18th Space Control Squadron
Combined Force Space Component Command
Vandenberg Air Force Base, California, USA
Tel +1-805-605-3533
www.space-track.org

SPACEFLIGHT SAFETY HANDBOOKFOR SATELLITE OPERATORSVERSION 1.5  AUGUST 2020

18 SPCS Processes for On-Orbit Conjunction Assessment & Collision AvoidanceTABLE OF CONTENTS
Contents

Significant Revision History _____________________________________________________________________________ 1
USSPACECOM SSA Sharing Program____________________________________________________________________ 3

Program Description ______________________________________________________________________________________________3
Space-Track.org____________________________________________________________________________________________________3

Conjunction Assessment Process _______________________________________________________________________ 4

On-Orbit Conjunction Assessment (CA) _________________________________________________________________________4
HAC vs HAC _____________________________________________________________________________________________________5
O/O Ephemeris vs HAC (O/O EPH vs HAC)___________________________________________________________________6

O/O Ephemeris vs O/O Ephemeris (O/O EPH vs O/O EPH) ________________________________________________6

On-Orbit Collision Avoidance (COLA)____________________________________________________________________________6
Basic Emergency CA and COLA Services ________________________________________________________________________7
Advanced CA and COLA Services _________________________________________________________________________________7
Screening Schedule _______________________________________________________________________________________________8
Screening Volumes ________________________________________________________________________________________________9
Reporting Criteria _______________________________________________________________________________________________ 10
Notifications _____________________________________________________________________________________________________ 11
Basic Emergency CA Notifications _____________________________________________________________________________ 12
Advanced CA Notifications _____________________________________________________________________________________ 12

Launch Conjunction Assessment_______________________________________________________________________________ 13

Early Orbit Conjunction Assessment __________________________________________________________________________ 13

End-of-Life/Disposal Support __________________________________________________________________________________ 14
Deorbit Support _________________________________________________________________________________________________ 14
Tasking ___________________________________________________________________________________________________________ 14

Ephemeris Formats _____________________________________________________________________________________ 15

Overview _________________________________________________________________________________________________________ 15
NASA Ephemeris Format _______________________________________________________________________________________ 16
UTC Ephemeris Format _________________________________________________________________________________________ 17

Generic On-Orbit Ephemeris Format __________________________________________________________________________ 18

TABLE OF CONTENTS
Modified ITC Ephemeris Format _______________________________________________________________________________ 19
Orbital Ephemeris Message (OEM) Format ___________________________________________________________________ 20

How to Name Ephemeris Files _________________________________________________________________________ 23

Overview _________________________________________________________________________________________________________ 23
File Name Examples ____________________________________________________________________________________________ 24

How to Submit Ephemeris Files _______________________________________________________________________ 25

Overview _________________________________________________________________________________________________________ 25

Submitting EphEmeris Through Space-Track.org_____________________________________________________________ 26
Manual Upload of Ephemeris Files_____________________________________________________________________________ 26
API Upload of Ephemeris Files _________________________________________________________________________________ 27

Email _____________________________________________________________________________________________________________ 27
Guidance for High-Interest Events _____________________________________________________________________________ 27

Maneuver Notification Format _________________________________________________________________________ 28

Overview _________________________________________________________________________________________________________ 28
Format ___________________________________________________________________________________________________________ 28

How to Name Maneuver Notifications ________________________________________________________________ 33

Overview _________________________________________________________________________________________________________ 33
Examples _________________________________________________________________________________________________________ 33

How to Submit Maneuver Notifications _______________________________________________________________ 34

Overview _________________________________________________________________________________________________________ 34

Submitting MANEUVERS Notifications Through Space-Track.org ___________________________________________ 35
Manual Upload of Maneuver Notifications ____________________________________________________________________ 35
API Upload of Maneuver Notifications_________________________________________________________________________ 36
Email _____________________________________________________________________________________________________________ 36

Contact Us _______________________________________________________________________________________________ 37

18 SPCS Conjunction Assessment Team _______________________________________________________________________ 37
18 SPCS SSA Sharing Team _____________________________________________________________________________________ 37

Space-Track.org Administration Team _________________________________________________________________________ 37

Annex A: 18 SPCS Probability of Collision ____________________________________________________________ 38

How 18 SPCS Calculates Probability of Collision _____________________________________________________________ 38

TABLE OF CONTENTS
Object Size _______________________________________________________________________________________________________ 39
Position and Velocity Vectors___________________________________________________________________________________ 40
Covariance and Error Ellipsoids _______________________________________________________________________________ 41
Assumptions _____________________________________________________________________________________________________ 42
Computation _____________________________________________________________________________________________________ 43
Notes _____________________________________________________________________________________________________________ 44
Bibliography _____________________________________________________________________________________________________ 44

Annex B: Frequently Asked Questions ________________________________________________________________ 46

1. How and when do I sign up for conjunction assessment (CA) alerts? ____________________________________ 46
2. Do I need to submit an Orbital Data Request for CA services? ____________________________________________ 46
3. Is there a charge for 18 SPCS spaceflight safety services? _________________________________________________ 46

4. My satellite has a predicted conjunction with another active satellite, how can I contact the otheroperator? ________________________________________________________________________________________________________ 46

5. I haven't received any conjunction data in a while, is something wrong? ________________________________ 46
6. Why is another group receiving conjunction data for our co-owned satellite when my group has notreceived any? ____________________________________________________________________________________________________ 46
7. How can I submit predicted ephemeris for screening? What about predicted maneuver information?
____________________________________________________________________________________________________________________ 46
8. I need to have larger than normal screenings for my satellite. What can 18 SPCS do? _________________ 47

9. Can I change the contacts in my Space-Track.org organization/CDM account? __________________________ 47
10. What does it mean when an object in the CDM has a number in the 80000’s? _________________________ 47

11. What does it mean when an object in the cDM has a number in the 799500000’s? ___________________ 47
12. Can the 18 SPCS analyze my data, make recommendations, or help me choose a plan of action? ____ 47
13. If I submit an Orbital Data Request for advanced CA services, can I pick which screening volume I
would like?_______________________________________________________________________________________________________ 47
14. I have questions, is there someone I can talk to? _________________________________________________________ 47

TABLE OF CONTENTS

SIGNIFICANT REVISION HISTORY
Significant Revision History
VersionDescription of Changes

Date

1.1

1. Corrected NORAD_CAT_ID in Maneuver Notification format, pg. 25
2. Addition of contact information for Space-Track.org, pg. 32
1. Definitions of ellipsoid and covariance screenings, pg. 5-6
1. Screening schedule, pg. 4
2. Correction to Basic Reporting Criteria for LEO CDMs, pg. 4
3. Added decimal notation requirement to OEM, pg. 18
4. Added “USER_DEFINED_MAN_ID” to maneuver notification, pg. 27
5. Added additional values to “USER_DEFINED_MAN_PURPOSE,” pg.
28
6. Changed “SOLVED” to “DETERMINED” for“USER_DEFINED_MAN_STATUS,” pg. 28
7. Under “How to Name Maneuver Notifications” update “File Names”
and added “File Verification,” pg. 29
8. Updated “Submitting Maneuver Notifications” to explain that eachorganization has their own maneuver folder, pg. 31
9. Added “Updating Maneuver Notifications,” pg. 31
1. Replaced JSpOC and JFCC SPACE references with 18 SPCS, CSpOC orJFSCC, throughout the document as needed
2. Added SSA Sharing Program description, pg. 2
3. Added HAC vs HAC, O/O Ephemeris vs HAC, and O/O Ephemeris vs
O/O Ephemeris descriptions, pg. 4-5
4. Added PDT/PST times to Screening Schedule, pg. 7
5. OEM state and covariance components must be in decimal notation,
pg. 21
6. USER_DEFINED_MAN_ID added to maneuver notification, pg. 30
7. Added additional options to USER_DEFINED_MAN_PURPOSE, pg. 30
8. Added Annex A: How 18 SPCS Calculates Probability of Collision
1. Replaced all references to USSTRATCOM and JFSCC with
USSPACECOM and CFSCC as needed
2. Replaced references to Orbital Safety Crew with Conjunction
Assessment Team as needed
3. Changed ‘all active satellites’ to ‘all resident space objects’, pg. 4
4. Updated Conjunction Assessment Screening Process in Figure 1,
pg.5
5. Added explanation of Concern List in HAC vs HAC screening
process, pg. 5
6. Added explanation of different types of HAC screenings, pg. 6
7. Added information on Concern List screening schedule, pg. 8
8. Updated screening schedule, pg. 8

12 Aug 16

1.2
1.3

1.4

1.5

Page 1

27 Aug 16
3 Jan 17

Feb 19Aug 20SIGNIFICANT REVISION HISTORY
9. Updated HAC screening volumes in Table 3, pg. 9
10. Updated basic reporting criteria in Table 5, pg. 10
11. Updated advanced reporting criteria in Table 6, pg. 10
12. Added information on 799500000 satellite number range, pg. 13
13. Removed ‘fewer than two sensors’ tasking criteria, pg. 14
14. Clarified requirements for covariance reference frames, pg. 15
15. Clarified requirements for covariance reference frames in OEM,pg. 21
16. Changed ‘CatalogNumber’ to ‘SatelliteNumber’ in ephemeris filenaming guidance, pg. 23
17. Added 9-digit temporary satellite numbers to Ephemeris File
Name Convention in Table 8, pg. 23
18. Clarified that deviations from CCSDS OPM standard are indicatedby ‘User Defined’ fields, pg. 28
19. Changed OBJECT_ID in Maneuver Notification OPM to not
obligatory, pg. 29
20. Changed USER_DEFINED_NORAD_CAT_ID in Maneuver
Notification OPM to obligatory, pg. 29
21. Added 9-digit option to USER_DEFINED_NORAD_CAT_ID in
Maneuver Notification OPM, pg. 29
22. Added Frequently Asked Questions, Annex B

Page 2

USSPACECOM SSA SHARING PROGRAMUSSPACECOM SSA Sharing Program
PROGRAM DESCRIPTIONThe Unites States Space Command (USSPACECOM), as the U.S. government entity responsible for spacedomain awareness (SDA) and space situational awareness (SSA), is committed to promoting a safe, stable,
sustainable and secure space environment through the sharing of SSA information. In 2009, the UnitedStates Strategic Command (USSTRATCOM) initiated the SSA Sharing Program to provide no-cost basic,
emergency, and advanced SSA data and services that cover the full scope of support needed through the
lifetime of a satellite from pre-launch preparation to end-of-life disposal. In 2019, the program was handed
over to USSPACECOM.

Services include Launch Conjunction Assessment (LCA), Launch and Early Orbit Phase (LEOP) support, OnOrbit Conjunction Assessment (CA), Collision Avoidance (COLA), anomaly support, end-of-life/disposal
support, de-orbit support, and re-entry assessment. These services are available to all operators of active
spacecraft at the basic emergency level, and at the advanced level for entities who have signed SSA Sharing
Agreements with USSPACECOM. Basic SSA data is disseminated to the world through the website
www.space-track.org, which is accessible to anyone with a registered user account. USSPACECOM hasdelegated management of the SSA Sharing Program to the Combined Force Space Component Command(CFSCC). While CFSCC oversees the SSA Sharing program as a whole, the 18th Space Control Squadron (18SPCS) has been directed to execute day-to-day SSA data sharing and support, and act as the direct interface
between satellite operators and the U.S. Department of Defense. The 18 SPCS performs the spacesurveillance mission for the U.S. Space Force, and provides foundational SSA for the U.S. government andglobal space partners through the SSA Sharing Program. This role was performed by the Joint Space
Operations Center (JSpOC) until July 2016, at which time 18 SPCS was activated and assumed all spacesurveillance functions. In July 2018, the JSpOC became the Combined Space Operations Center (CSpOC).The
18 SPCS is currently co-located with the CSpOC at Vandenberg Air Force Base, but now has the separate anddistinct mission of providing frontline space defense, maintaining the space catalog, and providing
foundational SSA to U.S. and global partners.

SPACE-TRACK.ORG

Space-Track.org (www.space-track.org) is a public website owned by USSPACECOM and CFSCC, andmanaged and populated by 18 SPCS. It is the primary method of sharing SSA information with the global
space community at the basic, emergency, and advanced levels. All satellite operators should register for auser account in order to access the full scope of SSA data and services available through the SSA Sharing
Program.

Page 3

CONJUNCTION ASSESSMENT PROCESS
Conjunction Assessment Process
ON-ORBIT CONJUNCTION ASSESSMENT (CA)The 18 SPCS Conjunction Assessment (CA) process identifies close approaches between all resident space
objects (RSOs) in the 18 SPCS catalog. It begins with satellite observations from the U.S. Space Surveillance
Network (SSN), which includes a variety of sensors throughout the world that detect, track, catalog, andidentify man-made objects orbiting Earth. SSN observations are input into the 18 SPCS mission system,
which implements “Special Perturbations” (SP) orbit propagation theory. Orbit determination (OD) is
performed automatically multiple times per day to determine the position and velocity of each object,which is then updated in the 18 SPCS High Accuracy Catalog (HAC). The 18 SPCS Conjunction Assessment
Team uses the HAC to screen the orbital trajectories of all RSOs against all other RSOs, to include active
satellites and non-active objects (debris, rocket bodies, dead payloads, etc).

18 SPCS performs three types of screenings:
1.
2.

3.

Page 4

HAC vs. HAC: SP catalog data for all RSOs screened against SP catalog data for all other RSOs
O/O Ephemeris vs. HAC: Ephemeris provided by the satellite owner/operator (O/O) screened
against the SP catalog data for all RSOs
O/O Ephemeris vs. O/O Ephemeris: Ephemeris provided by the satellite O/O screened against
ephemeris provided by all other O/O’s

CONJUNCTION ASSESSMENT PROCESS
18 SPCS performs screenings for every RSO and owner/operator (O/O) ephemeris a minimum of once
every 24 hours in accordance with the process in the following diagram. The initial screening may begin
with all near earth objects, all deep space objects, near earth concern lists, deep space concern lists, orO/O-provided ephemeris.

Figure 1: Conjunction Assessment Screening Process

HAC vs HAC
The screening process starts with the update of orbital information for the entire catalog based on datafrom the SSN sensors and updated Dynamic Calibration Atmosphere (DCA) coefficients, which is thenpropagated 7 days for near-earth (NE) objects and 10 days for deep-space (DS) objects. These updates takeplace every 8 hours. Using this data, 18 SPCS performs an initial screening of RSOs against the rest of thecatalog to identify conjunction candidates within screening criteria. Based on these results, 18 SPCS also
generates Concern Lists to use in follow-on screenings. Concern Lists include all candidates that produce
conjunctions with probability of collision (Pc) ≥ e^-7 in NE, and miss distance ≤ 5km in DS. These
candidates are reevaluated by the Conjunction Assessment Team to ensure that all of the most current
observations are incorporated into the OD. The 18 SPCS then conducts a refinement screening to update
the conjunction estimates of all of the candidates identified in the initial screening. If the parameters of the
conjunction fall within criteria that identify a close approach and the close approach involves an active
satellite, the 18 SPCS will notify the O/O of the active satellite(s) in accordance with the methods listed inReporting Criteria. Depending on the quality of the OD, 18 SPCS may increase sensor tasking on the
primary or secondary objects. HAC vs HAC screenings include:
Page 5CONJUNCTION ASSESSMENT PROCESS
1.

2.

3.
4.

NE All HAC: All NE objects vs all NE objects, based on 18 SPCS SP data (NE is defined as Period ≤ 225
minutes)
DS All HAC: All DS objects vs all DS objects, based on 18 SPCS SP data (DS is defined as period ≥ 225
minutes)
NE Concern List HAC: Screening of all conjunction pairs identified in NE All HAC screening with Pc ≥e^-7 and the time of closest approach (TCA) ≤ 5 days. Concern List objects will be screened throughTCA.
DS Concern List HAC: Screening of all conjunction pairs identified in DS All HAC screening with overall
miss distance ≤ 5km, and the time of closest approach (TCA) ≤ 10 days. Concern List objects will bescreened through TCA.

O/O Ephemeris vs HAC (O/O EPH vs HAC)

All O/O’s may submit predictive ephemeris to the 18 SPCS for screening against the HAC. O/Os must submit
ephemeris as Operational or Special. An Operational file represents where the satellite is planned to go
and may or may not include maneuvers. These files typically incorporate normal station-keeps or represent
a freefall orbit. If maneuvers are included, 18 SPCS assumes these will definitely occur; otherwise, the files
should be submitted as Special. Operational files will be screened according to the schedule in Tables 1 and
2. A Special file represents where the satellite is planned to go if a maneuver is being considered for a nonroutine event, such as orbit raising, relocations, or COLA. A Special file is used for planning purposes only,
unless the maneuver becomes operational, in which case it must be resubmitted as Operational. All Special
files will be treated as high-interest and screened as soon as possible after receipt by the 18 SPCS
Conjunction Assessment Team. Multiple special files may be submitted for the same satellite, but only one
operational file at a time can be submitted per satellite. Results will be provided in accordance with
reporting criteria.
O/O Ephemeris vs O/O Ephemeris (O/O EPH vs O/O EPH)

All Operational O/O ephemeris will be screened against all other Operational O/O ephemeris on ascheduled basis. O/O ephemeris labeled as Special will not be screened against O/O ephemeris. Results
will be provided in accordance with reporting criteria. Operational O/O-provided ephemeris isscreened through its duration, meaning that 18 SPCS will retain it in the system and continually
screen it every 8 hours until there is less than 8 hours of propagated ephemeris for NE objects or less than
12 hours for DS objects remaining in the file. This is only applicable to O/O EPH vs. O/O EPH screenings.

ON-ORBIT COLLISION AVOIDANCE (COLA)In response to a close approach, an O/O may consider performing collision avoidance (COLA), which is theprocess of planning and possibly executing a maneuver to mitigate the risk of collision. Based on
information received in the CA notifications, or from other data sources, the O/O decides whether or not to
perform collision avoidance by maneuvering their satellite. If the O/O decides to consider COLA actions,they may send 18 SPCS their predictive ephemeris data (in approved formats and coordinate systems)
which 18 SPCS will then screen against the HAC and provide results within reporting criteria so that the

Page 6

CONJUNCTION ASSESSMENT PROCESS
O/O may decide how to proceed. This exchange of data may continue until the time of closest approach(TCA), after which 18 SPCS will resume routine screening of the active satellite in accordance with thescreening schedule. If they do not perform COLA, 18 SPCS will continue to monitor the conjunction andprovide updates based on data from the SSN until the TCA has passed. 18 SPCS cannot provide maneuver
recommendations.

BASIC EMERGENCY CA AND COLA SERVICES

18 SPCS performs CA and provides COLA support for all satellite operators of active spacecraft as a basic
emergency service to ensure spaceflight safety. All operators are eligible for this basic emergency service,
which includes the following using basic screening volumes and reporting criteria:

1.
2.
3.
4.

HAC vs HAC screenings
Operational O/O Ephemeris vs HAC screenings
Operational O/O Ephemeris vs Operational O/O Ephemeris screenings
Special O/O Ephemeris vs HAC screenings

5.

HAC ‘1-versus-1’ requests: screening one primary object against one secondary using HAC data

4.1 O/O Ephemeris versus secondary object, or
4.2 O/O Ephemeris versus full catalog

ADVANCED CA AND COLA SERVICES

O/Os who have signed an SSA Sharing Agreement with USSPACECOM may request Advanced CA and COLA
through the Orbital Data Request (ODR) process. (Visit https://www.space-track.org/documentation#/odr
for more information.) Advanced CA and COLA support includes the following using advanced screening
volumes and reporting criteria. Advanced screening volumes will be assigned based on the orbital regimeof the satellite, in accordance with Table 3.

1.
2.
3.
4.
5.
6.
7.

Page 7

HAC vs HAC screenings
Operational O/O Ephemeris vs HAC screenings
Operational O/O Ephemeris vs Operational O/O Ephemeris screenings
Special O/O Ephemeris vs HAC screenings

4.1 Ephemeris versus secondary object, or
4.2 Ephemeris versus full catalog

HAC ‘1-versus-1’ requests: screening one primary object against one secondary using HAC data
Access to propagated SP ephemeris (without covariance) for all RSOs in the unclassified space catalog
Access to SP state vectors (without covariance) for all RSOs in the unclassified catalog

CONJUNCTION ASSESSMENT PROCESSSCREENING SCHEDULE
18 SPCS performs HAC vs. HAC screenings for all NE and DS objects once every 24 hours, followed byConcern List screenings for each regime every 8 hours. (i.e., one full HAC vs HAC screening which includes aConcern List screening, followed by two Concern List screenings, 8 hours apart, every 24 hours.) For O/O
Ephemeris screenings, the ephemeris file name dictates how 18 SPCS will process files. If the O/O
designates it as Special, the 18 SPCS will process it as high-interest and screen it as soon as possible. If it isdesignated as Operational, the 18 SPCS will screen it according to the schedule in Table 1. Results forSpecial ephemeris are provided within 4 hours of receiving the ephemeris, and Operational results areprovided within 8 to 12 hours of the scheduled screening times, depending on when it is submitted by the
O/O.
The 18 SPCS screening schedule shifts one hour when the state of California (United States) transitions
between Pacific Standard Time (PST) and Pacific Daylight (PDT) time, which generally occurs in March andNovember each year. Both schedules are provided below:

Table 1: PST Screening Schedule (24-hour cycle)

Table 2: PDT Screening Schedule (24-hour cycle)

Page 8

CONJUNCTION ASSESSMENT PROCESSSCREENING VOLUMESThe following tables define the screening volumes and durations 18 SPCS uses for basic CA, advanced CA,
and ephemeris screenings. 18 SPCS conducts two types of screenings: ellipsoid and covariance. Bothscreenings use covariance-based “uncertainty volumes” around the satellites and the physical size of thesatellites themselves (referred to as “exclusion volumes”). The same basic mathematical approach is used
for both ellipsoid and covariance options, although probability of collision (Pc) is only computed for thecovariance option. For the ellipsoid screening option, the uncertainty volume is static throughout thescreening process, whereas covariance screenings employ a joint uncertainty volume that is based on timevarying covariance values for the primary and secondary objects at the time of closest approach. Pleasereference Annex A for more information on how 18 SPCS calculates probability of collision.

Table 3: HAC Screening Volumes
Screening
Deep Space(GEO/HEO/MEO)
Ellipsoid
LEO 4Covariance
LEO 3
CovarianceLEO 2
Covariance
LEO 1
CovarianceOrbit Regime Definition

Propagation

RadialIn-Track

Cross-Track

1300 min < Period < 1800 min
Eccentricity < 0.25 & Inclination <35º

10 days

10 km

10 km

10 km

750 km < Perigee ≤ 1200 km
Eccentricity < 0.25

5 days
5 days

0.4 km2 km

2 km

5 days

0.4 km

25 km

25 km

1200 km < Perigee ≤ 2000 km
Eccentricity < 0.25
500 km < Perigee ≤ 750 km
Eccentricity < 0.25
Perigee ≤ 500 km
Eccentricity < 0.25

5 days

0.4 km
0.4 km

12 km
44 km

12 km
51 km

Table 4: O/O Ephemeris Screening Volumes
Screening
Deep Space
Ellipsoid
Near Earth
Covariance

Page 9Orbit Regime Definition

Propagation

RadialIn-Track

Cross-Track

Period > 225min

10 days

20 km

20 km

20 km

Period < 225min

7 days

2 km

25 km

25 km

CONJUNCTION ASSESSMENT PROCESSREPORTING CRITERIAThe following tables define the reporting criteria used for basic and advanced CA and COLA. The advanced
service provides more data further in advance of TCA and may be requested through the Orbital Data
Request (ODR) process. These tables apply to both High Accuracy Catalog (HAC) and ephemeris screenings.
“Deep space” includes Geosynchronous Earth Orbit (GEO), Highly Elliptical Orbit (HEO) and Medium Earth
Orbit (MEO). “Near earth” includes all Low Earth Orbit (LEO) regimes.

Table 5: Basic Reporting Criteria

Space-Track Criteria

Emergency Criteria

Emergency
Phone Call Criteria

Notification
MethodConjunction Data Message(CDM)

Conjunction Data Message(CDM) & Close Approach
Notification (CAN) email

CDM, CAN email &phone call

Deep SpaceHAC

TCA ≤ 10 days and Overall
miss ≤ 5km

TCA ≤ 3 days and Overall
miss ≤ 5km

TCA ≤ 3 days and Overall
miss ≤ 500m

TCA ≤ 3 days &Overall miss ≤ 1km &TCA ≤ 3 days andOverall miss ≤ 1km andDeep SpaceO/O Ephemeris
Near Earth
HAC
Near EarthO/O Ephemeris

TCA ≤ 10 days and Overall
miss ≤ 5km
TCA ≤ 3 days andOverall miss ≤ 1km

TCA ≤ 3 days andOverall miss ≤ 1km

Table 6: Advanced Reporting Criteria
Space-Track Criteria
Notification
MethodDeep Space
HAC
Deep SpaceO/O Ephemeris
Near Earth(LEO 1-4)
HAC

Near Earth(LEO 1-4)
O/O Ephemeris

Page 10

Conjunction Data Message(CDM)
TCA ≤ 10 days & all results
w/in 5km x 5km x 5km

TCA ≤ 10 days & all results
w/in 20km x 20km x 20km

TCA ≤ 5 days &Probability of Collision ≥ e^‐7
w/in HAC screening volumes

TCA ≤ 7 days & all results
w/in 2km x 25km x 25km

TCA ≤ 3 days and Overall
miss ≤ 5km
Probability of Collision ≥ e^‐4
TCA ≤ 3 days &Overall miss ≤ 1km &Probability of Collision ≥ e^‐4
Emergency Criteria
Conjunction Data Message(CDM) & Close Approach
Notification (CAN) email
TCA ≤ 3 days &Overall miss ≤ 5km

TCA ≤ 3 days &Overall miss ≤ 5km
TCA ≤ 3 days &Overall miss ≤ 1km &Probability of Collision ≥ e^‐4

TCA ≤ 3 days andOverall miss ≤ 1km &Probability of Collision ≥ e^‐4

N/A

Probability of Collision ≥ e^‐2
N/A

Emergency
Phone Call Criteria
CDM, CAN email &phone call
TCA ≤ 3 days &Overall miss ≤ 500 m
N/A

TCA ≤ 3 days &Overall miss ≤ 1km &Probability of Collision ≥ e^‐2
N/A

CONJUNCTION ASSESSMENT PROCESSNOTIFICATIONSO/Os will receive a variety of email notifications depending on the screening performed and results
produced. All of these emails are generated and transmitted by the Space-Track.org website based on files
that the 18 SPCS Conjunction Assessment Team uploaded to the website. The messages are:
•

•
•
•

Close Approach Notification (CAN) email: sent for every prediction that meets emergency reportable
criteria. Includes primary object, secondary object, miss distances, TCA, and for near earth events,
probability of collision (Pc). Only sent to email addresses that the O/O has designated to receive CANs.
(Controlled by each organization’s Primary Representative or 18 SPCS through the Operator Panel onSpace-Track.org. Contact 18SPCS.doo.customerservice@us.af.mil for assistance.)
CDM email: notifies O/Os that new CDMs are available on Space-Track for their organization. All users
with ‘CDM Notification’ permissions receive this email. (Controlled by each organization’s Primary
Representative or 18 SPCS through the Operator Panel on Space-Track.org.)

Negative results email: Confirms that a specific ephemeris file has been screened and states that there
are no results within the ephemeris screening volume. All users with ‘CDM Notification’ permissions
receive this email.

Expanded results email: Confirms that a specific ephemeris file has been screened, and that there areresults that are within the ephemeris screening volumes, but not within emergency reportable criteria.
O/Os who do not have the advanced CA service may receive this notification. All users with ‘CDM
Notification’ permissions receive this email.

There are slight differences between the notifications sent for basic and advanced services. The following
figures show which messages should be expected for different scenarios within the CA and COLA process.

Page 11

CONJUNCTION ASSESSMENT PROCESSBASIC EMERGENCY CA NOTIFICATIONS
18 SPCS Screening

Figure 2: Basic Emergency CA Notifications

ADVANCED CA NOTIFICATIONS
18 SPCS Screening

Figure 3: Advanced CA Notifications

Page 12CONJUNCTION ASSESSMENT PROCESSLAUNCH CONJUNCTION ASSESSMENT
18 SPCS also provides launch conjunction assessment (CA), which identifies potential conjunctions that
may result in a collision between launching objects and on-orbit objects. Using O/O-provided information,
18 SPCS screens the launch vehicle against the space catalog and identifies periods during the launch
window which may put the rocket and payload at increased risk for collision. For more information on thisservice, reference the Launch Conjunction Assessment Handbook, which is available on Space-Track’s HelpPage.

EARLY ORBIT CONJUNCTION ASSESSMENT

Early orbit CA includes the screening of O/O-provided ephemeris against the catalog to facilitate the safe
maneuvering of a newly launched object into its final orbit. 18 SPCS will screen the ephemeris using early
orbit screening volumes and report all results in accordance with advanced reporting criteria. The O/O
may provide more than one ephemeris file for each maneuver to allow analysis of multiple scenarios, butthey must be labeled Special. 18 SPCS may pre-assign temporary satellite numbers in the 799500000
range to be used in the ephemeris file name. This will allow the O/O to receive screening results throughthe Space-Track CDM database. Once the newly launched satellites are cataloged in the 5-digit range, theO/O can seamlessly transition to the new catalog number. To receive early orbit CA support the O/O needs
to:
•

•

Pre-launch:o Submit an ODR requesting early orbit CA, specifying the preferred screening volume
o Register for a user account on Space-Track.org
o Provide the early orbit maneuver plano Send in pre-launch ephemeris for testing, if desired
Post-launch:o Provide ephemeris in an approved format and using the correct file name format for eachscreeningo Provide an updated maneuver plan, as needed

Table 7: Early Orbit Screening Volumes
Screening
Deep Space
Ellipsoid
Near Earth
Covariance

Page 13

Orbit Regime Definition

Propagation

RadialIn-Track

Cross-Track

Perigee > 2000 km &Eccentricity > 0.25

10 days

40 km

77 km

107 kmPerigee ≤ 2000 km
Eccentricity < 0.25

7 days

2 km

44 km

51 km

CONJUNCTION ASSESSMENT PROCESSEND-OF-LIFE/DISPOSAL SUPPORT
If an O/O decides to move a satellite to a less-populated orbit at the end of its lifetime, 18 SPCS will assist
the O/O by screening maneuver ephemeris and providing results. All O/O-provided ephemeris will bescreened using standard ephemeris screening volumes, and results will be provided in accordance withbasic or advanced reporting criteria. To receive end-of-life/disposal CA the O/O needs to:•••

Submit an Orbital Data Request (ODR) if all results within advanced reporting criteria are desired(no ODR is required for basic reporting criteria)
Provide the maneuver plan
Provide ephemeris in an approved format and using the correct file name format for eachscreening

DEORBIT SUPPORTA deorbit is the controlled reentry of a satellite into the Earth’s atmosphere. If an O/O decides to deorbit asatellite or rocket stage through a series of maneuvers, 18 SPCS can provide CA screenings, as well as
coordinate with NASA to ensure the deorbiting spacecraft safely descends through the International Space
Station’s (ISS) orbit. After the spacecraft completes its maneuvers, 18 SPCS can confirm final reentry. To
receive this service, the O/O needs to:•••

Submit an ODR if all results within advanced reporting criteria are desired (no ODR is required forbasic reporting criteria)
Provide the maneuver plan
Provide ephemeris in an approved format and using the correct file name format for eachscreening

TASKING

In certain situations, more observations on an object will improve the quality of the conjunction prediction.
To collect more observations, 18 SPCS can increase the tasking priority and revisit frequency assigned tosensors. 18 SPCS has embedded this in the routine screening cycle, as seen in Figure 1. If an object meets
any of the following criteria, its tasking will be automatically increased:•••

Not tracked within 72 hours, orLess than 20 observations in current Differential Correction (DC), or
At least one component of covariance over 100,000 m2

For emergency reportable events, the O/O may contact 18 SPCS to confirm that both objects in the
conjunction are tasked appropriately by emailing 18SPCS.doo.orbitalsafety@us.af.mil.

Page 14EPHEMERIS FORMATS
Ephemeris Formats
OVERVIEW

Satellite operators may provide ephemeris in various formats, which will be converted into formats thatcan be processed by 18 SPCS’ ASW (Astrodynamics Support Workstation). Using the Super Computation ofMiss Between Orbits (COMBO) software, 18 SPCS screens O/O ephemeris against the HAC or other O/O
ephemeris to identify potential conjunctions and generate conjunction data messages. Operators may electto include covariance data in order to accommodate probability of collision calculations.
All ephemeris formats must be in the mean equator/mean equinox (MEME) J2000.0 frame with positional
values (x, y, z) given in kilometer units and velocity values (dX, dY, dZ) given in units of kilometers/second.
If covariance values are provided, they must be in decimal notation and in the same reference frame as the
positional values unless otherwise specified in the ephemeris file (see OEM format CCSDS Orbit Data
Message (ODM) Blue Book).

All ephemeris formats may include informational header lines prior to the data lines which provide date,time, and state vector (position and velocity) values. Each format differs in the number and content ofheader lines, format of the date and time values, and different precision (number of decimal places) for thestate vector components.

18 SPCS’ conversion utility software converts all ephemeris formats to true equator/mean equinox (TEME)
of Date for epoch J2000. The most recent time constants data file within the 18 SPCS mission systemcorrects for leap seconds.
The NASA and UTC formats include position and velocity only. 18 SPCS accepts three formats withcovariance:•••

Page 15

General On-Orbit (GOO) may include 3 x 3 (6 lower triangular matrix) position covariance data values,

Modified ITC may include 6 x 6 (21 lower triangular matrix) position and velocity covariance data
valuesOrbital Ephemeris Message (OEM) format, both with and without covariance data, which includes acapability for processing 6 x 6 (21 lower triangular matrix) position and velocity covariance data
values. Visit the Consultative Committee for Space Data Systems (CCSDS) website for more
information on the OEM.

EPHEMERIS FORMATS
NASA EPHEMERIS FORMATThe NASA ephemeris data file format contains no descriptive header lines preceding the ephemeris data.
Each data line contains a date formatted as YYDOY (last two digits of year and Day of Year (DOY) in place ofmonth and day), a time stamp formatted as HHMMSS.SSS, and the state vector position (x, y, z) and velocity(dx, dy, dy) values.

Figure 4: NASA Ephemeris Format Example

18 SPCS’ conversion utility separates the entries on each ephemeris data line wherever one or more space(i.e. “ “) characters are found. For each data line this processing results in a combined date/time field (i.e.
“yyDOYhhmmss.sss”) and each state vector component (i.e. position (x, y, z) and velocity (i.e. dx, dy, dz))value. This ephemeris format does not include covariance values.

Page 16

EPHEMERIS FORMATS
UTC EPHEMERIS FORMATThe UTC ephemeris data file format contains 21 descriptive and header lines preceding the ephemeris
data. Each data line contains a date formatted as YYYY/MM/DD, a time stamp formatted as HH:MM:SS.SSS,
and the state vector position (x, y, z) and velocity (dx, dy, dy) values.

Figure 5: UTC Ephemeris Format Example

The conversion utility ignores the 21 header and descriptive lines and separates the entries on each
ephemeris data line wherever one or more space (i.e. “ “) characters are found. For each data line thisprocessing results in a date field (i.e. “yyyy/mm/dd”), a time field (i.e. “hh:mm:ss.sss”) and each statevector component (i.e. position (x, y, z) and velocity (i.e. dx, dy, dz)) value.

The date field is separated into month, day, and year values wherever a forward slash (i.e. “/”) character isfound; and the time field is separated into hour, minute, and second values wherever a colon (i.e. “:”)character is found. The Day of Year (DOY) value is calculated from the month and day, taking into accountany adjustment needed for a leap year.
This ephemeris format does not include covariance values.

Page 17

EPHEMERIS FORMATS
GENERIC ON-ORBIT EPHEMERIS FORMATThe Generic On-Orbit ephemeris data file format is the only format that is required to contain position
covariance data in addition to ephemeris data. It contains four descriptive and header lines, where thefourth indicates the orbital reference frame of the covariance data. For each ephemeris data point, the data
section includes one line which contains the epoch date/time and state vector, followed by one line holding
the six values of the 3x3 lower triangular position covariance matrix.

Figure 6: Generic On-Orbit Data Example

The conversion utility makes a rudimentary check that the correct number of data lines are present. The
number of header lines is subtracted from the number of lines in the ephemeris data file; if the result is notdivisible by 2 (a state vector line plus a covariance data line) a warning message is output, but theconversion continues.

The conversion utility ignores the header and descriptive lines except for the covariance orbit framereference value. (Figure 6 depicts ‘UVW’ which is the same as ‘RTN.’) It then reads the data lines in groupsof two and separates the entries on each data line wherever one or more space (i.e. “ “) characters arefound. For each group of two data lines this processing results in a date/time field (i.e.
“yyyDOYhhmmss.sss”), each state vector component (i.e. position (x, y, z) and velocity (i.e. dx, dy, dz)) value
and 6 covariance values.
The combined date/time field is separated into year, Day of Year, hour, minute, and second values.

Page 18

EPHEMERIS FORMATS
MODIFIED ITC EPHEMERIS FORMATThe Modified ITC ephemeris data file format is the only format that is required to contain both positionaland velocity covariance data in addition to ephemeris data. It contains four descriptive and header lines,
where the fourth indicates the orbital reference frame of the covariance data. For each ephemeris point,
the data section includes one line which contains the epoch date and time and state vector, followed bythree lines holding the twenty-one values of the 6 x 6 lower triangular position and velocity covariancematrix.

Figure 7: Modified ITC Data Example

The conversion utility makes a rudimentary check that the correct number of data lines are present. The
number of header lines is subtracted from the number of lines in the ephemeris data file; if the result is notdivisible by 2 (a state vector line plus a covariance data line) a warning message is output, but theconversion continues.

The preprocessing script ignores the header and descriptive lines except for the covariance orbit framereference value. It then reads the data lines in groups of four and separates the entries on each data line
wherever one or more space (i.e. “ “) characters are found. For each group of four data lines this results in adate/time field (i.e. “yyyDOYhhmmss.sss”), each state vector component (i.e. position (x, y, z) and velocity(i.e. dx, dy, dz)) value and 21 covariance values.
The combined date/time field is separated into year, Day of Year, hour, minute, and second values.

Page 19

EPHEMERIS FORMATS
ORBITAL EPHEMERIS MESSAGE (OEM) FORMATThe OEM ephemeris data file format contains a variable number of optional descriptive lines interspersedwith blocks of ephemeris and optionally covariance data. Note that blocks of covariance data may containmore than one set of covariance data separated by EPOCH keywords.
For a complete discussion of this ephemeris data format refer to please visit the Consultative Committee
for Space Data Systems (CCSDS) website and reference the ‘Orbit Data Messages’ Blue Book.

Figure 8: OEM (without covariance) Example

Page 20

EPHEMERIS FORMATS

Figure 9: OEM (with covariance) Example

The conversion utility removes all lines that are blank or contain the keywords (defined in the format
document) CCSDS_OEM_VERS, CENTER_NAME, COMMENT, COV_REF_FRAME, CREATION_DATE,INTERPOLATION, INTERPOLATION_DEGREE, META_START, META_STOP, OBJECT_ID, OBJECT_NAME,ORIGINATOR, REF_FRAME, START_TIME, STOP_TIME, TIME_SYSTEM, USEABLE_START_TIME, or
USEABLE_STOP_TIME. This reduces the data file to lines containing blocks of ephemeris data and optional
blocks of covariance data. The covariance data blocks are delimited by lines containing the keywords
COVARIANCE_START and COVARIANCE_STOP. The reference frame must be annotated for each covariance
Page 21

EPHEMERIS FORMATS
data block throughout the OEM file (COV_REF_FRAME, Figure 9). If no annotation is provided, the 18 SPCS
system defaults to the reference frame annotated in the header of the file (REF_FRAME, Figure 9). Therecan be more than one section of covariance data within a block, each delimited by an EPOCH line. The
date/time values of the optional covariance data on the EPOCH lines are not guaranteed by the format
standard to match any ephemeris data date/time values.
The values on each ephemeris data line are separated out wherever one or more space (i.e. “ “) characters
are found.

For each ephemeris data line, further processing results in date/time fields (i.e. “yyyy-mm-dd” and“hh:mm:ss.sss”) and each state vector component (i.e. position (x, y, z) and velocity (i.e. dx, dy, dz)) value.
For each optional block of covariance data, processing results in date/time fields (i.e. “yyyy-mm-dd” and“hh:mm:ss.sss”) and the 21 covariance values. Note that state vector and covariance components must
be in decimal notation as seen in Figure 9.
The date field is separated into month, day, and year, values wherever a dash (i.e. “-”) character is found;and the time field is separated into hour, minute, and second values wherever a colon (i.e. “:”) character isfound. The Day of Year (DOY) value is calculated from the month and day, taking into account any
adjustment needed for a leap year.

The conversion utility then matches the covariance data, if it exists, by date/time to a line of ephemeris
data. If the date/time exactly matches, the covariance data is appended to the ephemeris state vector forthat date/time. The covariance data is discarded if the date/time does not match for a section of ephemeris
data. Ephemeris data lines that do not have date and time matches of covariance data will have twenty-one
zero (i.e. “0.0”) values following the state vector.

Page 22

HOW TO NAME EPHEMERIS FILES
How to Name Ephemeris FilesOVERVIEW

18 SPCS requires that satellite operators name their files following a specific format, which dictates how
the ephemeris file will be processed. When the O/O submits their files through the website SpaceTrack.org, Space-Track will verify the file is named correctly and return error messages if it is not. The filename format is:<DataType>_<SatelliteNumber#>_<CommonName>_<DayTimeGroup>_<Operational/Special>_<Met
aData>_<Classification>.<FileExtension>

Table 8: Ephemeris File Name Convention
Data Field

Description

DataType

The type of data being provided.

Catalog#

The 5-digit designator for the object as defined in
USSPACECOM’s satellite catalog https://www.spacetrack.org/#/catalog
If the object is not cataloged, use:

• UCN## for near-earth objects or UCD## for deepspace objects (Substitute ## with 01, 02, 03 etc. up
to the total number of files submitted), or

CommonName

DayTimeGroup• The 9-digit number assigned to you by 18 SPCS(Contact 18 SPCS SSA Sharing for details.)

The spacecraft name for the object. Recommend
using the common name listed in USSPACECOM’ssatellite catalog https://www.spacetrack.org/#/catalog
If the object is not cataloged, use the common namedesignated by the satellite operator

Start time of the ephemeris, using three-digit day ofyear and HH:MM in UTC, where HH is the hour in the
24-hour system

Continued on next page

Page 23

Normative Value (N) or
Example (E)(N) MEME (unlessotherwise directed by 18
SPCS) This entry must be
in uppercase letters(E) 25544(E) 00900(E) UCN01

Obligatory
Yes
Yes(E) UCD02(E) 799500000(E) 799599999(E) ISS (ZARYA)(E) CALSHERE 1

Yes(E) 3001224 = Oct 26,
2020 at 12:24pm UTC

Yes

HOW TO NAME EPHEMERIS FILES
Table 8: Ephemeris File Name Convention, cont.
Normative Value (N) or
Example (E)Obligatory(N) Operational

Yes

Additional information provided at the discretion of
the satellite operator. Often used to indicate
maneuver status, or maneuver option plan. If there
is no additional information to provide there
must be a double underscore between
Operational/Special and Classification(E) nomnvr

Yes

The security classification of the data. Only
unclassified files will be accepted throughwww.space-track.org(E) unclassified

Yes(N) .txt (unlessotherwise directed by 18
SPCS)

Yes

Data Field

Description

Operational/
SpecialAn Operational file represents where the satellite isplanned to go and may or may not include maneuvers
These files typically incorporate normal stationkeeps, or represent a freefall orbit
If maneuvers are included, 18 SPCS assumes thesewill definitely occur. Otherwise, the files should besubmitted as Special.

(N) Special

A Special file represents where the satellite isplanned to go if a special maneuver is executed

A Special file is used for planning purposes only,
unless the maneuver becomes operational, in whichcase it must be resubmitted as Operational.
All Special files will be treated as high-interest.

MetaData

Classification

File Extension*Multiple Special files may be submitted for the same
satellite, but only one Operational file at a time can besubmitted per satellite*

Indicates the type of file(E) stationkeepingmnvr(E) burn02(E) __(E) UNCLASSIFIED(E) Unclassified

FILE NAME EXAMPLES
•
•
•
•
•

Page 24

MEME_25544_ISS_1651200_oper__unclassified.txt

MEME_25544_ISS(ZARYA)_1651200_operational_nomnvr_UNCLASSIFIED.txt

MEME_25544_ISS_1651200_special_mnvr01_Unclassified.txt

MEME_UCN01_SPACESAT1_1651200_special_burn01_Unclassified.txt

MEME_799500234_Sat1_1651200_special_separation_unclassified.txt

HOW TO SUBMIT EPHEMERIS FILES
How to Submit Ephemeris FilesOVERVIEW

Ephemeris files may be submitted in three ways:
1.

2.

Through the website Space-Track.org (preferred):

1.1 Manually, or
1.2 Using Application Programming Interface (API)By email to the 18 SPCS Orbital Safety Crew at 18SPCS.doo.orbitalsafety@us.af.mil. This method should
only be used if the satellite operator cannot access Space-Track.

Space-Track.org is the most efficient and secure method of submitting ephemeris files on a recurring basis.
To set up access, contact the 18 SPCS SSA Sharing Team at 18SPCS.doo.customerservice@us.af.mil or +1805-605-5219. The SSA Sharing Team will request the following information:
1.

2.

The title of your CDM organization (the organization name under which you access CDMs on the
Operator Panel)
The Space-Track user names of the personnel who will upload ephemeris for your satellite
constellation

The SSA Sharing Team will create a permissions-based ephemeris folder for your organization that will
only be accessed by 18 SPCS and the personnel you authorize. You will have upload, download, and delete
permissions to the folder, which you will access through the Files Panel:

Figure 10: Files Panel on Space-Track.org

Page 25

HOW TO SUBMIT EPHEMERIS FILESSUBMITTING EPHEMERIS THROUGH SPACE-TRACK.ORG
Once you have an ephemeris folder on the Files Panel, you will also have access to the ‘Download’ and‘Upload’ tabs. On the ‘Upload’ tab you can upload a variety of files to the folders you have permissions to.
All of these folders will display in the ‘Destination’ dropdown menu:

Figure 11: Files Panel Upload Tab - Ephemeris

MANUAL UPLOAD OF EPHEMERIS FILES
1.
2.

3.
4.
5.

Page 26

Log in to Space-Track.org, click on ‘Files’ at the top of the page, and then click on the ‘Upload’ tab
Click ‘Choose Files’ and select your ephemeris files

2.1 Maximum number of files in a single upload is 100
2.2 Maximum total size per upload is 60 MB
2.3 Files must be named in accordance with guidelines in ‘How to Name Ephemeris Files’

Using the ‘Destination’ dropdown menu, select the ‘/Ephemeris/’ folder for your organization
Click ‘Upload’ to upload the files
After a successful upload, the files will display in ‘My Uploads (Last 30 Days)’ Table

HOW TO SUBMIT EPHEMERIS FILES
6.

The 18 SPCS Orbital Safety Crew will receive a notification that you have uploaded new ephemeris files
for screening. However, if the ephemeris is Special or in response to a high-interest event, please
phone or email the Conjunction Assessment Team to notify them that you need an immediate
response: +1-805-605-3533 or 18SPCS.doo.orbitalsafety@us.af.mil.

API UPLOAD OF EPHEMERIS FILES

Please visit Space-Track.org’s ‘API’ and ‘How To’ pages for the most up-to-date guidance (including usage
limitations) on API capabilities: https://www.space-track.org/documentation#/api andhttps://www.space-track.org/documentation#/howto. Similar to manual uploads:

1.
2.
3.

Files must be named in accordance with guidelines in ‘How to Name Ephemeris Files’
After a successful upload, the files will display in ‘My Uploads (Last 30 Days)’ Table
The 18 SPCS Orbital Safety Crew will receive a notification that you have uploaded new ephemeris files
for screening. However, if the ephemeris is Special or in response to a high-interest event, please
phone or email the Conjunction Assessment Team to notify them that you need an immediate
response: +1-805-605-3533 or 18SPCS.doo.orbitalsafety@us.af.mil.

EMAIL

If your organization does not have an ephemeris folder on the Files Panel, you may send your ephemeris byemail to the 18 SPCS Conjunction Assessment Team at 18SPCS.doo.orbitalsafety@us.af.mil. Please:1.
2.

Name files in accordance with guidelines in ‘How to Name Ephemeris Files’
Send only .txt files - .zip files cannot be accepted

GUIDANCE FOR HIGH-INTEREST EVENTS

After you submit your ephemeris, please send an email or phone the 18 SPCS Conjunction Assessment
Team (18SPCS.doo.orbitalsafety@us.af.mil or +1-805-605-3533) to provide the following information
regarding the high-interest request:
1.

2.

3.
4.

Page 27

The conjunction event that you are concerned about (provide secondary object, CDM ID number,
and/or time of closest approach)
The object(s) you need your ephemeris screened against (for example, one object, a short list of
objects, or the whole catalog)
Reference your approved Orbital Data Request, if applicable
Confirmation that you do or do not have an SSA Sharing Agreement with USSPACECOM (For more
information on SSA Sharing Agreements, please visit https://www.spacetrack.org/documentation#/odr)

MANEUVER NOTIFICATION FORMAT
Maneuver Notification Format
OVERVIEW

18 SPCS respectfully requests that satellite operators notify 18 SPCS of planned, confirmed, and cancelled
maneuvers. This allows 18 SPCS to maintain a more accurate catalog, anticipate spaceflight safety risks, andprovide more relevant conjunction notifications. 18 SPCS has chosen the Orbital Parameter Message (OPM)
as the most appropriate method of exchanging maneuver information. However, to make it applicable to 18
SPCS operations and reporting procedures, 18 SPCS has made modifications to the message, which aredetailed in the following Maneuver Notification Format. Guidelines that add to or deviate from thedirection provided in the CCSDS Orbit Data Message Blue Book are indicated by “USER_DEFINED” in the
keyword. To access the Blue Book visit the CCSDS website.

FORMATThe OPM shall be represented as a combination of the following: (1) a header, (2) metadata (data aboutdata), (3) data, and (4) optional comments. Space-Track only accepts KVN (Key/Value Notation).

The following tables specify for each section of the OPM: (1) the keyword to be used, (2) a short descriptionof the item, (3) examples of allowed values or the units of the time, when applicable, and (4) whether theitem is obligatory or optional.

Table 9: OPM Header
Keyword

Description

ExampleObligatory

CCSDS_OPM_VERS

Format version in the form of‘x.y’, where ‘y’ is incremented
for corrections and minorchanges, and ‘x’ isincremented for majorchanges.
Reference ODM Blue Book
6.7
File creation date/time inUTC
Creating agency or operator.
Must be the same title as the
CDM account on SpaceTrack.org
Acceptable values: PUBLIC,PRIVATEPUBLIC: Operator agrees toshare file with all othersatellite operators who haveaccess to Space-Track’s
Operator Panel

2.0

Yes

This is a comment

No

COMMENTCREATION_DATEORIGINATOR

USER_DEFINED_RELEASABILITY

Page 28

2015-0704T12:00:00
CNES, JAXA, ESA,IRIDIUM

Yes

PUBLIC

No. If notprovided,
will default
to PRIVATEYes

MANEUVER NOTIFICATION FORMAT

USER_DEFINED_CLASSIFICATIONTABLE 10: OPM METADATAPRIVATE: Operators agrees
to share file with 18 SPCS
only
Acceptable value:
UNCLASSIFIED
18 SPCS will only accept
unclassified files.

UNCLASSIFIED

Yes

Keyword

Description

ExampleObligatory

COMMENT

Reference Orbital Data Message Blue
Book 6.7
Spacecraft name for which the orbit
state or maneuver information isprovided. Recommend using
common names in the Satellite
Catalog on www.space-track.org
Object identifier of the object for
which the orbit state is provided.
Use international designator as
published on Space-Track.org using
format YYYY-NNNP{PP}, where:
YYYY = Year of launch.
NNN = Three digit serial number oflaunch in year YYYY (with leading
zeros).
P{PP} = At least one capital letter for
the identification of the part brought
into space by the launch.

This is a commentNo

OBJECT_NAMEOBJECT_ID

USER_DEFINED_NORAD_CAT_ID

CENTER_NAME
REF_FRAME

REF_FRAME_EPOCH
TIME_SYSTEM

Page 29• 5-digit satellite catalog number
assigned by USSTRATCOM, or• 9-digit satellite number assignedby 18 SPCS
Origin of reference frame
Name of reference frame in which
the state vector and optional
Keplerian element data are given

Epoch of reference frame, if not
intrinsic to the definition of thereference frame.
Time system used for state vector,
maneuver, and covariance data.
Must be UTC.

ISS (ZARYA)

Yes

1998-067A

No

25544
799500234

Yes

Earth
MEME2000International Terrestrial
Reference Frame (ITRF)
ICRF
TOD
TDR
2001-11-06T11:17:33

Yes
Yes, if statevectorincluded

UTC

Yes

No

MANEUVER NOTIFICATION FORMATTABLE 11: OPM DATA – STATE VECTOR COMPONENTS IN SPECIFIED COORDINATE SYSTEM
Keyword

Description

Units

Obligatory

COMMENT
EPOCH
X
Y
Z
X_DOT
Y_DOT
Z_DOT

Reference Orbital Data Message Blue Book 6.7
Epoch of state vector in UTC
Position vector X-component
Position vector Y-component
Position vector Z-component
Velocity vector X-component
Velocity vector Y-component
Velocity vector Z-component

N/A
N/A
km
km
km
km/s
km/s
km/s

No
No
No
No
No
No
No
No

Keyword

Description

Units

Obligatory

COMMENT
SEMI_MAJOR_AXISECCENTRICITYINCLINATION
RA_OF_ASC_NODE
ARG_OF_PERICENTER
MEAN_ANOMALY
GM

Reference Orbital Data Message Blue Book 6.7
Semi-major axis
Eccentricity
Inclination
Right ascension of the ascending node
Argument of pericenter
Mean anomaly
Gravitational coefficient (Gravitational Constant x Central
Mass)

n/a
km
n/a
deg
deg
deg
deg
km**3/s**2

No
No
No
No
No
No
No
No

Keyword

Description

Units

Obligatory

COMMENTMASSSOLAR_RAD_AREA
SOLAR_RAD_COEFF
DRAG_AREA
DRAG_COEFF

Reference Orbital Data Message Blue Book 6.7
Spacecraft mass
Solar Radiation Pressure Area (AR)Solar Radiation Pressure Coefficient (CR)Drag Area (AD)Drag Coefficient (CD)

n/a
kg
m**2
n/a
m**2
n/a

No
No
No
No
No
No

Keyword

Description

Units

Obligatory

COMMENT
COV_REF_FRAME
CX_X
CY_X
CY_Y
CZ_X
CZ_Y
CZ_Z

Reference Orbital Data Message Blue Book 6.7
Coordinate system for covariance matrix
Covariance matrix [1,1]Covariance matrix [2,1]
Covariance matrix [2,2]Covariance matrix [3,1]
Covariance matrix [3,2]Covariance matrix [3,3]

n/a
n/a
km**2
km**2
km**2
km**2
km**2
km**2

No
No
No
No
No
No
No
No

TABLE 12: OPM DATA – Osculating Keplerian Elements in Specified Reference FrameTABLE 13: OPM DATA – SPACECRAFT PARAMETERSTABLE 14: OPM DATA – POSITION/VELOCITY COVARIANCE MATRIXPage 30

MANEUVER NOTIFICATION FORMATCX_DOT_X
CX_DOT_Y
CX_DOT_Z
CX_DOT_X_DOT
CY_DOT_X
CY_DOT_Y
CY_DOT_Z
CY_DOT_X_DOT
CY_DOT_Y_DOT
CZ_DOT_X
CZ_DOT_Y
CZ_DOT_Z
CZ_DOT_X_DOT
CZ_DOT_Y_DOT
CZ_DOT_Z_DOT

Covariance matrix [4,1]
Covariance matrix [4,2]Covariance matrix [4,3]Covariance matrix [4,4]Covariance matrix [5,1]
Covariance matrix [5,2]Covariance matrix [5,3]Covariance matrix [5,4]Covariance matrix [5,5]Covariance matrix [6,1]
Covariance matrix [6,2]
Covariance matrix [6,3]Covariance matrix [6,4]Covariance matrix [6,5]
Covariance matrix [6,6]TABLE 15: OPM DATA – MANEUVER PARAMETERS

km**2/s
km**2/s
km**2/s
km**2/s**2
km**2/s
km**2/s
km**2/s
km**2/s**2
km**2/s**2

No
No
No
No
No
No
No
No

km**2/s
km**2/s
km**2/s
km**2/s**2
km**2/s**2
km**2/s**2

No
No
No
No
No
No
No

Keyword

Description

Units

Obligatory

COMMENT
MAN_EPOCH_IGNITION
MAN_DURATION
MAN_DELTA_MASS
MAN_REF_FRAME

Reference ODM Blue Book 6.7
Epoch of ignition. Reference ODM Blue Book 6.5.9
Maneuver duration (If = 0, impulsive maneuver)
Mass change during maneuver (value is < 0)
Coordinate system for velocity increment vector (value
must be selected from OPM Blue Book annex A)
1st component of the velocity increment
2nd component of the velocity increment
3rd component of the velocity increment
A unique ID applied to the specific maneuver by theoperator. Unique IDs may be 1-30 alphanumericcharacters, dashes, or underscores
If this field is not populated, Space-Track will calculate it
based on component DVs
Name of the corresponding ephemeris file, if the operator
has submitted ephemeris to 18 SPCS for screening
Specifies the purpose of the maneuver. Acceptable values:
AEROBRAKE (Aerobraking)
ATT_ADJUST (Attitude adjust)
COLA (Collision avoidance)
DEORBIT (Deorbit)
DISPOSAL (Disposal)
FLYBY_TARG (Flyby targeting)
LEOP (Launch & Early Orbit)
MNVR_CLEANUP (Maneuver cleanup)
MASS_ADJUST (Mass adjust)
TRIM (Orbit trim)

n/a
UTC
s
kg
n/a

No
Yes
Yes
No
Yes

km/s

No

n/a

Yes

MAN_DV_1
MAN_DV_2
MAN_DV_3
USER_DEFINED_MAN_ID
USER_DEFINED_DV_
OVERALL
USER_DEFINED_EPHEM
USER_DEFINED_MAN_
PURPOSE

Page 31

km/s
km/s
km/s
n/a

n/a

Yes
Yes
Yes
No

No

MANEUVER NOTIFICATION FORMAT

USER_DEFINED_TCA

USER_DEFINED_MAN_STATUS

Page 32

OTHER (Other)
PER_RED (Period reduction)
RELOCATION (Relocation)
SCI_OBJ (Science objective)
SPIN_RATE_ADJUST (Spin rate adjust)
SK (Station-keeping)
TRAJ_CORR (Trajectory correction)
For COLA maneuvers, provide the Time of Closest
Approach (TCA) in UTC of the corresponding conjunction
event. Recommend using the TCA in the Conjunction Data
Message.
Acceptable values: PREDICTED, DETERMINED,CANCELLED.
PREDICTED = planned maneuver
DETERMINED = confirmed maneuver
CANCELLED = cancelled maneuver

UTC

n/a

Yes forCOLA
maneuver,No for allothersYesHOW TO NAME MANEUVER NOTIFICATIONS
How to Name Maneuver Notifications
OVERVIEW

To simplify the process for O/Os, Space-Track will generate the file name for each maneuver notification
using information provided within the OPM, specifically the RELEASABILITY, USER_DEFINED_NORAD_CAT_ID,
ORIGINATOR, and CLASSIFICATION fields. In the file name, the O/O only needs to include their organization
name (must be the same as their CDM account on Space-Track) and a unique identifier, such as a sequencenumber or timestamp, followed by the .opm extension:<CDM Organization>_<unique identifier>_<metadata>.opm

EXAMPLESAs long as the obligatory fields are correctly included within the OPM, the operator may name their file
anything they want as long as the first two fields are the CDM Organization and a unique identifier:
•

•

•

•

Page 33

NASA_1234_ISS.opm

NASA_1235_25544.opm

NASA_165120000.opm

NASA_165120001_25544COLA.opm

HOW TO SUBMIT MANEUVER NOTIFICATIONS
How to Submit Maneuver Notifications
OVERVIEW

Maneuver notifications may be submitted in three ways:
1.

Through the website Space-Track.org (preferred)

2.

By email to the 18 SPCS Conjunction Assessment Team at 18SPCS.doo.orbitalsafety@us.af.mil. (Thismethod should only be used in the event the satellite operator cannot access Space-Track.)

1.1 Manually, or
1.2 Using Application Programming Interface (API)Space-Track.org is the most efficient and secure method of submitting maneuver notifications on arecurring basis. All operators who have access to the Operator Panel will automatically be given
permissions to upload maneuver notifications for the satellites assigned to their CDM account. To set up a
CDM account or a Maneuver folder, contact the 18 SPCS SSA Sharing Team at
18spcs.doo.customerservice@us.af.mil or +1-805-605-5219.
Once an active CDM account is established, the operator(s) assigned to the account will have access to the
Operator and Files Panels:

Figure 12: Files Panel on Space-Track.org

Page 34HOW TO SUBMIT MANEUVER NOTIFICATIONSSUBMITTING MANEUVERS NOTIFICATIONS THROUGH SPACE-TRACK.ORG
On the Files Panel, you will have access to the ‘Download’ and ‘Upload’ tabs. On the ‘Upload’ tab you can
upload a variety of files to the folders you have permissions to. All of these folders will display in the‘Destination’ dropdown menu:

Figure 13: Files Panel Upload Tab - Maneuvers

MANUAL UPLOAD OF MANEUVER NOTIFICATIONS
1.
2.

3.

Page 35

Log in to Space-Track.org, click on ‘Files’ at the top of the page, and then click on the ‘Upload’ tab
Click ‘Choose Files’ and select your OPM maneuver notification files

2.1 Maximum number of files in a single upload is 100
2.2 Maximum total size per upload is 60 MB
2.3 Files must be formatted in accordance with ‘Maneuver Notification Format’

Using the ‘Destination’ dropdown menu, select the ‘/Maneuvers/YourOrganization’ folder. (Note: To set
up a maneuver folder, contact the 18 SPCS SSA Sharing Team at 18SPCS.doo.customerservice@us.af.mil
or +1-805-605-5219.)

HOW TO SUBMIT MANEUVER NOTIFICATIONS
4.
5.
6.

Click ‘Upload’ to upload the files.
After a successful upload, the files will display in ‘My Uploads (Last 30 Days)’ Table
The 18 SPCS Orbital Safety Crew will receive a notification that you have uploaded new maneuver
information.

API UPLOAD OF MANEUVER NOTIFICATIONS

Please visit Space-Track.org’s ‘API’ and ‘How To’ pages for the most up-to-date guidance (including usage
limitations) on API capabilities: https://www.space-track.org/documentation#/api andhttps://www.spacetrack.org/documentation#/howto. Similar to manual uploads:

1.
2.
3.

Files must be formatted in accordance with ‘Maneuver Notification Format’
After a successful upload, the files will display in ‘My Uploads (Last 30 Days)’ Table
The 18 SPCS Conjunction Assessment Team will receive a notification that you have provided new
maneuver information. However, if the maneuver requires attention as a high-interest event, please
phone or email the Conjunction Assessment Team at: +1-805-605-3533 or
18SPCS.doo.orbitalsafety@us.af.mil.

EMAIL

If your organization doesn’t have access to the Operator and Files Panels, you may send your maneuver
notifications by email to the 18 SPCS Conjunction Assessment Team at 18SPCS.doo.orbitalsafety@us.af.mil.
Please:1.
2.
3.

Page 36

Format the files in accordance with ‘Maneuver Notification Format’
Send only .opm files - .zip files cannot be accepted. Or,
If it’s not possible to use the OPM format, maneuver notification may be provided in the body of anemail.

CONTACT US
Contact Us

18 SPCS CONJUNCTION ASSESSMENT TEAM
For questions on conjunction assessment and collision avoidance support, please contact the 18 SPCS
Orbital Safety Crew by email at 18SPCS.doo.orbitalsafety@us.af.mil or by phone at +1-805-605-3533.
Examples of support include:•••

Questions about screening results
Screenings for high-interest events
Missing CDMs

18 SPCS SSA SHARING TEAM

For questions about specialized SSA support or data products, please contact the 18 SPCS SSA Sharing
Team by email at 18SPCS.doo.customerservice@us.af.mil or by phone at +1-805-605-5219. Examples
include:•••••Submitting an Orbital Data Request for advanced services or support
Questions about data formats
Space-Track access and permissions
Registering your satellite to receive spaceflight safety support
Access to Space-Track.org’s for-testing-only website

SPACE-TRACK.ORG ADMINISTRATION TEAM

For questions about the Space-Track.org website, please contact admin@space-track.org. Examples include:•••

Page 37

API queries
Automation
Website performanceANNEX A: 18 SPCS PROBABILITY OF COLLISION
Annex A: 18 SPCS Probability of Collision

Figure X: Geometry of a Conjunction

HOW 18 SPCS CALCULATES PROBABILITY OF COLLISION
For a conjunction 1 between two objects in earth orbit, the 18th Space Control Squadron (18 SPCS) can
compute and report a value commonly referred to as probability of collision (Pc 2). This value can beused by a satellite owner/operator (O/O) as a warning and may motivate further study of theencounter on their part 3.

Also referred to as a “close approach”
Also PoC, POC
3
When an assumption is made in the calculation of Pc, it’s made on the side of overestimating the Pc, in otherwords, being conservative. In this way O/O’s are made aware of all potential encounters. The first place where
this conservatism appears is in what is actually calculated. What is computed is not probability of collision but
rather the probability that two objects are less than a specified distance apart at their time of closest approach(TCA). This is due to several factors, 18 SPCS not knowing the exact size, shape and orientation of both objects
at TCA being one of the major ones. So the approach is to determine the longest distance the two satellite’scenters of mass can be apart and still have the two satellites touch. This defines the “specified distance apart”
that is used in the Pc calculation. Note that if the two satellites are not spheres, then a simple change inorientation means that they may not touch and no collision would occur. So the Pc value calculated always has
this factor of conservatism built in.
1
2

Page 38

ANNEX A: 18 SPCS PROBABILITY OF COLLISION
The data at the time of closest approach (TCA) required to compute Pc includes:
•
•
•
•
•
•

The size of the primary object
The size of the secondary object
The inertial position and velocity vectors of the primary object
The inertial position and velocity vectors of the secondary object
The 3-dimensional position covariance of the primary object
The 3-dimensional position covariance of the secondary object

If available and reliable these data items are provided in the Conjunction Data Message (CDM).

OBJECT SIZE
The Pc calculation requires an estimate of the sizes of the primary and secondary objects. Because ofa dimensionality reduction of the problem (to be described subsequently), the combined sizes of thetwo objects ultimately will be represented as an area in a projected plane—the “conjunction plane.”
The typical procedure is to circumscribe the primary and secondary objects each by a sphere, add thetwo sphere radii to generate a supervening sphere that can contain both circumscribing spheres, andproject this supervening sphere into the conjunction plane as a circle.
The size of the objects 4 is called AREA_PC in the CDM and given in square meters. The CDM Blue
Book 5 states:
AREA PC: The actual area of the object (m**2). The area could be known by theowner/operator of the satellite or defined by using a Radar Cross Section (RCS) as in the caseof debris. If the value of the area is unknown or not available, “0.0” may be displayed. Thisparameter can be useful for calculation collision probability.
SuperCOMBO 6 is used to identify conjunctions in 18 SPCS. It has three modes: standoff radius,
ellipsoid, and covariance. Pc is computed in covariance mode. It requires that the sizes of both objects
be input by the operator. Size is specified (in meters) by the Radius of Exclusion Volume; as stated

4 The primary and secondary objects are referred to as OBJECT1 and OBJECT2 in the CDM.
5

Conjunction Data Message Recommended Standard CCSDS 508.0-B-1 BLUE BOOK, June 2013

6

Super Computation of Miss Between Orbits. SuperCOMBO is an application program in the Astrodynamics
Support Workstation (ASW). It is based on the Air Force Space Command (AFSPC) Astrodynamics Standards
program COMBO.

Page 39

ANNEX A: 18 SPCS PROBABILITY OF COLLISION
above, it represents the minimum radius of a sphere that can contain the object 7 8. SuperCOMBO canalso assign specific values or use an RCS catalog to establish size.
Caution is advised if RCS is used to establish size. For many reasons RCS may not represent thephysical size of an object, and certainly not its shape or orientation at TCA.

POSITION AND VELOCITY VECTORSThe position and velocity vectors 9 of the primary and secondary objects at TCA are given in the CDM
in the fields X, Y, Z, X_DOT, Y_DOT, and Z_DOT. Position units are km and velocity units are km/sec.
They are normally referenced to the International Terrestrial Reference Frame (ITRF), but othercoordinate frames may be specified in accordance with the CDM Blue Book. The velocity vectors are
not explicitly used in the computation of Pc. However, they are required in order to establish the point
and time of closest approach, to perform needed coordinate transformations/rotations to prepare thedata properly for the Pc calculation, and to determine encounter geometry at TCA.
In 18 SPCS the position and velocity of the objects at TCA are normally computed by interpolating
between ephemeris points 10. The ephemeris points are obtained by propagating forward in time theobject’s special perturbations (SP) state vector at epoch 11. The state vector at epoch is computed
using an orbit determination method based on minimum variance differential correction (DC).
In some cases ephemeris points of an object are provided to 18 SPCS by the satellite
owner/operator 12. If so, these are used in lieu of, or in addition to, internal ephemeris.
While not explicitly input to compute Pc, the position and velocity of the secondary relative to theprimary at TCA are included in the CDM. They are given in Radial, Transverse, and Normal (RTN)

If an O/O reports object size to 18 SPCS in m**2 then that should be the area of a circle that completely“covers” the object when viewed from any angle. 18 SPCS would then compute the Radius of Exclusion Volume
from this area as (O/O-reported-size divided by π)**0.5.
8Pre-assigned default values for payloads and platforms (5 meters), rocket bodies and unknown objects (3meters) and debris (1 meter) were determined through a study of sizes of objects in the space object catalog
and are normally used. Plans are being developed to allow O/O’s to provide a more accurate value of thisparameter for use in CA screening in the future.
9
Together, often referred to as the state vector
10
An ephemeris is a time ordered listing of an object’s position and velocity vectors (that may include
covariance).
11
Or general perturbations (GP) element set (ELSET) in the absence of an SP state vector
12
In J2000 mean equator mean equinox coordinates
7

Page 40

ANNEX A: 18 SPCS PROBABILITY OF COLLISION
coordinates of the primary object 13. Also provided are overall MISS_DISTANCE and RELATIVE_SPEED.
Relative position and velocity offer a more intuitive view of the conjunction 14 and tell the user if thesecondary is moving fast or slow relative to the primary at TCA.

COVARIANCE AND ERROR ELLIPSOIDS
The covariance matrix, provided separately for the primary and secondary object (as described in
Annex C of CCSDS 508.0-B-1), is routinely furnished in 6 x 6 form, even though only the position
portion is needed for the Pc calculation as described in this memorandum. A covariance matrix
characterizes the uncertainty in a satellite state vector, similar to the way that variance, the square of
the standard deviation, is a metric for assessing the spread of student test scores about the mean. An
example of a position covariance, using the notation of the CCSDS standard, is given as the symmetricmatrix below. The diagonal elements represent the variance in each of the components (R, T, and N),
and the off-diagonal terms give the covariance between the two named components (the product of
the two components’ standard deviations and their correlation coefficient):

 CR _ R CT _ R CN _ R Cov =  CT _ R CT _ T CN _ T  CN _ R CN _ T CN _ N The covariance matrix for each object is referenced to its own RTN coordinate frame. For each object
matrix components are computed using 5-point Lagrange interpolation of the covariance in theephemeris file produced by the 18 SPCS 15.
An owner/operator may also send 18 SPCS an ephemeris that includes covariance 16. In these cases thecovariance values in the CDM are interpolated from the ephemeris (with covariance) provided by theowner/operator.

13

Also called the Radial-Intrack-Crosstrack (RIC) coordinate frame or the UVW system

14 For example, at TCA the secondary relative to the primary is at “eleven o’clock high.”

Covariance at TCA quantifies uncertainty in the state vector at TCA. Covariance at epoch quantifies uncertainty
at epoch. Covariance at epoch in essence maps the observed-minus-computed residuals in the observations
used in the DC to the uncertainty in the state vector produced by the DC.

15

Owner/operators provide ephemeris with covariance in three formats: (1) the Generic On-Orbit (GOO) (2)Modified ITC, or Orbital Ephemeris Message (OEM)16

Page 41

ANNEX A: 18 SPCS PROBABILITY OF COLLISION
The one-standard-deviation 17 three dimensional (3D) error ellipsoid may be used to visualize the“size” of the position uncertainty at TCA. Diagonalization of the 3 x 3 covariance matrix yields the size,
shape, and orientation of the error ellipsoid 18. Often, because of drag, the largest uncertainty will bein the direction of the satellite’s motion relative to the atmosphere 19.

ASSUMPTIONSWhen computing Pc at 18 SPCS several assumptions are made. These include:
•
•
•
•
•
•
•

Object sizes are known or can otherwise be assigned an upper bound.
The conjunction is “hyperkinetic, meaning that the conjunction duration is very short; thisallows the additional simplifying assumption that the relative motion between objects is
rectilinear throughout the encounter.
Gaussian theory and statistics apply.
Covariance for both objects is known and constant throughout the encounter.
Primary and secondary errors are independent allowing “combined” covariance to be thesimple sum of the individual covariances (in a common frame), resulting in the “joint”
covariance.
The covariance is not “too large.”
The covariance is not “too small 20.”

Technical papers have been written to address the computation and/or validity of Pc when one ormore of these assumptions come into question. If at TCA (1) covariance is too small, (2) covariance is
too large, or (3) the relative speed of the secondary relative to the primary is too small, then Pc is notcomputed in SuperCOMBO. The values for covariance “too large” and relative speed “too small” areuser-settable.
Another concern is covariance realism: does the covariance used in the computation of Pc truly reflect
the uncertainty in the state vectors at TCA? Because quantitative studies have shown that covarianceis often underestimated, empirical techniques have been devised to scale or otherwise inflate thecovariance – make it larger – to compensate for the underestimation.

17 1 sigma or 1σ

The square root of each of the eigenvalues of the covariance matrix gives the sizes of the ellipsoid axes. The
eigenvectors provide the orientation of the ellipsoid axes relative to the object’s RTN coordinate frame.
19 A very rough estimate of the sizes of the three axes of the error ellipsoid can be obtained by taking the squareroot of each of the diagonal elements CR_R, CT_T, and CN_N.
20 This test is needed to trap zero covariance.
18

Page 42

ANNEX A: 18 SPCS PROBABILITY OF COLLISIONCOMPUTATION
Computation of Pc takes place in the collision plane 21. This is the plane perpendicular to the relative
velocity vector at TCA. This reduces the mathematics from 3D to 2D, and the kinematics from dynamic
to static. In 2D the equation used to compute Pc is:

PoC =

1

 1
exp − (r − rS/P )T C −1 (r − rS/P ) dxdy
1/ 2∫∫
2π | Det (C ) | x2 + y 2 ≤d 2
 2

In this double integral equation:
•
•
•
•
•
•
•
•

π = 3.141592653589793.

C is the 2X2 projection of the combined 3X3 covariance at TCA onto the collision plane 22.
Det(C) is the determinant of C.
d is the sum of the two object sizes 23.

“exp” is the exponential function, i.e., e to the power in parentheses with e =2.718281828459045.
r = (x, y)T is any point in the collision plane such that x2 + y2 ≤ d2.
rS/P = (rS/P, 0)T is the position of the secondary relative to the primary along the x-axis in thecollision plane.
C-1 is the inverse of C.

This equation integrates the 2D Gaussian probability density function (centered on the secondary
object) over the circle of radius d (centered on the primary object 24).

Also called the encounter plane
The combined covariance is the sum of the covariance matrices corresponding to each object (bothreferenced to the same coordinate frame). The applicability of Gaussian statistics allows for combining two
covariance matrices into one using term-by-term summation.
23
The sum of the radii of exclusion volumes for the two objects
24 With the primary object located at the origin of a 2D coordinate frame in the collision plane
21
22

Page 43

ANNEX A: 18 SPCS PROBABILITY OF COLLISION
Methodologies, coordinate transformations, assumptions, combining Gaussian distributions,limitations, and techniques used to facilitate computation of Pc are discussed at length in technicalpapers listed in the bibliography 25.

NOTES
18 SPCS uses error functions (ERF) for computing the double integration in the Pc equation. In
addition 18 SPCS performs integration over a square circumscribing the circle of radius d. This squareis aligned with the axes of the combined 2D probability density function in the collision plane. This
simplifies the computation of Pc but gives a very slightly larger – but safe – value.
For these and other reasons agencies may compute slightly different values for Pc for the same
conjunction. If the difference is large however further investigation is warranted 26.

BIBLIOGRAPHY
Several excellent references for understanding the computation of Pc are listed at the Space Assigned
Number Authority (SANA) registry at http://sanaregistry.org/r/cdm_cpm/cdm_cpm.html.
In addition the following references are valuable because in the 1990s Doctor Foster matured much of
the theory and methodology used by NASA to compute Pc for Space Shuttle and International Space
Station (ISS) safety of flight analysis. A version of the NASA algorithm for computing Pc was integrated
into the ASW program SuperCOMBO in 2000. Certain theoretical issues were modified and expanded

The computation of Pc is a dynamic 3D problem: the two objects are moving in 3-dimensions. However, it canbe simplified by reducing the dynamic 3D problem to a static 2D problem. This is accomplished by performing
calculations in the 2D collision plane. Consider the two error ellipsoids of the primary and the secondary objects
at the instant of TCA as they “punch holes” in the collision plane that’s perpendicular to the relative velocity
vector. The problem of computing Pc immediately collapses to a static 2D problem in the collision plane. The
25

ellipsoids become ellipses in the collision plane representing the 1σ “contour lines” of the two-dimensional
Gaussian probability density functions (pdf) of the objects. One can think of the 2D Gaussian (“bell-shaped”)
probability density functions for the primary and the secondary as being “little hills” sitting over their respective
satellite positions at TCA in the collision plane. In effect, the ellipse for one object is but one of many nested“Russian Doll” contour lines going out to infinity in the 2D collision plane for the Gaussian pdf, just as in 3D theerror ellipsoid is but one of an infinite number of nested Russian dolls. These two “little hills” combine into one
hill – one pdf – centered over the secondary for the actual computation of the Pc.
26 In 2000 AFSPC/A9 numerically validated the computation of Pc in SuperCOMBO.

Page 44

ANNEX A: 18 SPCS PROBABILITY OF COLLISION
by F.C. Chan in his important monograph Spacecraft Collision Probability (El Segundo, CA: Aerospace
Press, 2008).
Foster, J.L., and Frisbee, J.H., Comparison of the Exclusion Volume and Probability Threshold Methods
for Debris Avoidance for the STS Orbiter and International Space Station. NASA /TP-2007-214751.
Houston, Texas: NASA Johnson Space Flight Center, May 2007 (written in October 1999).
Foster, J.L., and Wortham, M.B, ISS Debris Avoidance Maneuver Threshold Analysis. NASA /TP-2007214752. Houston, Texas: NASA Johnson Space Flight Center, May 2007 (written in October 1999).
Foster, J.L., The Analytic Basis for Debris Avoidance Operations for the International Space Station.
Proceedings of the Third European Conference on Space Debris, p. 441-445, Darmstadt, Germany, 19 21 March 2001.

Page 45

ANNEX B: FREQUENTLY ASKED QUESTIONS
Annex B: Frequently Asked Questions

1. HOW AND WHEN DO I SIGN UP FOR CONJUNCTION ASSESSMENT (CA) ALERTS?
First, register for a user account on Space-Track.org. Then fill out a satellite registration form and send it to
18SPCS.DOO.CustomerService@us.af.mil. We will set up a CDM account for your organization that helps us
route alerts to the right people. You can do this at any time, whether you have a satellite on orbit, or are
waiting for the satellite to be launched. We recommend contacting us a few weeks prior to launch.

2. DO I NEED TO SUBMIT AN ORBITAL DATA REQUEST FOR CA SERVICES?

You do not need to submit an ODR for basic CA services. ODRs are only required for advanced services.

3. IS THERE A CHARGE FOR 18 SPCS SPACEFLIGHT SAFETY SERVICES?

All of our services are provided at no cost to the owners and operators (O/Os) of active spacecraft.

4. MY SATELLITE HAS A PREDICTED CONJUNCTION WITH ANOTHER ACTIVE SATELLITE, HOW
CAN I CONTACT THE OTHER OPERATOR?
If the other O/O has chosen to share their contact information with other O/Os on Space-Track.org, you canfind it on the Directory Tab of the Operator Panel. 18 SPCS highly encourages all O/Os to share theircontact information with other O/Os. If it's not available there, you can contact 18 SPCS, but it will likely
take extra time as we will ask to receive their permission before we give you their contact information.

5. I HAVEN'T RECEIVED ANY CONJUNCTION DATA IN A WHILE, IS SOMETHING WRONG?

This likely indicates that 18 SPCS has not predicted any conjunction events that meet reportable criteria.
(Reference Tables 5 and 6.) You may contact the Conjunction Assessment Team at
18SPCS.doo.orbitalsafety@us.af.mil to confirm.

6. WHY IS ANOTHER GROUP RECEIVING CONJUNCTION DATA FOR OUR CO-OWNED SATELLITE
WHEN MY GROUP HAS NOT RECEIVED ANY?
The other group likely has advanced CA services while yours are at the basic level, so they will have accessto more data. To confirm, contact the 18 SPCS SSA Sharing Team at 18SPCS.doo.customerservice@us.af.mil.

7. HOW CAN I SUBMIT PREDICTED EPHEMERIS FOR SCREENING? WHAT ABOUT PREDICTEDMANEUVER INFORMATION?

Contact 18SPCS.DOO.CustomerService@us.af.mil, and we'll set up folders on Space-Track.org where you
can upload your predicted ephemeris and maneuver files. You can specify who should have access to thefolder.

Page 46

ANNEX B: FREQUENTLY ASKED QUESTIONS
8. I NEED TO HAVE LARGER THAN NORMAL SCREENINGS FOR MY SATELLITE. WHAT CAN 18
SPCS DO?
If you have a valid SSA Sharing Agreement with USSPACECOM, you may submit an Orbital Data Request(ODR) form to request advanced CA services. For more information, on pursuing an SSA Sharing Agreement
contact stratcom.offutt.j51.mbx.j513@mail.mil. For more information on how to submit an ODR contact
18SPCS.doo.ssasharing@us.af.mil.

9. CAN I CHANGE THE CONTACTS IN MY SPACE-TRACK.ORG ORGANIZATION/CDM ACCOUNT?
Primary Representatives (PR) for the account can make the changes. If you don't have a PR or need to
add/change one, contact us at 18SPCS.DOO.CustomerService@us.af.mil for assistance.

10. WHAT DOES IT MEAN WHEN AN OBJECT IN THE CDM HAS A NUMBER IN THE 80000’S?
A satellite number from 80,000-89,999 indicates that it is an "analyst object." These are on-orbit objects
that are tracked by the U.S. Space Surveillance Network (SSN) but with insufficient fidelity for publicationin the public satellite catalog (SATCAT).

11. WHAT DOES IT MEAN WHEN AN OBJECT IN THE CDM HAS A NUMBER IN THE
799500000’S?

A satellite number from 799500000-799999999 is a temporary number that 18 SPCS has assigned to a
newly launched satellite. This allows the O/O of the satellite to submit ephemeris and receive CDM results
prior to the satellite being entered into the public catalog and assigned a 5-digit number.

12. Can the 18 SPCS analyze my data, make recommenda�ons, or help me choose a plan ofac�on?

We are legally prohibited from performing analysis or making recommendations, but we will provide youwith the best possible data to assist in your decision making.

13. IF I SUBMIT AN ORBITAL DATA REQUEST FOR ADVANCED CA SERVICES, CAN I PICK WHICH
SCREENING VOLUME I WOULD LIKE?
No, you will receive the screening volume for the orbital regime that your satellite is operating in, in
accordance with Table 3. If this changes due to orbit raising or deorbiting, 18 SPCS may adjust thescreening volume.

14. I HAVE QUESTIONS, IS THERE SOMEONE I CAN TALK TO?

Contact the 18 SPCS SSA Sharing Team at 18SPCS.doo.customerservice@us.af.mil or +1-805-605-5219.

Page 47