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Constellation Operations: InterSatellite Communications

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RF, optical, and digital communications technologies. Communications protocols standards ... Key Driver for Use of this Technology is System Responsiveness ... – PowerPoint PPT presentation

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Title: Constellation Operations: InterSatellite Communications


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
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

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

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

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
    theres 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

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

7
Information that Needs to be Exchanged
  • Spacecraft and Instrument HS 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

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

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

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 HS engineering telemetry
  • Routine, emergency out-of-limits
  • Receive science instrument data
  • Potential bandwidth problem if high rate, high
    volume

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 router-in-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

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 HS 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

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.

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?

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

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

17
Backup Slides

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

19
LEO Aggregations
Constellation
String of Pearls
Cluster
20
Elliptical Orbit Aggregations
Constellation
String of Pearls
Cluster
21
Lissajous Orbits
L2
1.5 million km
1.5 million km
Sun-Earth Line
L1
22
Interspacecraft Communications TopologiesConstell
ations
Adjacent planes
23
Interspacecraft Communications TopologiesClusters
24
Interspacecraft Communications TopologiesString
of Pearls
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

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.

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 TTC and mission operations systems
    (e.g., expert or rule-based systems)
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