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
NASA Goddard Space Flight Center
Space Systems Protection Mission Support Office/Code 590.1
301-286-3155
Lauri.K.Newman@nasa.gov
April 15, 2008
GSFC Conjunction Assessment Team:
D. McKinley, R. Frigm
a.i. solutions, Inc.
Agenda
•
•
NASA Policy for Conjunction Assessment
NASA Robotic Conjunction Assessment
Process
•
•
•
•
•
Operations Process
Tool Suite Description
Statistics
Terra vs. 14222 Case Study
Lessons Learned
2
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).
3
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.
4
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
5
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.
WSC
TDRS-8
174.3°W
Stored
TDRS-7
150°
Stored
TDRS-6
173.7°W
TDRS-5
171°W
TDRS-9
062°W
Stored
GRGT
TDRS-1
049°W
TDRS-4
046°W
TDRS-3
275°W
TDRS-10
041°W
6
FY09 CA Customer Base
Earth Science
Constellation
GEO Regime
Other NASA
Missions
14780 - Landsat -5
25682 - Landsat-7
25994 - Terra
26619 - EO-1
26620 - SAC-C
27424 - Aqua
27642 - ICESat
28376 - Aura
28498 - PARASOL
29107 - CloudSat
29108 - CALIPSO
TBD – OCO (launch 12/15/08)
TBD – Glory (launch 3/1/09)
13969 - TDRS 1
19548 - TDRS 3
19883 - TDRS 4
21639 - TDRS 5
22314 - TDRS 6
23613 - TDRS 7
26388 - TDRS 8
27389 - TDRS 9
27566 - TDRS 10
TBD - GOES-8 (launch 11/08
– L&EO only)
TBD - SDO (launch ~ 4/09)
26997 - JASON
22076 - TOPEX
25063 - TRMM
25789 - QuickSCAT
27391 - GRACE-1
27392 - GRACE-2
TBD - GLAST (launch5/16/08)
TBD - IBEX (launch 7/15/08)
TBD - OSTM (launch 6/15/08)
7
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
8
CA Functional Overview
JSpOC
CA Screening
GSFC CA Team
Mission
Owner/Operator
Risk
Risk
Curvilinear Collision Probability
Assessment
Mitigation
• 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
9
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
10
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 (crosstrack)
• 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
11
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
12
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
13
Risk Assessment Process
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
15
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
16
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
17
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
18
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 postmaneuver close approaches
– plan the final maneuver
– Upload commands to the spacecraft
19
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
20
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:
1.
2.
3.
4.
5.
6.
•
•
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
21
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
22
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.
23
Screening Data Processing: Watch List
•CA Analyst examines all data on Portal daily to produce a
“watch list” of events warranting further analysis.
24
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.
25
OCM Analysis: Pc Sensitivity
26
OCM Analysis: Conjunction Plane
27
Earth Science Constellation
Conjunction Statistics
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
29
ESC Safety Volume Violations
Per Month
30
Average Number of Watch Volume Violations
per Asset per Month
ESC Watch Volume Violations - Monthly Averages
2.5
Number of Unique Violations
2
1.5
1
0.5
0
L5
L7
Terra
EO-1
SAC-C
Aqua
ICESat
Aura PARASOL CloudSat Calipso
31
ESC Risk Mitigation Maneuvers
Performed
Asset
Secondary
Maneuver Date
Terra
14222 (SCOUT G-1)
21-Oct, 2005
PARASOL
81257 (Analyst SAT)
16-Jan, 2007
SAC-C
14345 (SL-8 DEB)
16-Feb, 2007
Terra
31410 (FENGYUN 1C
DEB)
22-Jun, 2007
CloudSat
28893 (SINAH 1)
04-Jul, 2007
32
Chinese ASAT Event
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
34
Debris Environment Growth
March 2007
Tracked objects >10 cm diameter
(FENGYUN 1-C Debris in red)
Images courtesy NASA Orbital Debris Program Office
35
FENGYUN 1C DEB
Mean Equatorial Height vs. Inclination Height vs. Inclination - FENGYUN 1C DEB
3000
Height Statistics (Oct 2007)
(Min, Max, Mean, Std)
2500
Equatorial Height (km)
195.7 2577.9 872.5 174.8
FENGYUN 1C DEB - Height Distribution
1
0.9
Cumulative Distribution
0.8
2000
1500
1000
●
0.7
500
0.6
0.5
0
94
ESC orbit
96
98
100
102
104
106
Inclination (deg)
0.4
Inclination Statistics
(Oct 2007)
0.3
0.2
(Min, Max, Mean, Std)
0.1
0
95.2 105.6 99.0 0.7
0
500
1000
1500
2000
Mean Equatorial Height (km)
2500
3000
36
ASAT Safety Volume Violations
37
ASAT - Percent of Total
38
ESC Monitor Volume Violations
FENGYUN 1C Debris
ESC MV Violations - ASAT
80
Number of Unique Violations
70
60
50
40
30
20
10
0
L5
L7
Terra
EO-1
SAC-C
Aqua
ICESat
Aura PARASOL CloudSat Calipso
39
Case Study
Terra vs. 14222
TCA October 23, 2005
Pc Trend
Day -5
Day -3
• 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˚
Day -1
-1
10
Probability
Collision
Collision Probability
Day -6
Day 0
GSFC-Computed Pc Values
For Each OCM Solution
-2
10
-3
10
7
6
5
4
Days to TCA
3
2
1
Days to TCA
• Throughout the week, the Pc remained high primarily due to the
decreasing miss distance and the close approach geometry.
41
Avoidance Maneuver Planning
Day -6
Day -3
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 JSpOCMountain for screening:
Option #
DV (m/s)
Burn Time
Duration
DSMA (m)
Separation @ TCA
1
0.0114
10/21 22:30 Z
2.0 sec
+21.6
5.5 km
2
0.0157
10/21 22:30 Z
2.7 sec
+29.6
7.5 km
3
0.0172
10/21 22:30 Z
3.0 sec
+32.4
8.5 km
4
0.0173
10/22 14:07 Z
3.0 sec
+32.6
5.5 km
• Performing any of these maneuver options would increase the miss
distance to a safe level and decrease the Pc by several orders of
magnitude
42
Miss Distance Trend
Day -6
Day -5
Day -3
• On Friday, October 21st the
reported miss distance reached a
local minimum and the collision
probability reached a local
maximum
• 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
Day 0
450
400
350
Miss Distance (meters)
– Miss distance 50 – 60 m
– Collision probability still on the
order of 1e-2
Day -1
Day -2
300
250
200
150
100
50
0
7
6
5
4
Days to TCA
3
1
2
43
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
44