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AIAA Space Operations & Support Technical Committee 14th Annual Improving Space Operations Workshop Spacecraft Collision Avoidance & Co-location Track. NASA Robotic Conjunction Assessment Process: Overview and Operational Experiences. Lauri Kraft Newman Conjunction Assessment Manager

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nasa robotic conjunction assessment process overview and operational experiences

AIAA Space Operations & Support Technical Committee 14th Annual Improving Space Operations Workshop

Spacecraft Collision Avoidance & Co-location Track

NASA RoboticConjunction Assessment Process:Overview and Operational Experiences

Lauri Kraft Newman

Conjunction Assessment Manager

NASA Goddard Space Flight Center

Space Systems Protection Mission Support Office/Code 590.1


April 15, 2008

GSFC Conjunction Assessment Team:

D. McKinley, R. Frigm

a.i. solutions, Inc.

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

existing nasa ca process
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.
missions supported 1 of 2 earth science constellation
Missions Supported [1 of 2]Earth 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
missions supported 2 of 2 tracking data relay satellite system
Missions Supported [2 of 2]Tracking Data & Relay Satellite System
  • Relay system composed of ground systems and nine spacecraft in geosynchronous orbit positioned at various longitudinal slots about the Earth.

























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
ca functional overview
CA Functional Overview

Mission Owner/Operator



CA Screening





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
gsfc ca operational summary
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
leo safety volumes
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
geo safety volumes
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
data products from jspoc
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
risk assessment by ca team
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
routine operations
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
high interest event risk assessment
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
risk mitigation
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
typical leo risk mitigation maneuver planning process
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
the collision assessment system
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
collision assessment and mitigation tool suite
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
screening data processing conjunction summary report
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
screening data processing ca calendar
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.
screening data processing watch list
Screening Data Processing: Watch List
  • CA Analyst examines all data on Portal daily to produce a “watch list” of events warranting further analysis.
ocm analysis conjunction orientation
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.

ca statistics esc
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
asat event background
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

Debris Environment Growth

March 2007

Tracked objects >10 cm diameter (FENGYUN 1-C Debris in red)

Images courtesy NASA Orbital Debris Program Office

fengyun 1c deb mean equatorial height vs inclination
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

p c trend
Pc Trend

Day -3

Day -6

Day -5

Day -1

Day 0

  • On Monday Oct 17th, 1st SPCS predicted a close approach between Terra and object 14222 (SCOUT G-1 debris)
    • TCA: Oct 23rd
    • Miss distance < 500 m
    • 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.
avoidance maneuver planning
Avoidance Maneuver Planning

Day -3

Day -6

Day -5

Day -1

Day 0

  • Throughout the week, the miss distance trended downward from solution to solution
  • On Thursday, October 20th the miss distance had dropped to <200 m, risk mitigation maneuver 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
miss distance trend
Miss Distance Trend

Day -3

Day -6

Day -5

Day -1

Day 0

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 22:30 Z
    • Actual miss distance = 4.6 km
    • Actual Pc≈ 0
lessons learned
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