Mission Planning for Constellations Planning for multiple spacecraft and ground stations

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Mission Planning for ConstellationsPlanning for
multiple spacecraft and ground stations
SpaceOps 2002 Track 3 Operations Mission
Planning and Control

• Wayne Harris, Rick Blake, Roger Thompson, Duncan
  Woods, Emlyn Purvis, Johan Stjernevi
• Science Systems (Space) Ltd.
• Methuen Park
• Chippenham, Wiltshire, UK SN14 0GB
• 44 (0)1249 466466
• wayne.harris_at_scisys.co.uk
• www.scisys.co.uk

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Introduction

• Targeted at missions that require
• Pass-based operations
• Scheduling limited duration contacts between
  multiple satellites and multiple ground stations.
• LEO, MEO and Deep Space Missions
• Earth Observation and Science Missions with one
  or more satellites
• Constellations of satellites
• For example, GalileoSat
• Interactions with S/C not highly constrained
• Limited contact time due to visibilities
• More visibility than is needed for control
• Spacecraft operation is mostly independent

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Mission Management Model of Operations
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Plans

• Planner prepares a schedule of operations for
  automated execution.
• External inputs to the planning process
• Predicted visibilities (AOS-LOS) generated by the
  Flight Dynamics (FDS)
• Other predicted geometric events for each
  satellite, generated by the FDS.
• Planning requests and responses.
• prepared command queue for uplink to the
  satellite
• Most operations performed out-of-pass
• Sequences of telecommands loaded into on-board
  time tagged buffers
• Operations executed in real-time during the pass

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On-Board Activities

• A command sequence, or externally prepared
  command queue
• Loaded into the time-tagged buffers on-board the
  satellite during a contact
• Executed later, probably out-of-contact.
• Prepared and uplinked during a contact prior to
  execution time.
• Uplink is handled by a generic Contact Control
  Procedure

CONTACT CONTROL TASK
CONTACT CONTROL ACTIVITY
Contact Control Procedure
Uplink
TASK
ONBOARD ACTIVITY
Command Sequence/Queue
TIME
Contact Event
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Ground Based Activities

• An automated operations procedure
• A satellite telecommand or other SCC command
• A manual activity e.g. maintenance
• Able to handle
• Command sequences
• Externally prepared command queues.

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Schedules

• Generated from plans after checking of
  constraints
• Conflict-free
• Automated execution
• Residual schedule
• Unexpired portion of active schedule
• May also be used as input to the planning
  process.
• Ground-based satellite operations are
  automatically scheduled in real-time.
• On-board and ground-based activities
• May correspond to the automated up-link of
  command queues

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On-board activities

• Managed differently to ground based activities
• Associated with a pre-defined command sequence.
• Command Sequences expanded and interleaved into
  sequence of on-board activities.
• On-board schedule (or time-tagged command queue)
• Set of on-board activities
• Forwarded to the on-line environment.
• Uplinked to the satellite during the pass

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Gangplank Command Queues

• List of commands for sequential uplink to the
  satellite.
• Generated for uplink during contacts
• Generation expansion of any command sequence
  references.
• Contain immediate or time-tagged commands
• Gangplank queue is not an onboard queue
• Commands in gangplank queues are loaded into the
  onboard queues
• Could also be externally prepared command queues
• Flight Dynamics manoeuvre
• Uplink of new onboard software.
• Commands may be grouped into blocks to be
  uplinked together.

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Ground - Spacecraft Queue Mapping
GANGPLANK COMMAND QUEUE REPOSITORY
EXTERNALLY PREPARED COMMAND QUEUE REPOSITORY
Gangplank Command Queues
External Command Queues
A
C
B
GROUND
SPACECRAFT
A
B
C
Real-time Queue
Timetagged Queues
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Mission Management Architecture
Spacecraft Control System
ParametersCommandsEvents
Commands
Mission Management Manage-iT
UplinkInitiation
Patch TC Sets
Procedure Execution
Command Queue Uplinker
OBSM O/B Software Management
Schedule Display
ProcedureInitiation
O/B ActivityStatus
Schedule Execution
ExternalPlanningCoordination
Plans
External Systems
Executable Schedules
On-board Schedules
Mission Planning
MPS DB
Planning Inputs
FDS Flight Dynamics
Visibility Generation
Orbit Vectors
S/C Defn
G/S Defn
Contact Reqs
Contact Plan
Contact Scheduler
Station Visibilities
External Interfaces
Baseline UNiT Applications
Internal Interfaces
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Visibility Generation

• Orbital propagator
• Known starting positions
• Known orbit vectors for the spacecraft
• Specified positions of the ground-stations
• Calculates when ground-stations have line of
  sight visibility to spacecraft.
• Specific ground-station fixed limitations, for
  example
• The surrounding landscape
• Antennae restrictions at the zenith and horizon
• Variable limitations, for example
• Atmospheric conditions
• Maintenance down-times
• Visibilities generated for contact planning

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Contact Scheduler

• Takes
• The generated visibilities
• A set of Contact Requirements defined by the user
• Spacecraft and ground segment definitions
• Contact includes the type of contact it requires
  (eg FD or TTC).
• Ground stations indicate the types of contact
  they provide.
• Contact Plan is created by
• Matching the visibilities to the Contact
  Requirements
• Meeting the constraints on type
• Minimising the total cost of contact, according
  to a cost function.

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Contact Requirements

• Standing Requirement
• A regular demand for contact.
• Defined by S (Span), I (Maximum Interval), D
  (Minimum Duration)
• There must be D seconds of contact in every
  period of size S seconds (Quantity)
• There must be no period longer than I seconds
  without contact (Frequency)
• One-off Requirement
• A single demand for contact.
• Defined by EST (Earliest start), LET (Latest
  end), D (Minimum Duration)
• There must be D seconds of contact between times
  EST and LET

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Mission Planning

• Contact Plan is imported into a plan
• Contacts trigger automatic placement of items on
  the plan
• User can
• Import requests such as from Flight Dynamics
• Add further planning requests, edit the plan, etc
• Conflict detection and resolution
• Checks that activities that require contact are
  in a contact period
• User resolves all conflicts then generates an
  executable schedule
• Pass executable schedule to schedule execution
• On-board commands passed to the command queue
  uplinker

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Execution and Display

• Schedule Execution of Executable schedule
  contains
• On-board commands
• Displayed to the user as they execute,
• Loaded via the command queue uplinker
• Not executed from Schedule Execution
• Schedule execution is a server process with full
  failover support.
• Schedule Display
• Access is controlled on a per domain process
• Provides a Gantt based timeline view and a
  timetable view
• Procedure Execution
• Server process with failover capability.
• Initiation of a command or uplink of a command
  queue.

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Command Queue Uplinker

• On-board Schedules and predefined queues contain
  time tagged commands
• Command queue expansion requires customisation
  for specific missions
• Uplinker
• Uploads command queues onto the spacecraft
• Function of the underlying monitoring and control
  system
• Could be initiated by the procedure execution
  engine
• Commands could be loaded in batches as follows
• an entire command queue
• the next n commands from the queue
• commands up to a specified on-board time

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Contact Scheduling Approach

• Takes generated visibilities
• Schedules a Contact Plan containing contacts
  which must
• Satisfy the set of Contact Requirements
• Minimise the total cost.
• Slotted time
• Scheduling interval is broken up into
  consecutive, indivisible periods of equal
  duration.

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Galileo Case Study

• 30 satellites in MEO orbit
• 5 ground stations, globally distributed.
• Routine operations
• Fully automated
• Require one 30 min contact per orbit ca. 14
  hours
• Occasional additional or extended contacts for
  routine maintenance
• Satellites in critical operations may need
  extended contact
• Support fault diagnosis and recovery operations
• Include planned activities such as manoeuvres and
  major software uploads
• LEOP and commissioning activities may also be
  critical operations
• Assessing trade off between performance and
  requirements

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Galileo Case Study
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Conclusion

• System has been designed and built
• Enhancements to an existing mission planning and
  scheduling solution
• Supports pass-based operations for satellite
  constellation missions
• On-board scheduling is relatively unconstrained
• Contains Spacecraft visibilities, contact plans
  and on-board queues
• System is modular and fully configurable
• Implementation of the external interfaces, can be
  customized
• The main points of investigation
• The trade-offs between performance and finding a
  useful solution
• Effect of standing requirements on performance
• Optimal solution takes an extended time to solve
  for no particular advantage,