for Fleets of Earth Observing system. Satellites article stated, “ mission required a detailed model of the satellites and the communications Landsat 9 will be the next satellite in the Landsat series that environment when scheduling operations. (Frank, Jonsson, images the Earth’s surface. It is currently scheduled for Morris, and Smith 2001) CPAW will ensure this detailed launch in December 2020. Orbit Logic software will model is implemented for the Landsat-9 Multi-mission streamline and modernize the mission planning and operations Center. collection planning process, taking over for the Generic Mission Planning System and the Collection Activity

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Planning System Inputs The LMOC planning system receives a number of inputs from a variety of systems. The inputs breakdown into the following categories – flight dynamics information, collection requests, and communication information. The flight dynamics package in use at LMOC is from a.i. solutions. Flight dynamics provides observatory spacecraft ephemeris information. It also takes into account Tracking Data Relay Satellite System (TDRSS) ephemeris Figure 1 Resources Modeled in STK Pro information; as well as attitude and orbital maneuver information. One other special input that is generated by the STK Scheduler COTS solution is used for contact flight dynamics system is the WRS time transition table deconfliction and schedule optimization. It provides a robust (WRSTTT) which defines when the observatory will be over task and resource specification with real world constraints. each specific WRS grid. STK Scheduler uses a configurable figure-of-merit and USGS’ Data Processing and Archive System (DPAS) is the configurable algorithms that create a valid optimized collection request system for Landsat 8 and 9. DPAS schedule. The STK Scheduler COTS solution is used in generates Long-Term Acquisition Plan Collection Requests Landsat for contact deconfliction and schedule optimization. (LCRs) and Special Collection Requests (SCRs) which STK Scheduler COTS is configured to manage the different serve as task orders for the LMOC collection planning Landsat ground station types and TDRSS Satellite system. The LCR includes a set of WRS grids that are scheduling on a weekly basis schedule for Landsat contact nominally requested to be collected at nadir every time the forecasting. STK Scheduler outputs the COTS report observatory passes overhead. The LCR more or less format. For the Landsat program it is required that the includes all of the landmass on earth, but is configurable as schedule inputs and outputs use the Landsat specific the needs of the science mission changes. SCRs include formatted reports. Therefore, the Landsat Interface was requests for collections at night, ad-hoc tasks, and off-nadir developed to translate STK Scheduler format into the targets. The LMOC planning system receives Calibration required Landsat output and process and ingest Landsat Collection Requests (CalCRs) from a legacy system called specific report updates into the STK Scheduler to update the Calibration Opportunity Scheduling Tool (COST) that was rolling Landsat contact schedules. created for the Landsat 8 mission. Since the Landsat mission interfaces with several communication networks it has several different types of communication inputs which include Near Earth Network (NEN) strawman files, Space Network (SN) Confirmed Forecast Event (CFE) files, and Landsat Ground Network (LGN) Contact Forecast Confirmation (CFC) files. These comm inputs describe activities on the various networks that the LMOC planning system needs to work around plus provide confirmation of requests for comm time from the LMOC planning system

LMOC Planning Operations STK Pro & STK Scheduler model are the resources utilized for the Landsat 8 and 9 missions such as well as the Figure 2 Contact Schedule in STK Scheduler Ground Stations (IC, LGN, TDRSS, NEN, LGN), and the Landsat 8 and 9 Satellites, and the active TDRSS Satellites.

specific formats. Once the different resources received their Each 28-day Contact Schedule is output as a Contact forecasted contacts, each one would provide feedback Forecast Request (CFR). The CFR file is pushed from the whether the contacts forecasted could be supported or not. LMOC to a passive directory at each LGN station in the This forecasting process leads to our two main challenges for Ground Network Element (GNE). Individual CFR Reports contact scheduling. The first challenge was creating a are sent to each ground station (USGS gets a combine feedback loop between the Landsat satellites and the different schedule report). STK Scheduler then receives responses types of contacts the satellite had. The second challenge was from the Ground Stations called the Contact Forecast maintaining the forecasting schedule from one week to the Confirmation (CFC) and updates the different scheduled next to remember not only the previously forecasted contacts, contacts accordingly. The contact schedule (CFR) is then but also the feedback received from the different resources. sent to CPAW to utilize for collection planning. Due to these challenges, the Landsat Interface and contact scheduling scripts were created to assist STK Scheduler CPAW is a software tool for creating collection plans for COTS in solving the Mission Planning aspect of the LMOC- one or more imaging satellites. It is a standalone application MPS. with the ability to run as part of a scalable architecture for rapidly running constraint de-confliction algorithms and Landsat Interface optimizing collection plans. The software allows for order management of ground targets and calibration requests and The Landsat Interface was initially developed to create Landsat custom format reports from the STK Scheduler data storage management. COTS generated reports. The Landsat Interface is a folder CPAW will be an integral part of the LMOC Activity monitoring service that responds to files with specific Planning Operations Concept. CPAW will accept inputs filenames being dropped into a specific folder. The Landsat from the Data Processing and Archive System (DPAS), Interface’s original purpose was strictly the input and output FDS, Flight Operations Team (FOT), and STK Scheduler of customized Landsat reports but eventually developed into to build a deconflicted collection plan and generate reports customizing reports for CPAW in addition to working closely to be sent to Galaxy. The diagram below displays the alongside the Mission Planning Scripts. The folder activity planning process flow. monitoring architecture breaks down the various different aspects that are now utilized to build and maintain the Landsat communication schedule from one forecasting week to the next. The high-level folders monitored by the service are CPAW, Forecast Files, Ingest Files, Input Files, Resource Reports, and Working Schedule. The primary folder that is monitored by the service is Resource Reports. Resource reports are the generic STK Scheduler COTS output that the Landsat Interface generates a majority of all other files from. The CPAW folder maintains a CPAW compatible communications contact schedule along with a CPAW compatible ephemeris file, both generated by the Landsat Figure 3 Collection Planning Analysis Workstation Interface. The Forecast Files folder is where all the Landsat (CPAW) 3-day Plan visual diagram. custom formatted forecast files are generated after a contact schedule is generated in STK Scheduler. The Ingest Files are STK Scheduler compatible command files generated by the The CPAW COTS software is supplemented with a Landsat Landsat Interface based on feedback from the different plug-in to enhance the collection planning model with resources’ feedback. The Input Files are various files that are mission-specific attributes. The plug-in handles slew and utilized by the Contact Scheduling Scripts to create the imaging modeling, interval planning, and constraint contact schedule and other reports such as ephemeris files and checking as defined in the Landsat operations concept. orbit number files. Lastly, the Working Schedule is where the active contact schedule is saved and loaded from along with the resource file, containing the various resources’ attributes. Customized Solutions for Mission Planning The Landsat Interface is a unique solution that works alongside STK Scheduler and the Contact Scheduling Scripts For the Landsat program, the contact scheduling had two in order to provide a maintainable forecasted contact schedule specific challenges that could not be solved simply through that solicits and implements feedback from resources from the STK Scheduler COTS product. The challenges stemmed one week to the next. from the unique process for the Landsat mission called forecasting. Forecasting is essentially planning the contact schedule for the next four weeks in STK Scheduler for the Landsat satellites. This forecasted contact schedule would then be sent to the different type of resources in their Landsat

Contact Scheduling Scripts Launch and Early Orbit Phase Planning for Landsat 9 The Contact Scheduling Scripts are designed to be able to carry the forecasted contact schedule from one week to the Launch and Early Orbit Phase (LEOP) the Landsat 9 satellite next, while implementing feedback into the schedule. STK will not be in line with the WRS2 path/row grid. During this Scheduler COTS in a traditional sense is utilized to phase the spacecraft is lower than expected in its sun deconflict everything in a schedule for the user selected synchronous orbit. Therefore, there is uncertainty on which period of time. For the Landsat Mission, this would mean path/row the spacecraft will be collecting at what time as it that every week on forecasting day an entirely new contact will be over multiple path/row scenes during its flyover. The schedule would be produced as the algorithm ran ECOSTRESS program which has a similar imaging conops deconflicting everything within the schedule. Also, going to Landsat also had an orbit uncertainty issue. However, this from one forecasting week to the next will add new days to was due to its command load sequences being uploaded the schedule that will need the algorithms to run to assign weekly the ISS experienced some drag which caused drifting contacts and deconflict the schedule. Running the in the imaging which caused missed imaging. (A. algorithms will erase the resources feedback for the Yelamanchili, S. Chien, K. Cawse-Nicholson, J. Padams, D previously forecasted weeks. This is where the concept of Freeborn, 2018) the rolling schedule in STK Scheduler came to be the ultimate solution. The rolling schedule concept is a mix of For the Landsat program, CPAW is required to produce all Landsat Interface folder architecture, STK Scheduler COTS output products as if the spacecraft was flying in the nominal functionality, and the Contact Scheduling scripts to generate operational mission orbit. The challenge for CPAW was the deconflicted forecasted contact schedule while also input and outputs rely heavily on the Landsat 9 spacecraft maintaining the confirmed schedule all in the same instance being lined up where the path/row grid was directly at nadir. of STK Scheduler. At the very core, the rolling schedule is However, during this period of time the spacecraft traversing essentially the updating of a single STK Scheduler file that over and covering multiple path/row scenes. utilizes STK Scheduler core product functionality to To overcome this challenge a LEOP mode was added to maintain the feedback system from the resources. The CPAW along with other components to calculate the closed Contact Scheduling Scripts comprise of two scripts, one for path row center point to the ground track center of the the first ever forecasting week and the second for all of spacecraft. remaining forecasting weeks. The scripts implement the rolling schedule concept described above. The Contact Daily Collection Planning Scheduling scripts both perform the following operations: loads the resources, sets the time period of the schedule, The LMOC-MPS ran into a very similar challenge for loads ephemeris files for the satellites, creates the potential Collection Planning as seen in Contact Scheduling when contacts for the resources, loads in the resource feedback, attempting to support daily collection planning. As Contact deconflicts the contact schedule, and saves the schedule. The Scheduling needed to maintain knowledge from one first script creates the schedule and the resources, whereas forecasting week to the next, Collection Planning needs to the second script loads the previous schedule and carries out maintain knowledge from one daily planning day to the next. the rolling schedule concept. The Contact Scheduling Daily planning in CPAW occurs every day for the next four Scripts allow the operators to flow effortlessly from one days, overlapping the previous last 3 days planned. There forecasting week to the next and provide a CPAW were several challenges in implementing a similar concept of compatible contact schedule to utilize for daily planning. the rolling schedule for Collection Planning. These challenges included a new time constraint task and re- planning. Creating a new task in CPAW was not very Customized Solutions for Collection Planning difficult, however the constraints for the task, called the buffer switch, was very challenging for daily planning. The For the Landsat program, the LMOC-MPS had numerous buffer switch is essentially switching from one recorder to the challenges due to the abundance of unique requirements for other on the satellite. The buffer switch had the following the Collection Planning aspect of the Landsat missions. constraints: must always be scheduled on the last day of the These challenges could be broken down into the following load, as close to 00:00:00 as possible within 5 minutes, and various facets of Collection Planning: daily collection cannot be scheduled during another activity. These planning, housekeeping, imaging model, recorder constraints were all met through custom code for the task management, calibrations, performance, and outputs. A created within the CPAW plugin that allowed daily planning CPAW plugin was created specifically for Landsat to solve to include the buffer switch in every daily load, while these various challenges. The plugin worked alongside the adhering to the constraints. The custom code added a new CPAW COTS product to provide an overall solution for the CPAW planning feature that allowed movement of locked Collection Planning. tasks to make room for other tasks, which was previously not possible. Another challenge was re-planning which refers to

keeping part of the previous daily load while re-planning the Landsat was accommodating the overlapping orders that are new section of the load. There were several features added inherent to the WRS-2 grid. Typically, in CPAW, large to CPAW to adhere to the re-planning requirement for the orders are divided into strips based on sensor characteristics Landsat program including: adding a revise planning as part of the planning process and any overlapping orders function, tracking the last planned state, clearing previous that are collected are referred to as a “bonus”, but tracked as data appropriately, and updating of transmit data storing. a partly fulfilled order. But within the Landsat system all Implementing these new features in CPAW allows for a orders have some level of overlap, so it was more efficient to smooth daily collection planning for operators. disable the bonusing feature in favor of the “interval” collection described. An interval defines when the imaging Housekeeping starts and stops and may include multiple orders (or scenes) as long as all constraints are met within the interval. For Housekeeping for the Landsat program refers to specific Landsat there is an additional constraint to keep imaging on Landsat tasks that do not exist within native CPAW and our over non-requested areas if there is only a small gap. This scheduled based on events or timed tasks. These items are “flywheel” functionality is covered by the imaging model and referred to as housekeeping as they are utilized to maintain reporting. the health and welfare of the satellites. The main challenge As is typical for most missions, a Landsat-specific maneuver with the Landsat housekeeping tasks was determining the model was implemented to plan slewing of the spacecraft in- scheduling constraints for each individual task to schedule between and during imaging tasks. within CPAW. These tasks were tremendously challenging due to their constraints not only with one another but also Recorder Management planning around conflicts and various constraints with all other Collection Planning activities such as calibrations and As stated, “EO and SAR Constellation Imagery Collection imaging. Testing all nominal and off nominal scenarios Planning” paper, “Recorder state tracking and downlink thoroughly needed to be assessed and determined to make planning must take into account High Gain Antenna (HGA) sure all housekeeping constraints did not conflict with one agility, playback rates, file management protocols, and another as well as the other activities. Once the Landsat recorder timing constraints.” (Herz 2014) Out of the box housekeeping tasks were defined appropriately within CPAW models the impact of scheduled collection planning CPAW, the ability for CPAW to then deconflict and activities on the spacecraft Solid State Recorder (SSR) based schedule the housekeeping tasks in the optimal position was on the recorder capacity, instrument record rates, and data possible. downlink rate. CPAW seeds the model using spacecraft SSR telemetry. There were several mission-specific challenges to Image Modeling modelling the recorder management for the Landsat program including: changing SSR properties throughout the mission, a The Landsat program developed a custom imaging model finite number of root file IDs, modeling of playback files, and within CPAW for Collection Planning to adhere to mission- syncing of the modeled SSR with the actual spacecraft SSR. specific imaging requirements. The Landsat imaging model To handle the finite, user configurable parameters were added required core CPAW features to be extended and tweaked to specify the range of IDs. The number of root file ids is so for a Landsat specific implementation of what to collect and small that within a standard three-day load, it may be when. For example, during planning, core CPAW has a necessary to reuse specific file ids. There are also process flow to calculate access, filter orders based on access complexities due to the root files being shared across scenes as well as other constraints, and schedule them in the form within an interval. In order to handle the fact that record, of sensor imaging tasks. In the Landsat specific imaging playback, and downlink don’t always go as planned, CPAW plugin, the filter mechanism leveraged the WRS2 Time was updated to accept Landsat specific recorder management Translation Table (WRS2TTT) (which pre-identifies when information files to overcome the unreliable modeling and the observatory will be over each grid point) to improve desyncing with the real spacecraft SSR. ), , The Scene Interval speed performance of the filter vs mathematically calculating File Mapping Table (SIFMT) shares the truth data with access time for each grid. Further simplifications to CPAW CPAW about what assigned file IDs have been played back functionality were also made during the filtering process to in the last 24-hours and the time of that playback and CPAW exclude tasks which are not aligned with the spacecraft updates the recorder model as needed based on this ground track since LCR orders for Landsat are by definition information. The SSR Telemetry seeding file shares the taken nadir pointing. However, Landsat added complexity observed size of each collected file ID in units of File to allow for multiple sensors (Operational Land Imager Allocation Blocks (FABs) with CPAW. This allows CPAW (OLI) and Thermal Infrared Sensor (TIRS) to collect at the to update the SSR model with telemetry information and same time, which nominally collect LCRs in tandem. recalculate the available SSR capacity for further collection Internal to CPAW, access calculations and the creation of the planning. segments to be scheduled use a combination of the capabilities of the two sensors. Calibration Planning One of the biggest imaging model challenges for

The Landsat program has many unique calibrations each • STS (Scene Transmit Schedule) – contains all the with their own unique set of requirements. Calibrations are scenes that have been scheduled for acquisition by planned for the satellite in CPAW either by standing orders the IC stations or by specific calibration requests. Requested calibrations • SIMT (Scene Interval Mapping Table) – contains the are performed by ingesting a calibration format file into scene to interval assignments delimited by time CPAW from DPAS that transforms that request into a • IDSR (Image Data Schedule Report) – contains a CPAW style order. These were relatively simple to handle status of all scenes and provides reasons for why or as the order would then be filtered naturally into planning why not they were collected windows. The greater challenge is with calibrations that are scheduled at regular intervals and are not specifically Creating five new outputs of CPAW came with several requested, therefore not corresponding to a specific CPAW difficulties. CPAW reports originally were trigger-based on style order. The Landsat plugin was able to surpass this the status of the planning, such as on save or on transmit. For challenge by implementing the routine calibrations to be Landsat, user created triggering of reports was more desired scheduled as an initial load building activity, avoiding the to allow for a more flexible creation of reports. This resulted need for requests. To cover the multitude of requirements in creating a new style of report generation that was based off from the numerous different types of calibrations all with a of user action instead of trigger-based on CPAW status. unique set of constraints the Landsat plugin has specific tasks Custom formatting for all the new reports were a challenge as types per calibration. With this architecture, it is relatively each report was not necessarily asking for a 1 to 1 what easy to add new calibrations for the Landsat Mission. CPAW outputs at the end of daily planning and to what Landsat puts in the report. An example of this can be seen Performance with the MAL, where there is not a 1-to-1 relationships between strips output by CPAW and the reported activities Considering the large number of orders for Landsat, are necessary for the MAL. This required custom formatting performance within the planning system was a key concern. and translation to be added to the Landsat plugin to output the In its goal of imaging the entire planet, the Earth is broken necessary information into the reports. The last challenge was down into individual paths and rows resulting in squares that specifically creating the IDSR. The IDSR is essentially a cover all land on the Earth’s surface. Each square makes up report for recording why tasks were omitted during planning. a single order, which broke down too close to 30,000 orders Post-processing was added to gain knowledge of Landsat- for the entire Earth. CPAW utilizes order stripping and order specific behavior to discover the reasons the strips were criteria to get the specific orders for a defined planning omitted. These new Landsat specific reports provide vital window. Filtering through these orders using access information to different avenues but most importantly are calculations took longer with such sheer large amount of utilized to send the appropriate commands up to the live orders. Landsat satellites to perform collection planning. Also, the vast amount of orders that were applicable to the window were quite strenuous on the deconflicting and Conclusion planning of the collection of those orders. This resulted in coming up with a unique solution to speed up the process of The software developed by Orbit Logic will streamline and daily planning to meet the requirements for the Landsat modernize the contact scheduling and collection planning program that pertained a vast amount of orders. A solution process. It replaces the system that was previously developed for filtering was adding prefiltering based on the adjacency and is operated by USGS. Orbit Logic’s planning software of scenes, the grid squares. The prefilter takes the start and solution provides a multi-mission planning system to support end scene, and calculates what scenes are between. Only L8 and L9 simultaneously. STK Scheduler will produce a these orders go through the prefilter, which greatly narrows deconflicted schedule for satellite communications between the amount of orders under consideration for the planning the Landsat satellites, U.S. and international ground stations, window. Enhancing the performance of CPAW in handling and TDRSS satellite communication nodes. CPAW will be a vast amount of orders allowed the requirements to be met used for Landsat 8 and 9 to generate validated, deconflicted, for the Landsat program’s daily planning needs. and optimized high fidelity imagery collection plans. Orbit Logic provided engineering services to integrate with other Outputs elements of the ground system and develop models of the Landsat spacecraft bus and sensor The Landsat program required several different outputs to be generated once the daily collection planning was completed References in CPAW. The following Landsat formatted files were created: Herz, E., 2014. EO and SAR Constellation Imagery • CCS (Confirmed Contact Schedule) – contains Collection Planning. Orbit Logic Inc. confirmed contacts for each IC ground station

• MAL (Master Activity List) – contains all activities Frank, J., Jonsson, A., Morris, R., and Smith, D. E., 2001. in the collection plan Planning and Scheduling for Fleets of Earth Observing

Satellites. NASA Ames Research Center.

STK Scheduler, Ver. 11.6.0.12, Orbit Logic Inc., Greenbelt, MD, 2019.

CPAW, Collection Planning and Analysis Workstation, Ver. 2.3.32.83, Orbit Logic Inc., Greenbelt, MD, 2019

A. Yelamanchili, S. Chien, K. Cawse-Nicholson, J. Padams, D Freeborn Automated Policy-based Scheduling for the ECOSTRESS mission Earth Science Technology Forum, Moffett Field, CA, June 2019.