Newman, Lauri K.

NASA Technical Reports Server

National Aeronautics and Space Administration
www.nasa.gov
NASA ROBOTIC CARA
Lauri K. Newman
NASA Robotic Conjunction Assessment Manager
30 MAR 2017
NASA Conjunction Assessment 
Risk Analysis (CARA)
https://ntrs.nasa.gov/search.jsp?R=20170003047 2019-08-29T22:39:41+00:00Z
N A S A C A R A
• NASA performs conjunction 
assessment risk analysis for 
safety of flight of all of its 
operational assets
– Performed by CARA at NASA 
GSFC for robotic satellites
– Performed by TOPO at NASA 
JSC for human spaceflight
• The Conjunction Assessment 
Risk Analysis (CARA) was stood 
up to offer this service to all 
NASA robotic satellites
– Currently provides service to 
~65 operational satellites
• NASA unmanned assets
• Other agency assets such 
as NOAA, DMSP
• Foreign partner assets
• Commercial assets
NASA’s Process:  CARA
2
N A S A C A R A
NASA Conjunction Assessment History
Courtesy of NASA/JSC
Ansley C. Browns
1988:
Space Shuttle Discovery
Return to Flight;
Box method used for CA; later 
Shuttle adopts Pc method
1986:
Challenger accident
1992:
NASA begins Pc 
development for ISS CA
1998:
ISS First Element 
Launch
1996:
NASA begins conjunction 
assessment of Mir space 
station
1999:
First attempted ISS DAM 
attempted and fails; a few 
months later first ISS DAM 
successfully executed
1990s – present:
NASA works with USSTRATCOM to  
develop tools, data exchange formats, 
improve processes for catalog 
maintenance and CA 
Present:
NASA continues work with 
USSTRATCOM to maintain high 
quality CA for human spaceflight 
and robotic missions
2005:
NASA begins CA for 
robotic missions
NASA has performed CA for 29 years.  Initial USSTRATCOM capability 
developed with NASA.
N A S A C A R A
The CARA Process Helps Manage On-
Orbit Collision Risk
Conjunction Assessment (CA) is the 
process of identifying close approaches 
between two orbiting objects; sometimes 
called conjunction “screening”
The 18th Space Control Squadron at the 
Joint Space Operations Center (JSpOC)
– a USAF unit at Vandenberg AFB, 
maintains the high accuracy catalog of 
space objects, screens CARA-supported 
assets against the catalog, performs 
OD/tasking, and generates close approach 
data
CA Risk Analysis (CARA) is the process 
of assessing collision risk and assisting 
satellites plan maneuvers to mitigate that 
risk, if warranted
The CARA Team at NASA-GSFC provides 
CARA for all NASA operational robotic 
satellites, as well as a service provider for 
some other external agency/organizations
∆V
Collision Avoidance (COLA) is the 
process of executing mitigative action, 
typically in the form of an orbital 
maneuver, to reduce collision risk due to 
a conjunction
Each satellite Owner/Operator (O/O) –
mission management, flight dynamics, 
and flight operations – are responsible for 
making maneuver decisions and 
executing the maneuvers 
N A S A C A R A
CARA Operational Process: 
Close Approach Predictions at the JSpOC
• The JSpOC maintains an accurate state for all trackable
objects
– Note that these solutions use non-cooperative tracking 
from the Space Surveillance Network (SSN), and do 
not contain maneuvers
• In support of CARA, the CARA-dedicated Orbital Safety 
Analysts (OSA) 
– Perform routine screenings – 3x day for LEO, 2x for 
GEO/HEO
• Against JSpOC’s Astrodynamics Support 
Workstation (ASW) solution and for some missions 
the O/O solution as well
– Inspect orbit determination
– Perform manual orbit determination, if warranted
– Adjudicate tasking level of secondary objects; request 
increased tasking, if warranted
– Generate and deliver necessary data products
• JSpOC is staffed by CARA-dedicated OSAs 20 hours/ day
The Screening Duration is the “lookout” period 
of time for which conjunctions are identified.  
This is 7 days for LEO assets and 10 days for 
GEO/HEO assets
The Screening Volume is the geometric 
volume placed around the asset during the 
conjunction screening process; any objects that 
violate this volume trigger data products to be 
generated and delivered.  The screening 
volumes are re-sized annually by CARA using a 
95% capture of the relative uncertainties in 
each orbital regime based two-year moving 
window historical conjunction data
N A S A C A R A
CARA Operational Process: 
Collision Risk Analysis at NASA-GSFC
• CARA is responsible for assessing, 
communicating, and assisting with 
mitigation of on-orbit collision risk
• As data is received, the CARA system 
automatically processes that data, and 
generates & delivers 
– CARA Summary Reports to O/O
– Work List sent to CARA OSAs
• CARA team performs routine risk analysis
– Pc; Pc sensitivity
– Conjunction Geometry
– OD Evaluation / Solution Consistency
– Space Weather Sensitivity
– Maneuver planning & evaluation
• For high-risk conjunctions, CARA builds 
and delivers a High Interest Event (HIE) 
briefing with detailed analyses, and 
planning & decision information
The Collision Probability (Pc) is the 
probability that, given the uncertainty in the two 
objects’ positions as described by their 
covariance matrix, that the actual miss distance 
is less than the hard-body region
N A S A C A R A
Sep05 Mar06 Sep06 Mar07 Sep07 Mar08 Sep08 Mar09 Sep09 Mar10 Sep10 Mar11 Sep11 Mar12 Sep12 Mar13 Sep13 Mar14 Sep14 Mar15 Sep15 Mar16 Sep16
0
200
400
600
800
1000
 
 
 
 
 
 
All Secondary Objects
All Debris Objects
Fengyun 1-C Debris
Iridium-33/Cosmos-2251 Debris
DMSP 5D-2 F13 Debris
NOAA 16 Debris
Analysts
Mission Context:  Number of 
Conjunctions in LEO
Unique Events within 0.5x5x5-km Volume by Object Type, LEO
Jason-1 / 
TOPEX 
Repeating 
Conjunction
Landsat-5 / 
A-Train 
Crossover
Addition 
of NOAA 
& DMSP 
Satellites
Chinese ASAT
11 Jan 2007
Iridium/Cosmos 
Collision
10 Feb 2009
NPR requiring all operational 
assets, not just maneuverable 
May 2009 SHY Changes
GRACE
Satellite
Re-positioning
N A S A C A R A
Collision Avoidance Maneuvers History
8
N A S A C A R A
CARA Summary Report:  Event Summary
Grouped 
by Risk 
using Pc 
thresholds
Ordered 
within group 
by Days to 
TCA
Days to TCA TCA (GMT) Secondary Object
Primary 
Ephem
Source
Secondary 
Ephem 
Source
Screening 
Epoch 
(GMT)
Miss [m] R [m] I [m] C [m]
Tracked 
Since 
Previous 
OCM?
Pc
Above
Mission
Threshold?
4.2 8 Nov 2015 04:45:41
TITAN 3C 
TRANSTAGE 
DEB (01722)
ASW ASW 3 Nov 2015 19:45:32 783.0 22.8 334.1 708.4 Y
4.90e-4
(1:2K) ---
4.2 8 Nov 2015 04:45:41
TITAN 3C 
TRANSTAGE 
DEB (01722)
O/O + ASW 
cov. ASW
3 Nov 2015 
19:38:46 91.0 17.7 37.6 81.1 Y
2.03e-2
(1:49) ---
GCOM-W1 (38337) [HBR = 20m]
Days to 
TCA TCA (GMT)
Secondary 
Object
Primary 
Ephem
Source
Secondary 
Ephem 
Source
Screening 
Epoch 
(GMT)
Miss [m] R [m] I [m] C [m]
Tracked 
Since 
Previous 
OCM?
Pc
Above
Mission
Threshold?
4.6 8 Nov 2015 15:04:53
UNKNOWN 
(87798) ASW ASW
3 Nov 2015 
19:46:16 9503 -7.4 1224 9424 N
6.38e-7
(1:2M) ---
4.6 8 Nov 2015 15:04:53
UNKNOWN 
(87798)
O/O + ASW 
cov. ASW
3 Nov 2015 
19:38:48 9265 18.0 1194 9188 Y
6.39e-7
(1:2M) ---
Days to TCA TCA (GMT) Secondary Object
Primary 
Ephem 
Source
Secondary 
Ephem 
Source
Screening 
Epoch 
(GMT)
Miss [m] R [m] I [m] C [m]
Tracked 
Since 
Previous 
OCM?
Pc
Above
Mission
Threshold?
4.5 8 Nov 2015 13:25:58
UNKNOWN 
(87798) ASW ASW
3 Nov 2015 
19:46:16 14857 111.2 1933 14730 N 0.00e00 ---
4.5 8 Nov 2015 13:25:58
UNKNOWN 
(87798)
O/O + ASW 
cov. ASW
3 Nov 2015 
19:38:48 14622 136.4 1906 14497 Y 0.00e00 ---
4.9 8 Nov 2015 21:40:36
UNKNOWN 
(87798) ASW ASW
3 Nov 2015 
19:46:18 12239 34.9 -1516 -12144 N
2.91e-8
(1:34M) ---
A. High Risk Conjunction Events [Collision Probability >= 4.4e-4]
B. Monitor Conjunction Events [1e-7 <= Collision Probability < 4.4e-4]
C. Low Risk Conjunction Events [Collision Probability < 1e-7]
N A S A C A R A
CARA Summary Report:  Event Details
1. Summary header
 Days to TCA
 Secondary Name & ID
 Screening Epoch
 Latest Miss Distance
 Latest Pc & Risk 
Characterization
2. Pc History and Event Flags
3. Latest secondary object OD & 
tracking information
 Avg Tracks / Day
 Time Since Last 
Observation
 Total Propagation Time 
of vector
 Single Station Indicator
4. Maneuver information
5. Filenames of O/O Products 
used
6. ASW and O/O Miss 
Component History
N A S A C A R A
CARA Summary Report:  Continued
1. ASW and O/O Conjunction 
Planes
2. Miss History
3. ASW and O/O Event 
Geometry
N A S A C A R A
• CARA system automatically generates & delivers a prioritized work list
– CARA OSAs perform their duties in priority order
– Ensures limited resources are used effectively – in the order of risk or 
potential to become high risk
– Closed-loop process between OSAs and CARA
– Representative format:
1. Aqua vs. 12345
2. Aqua vs. 23456
3. Aqua vs. 34567
4. Aqua vs. 45678
5. Aqua vs. 56789
• Also includes list of recent (for indicating when OD should be cut) and 
upcoming maneuvers (satisfies NASA maneuver reporting requirement) 
OSA Work List
Grouped by 
Risk using Pc 
thresholds
Rank-ordered within group by 
increasing OD quality
N A S A C A R A
Maneuver Planning
• A trade-space contour plot 
shows the effect that a 
range of phase times and 
delta-v magnitudes have 
on miss distance
– Single conjunction 
event (top)
– Multiple events (bottom)
• Assists with initial 
maneuver planning
– Save time-expensive 
iteration cycles for high 
fidelity maneuver 
planning
Burn dv, cm/s
P
ha
si
ng
 T
im
e 
(U
TC
)
Log10 Pc Contour
25994 vs. 32081 | TCA 11/12 06:38
 
 
0 2 4 6 8 10 12 14 16 18 20
11/11 14:00
11/11 14:53
11/11 15:46
11/11 16:40
11/11 17:33
11/11 18:26
11/11 19:20
11/11 20:13
11/11 21:06
11/11 22:00 -10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
N A S A C A R A
• CARA is continuously trying to enhance its service offering through 
analysis 
• Recent Enhancements
– Calculation of 3D Pc
– Space weather trade space
– Multiple event maneuver planning
– Covariance realism and Pc uncertainty
• Current/ongoing areas of inquiry
– Screening Volume sizing/shaping
– S-band Fence CA impacts
– Automated OD quality assessment, covariance quality estimates, and 
related sensor tasking modification recommendations
– Pc calculations that accommodate non-Gaussian uncertainty 
volumes 
Continuous Enhancement Process
N A S A C A R A
• Low / No Thrust Protected Assets
• Space Fence
– Compensatory algorithm development
– Advanced risk assessment methods (event aggregation)
– Non-traditional risk mitigation techniques
– Threshold Agency Standards
• CubeSats / SmallSats
• Mega Constellations
• Improved Atmospheric Density Modeling (and Uncertainty 
Quantification)
• Extremely fast non-linear orbit propagation
• Co-location & Systematic Conjunctions
• Space Traffic Management
Future Challenges


NASA Conjunction Assessment Risk Analysis (CARA)

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