Inter satellite communications

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Inter satellite communications

  1. 1. Constellation Operations: Inter-Satellite Communications 8th Annual AIAA SOSTC Improving Space Operations Workshop April 24-25, 2002 Naval Satellite Operations Center (NAVSOC) Point Mugu, California
  2. 2. What are the Drivers for Interspacecraft Communications? NASA Near- mid- and long-term strategic plans (2000-2025 timeframe)  HQ, Earth Science Enterprise, Space Science Enterprise Innovative Science Observing Concepts     Formation Flying Missions Collaborative Earth- and Space-Science Observations Autonomous Event Recognition, Reconfiguration, and Response Sensor Webs Evolving Technologies  MEMS & microelectronics  Electron beam lithography systems will contribute to the development of nanospacecraft components with extremely small mass  The challenge: nanospacecraft transmitter/receiver mass vs. on-board communications infrastructure and power for effective RF or optical link closure   RF, optical, and digital communications technologies Communications protocols standards  Mature terrestrial protocols: Network (IP, IPv6), Transport (UDP, TCP), Application (FTP)  NASA space communications protocols: CCSDS suite, CCSDS Proximity-1, SCPS April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 2
  3. 3. Space Mission Architecture - Today Bent pipe communications Science Processing Center Science Processing Center • Classic “stovepipe” science data collection and mission operations • Single or separate spacecraft missions with little or no dynamic planning for opportunistic science observations • No real time collaborative information sharing between sensors, spacecraft, or investigators • Bent pipe interspacecraft communications –via TDRSS in support of command uplinks, telemetry downlinks April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 3
  4. 4. Space Mission Architecture – A Future Sensor Web • High degree of synergy between a diverse suite of platforms –Space-based –Atmospheric (e.g., aircraft, balloons) –Land (e.g., river gauges) –Sea (e.g., buoys) • Automated science data collection and mission operations –On-board spectral signature detection algorithms • Multiple spacecraft and platforms perform dynamic planning for targets of opportunity • Real time collaborative information sharing between sensors, spacecraft, or investigators • Interspacecraft communications becomes an intrinsic characteristic of space platforms April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 4
  5. 5. Architectural Implications for Interspacecraft Communications Constellations  Knowledge of the “whereabouts” of member spacecraft within their orbits is reasonably well constrained.  Spacecraft immediately “ahead of” or “behind” another in the same orbital plane  Phasing relationships between spacecraft in adjacent planes   Homogeneous Constellations  Communications infrastructure is inherently the same  Simplifies communications architecture since there’s only one solution set implemented for the protocol stack (e.g., ISO/OSI 7 layer model components) Heterogeneous Constellations  Drives need for standard communications protocol stacks    Facilitate interoperability between S/C and ground segment Reduce mission implementation and ops costs Mitigate implementation risk April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 5
  6. 6. Architectural Implications for Interspacecraft Communications Formation Fliers  Knowledge of relationship between S/C that comprise the formation may simplify communications architecture  Point-to-point  Broadcast  Proximity  May permit low power communications: especially important for low mass “nanospacecraft”  Accretionary Formations  Since they are not “a priori” known to come into being, standards are a must for communications protocol layers 1-4, 7 if these S/C might eventually communicate among one another April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 6
  7. 7. Information that Needs to be Exchanged Spacecraft and Instrument H&S Telemetry Data   Characterized by relatively low data rates, low volumes Spacecraft operational “status” messages  S/C orbit and attitude information  Instrument(s) mode(s) of operation  Instrument Pointing information Spacecraft Instrument Data   Can be characterized by relatively high volumes and high data rates Typically unidirectional  Collaborative missions may require bi-directional science data exchange  May be used to facilitate distributed space-based computing  On-board spectral (signal) signature processing  Event recognition software  Event response software  Duty cycle will depend upon mission needs April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 7
  8. 8. Information that May be Exchanged Ancillary information     Most likely characterized by low rate, low volume Interspacecraft range and range-rate Status messages that facilitate or help to coordinate science observations, on-board processing status, etc. Science instrument calibration coefficients/tables Rate of data exchange and duty cycle of link utilization will depend upon individual mission needs April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 8
  9. 9. Mission Needs & Ops Concepts will Drive Protocol Issues Differences between space & terrestrial communications environments  Spatial relationship between two communicating S/C is continually changing  In and out of RF range  In and out of line-of-sight  Changing pointing angles  Available (on-board) communications transmitter power to close the link  Directional (RF,Optical): less transmit power; pointing knowledge required  Omnidirectional: more transmit power required; broadcast can create duplicate packets in network  Handling lost packets  Terrestrial networks assume congestion; slow down packet traffic to compensate  Space networks assume noisy link: re-transmit packet as soon as practicable  Propagation delays can be (but are not necessarily) longer April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 9
  10. 10. Interspacecraft Comms: Potential Uses/Benefits For S/C presently not within view of a ground station   Route all uplinks to the S/C that is within view of ground station Ground station antenna and support equipment      S/C contact activity planning & scheduling independent of ground station “GEO-like” nearly-continuous contacts may be possible with any S/C An increase of the uplink data rate may be required to serve multiple S/C Multiple S/C yield aggregate downlink data rates that may necessitate wider bandwidth (i.e., higher data rate) to the ground Uplink & route commands to one, some, all spacecraft  Routine, emergency  Receive H&S engineering telemetry  Routine, emergency out-of-limits  Receive science instrument data  Potential bandwidth problem if high rate, high volume April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 10
  11. 11. Interspacecraft Comms: Potential Uses/Benefits For S/C presently within view of a ground station  Formation flying or “cluster” missions  Contact with just one S/C in the cluster may eliminate multiple, successive uplink contacts for each S/C in cluster  Uplink one set of commands to “mothership” which serves as a routerin-space for all “drone” spacecraft Independent of ground station view  Unplanned science events, opportunistic science  Automated identification (e.g., autonomous spectral/signal detection)  Autonomous mission “reconfiguration”  Notify or “cue” other spacecraft to conduct coordinated observations  Event notification to mission operations  Especially when S/C is not in view of ground station for long times (e.g., highly elliptical orbits)  Anomaly identification and resolution April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 11
  12. 12. Potential Impacts to Mission Operations If interspacecraft communications requires pointing and if it is not performed autonomously on-orbit  Plan and schedule contact times and pointing angles for communicating S/C Additional mission ops responsibility and ground resources to plan, schedule, and upload communications activity commands and data    Times when S/C can communicate On-board resources required Pointing information Monitoring system performance, especially when things go wrong  Additional engineering H&S telemetry data relative to comms subsystems to monitor and interpret      Transmitter/receiver status On-board data buffer utilization (e.g., packets/files sent/received) Communications traffic volume, duty cycle Communications error rates Reconfigure the communications “network” between spacecraft to facilitate work-arounds, degradations, failures April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 12
  13. 13. Potential Impacts to Mission Operations Data routing to the ground from a S/C not in view of a ground station  Are ground equipment resources available?     Antennas and front-end electronics Front-end processors Ground data storage Communications networks Planning science observations becomes intrinsically more complex and more than one observation scenario may be available due to multiple S/C.     Need robust science observation activity planning, scheduling, resource utilization, and conflict resolution tools Simulators may be used to better identify and evaluate several alternative “what if” scenarios Rule-based “assistants” may evaluate and recommend optimal performance criteria depending upon mission complexity On-board recorder management becomes more complex Navigation planning  “Tight” formations will likely require high fidelity simulations to ensure collision avoidance and to test various “what if” navigation alternatives. April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 13
  14. 14. Potential Impacts to Mission Operations Commanding  Increases in complexity if the mission permits commands to be routed to S/C other than those in view of the ground station.  Protocols such as IP (and IPv6 with multicasting) could be beneficial if suited to mission parameters Telemetry monitoring   If routed through the constellation, telemetry data may be available nearly continuously from all S/C not just during those periods when a “pass” occurs. Impacts ground system resource utilization and mission ops personnel utilization.  Today: after loss-of-signal, ground resources are often released, and reconfigured. Mission ops personnel perform other functions when no S/C contact is in progress.  Tomorrow: But what if spacecraft contacts were effectively “continuous” from multiple spacecraft? April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 14
  15. 15. Last Years Recommendations and Results Key Driver for Use of this Technology is System Responsiveness Inter-spacecraft Communications provides Information Exchange between vehicles to Enhance Autonomy to meet response time (latency) required to accommodate specific mission payload objectives      Telemetry Commands Timing Ancillary Information Alerts/Event collaboration Provides Data Relay for (near) Global Coverage  100% Duty Cycle would be possible  Relay information from one point to another  Faster delivery to end-user  Information presentation of data from multiple sources needs study  Impact on operations staff  Impact on Ground System performance April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 15
  16. 16. Last Years Results – Key Issues Validation and/or verification that an activity is complete and correct when out of view of ground operations (eg: commanded maneuver) NEED TO BUILD TRUST IN AUTONOMY Management of multiple spacecraft with transition from sequential operations to potentially continuous view of all vehicles simultaneously   No more concept of “post-pass analysis” as everything is potentially received in “real-time” System loading on “real-time” system April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 16
  17. 17. Backup Slides
  18. 18. The Future Space Mission Paradigm The long held paradigm of deploying and operating single spacecraft missions will be changed by the deployment and operation of Distributed Observing Systems.    Constellations Formation Flyers Sensor Webs Interspacecraft communications can offer benefits to mission operations, however it will also impose other challenges that must be identified, understood, and resolved. Constellation orbits    Will be a key driver relative to how interspacecraft communications may be conducted. Orbits and S/C configurations within orbits will impact the ground segment and mission operations support. Based upon JPL study  Multiple Mission Platform Taxonomy ; A. Barrett; JPL/CIT, Jan. 30, 2001 April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 18
  19. 19. LEO Aggregations Constellation String of Pearls Cluster April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 19
  20. 20. Elliptical Orbit Aggregations Constellation String of Pearls Cluster April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 20
  21. 21. Lissajous Orbits L2 1.5 million km 1.5 million km Sun-Earth Line L1 April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 21
  22. 22. Interspacecraft Communications Topologies Constellations Adjacent planes April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 22
  23. 23. Interspacecraft Communications Topologies Clusters Distributed Topology Centralized Mothership Drone Drone Drone April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 23
  24. 24. Interspacecraft Communications Topologies String of Pearls April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 24
  25. 25. Mission Operations: Present and Future The present  Mission operation are simple (e.g., SMEX, survey missions) to challenging (e.g., HST, “AM-train”) depending upon mission design and ops concept The future  Challenging even for relatively “simple” (e.g., survey) mission designs  Multiple S/C for each mission  More complex mission observation & planning scenarios  Potentially increased time to plan ground station contacts and create command loads  Increased impact on ground station resources (e.g., antennas)  Shorter duration between contacts for formation flyers or clusters  Larger aggregate return link data volumes April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 25
  26. 26. Mission Needs & Ops Concepts will Drive Protocol Issues IP, UDP/TCP, FTP        Mature, robust, open layered protocol architecture In wide commercial use for terrestrial applications Promotes interoperability between space and terrestrial networks Widespread use promotes lower ground system implementation costs Mitigates implementation risk and shortens implementation schedule Familiarity (terminology, concepts, usage) with user community Out-of-the box implementation of TCP “slow-start” algorithm may not be suitable to every space mission CCSDS     Mature and in wide use for NASA space missions Interoperability with other foreign space- and ground- networks Well adapted to “noisy” space communications environment SCPS and Proximity-1 emerging to address current protocol deficiencies vis-a-vis terrestrial protocols; use in future constellation communications. April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 26
  27. 27. Conclusions and Candidate Recommendations Alternative mission architectures, as well as functional and performance objectives for distributed space observing systems require a variety of interspacecraft communications solutions Regardless of the details, mission operations ground resources and especially mission operations staff workload will be impacted without the luxury of increased mission operations budgets Greater on-board autonomy and more effective ground-based automation will be beneficial and contribute to alleviate the impact to mission operations Simulation software will be highly desirable by helping to identify alternative mission scenarios and to objectively and quantitatively assess specific impacts upon science missions in the design and operational phases Introduce advanced concepts into control centers and ground systems    Goal-oriented commanding Mothership may serve as central relay for drones Automated TT&C and mission operations systems (e.g., “expert” or “rule-based” systems) April 25-26, 2002Improving Space Operations Workshop - Intersatel Slide 27

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