NASA Robotic Conjunction Assessment Process: Overview and Operational Experiences

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NASA RoboticConjunction Assessment
ProcessOverview and Operational Experiences
AIAA Space Operations Support Technical
Committee 14th Annual Improving Space Operations
Workshop Spacecraft Collision Avoidance
Co-location Track
Lauri Kraft Newman Conjunction Assessment
Manager NASA Goddard Space Flight Center Space
Systems Protection Mission Support Office/Code
590.1 301-286-3155 Lauri.K.Newman_at_nasa.gov April
15, 2008 GSFC Conjunction Assessment Team D.
McKinley, R. Frigm a.i. solutions, Inc.
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Agenda

• NASA Policy for Conjunction Assessment
• NASA Robotic Conjunction Assessment Process
• Operations Process
• Tool Suite Description
• Statistics
• Terra vs. 14222 Case Study
• Lessons Learned

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NASA CA Policy

• Policy for Limiting Orbital Debris (NPR 8715.6)
  requires routine CA for all NASA assets with
  maneuvering capability (signed 8/17/07).
• FDAB has the capability to offer this service to
  any mission
• 3.4 Conjunction Assessments during Mission
  Operations (for Earth-Orbiting Spacecraft)
• 3.4.1 The NASA Program/Project Manager shall
  have conjunction assessment analyses performed
  routinely for all maneuverable Earth-orbiting
  spacecraft with a perigee height of less than
  2000 km in altitude or within 200 km of GEO
  (Requirement 56891).
• 3.4.2 Conjunction assessment analyses shall be
  performed using the USSTRATCOM high-accuracy
  catalog as a minimum (Requirement 56892).
• 3.4.3 The NASA Program/Project Manager shall
  have a collision risk assessment and risk
  mitigation process in place for all maneuverable
  Earth-orbiting spacecraft that are performing
  routine conjunction assessment analyses
  (Requirement 56893).

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Existing NASA CA Process

• NASA Performs CA for its Human space assets
  (Shuttle and Station) as well as for various
  unmanned assets.
• Requirements dictated by NPR 8715.6
• NASA/JSC performs CA for Human Space Flight
  assets 3 times a day
• NASA/GSFC manages the CA for all unmanned NASA
  assets
• GSFC has performed CA routinely since January
  2005 for
• 11 Earth Science Constellation members, including
  USGS-owned Landsat missions
• 9 TDRS satellites
• GSFC program is expanding to encompass all NASA
  unmanned missions per the new requirement.
• Plan to add 12 more missions over the next year.

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Missions Supported 1 of 2Earth Science
Constellation

• Combination of NASA and Foreign assets
• Each mission makes its own risk mitigation
  decisions
• Each mission subject to own maneuverability,
  comm, and ops concept constraints

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Missions Supported 2 of 2Tracking Data Relay
Satellite System

• Relay system composed of ground systems and nine
  spacecraft in geosynchronous orbit positioned at
  various longitudinal slots about the Earth.

WSC
TDRS-7 150 Stored
TDRS-8 174.3W Stored
TDRS-9 062W Stored
GRGT
TDRS-4 046W
TDRS-5 171W
TDRS-3 275W
TDRS-6 173.7W
TDRS-1 049W
TDRS-10 041W
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FY09 CA Customer Base
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Current GSFC CA Effort

• Pertinent National Space Policy excerpt
• National Security Space Guidelines To achieve
  the goals of this policy, the Secretary of
  Defense (SECDEF) shall Have responsibility for
  space situational awareness in this capacity,
  the SECDEF shall support the space situational
  awareness requirements of the Director of
  National Intelligence and conduct space
  situational awareness for . civil space
  capabilities and operations, particularly human
  space flight activities.
• GSFC has an agreement with the Joint Space
  Operations Center (JSpOC)/Space Superiority Cell
  to obtain conjunction assessment screening
  predictions for NASA robotic assets

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CA Functional Overview
Mission Owner/Operator
JSpOC
GSFC CA Team
CA Screening
Risk Assessment
Risk Mitigation
Curvilinear Collision Probability

• Generate Close Approach Predictions
• Consists of
• Performing Orbit Determination for catalog
  objects
• Computing separation distance between objects in
  high accuracy space object catalog
• Summarizing and reporting results

• Analyze data to determine threat
• Consists of
• Trending miss distance and specific orbit
  determination related parameters
• Computing collision probability
• Performing collision probability sensitivity
  analysis

• CA analysts assist the Flight Operations Team
• Consists of
• Maneuver planning
• Maneuver execution

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GSFC CA Operational Summary

• Goddard-dedicated Orbital Safety Analysts at the
  JSpOC generate CA data M-F (weekends as needed)
  using the high-accuracy (SP) catalog
• Close approach predictions are made 7 days into
  the future for LEO missions
• Close approach predictions are made 10 days into
  the future for GEO missions
• Any planned maneuvers are modeled in the
  ephemerides provided by the mission.
• The CA data is provided to Goddard via secure FTP
  and e-mail.
• The GSFC CA team processes the data and provides
  risk assessment analysis results to the mission
  stakeholders

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LEO Safety Volumes

• Three different mission safety volumes define
  data product delivery from JSpOC/SCC and data
  processing by GSFC CA team
• The safety volumes are expressed in the primary
  UVW coordinate frame U (radial), V (in-track)
  and W (cross-track)
• Monitor Volume (ellipsoid) /- 2 x 25 x 25 km
• Largest filter used to initially identify and
  report potential close approaches
• Tasking Volume (box) /- 0.5 x 5 x 5 km
• Serves as a second warning and an elevated level
  of concern
• Tasking level on the secondary object is
  increased (if necessary)
• Watch Volume (standoff distance) 1 km

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GEO Safety Volumes

• Monitor Volume (standoff distance) 40 km
• Largest filter used to initially identify and
  report potential close approaches
• Alert/Tasking Volume (standoff distance) 15 km
• Serves as a second warning and an elevated level
  of concern
• Tasking level on the secondary object is
  increased (if necessary)
• Watch Volume (standoff distance) 2 km
• Risk mitigation maneuver planning options
  examined

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Data Products from JSpOC

• All Monitor Volume violations are summarized in a
  Conjunction Screening Summary and delivered to
  the CA SFTP server. The Screening Summary
  contains
• Time of Closest Approach (TCA)
• Total Miss Distance
• Miss Distance Position and Velocity Components in
  RIC frame
• An additional email is sent documenting tracking
  data and tasking level
• An Orbital Conjunction Message (OCM) is provided
  for Tasking/Alert Volume violations. The OCM
  contains
• TCA
• Asset State/Covariance at TCA
• Object State/Covariance at TCA
• Other orbit determination information helpful in
  performing collision risk assessment.
• Vector Covariance Messages (VCMs) for both
  objects are provided for Watch Volume violations.
• VCMs contain epoch state and covariance
  information
• Used for maneuver planning

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Risk Assessment Process
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Risk Assessment by CA Team

• Screening data is analyzed in two distinct ways
• Routine Operations
• Daily activity to assess most recent delivery of
  close approach predictions
• Disposition conjunctions as a threat, not a
  threat, or monitor event based on analysis
• High Interest Events
• Events that have significant potential to be a
  threat or provide a unique analysis opportunity
• Trending of orbit determination parameters and
  conjunction geometry
• Probability of Collision Sensitivity analysis
• Risk Mitigation Maneuver planning

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Routine Operations

• At the end of the day, the OSA provides data
  products to the GSFC CA team
• JSpOC OSA posts data products to the SFTP site.
• CAS automatically parses the data and puts it
  into the database for trending and use with other
  tools
• The CAM Tool Suite is run each time new data is
  received
• Data is processed by the automated CAS utility
  and generates various reports
• A summary report is generated containing all
  pertinent information and delivered to the
  stake-holders
• An OCM Analysis Report is generated for each
  event and posted to a secure website
• The following morning the CA Analyst
• Verifies all data delivered to CA team and
  mission stakeholders
• Reviews Screening Summary
• Reviews all OCM Analysis Reports
• Creates Watch List detailing all conjunctions in
  the Screening Summary and the action to be taken
• Performs additional analysis on conjunctions
  using the Collision Risk Assessment Tool Suite

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High Interest Event Risk Assessment

• Pc and miss distance data alone cannot be used to
  fully assess the threat
• Additional analyses to help establish and
  quantify risk include
• Orbit determination (OD) consistency from
  solution to solution
• Number of tracks and observations
• Ballistic Coefficient
• Solar Radiation Pressure Coefficient
• Energy Dissipation Rate
• Radar Cross Sectional Area
• Probabilistic Risk Assessment Analysis
• Realistic probability calculations based on
  realistic state and covariance predictions
• Pc evolution as the time to the close approach
  event gets shorter
• Pc sensitivity analysis based on changes to
  inputs
• Conjunction Geometry (clock angle, approach
  angle)
• Position of hard body radius with respect to the
  3-sigma covariance ellipse

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Risk Mitigation

• If the threat evaluation indicates the need to
  plan and (possibly) execute a maneuver
• CA Team notifies Mission Owner/Operator
• CA Team analyzes maneuver options that will
  mitigate the threat - first guess
• CA Team works with Mission Owner/Operator to plan
  risk mitigation options.
• Maneuver must sufficiently increase the
  separation distance and decrease the collision
  probability
• Maneuver must meet orbit requirements if at all
  possible
• CA Team analyzes sensitivity of Pc to expected
  variations in burn performance

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Typical LEO Risk Mitigation Maneuver Planning
Process

• Maneuver planning begins TCA-3 days
• As TCA approaches, uncertainty decreases, but
  avoidance options decrease
• Allows time to
• Improve the OD solution on the secondary object
• Evaluate several maneuver options
• Have 1st SPCS screen the options for
  post-maneuver close approaches
• plan the final maneuver
• Upload commands to the spacecraft

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The Collision Assessment System

• Collision Assessment System (CAS) was developed
  to store and analyze the large volumes of data
  received.
• CAS is automated and comprised of several
  elements
• Secure File Transfer Protocol Server
• Parser / Monitor Scripts
• Database
• Collision Assessment and Mitigation (CAM) Tool
  Suite
• Secure Website
• Configuration Management System

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Collision Assessment and Mitigation Tool Suite

• The CAM Tool Suite is the part of CAS that
  provides analysis utilities
• The CAM Tool Suite consists of 6 modules
• Conjunction Visualization Script
• 2-D Collision Probability Utility
• Monte Carlo Simulation
• 3-D / Curvilinear Collision Probability Tool
• Time History Trending Utility
• Collision Avoidance Planning Tool
• The modules are built using FreeFlyerTM and
  MatlabTM
• Output from tools is formatted into a single PDF
  report for each OCM

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Screening Data Processing Conjunction Summary
Report

• Overlap compare computes differences between
  subsequent solutions for the same close approach
• JSpOC and Owner/Operator solutions are compared
• Results are posted to the Portal website

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Screening Data Processing CA Calendar

• A CA Calendar is produced and posted to the
  Portal
• Contains close approach predictions of less than
  1 km, events having Pc 1e-7, and planned
  maneuver dates/times.

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Screening Data Processing Watch List

• CA Analyst examines all data on Portal daily to
  produce a watch list of events warranting
  further analysis.

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OCM Analysis Conjunction Orientation
Conjunction Orientation Shows the position and
position covariance of the Primary (blue) and
Secondary (green) Objects in Earth Centered
Inertial (ECI) coordinates.
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OCM Analysis Pc Sensitivity
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OCM Analysis Conjunction Plane
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Earth Science ConstellationConjunction
Statistics
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CA Statistics - ESC

• For the Earth Science Constellation
• Each asset averages 15 unique conjunctions per
  week within the Monitor Volume (780/yr)
• Each asset averages 1 unique conjunction per week
  within the Tasking Volume (52/yr)
• Each asset averages 3 high interest events per
  year - ops team engages in maneuver planning
  process
• International Space Station (ISS) statistics for
  comparison (340 km altitude, 51.6 deg inc)
• For 2005, saw 24 Monitor Volume conjunctions,
  none with Pc 1 x 10-5
• Have seen 251 conjunctions from 7/99 12/05
• Have executed 4 debris avoidance maneuvers
• Average of 1.2 maneuvers per year predicted

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ESC Safety Volume ViolationsPer Month
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Average Number of Watch Volume Violations per
Asset per Month
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ESC Risk Mitigation Maneuvers Performed
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Chinese ASAT Event
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ASAT Event - Background

• On January 11th, 2007 China performed a
  successful test of an anti-satellite (ASAT)
  weapon
• The ASAT test consisted of a medium-range
  ballistic missile destroying a Chinese weather
  satellite
• Event occurred at an altitude of 535 miles (861
  km)
• First close approach with an ESC mission was
  predicted weeks after the event (04 Feb)
• Current number of cataloged objects 2000
• The NASA Orbital Debris Program Office estimates
  35,000 pieces larger than 1 cm

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Debris Environment Growth
March 2007
Tracked objects 10 cm diameter (FENGYUN 1-C
Debris in red)
Images courtesy NASA Orbital Debris Program Office
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FENGYUN 1C DEB Mean Equatorial Height vs.
Inclination -
Height Statistics (Oct 2007) (Min, Max, Mean,
Std) 195.7 2577.9 872.5 174.8
?
ESC orbit
Inclination Statistics (Oct 2007) (Min, Max,
Mean, Std) 95.2 105.6 99.0 0.7
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ASAT Safety Volume Violations
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ASAT - Percent of Total
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ESC Monitor Volume Violations FENGYUN 1C Debris
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Case StudyTerra vs. 14222TCA October 23, 2005
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Pc Trend

• On Monday Oct 17th, 1st SPCS predicted a close
  approach between Terra and object 14222 (SCOUT
  G-1 debris)
• TCA Oct 23rd
• Miss distance
• Pc 1e-2
• 14222 characteristics at TCA
• Period 98.66 min
• Apogee Height 710.79 km
• Perigee Height 679.20 km
• Inclination 82.39

GSFC-Computed Pc Values For Each OCM Solution
Collision Probability
Days to TCA

• Throughout the week, the Pc remained high
  primarily due to the decreasing miss distance and
  the close approach geometry.

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Avoidance Maneuver Planning

• Throughout the week, the miss distance trended
  downward from solution to solution
• On Thursday, October 20th the miss distance had
  dropped to planning took place
• Four different maneuver options were generated
  and sent to JSpOC-Mountain for screening
• Performing any of these maneuver options would
  increase the miss distance to a safe level and
  decrease the Pc by several orders of magnitude

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Miss Distance Trend
Day -3
Day -6
Day -5
Day 0
Day -1
Day -2

• On Friday, October 21st the reported miss
  distance reached a local minimum and the
  collision probability reached a local maximum
• Miss distance 50 60 m
• Collision probability still on the order of 1e-2
• Decision was made to perform maneuver option 2
• Based on trends throughout the week and the
  post-maneuver close approach screening results
• Executed at 2230 Z
• Actual miss distance 4.6 km
• Actual Pc 0

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Lessons Learned

• Automation is essential for managing the workload
  of routine data processing
• Personnel experienced in orbit determination are
  required to assess the threat using multiple
  criteria
• Each event appears to be sufficiently unique such
  that a standardized mitigation approach cannot be
  adapted
• Each spacecraft sees a handful of conjunctions
  per year for which avoidance maneuver planning is
  considered