18th & 19th Space Defense Squadron
Combined Force Space Component Command
Vandenberg Space Force Base, California, USA
19th Tel +1-540-284-3999
18th Tel +1-805-605-6551
www.space-track.org

SPACEFLIGHT SAFETY HANDBOOKFOR SATELLITE OPERATORSVERSION 1.7 APRIL 2023
18 & 19 SDS Processes for On-Orbit Conjunction Assessment & Collision AvoidanceTABLE OF CONTENTS
Contents
Revision History _________________________________________________________________________________________ 1
USSPACECOM SSA Sharing Program____________________________________________________________________ 3
Program Description ______________________________________________________________________________________________3
Space-Track.org____________________________________________________________________________________________________3

Conjunction Assessment Process _______________________________________________________________________ 5
On-Orbit Conjunction Assessment (CA) _________________________________________________________________________5
HAC vs HAC _____________________________________________________________________________________________________6
O/O Ephemeris vs HAC (O/O EPH vs HAC) ___________________________________________________________________7
O/O Ephemeris vs O/O Ephemeris (O/O EPH vs O/O EPH) ________________________________________________7
On-Orbit Collision Avoidance (COLA) ___________________________________________________________________________8
Basic Emergency CA and COLA Services ________________________________________________________________________8
Advanced CA and COLA Services _________________________________________________________________________________8
Screening Schedule _______________________________________________________________________________________________9
Screening Volumes ______________________________________________________________________________________________ 10
Reporting Criteria _______________________________________________________________________________________________ 11
Notifications _____________________________________________________________________________________________________ 12
Basic Emergency CA Notifications _____________________________________________________________________________ 12
Advanced CA Notifications _____________________________________________________________________________________ 13
Launch Conjunction Assessment _______________________________________________________________________________ 13
Early Orbit Conjunction Assessment __________________________________________________________________________ 13
End-of-Life/Disposal Support __________________________________________________________________________________ 14
Deorbit Support _________________________________________________________________________________________________ 14
Tasking ___________________________________________________________________________________________________________ 15

Ephemeris Formats _____________________________________________________________________________________ 16
Overview _________________________________________________________________________________________________________ 16
NASA Ephemeris Format _______________________________________________________________________________________ 17
UTC Ephemeris Format _________________________________________________________________________________________ 18
Generic On-Orbit Ephemeris Format __________________________________________________________________________ 19

TABLE OF CONTENTS
Modified ITC Ephemeris Format _______________________________________________________________________________ 20
Orbital Ephemeris Message (OEM) Format ___________________________________________________________________ 21

How to Name Ephemeris Files _________________________________________________________________________ 25
Overview _________________________________________________________________________________________________________ 25
File Name Examples ____________________________________________________________________________________________ 26

How to Submit Ephemeris Files _______________________________________________________________________ 27
Overview _________________________________________________________________________________________________________ 27
Submitting EphEmeris Through Space-Track.org _____________________________________________________________ 28
Manual Upload of Ephemeris Files_____________________________________________________________________________ 29
API Upload of Ephemeris Files _________________________________________________________________________________ 30
Email _____________________________________________________________________________________________________________ 30
Guidance for High-Interest Events _____________________________________________________________________________ 30

Maneuver Notification Format _________________________________________________________________________ 31
Overview _________________________________________________________________________________________________________ 31
Format ___________________________________________________________________________________________________________ 31

How to Name Maneuver Notifications ________________________________________________________________ 36
Overview _________________________________________________________________________________________________________ 36
Examples _________________________________________________________________________________________________________ 36

How to Submit Maneuver Notifications _______________________________________________________________ 37
Overview _________________________________________________________________________________________________________ 37
Submitting MANEUVERS Notifications Through Space-Track.org ___________________________________________ 38
Manual Upload of Maneuver Notifications ____________________________________________________________________ 38
API Upload of Maneuver Notifications _________________________________________________________________________ 39
Email _____________________________________________________________________________________________________________ 39

Contact Us _______________________________________________________________________________________________ 40
19 SDS Conjunction Assessment Team ________________________________________________________________________ 40
18 SDS SPACE Office ____________________________________________________________________________________________ 40
Space-Track.org Administration Team _________________________________________________________________________ 40

Annex A: 19 SDS Probability of Collision ______________________________________________________________ 41
How 19 SDS Calculates Probability of Collision _______________________________________________________________ 41

TABLE OF CONTENTS
Object Size _______________________________________________________________________________________________________ 42
Position and Velocity Vectors___________________________________________________________________________________ 43
Covariance and Error Ellipsoids _______________________________________________________________________________ 43
Assumptions _____________________________________________________________________________________________________ 44
Computation _____________________________________________________________________________________________________ 45
Notes _____________________________________________________________________________________________________________ 46
Bibliography _____________________________________________________________________________________________________ 47

Annex B: Frequently Asked Questions _________________________________________________________________ 0
1. How and when do i sign up for conjunction assessment (ca) alerts? _______________________________________0
2. Do i need to submit an orbital data request for ca services? ________________________________________________0
3. Is there a charge for 18 SDS and 19 SDS spaceflight safety services? _______________________________________0
4. My satellite has a predicted conjunction with another active satellite, how can i contact the otheroperator? __________________________________________________________________________________________________________0
5. I haven't received any conjunction data in a while, is something wrong? __________________________________0
6. Why is another group receiving conjunction data for our co-owned satellite when my group has notreceived any? ______________________________________________________________________________________________________0
7. How can i submit predicted ephemeris for screening? What about predicted maneuver information? _1

Annex C: 19 SDS CDM Fields Explained ________________________________________________________________ 0
Overview ___________________________________________________________________________________________________________0

REVISION HISTORY
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

12 Aug 16

1.2
1.3

1.4

1.5

Page 1

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 reference to launch support and early orbit determination to
Launch Early Orbit Protection pg. 2
4. Provided various edits for cleaner communication as needed
5. Replaced UVW references to include the interchangeable value of
RTN/UVW
6. Replaced references to "Day of Year" to Julian Day
7. Changed ephemeris time formats to reflect "JJJ"
8. Replaced "OEM" ephemeris format examples lost in previous version
9. Added additional guidance for "OEM" format regarding reference
frame annotations
10. Added clarification for submitting ephemeris via email pg. 24
11. Added clarification for Space-track username pg. 24
12. Re-formatted tables pg. 28-31

27 Aug 16
3 Jan 17

Feb 19Aug 20REVISION HISTORY
1.6

1.
2.
3.

Replaced 18 SPCS Patch on Front Page
Removed instances of SSA Sharing phone number
Removed instances of HAC 1-v-1 on demand as a supported service
pg. 7
4. Removed 18 SPCS co-location with CSpOC pg. 3
5. Replaced all references to Vandenberg Air Force Base to
Vandenberg Space Force Space
6. Corrected Table 6: Advanced Reporting Criteria for a CDM
generated for Near Earth (LEO 1-4) O/O Ephemeris screening to
2km x 25km x 25km pg. 10
7. Removed Phone Call criteria from Tables 5 and 6 pg. 10
8. Added paragraph describing propagation time constraints forephemeris-based screenings pg. 15
9. Removed mention of using UCN/UCD as acceptable options forephemeris file naming pg. 23
10. Clarified that e-mailing ephemeris should be utilized for urgent
situations and not for nominal operations pg. 25
11. Adjusted maximum total size for Space-Track uploads to 200 MB
pg. 26/35
12. Changed instance of operators who have access to the Operator
panel ‘will automatically be given permissions’ to ‘may be given
permissions’ pg. 34
13. Clarified that e-mailing a maneuver notification should be utilized
for urgent situations and not for nominal operations pg. 36
14. Added Annex C: 18 SPCS CDM Fields Explained pg. 47

Apr 221.7

1.
2.

Apr 23

3.
4.
5.
6.
7.
8.
9.

Page 2Updated 18 SDS patch & added 19 SDS patch on front page
Updated 18 SDS and 19 SDS unit responsibilities throughout
handbook
Updated email addresses and phone numbers throughout
handbook
Updated “SSA Sharing Team” to “SDA Partnership and Coalition
Engagement (SPACE) Office”
Included O/O Ephemeris vs HAC details
Updated tasking criteria
Updated Conjunction Assessment screening workflow and timeline
Updated 19 SDS Conjunction Assessment contact information
Adjusted maximum total size for Space-Track uploads to 512 MB.
Included note to check “Help” tab for regular updates to maximum
upload size

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 SDA 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, the 18th Space Defense Squadron (18 SDS) 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 SDS performs the space surveillance mission
for the U.S. Space Force and provides foundational SSA for the U.S. government and global space partners
through the SSA Sharing Program. This role was performed by the Joint Space Operations Center (JSpOC, or
CSpOC as of July 2018) until July 2016, at which time 18 SDS was activated and assumed all spacesurveillance functions. In 2022, 19 SDS was activated and assumed the mission of performing Conjunction
Assessment to include on-orbit CA and collision avoidance (COLA) functions, as well as launch conjunction
assessment and collision avoidance (LCA or LCOLA). 18 SDS still provides the support needed through the
lifetime of a satellite from pre-launch preparation to end-of-life disposal, including pre-launch support andearly orbit determination, anomaly support, end-of-life and disposal support, deorbit support, and reentry
assessment. 18 SDS is still responsible for all functions related to Human Spaceflight Safety and NASA
CARA, including Human Spaceflight Safety launch conjunction assessment (HSF LCA). 19 SDS is currently
located at Dahlgren Naval Base, Virginia. 18 SDS is currently located at Vandenberg Space Force Base. Bothunits support the mission of performing space surveillance, maintaining the space catalog, and providing
foundational SDA and 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. It ismanaged and populated by 18 SDS and 19 SDS. It is the primary method of sharing SSA information withthe global space community at the basic, emergency, and advanced levels. All satellite operators should

Page 3

USSPACECOM SSA SHARING PROGRAM
register for a user account to access the full scope of SSA data and services available through the SSA
Sharing Program.

Page 4

CONJUNCTION ASSESSMENT PROCESS
Conjunction Assessment Process
ON-ORBIT CONJUNCTION ASSESSMENT (CA)The 19 SDS Conjunction Assessment (CA) process identifies close approaches between all resident space
objects (RSOs) in the 18 SDS 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 SDS 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 SDS High Accuracy Catalog (HAC). The 19 SDS 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.).
19 SDS performs three types of screenings:
1.
2.
3.

Page 5

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
19 SDS 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 allnear earth objects, all deep space objects, near earth concern lists, deep space concern lists, or O/Oprovided 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, 19 SDS performs a conjunction assessment screening of RSOs against
the rest of the catalog to identify conjunctions within screening criteria. These objects are evaluated by the
Conjunction Assessment Team to ensure that the most current observations are incorporated into the OD, if
not they are placed on a “Concern List” for manual Differential Correction updates. If the parameters of the
conjunction fall within criteria that identify a close approach and the close approach involves an active
satellite, the 19 SDS will notify the O/O of the active satellite(s) in accordance the methods listed inReporting Criteria. Based on these results, 19 SDS also generates Concern Lists to use in follow-on

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CONJUNCTION ASSESSMENT PROCESS
screenings. Concern Lists include all candidates that produce conjunctions with probability of collision (Pc)≥ e^-7 in NE and miss distance ≤ 5km in DS. Throughout this cycle, 18 SDS is always performing DCs andrefining orbital states. Depending on the quality of the OD, 19 SDS works with 18 SDS to increase sensor
tasking on the primary or secondary objects. A tasking list is sent back to 18 SDS for integration into theirtasking process. HAC vs HAC screenings include:
1.
2.
3.
4.

NE All HAC: All NE objects vs all NE objects, based on 18 SDS SP data (NE is defined as Period ≤ 225
minutes)
DS All HAC: All DS objects vs all DS objects, based on 18 SDS 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
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) ≤ 5 days

O/O Ephemeris vs HAC (O/O EPH vs HAC)
All O/O’s may submit predictive ephemeris to the 19 SDS 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, 19 SDS assumes these will occur; otherwise, the files should besubmitted as Special. Operational files will be screened according to the schedule in Tables 1 and 2. Please
note for O/O EPH vs HAC screenings, O/O ephemeris is screened only once within 8 hours of the time theO/O uploaded that ephemeris to Space-Track. A Special file represents where the satellite is planning to go
if a maneuver is being considered for a non- routine 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 19 SDS Conjunction Assessment Team. Multiple Special files may besubmitted 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 is screened
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. Please note, this is only applicable to O/O EPH vs. O/O EPH
screenings—

Page 7

CONJUNCTION ASSESSMENT PROCESSON-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 toperform collision avoidance by maneuvering their satellite. If the O/O decides to consider COLA actions,they may send 19 SDS their predictive ephemeris data (in approved formats and coordinate systems)
which 19 SDS will then screen against the HAC and provide results within reporting criteria so that the
O/O may decide how to proceed. This exchange of data may continue until the time of closest approach(TCA), after which 19 SDS will resume routine screening of the active satellite in accordance with thescreening schedule. If they do not perform COLA, 19 SDS will continue to monitor the conjunction andprovide updates based on data from the SSN until the TCA has passed.

BASIC EMERGENCY CA AND COLA SERVICES
19 SDS performs CA and provides COLA support for all satellite operators of active spacecraft as an
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
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:
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
4.1 Ephemeris versus secondary object, or
4.2 Ephemeris versus full catalog

5.
6.

Page 8

Access to propagated SP ephemeris (without covariance) for all RSOs in the unclassified space catalog
Access to SP state vectors (without covariance) for all objects in the unclassified catalog

CONJUNCTION ASSESSMENT PROCESS
7. Access to propagated SP ephemeris (without covariance) for all objects in the unclassified catalog
SCREENING SCHEDULE
19 SDS 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 followed by two
Concern List screenings, 8 hours apart, every 24 hours.) For O/O Ephemeris screenings, the ephemeris filename dictates how 19 SDS will process files. If the O/O designates it as Special, the 19 SDS will process it
as high-interest and screen it as soon as possible. If it is designated as Operational, the 19 SDS will screen
it according to the schedule in Table 1. Results for Special ephemeris are provided within 4 hours ofreceiving the ephemeris, and Operational results are provided within 8 to 12 hours of the scheduled
screening times, depending on when it is submitted by the O/O.
The 19 SDS screening schedule shifts one hour when the state of Virginia (United States) transitions
between Eastern Standard Time (EST) and Eastern Daylight Time (EDT), which generally occurs in Marchand November each year. Both schedules are provided below:

Page 9

CONJUNCTION ASSESSMENT PROCESSSCREENING VOLUMESThe following tables define the screening volumes and durations 19 SDS uses for basic CA, advanced CA,
and ephemeris screenings. 19 SDS 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 19 SDS 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

1200 km < Perigee ≤ 2000 km
Eccentricity < 0.25

5 days

0.4 km

2 km

2 km

750 km < Perigee ≤ 1200 km
Eccentricity < 0.25

5 days

0.4 km

12 km

12 km

500 km < Perigee ≤ 750 km
Eccentricity < 0.25

5 days

0.4 km

25 km

25 km

Perigee ≤ 500 km
Eccentricity < 0.25

5 days

0.4 km

44 km

51 km

Orbit 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

TABLE 4: O/O EPHEMERIS SCREENING VOLUMES
Screening
Deep Space
Ellipsoid
Near Earth
Covariance

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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 CRITERIASpace-Track Criteria

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

Notification
MethodConjunction Data Message (CDM)

Deep SpaceHAC

TCA ≤ 10 days and Overall miss ≤ 5km

TCA ≤ 3 days and Overall miss ≤ 5km

Deep SpaceO/O Ephemeris

TCA ≤ 10 days and Overall miss ≤ 5km

TCA ≤ 3 days and Overall miss ≤ 5km

Near Earth:
HAC

TCA ≤ 3 days andOverall miss ≤ 1km andProbability of Collision ≥ e^-7

TCA ≤ 3 days, Overall miss ≤ 1km
andNear EarthO/O Ephemeris

TCA ≤ 3 days andOverall miss ≤ 1km andProbability of Collision ≥ e^-7

Probability of Collision ≥ e^-4
TCA ≤ 3 days andOverall miss ≤ 1km andProbability of Collision ≥ e^-4

TABLE 6: ADVANCED REPORTING CRITERIASpace-Track Criteria
Notification
MethodDeep Space,
HAC
Deep SpaceO/O Ephemeris
Near Earth(LEO 1-4)
HAC
Near Earth(LEO 1-4)
O/O Ephemeris

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TCA ≤ 10 days and all results w/in
10km x 10km x 10km

Emergency Criteria
Conjunction Data Message (CDM) &Close Approach Notification (CAN)
email
TCA ≤ 3 days andOverall miss ≤ 5km

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

TCA ≤ 3 days andOverall miss ≤ 5km

TCA ≤ 5 days andProbability of Collision ≥ e^-7

TCA ≤ 3 days, Overall miss ≤ 1km andProbability of Collision ≥ e^-4

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

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

Conjunction Data Message (CDM)

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 website based on files thatthe 19 SDS Conjunction Assessment Crew has 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). These notifications are only sent to email addresses that the O/O has
designated to receive CANs on their Space-Track account. (Contact 18 SDS SPACE Office –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 SDS 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.

•

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.

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.

BASIC EMERGENCY CA NOTIFICATIONS
19 SDS Screening

Figure 2: Basic Emergency CA Notifications

Page 12CONJUNCTION ASSESSMENT PROCESSADVANCED CA NOTIFICATIONS
19 SDS Screening

Figure 3: Advanced CA Notifications

LAUNCH CONJUNCTION ASSESSMENT
19 SDS 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, 19
SDS 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 this service,reference the Launch Conjunction Assessment Handbook, which is available on Space-Track’s Help Page.

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. 19 SDS 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. To receive early orbit CA support the O/O needs to:•Page 13Pre-launch:o Submit an ODR requesting early orbit CA, specifying the preferred screening volume

CONJUNCTION ASSESSMENT PROCESS•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
CovarianceOrbit 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

END-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 SDS will assist the
O/O by screening maneuver ephemeris and providing results. All O/O-provided ephemeris will be screenedusing standard ephemeris screening volumes, and results will be provided in accordance with basic 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, 19 SDS can provide CA screenings, and 18 SDS cancoordinate with NASA to ensure the deorbiting spacecraft safely descends through the International Space
Station’s (ISS) orbit. After the spacecraft completes its maneuvers, 18 SDS can confirm final reentry. To
receive this service, the O/O needs to:•••Page 14

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

CONJUNCTION ASSESSMENT PROCESSTASKING
In certain situations, more observations on an object will improve the quality of the conjunction prediction.
If an object meets any of the following criteria, 18 SDS will automatically increase the tasking priority andrevisit frequency assigned to sensors. 19 SDS has embedded this in the routine screening cycle, as seen in
Figure 1. We are not able to increase tasking upon demand:•••

Page 15

Less than 20 observations in current Differential Correction (DC), or
Most recent observation is over three days old, orAt least one component of covariance over 100,000 m2

EPHEMERIS FORMATS
Ephemeris Formats
OVERVIEW
Satellite operators may provide ephemeris in various formats, which will be converted into formats thatcan be processed by 19 SDS’ ASW (Astrodynamics Support Workstation). Using the Super Computation ofMiss Between Orbits (COMBO) software, 19 SDS 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.
19 SDS’ 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 19 SDS mission systemcorrects for leap seconds.
For any screening utilizing ephemeris, 19 SDS will only propagate out 7 days in advance for Near Earthephemeris and 10 days in advance for Deep Space. This propagation is from the moment the screening
commences from 19 SDS. Any ephemeris that is delivered with a starting time and date outside of the
propagation will not be screened.
The NASA and UTC formats include position and velocity only. 19 SDS accepts three formats withcovariance:•

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
values•Orbital 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,
https://public.ccsds.org/default.aspx) website for more information on the OEM.

Page 16

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

19 SDS’ 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 17

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, considering any
adjustment needed for a leap year.
This ephemeris format does not include covariance values.

Page 18

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 19

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 6x6 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 ina date/time field (i.e., “yyyDOYhhmmss.sss”), each state vector component (i.e., position (x, y, z) andvelocity (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 20

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 21

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 22

EPHEMERIS FORMATS
data block throughout the OEM file (COV_REF_FRAME, Figure 9). If no annotation is provided, the 19 SDS
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, considering 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.

EPHEMERIS REFERENCE FRAMES
Our system can support the following reference frames in ephemeris:

Table 8: Ephemeris Reference Frames

Page 23

Vector Reference Frame

Covariance Frame

EME2000

EME2000

EME2000

J2000

EME2000

RTN

EME2000

RSW

EME2000

UVW

J2000

EME2000

J2000

J2000

J2000

RTN

Page 24

J2000

RSW

J2000

UVW

ITRF

ITRF

TEME

RTN

TEME

RSW

TEME

UVW

HOW TO NAME EPHEMERIS FILES
How to Name Ephemeris FilesOVERVIEW
19 SDS requires that satellite operators name their files following a specific format, which dictates how theephemeris file will be processed. When the O/O submits their files through the website Space-Track.org,
Space-Track will verify the file is named correctly and return error messages if it is not. The file nameformat is:<DataType>_<Catalog#>_<CommonName>_<DayTimeGroup>_<Operational/Special>_<MetaData>_<Classification>.<FileExtension>

Table 9: Ephemeris File Name Convention
Normative Value (N) or
Example€)Data Field

Description

DataType

The type of data being provided.

(N) MEME (unlessotherwise directed by 18
SPCS) This entry must be
in uppercase letters

Yes

Catalog#

The 5-digit designator for the object as defined in
USSPACECOM’s satellite catalog https://www.spacetrack.org/#/catalog(E) 25544

Yes

If the object is not cataloged, use the 9-digit number
assigned to you by 18 SDS (Contact the 18 SDS SPACE
Office at 18SPCS.DOO.CustomerService@us.af.mil for
detail€CommonName

The spacecraft name for the object. Recommend
using the common name listed in USSPACECOM’ssatellite catalog https://www.spacetrack.org/#/catalog

Obligatory(E) 00900€(E) 795000000(E) 795999999(E)€S (ZARYA)(E) CALSHERE 1

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

Yes

If the object is not cataloged, use the common namedesignated by the satellite operator
DayTimeGroup

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. Please note, any portion of theephemeris file that takes place prior to the time ofscreening will not receive results. The system cannot
produce results for events in the past. Further, thesystem cannot produce results for ephemeris
projected too far in the future (generally, o€ 7-10days).

Continued on next page

Page 25

HOW TO NAME EPHEMERIS FILES

Table 9: Ephemeris File Name Convention, cont.
Data Field

Description

Normative Value (N) or
Example (E)Operational/
SpecialAn Operational file represents where the satellite isplanned to go and may or may not include maneuvers(N) Oper(N) Special

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(E) sationkeepingmnvr

Yes

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

Indicates the type of file(N) .txt (unlessotherwise directed by 18
SPCS)

Obligatory

These files typically incorporate normal stationkeeps, or represent a freefall orbit
If maneuvers are included, 18 SDS assumes these will
occur. Otherwise, the files should be submitted asSpecial.
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.
*Multiple Special files may be submitted for the same
satellite, but only one Operational file at a time can besubmitted per satellite*
MetaData

Classification

File Extension(E) burn02(E) __(E) Unclassified

FILE NAME EXAMPLES

Page 26

Yes(E) UNCLASSIFIED•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_799500234_Sat1_1651200_special_separation_unclassified.txt

YesHOW TO SUBMIT EPHEMERIS FILES
How to Submit Ephemeris FilesOVERVIEW
Ephemeris files may be submitted in three ways:
1.

Through the website Space-Track.org (preferred):
1.1 Manually, or
1.2 Using Application Programming Interface (API)2.

By email to the 19 SDS Orbital Safety Crew at 19SDS.orbital.safety@spaceforce.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 SDS SPACE Office at 18SPCS.doo.customerservice@us.af.mil. The SPACE
Office 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 e-mail addresses (as registered on Space-Track) of the personnel who will upload ephemeris foryour satellite constellation

The SPACE Office will create a permissions-based ephemeris folder for your organization that will only beaccessed by 18 SDS, 19 SDS, and the personnel you authorize. (Note: e-mail addresses that are notregistered on Space-Track cannot be included.) You will have upload, download, and delete permissions toPage 27

HOW TO SUBMIT EPHEMERIS FILES
the folder, which you will access through the Files Panel:

Figure 10: Files Panel on Space-Track.org

SUBMITTING 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 folders will display in the ‘Destination’ dropdown menu:

Page 28

HOW TO SUBMIT EPHEMERIS FILES

Figure 11: Files Panel Upload Tab - Ephemeris

MANUAL UPLOAD OF EPHEMERIS FILES
1.
2.

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 512 MB (This is subject to change, reference the “Help” tab on
Space-Track.org for updates)
2.3 Files must be named in accordance with guidelines in ‘How to Name Ephemeris Files’

3.
4.
5.
6.

Page 29

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
The 19 SDS Conjunction Assessment Crew will receive a notification that you have uploaded newephemeris files for screening. However, if the ephemeris is Special or in response to a high-interest
event, please phone or email the Conjunction Assessment Crew to notify them that you need an
immediate response: +1-540-284-3999 or 19SDS.orbital.safety@spaceforce.mil.

HOW TO SUBMIT EPHEMERIS FILESAPI 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 19 SDS Conjunction Assessment Crew will receive a notification that you have uploaded newephemeris files for screening. However, if the ephemeris is Special or in response to a high-interest
event, please phone or email the Conjunction Assessment Crew to notify them that you need an
immediate response: +1-540-284-3999 or 19SDS.orbital.safety@spaceforce.mil.

EMAIL
In a non-nominal and urgent situation, if your organization does not have an ephemeris folder on the Files
Panel, you may send your ephemeris by email to the 19 SDS Conjunction Assessment Crew at
19SDS.orbital.safety@spaceforce.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 19 SDS Conjunction Assessment Crew
(19SDS.orbital.safety@spaceforce.mil or +1-540-284-3999) to provide the following information regarding
the high-interest request:
1.
2.
3.
4.

Page 30

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
19 SDS respectfully requests that satellite operators notify 19 SDS of planned, confirmed, and cancelled
maneuvers. This allows 19 SDS to maintain a more accurate catalog, anticipate spaceflight safety risks, andprovide more relevant conjunction notifications. 19 SDS has chosen the Orbital Parameter Message (OPM)
as the most appropriate method of exchanging maneuver information. However, to make it applicable to 19
SDS operations and reporting procedures, 19 SDS 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 10: 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 commentNo

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

Yes

PUBLIC

No. If notprovided,
will default
to PRIVATECOMMENTCREATION_DATEORIGINATOR

USER_DEFINED_RELEASABILITY

Page 31Yes

MANEUVER NOTIFICATION FORMAT

USER_DEFINED_CLASSIFICATIONPRIVATE: Operators agrees
to share file with 18 SPCS
only
Acceptable value:
UNCLASSIFIED
18 SPCS will only accept
unclassified files.

UNCLASSIFIEDYes

TABLE 11: OPM METADATA
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

ISS (ZARYA)

Yes

1998-067A

No• 5-digit satellite catalog number
assigned by USSPACECOM, or• 9-digit satellite number assignedby 18 SDS
Origin of reference frame
Name of reference frame in which
the state vector and optional
Keplerian element data are given

25544
799500234

Yes

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

Yes
Yes, if statevectorincludedUTC

Yes

OBJECT_NAMEOBJECT_ID

USER_DEFINED_NORAD_CAT_ID

CENTER_NAME
REF_FRAME

REF_FRAME_EPOCH

TIME_SYSTEM

Page 32

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.

No

MANEUVER NOTIFICATION FORMATTABLE 12: 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

TABLE 13: OPM DATA – Osculating Keplerian Elements in Specified Reference Frame
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

TABLE 14: OPM DATA – SPACECRAFT PARAMETERS
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

TABLE 15: OPM DATA – POSITION/VELOCITY COVARIANCE MATRIX
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

Page 33

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

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]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

CZ_DOT_X
CZ_DOT_Y
CZ_DOT_Z
CZ_DOT_X_DOT
CZ_DOT_Y_DOT
CZ_DOT_Z_DOT

Covariance matrix [6,1]
Covariance matrix [6,2]
Covariance matrix [6,3]Covariance matrix [6,4]Covariance matrix [6,5]
Covariance matrix [6,6]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

TABLE 16: OPM DATA – MANEUVER PARAMETERS
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
km/s
km/s
n/a

Yes
Yes
Yes
No

km/s

No

n/a

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 34

MANEUVER NOTIFICATION FORMAT

USER_DEFINED_TCA

USER_DEFINED_MAN_STATUS

Page 35

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:•NASA_1234_ISS.opm•

NASA_1235_25544.opm•

NASA_165120000.opm•

NASA_165120001_25544COLA.opm

Page 36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)
1.1 Manually, or
1.2 Using Application Programming Interface (API)2.

By email to the 19 SDS Conjunction Assessment Crew at 19SDS.orbital.safety@spaceforce.mil. (Thismethod should only be used in the event the satellite operator cannot access Space-Track.)

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 may 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 SDS SPACE Office at 18spcs.doo.customerservice@us.af.mil.
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 37

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.

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 512 MB
2.3 Files must be formatted in accordance with ‘Maneuver Notification Format’

3.
4.

Page 38

Using the ‘Destination’ dropdown menu, select the ‘/Maneuvers/YourOrganization’ folder. (Note: To set
up a maneuver folder, contact the 18 SDS SPACE Office at 18SPCS.doo.customerservice@us.af.mil.)Click ‘Upload’ to upload the files.

HOW TO SUBMIT MANEUVER NOTIFICATIONS
5.
6.

After a successful upload, the files will display in ‘My Uploads (Last 30 Days)’ Table
The 19 SDS 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 19 SDS 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: +1-540-284-3999 or
19SDS.orbital.safety@spaceforce.mil.

EMAIL
In an urgent situation, if your organization doesn’t have access to the Operator and Files Panels, you may
send your maneuver notifications by email to the 19 SDS Conjunction Assessment Team at
19SDS.orbital.safety@spaceforce.mil. Please:
1.
2.
3.

Page 39

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
19 SDS CONJUNCTION ASSESSMENT TEAM
For questions on conjunction assessment and collision avoidance support, please contact the 19 SDS
Orbital Safety Crew by email at 19SDS.orbital.safety@spaceforce.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 SDS SPACE OFFICE
For questions about specialized SSA support or data products, please contact the 18 SDS SPACE Office byemail at 18SPCS.doo.customerservice@us.af.mil. 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

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

Page 40

API queries
Automation
Website performanceANNEX A: 19 SDS PROBABILITY OF COLLISION
Annex A: 19 SDS Probability of Collision

Figure 14: Geometry of a Conjunction

HOW 19 SDS CALCULATES PROBABILITY OF COLLISION
For a conjunction1 between two objects in earth orbit, the 19th Space Defense Squadron (19 SDS) can
compute and report a value commonly referred to as probability of collision (Pc 2). This value can be usedby a satellite owner/operator (O/O) as a warning and may motivate further study of the encounter on their
part3. If an O/O chooses to provide the Hard Body Radius (HBR) of their satellite on Space-Track, this canbe used in the calculation of Pc^2.

1

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/Os 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, 19 SDS not knowing the exact size, shape and orientation of both objects at
TCA being one of the major ones. The approach is to determine the longest distance the two satellite’s centersof mass can be apart and still have the two satellites touch. This defines the “specified distance apart” that isused in the Pc calculation. Note that if the two satellites are not spheres, then a simple change in orientationmeans that they may not touch and no collision would occur. The Pc value calculated always has this factor of
conservatism built in.
2

Page 41

ANNEX A: 19 SDS 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 of adimensionality reduction of the problem (to be described subsequently), the combined sizes of the two
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 the two sphere radii
to generate a supervening sphere that can contain both circumscribing spheres, and project thissupervening sphere into the conjunction plane as a circle.
The size of the objects4 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 the owner/operator of
the satellite or defined by using a Radar Cross Section (RCS) as in the case of debris. If the value of thearea is unknown or not available, “0.0” may be displayed. This parameter can be useful for
calculation collision probability.
SuperCOMBO6 is used to identify conjunctions in 19 SDS. It has three modes: standoff radius, ellipsoid, andcovariance. Pc is computed in covariance mode. It requires that the sizes of both objects be input by theoperator. Size is specified (in meters) by the Radius of Exclusion Volume; as stated above, it represents \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 42

ANNEX A: 19 SDS PROBABILITY OF COLLISIONPOSITION AND VELOCITY VECTORSThe position and velocity vectors9 of the primary and secondary objects at TCA are given in the CDM in thefields X, Y, Z, X_DOT, Y_DOT, and Z_DOT. Position units are km and velocity units are km/sec. They arenormally referenced to the International Terrestrial Reference Frame (ITRF), but other coordinate frames
may be specified in accordance with the CDM Blue Book. The velocity vectors are not explicitly used in thecomputation 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 the data properly for the Pc
calculation, and to determine encounter geometry at TCA.
In 19 SDS the position and velocity of the objects at TCA are normally computed by interpolating between
ephemeris points10. The ephemeris points are obtained by propagating forward in time the object’s special
perturbations (SP) state vector at epoch11. 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 19 SDS by the satellite owner/operator12. 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 the primaryat TCA are included in the CDM. They are given in Radial, Transverse, and Normal (RTN) coordinates of the
primary object13. Also provided are overall MISS_DISTANCE and RELATIVE_SPEED. Relative position andvelocity offer a more intuitive view of the conjunction14 and tell the user if the secondary 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 metricfor 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 symmetric matrix below. The diagonal elements
represent the variance in each of the components (R, T, and N), and the off-diagonal terms give the9

Together, often referred to as the state vector
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
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.”
10

Page 43

ANNEX A: 19 SDS PROBABILITY OF COLLISION
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 the ephemeris
file produced by the 19 SDS15.
An owner/operator may also send 19 SDS an ephemeris that includes covariance16. In these cases, thecovariance values in the CDM are interpolated from the ephemeris (with covariance) provided by theowner/operator.

The one-standard-deviation17 three-dimensional (3D) error ellipsoid may be used to visualize the “size” ofthe position uncertainty at TCA. Diagonalization of the 3X3 covariance matrix yields the size, shape, andorientation of the error ellipsoid18. Often, because of drag, the largest uncertainty will be in the direction of
the satellite’s motion relative to the atmosphere19.

ASSUMPTIONSWhen computing Pc at 19 SDS 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; this allows
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.

15

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.
16

Owner/operators provide ephemeris with covariance in three formats: (1) the Generic On-Orbit (GOO) (2)Modified ITC, or Orbital Ephemeris Message (OEM)17 1 sigma or 1
18
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.

Page 44

ANNEX A: 19 SDS PROBABILITY OF COLLISION•••

Primary and secondary errors are independent allowing “combined” covariance to be the simple
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 small20.”

Technical papers have been written to address the computation and/or validity of Pc when one or more ofthese 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 not computed inSuperCOMBO. The values for covariance “too large” and relative speed “too small” are user-settable.
Another concern is covariance realism: does the covariance used in the computation of Pc truly reflect theuncertainty in the state vectors at TCA? Because quantitative studies have shown that covariance is often
underestimated, empirical techniques have been devised to scale or otherwise inflate the covariance –make it larger – to compensate for the underestimation.

COMPUTATION
Computation of Pc takes place in the collision plane21. 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 tostatic. 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
2 | Det (C ) | x 2 + y 2 d 22In this double integral equation:
•
•
•
•
•
•
•
•

 = 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 sizes23.
“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.

20 This test is needed to trap zero covariance.
21

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
22Page 45

ANNEX A: 19 SDS PROBABILITY OF COLLISION
This equation integrates the 2D Gaussian probability density function (centered on the secondary object)
over the circle of radius d (centered on the primary object24).
Methodologies, coordinate transformations, assumptions, combining Gaussian distributions, limitations,and techniques used to facilitate computation of Pc are discussed at length in technical papers listed in the
bibliography25.

NOTES
19 SDS uses error functions (ERF) for computing the double integration in the Pc equation. In addition, 19
SDS performs integration over a square circumscribing the circle of radius d. This square is aligned withthe axes of the combined 2D probability density function in the collision plane. This simplifies thecomputation 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 warranted26.

24 With the primary object located at the origin of a 2D coordinate frame in the collision plane
25

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
ellipsoids become ellipses in the collision plane representing the 1 “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 46

ANNEX A: 19 SDS PROBABILITY OF COLLISION
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 thetheory 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 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-2007-214752.
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 47

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 SDS and 19 SDS spaceflight safety services?
At this time, 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 SDS and 19 SDS highly encourage all O/Os to share
their contact information with other O/Os. If it's not available there, you can contact 18 SDS, 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 19 SDS has not predicted any conjunction events that meet reportable criteria.
(Reference Tables 5 and 6.) You may contact the 18 SDS SPACE Office at
18SPCS.doo.customerservice@us.af.mil. to confirm.

6. Why is another group receiving conjunction data for our co-owned satellite when mygroup 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 SDS SPACE Office at 18SPCS.doo.customerservice@us.af.mil.

Page 0ANNEX B: FREQUENTLY ASKED QUESTIONS
7. How can I submit predicted ephemeris for screening? What about predicted maneuver
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 1

ANNEX C: 19 SDS CDM FIELDS EXPLAINED
Annex C: 19 SDS CDM Fields Explained
OVERVIEWThe Conjunction Data Message (CDM) is the primary product that 19 SDS will deliver for on-orbit
Conjunction Assessment. The format 19 SDS utilizes closely resembles the format recommended by CCSDS
Conjunction Data Message Recommended Standard (CDM) 508.0-P-1.0.1. The table below is acomprehensive reference on the fields included in a 19 SDS CDM.

Table 17: 19 SDS CDM Fields
Keyword

Description

ExampleCCSDS_CDM_VERS

CDM format version in theform of X.Y.
A comment can be placed
here for reader’sinformation. Currently 18
SPCS places the CDM ID in
the comment section
File creation date/time inUTC
Creating agency oroperator
Spacecraft name for which
the CDM is provided
ID that uniquely identifies
the CDM message.
The Date and Time of the
conjunction in UTC
The overall separation
distance of both objects at
TCA in meters
The magnitude of therelative velocity vector inmeters/sec. The speed atwhich both objects are
moving relative to eachother at TCA inmeters/second
The R component of Object
2’s position relative to
Object 1 in an RTN
coordinate frame in meters
The T component of Object
2’s position relative to
Object 1 in an RTN
coordinate frame in meters

1.0

COMMENTCREATION_DATEORIGINATORMESSAGE_FOR
MESSAGE_ID
TCA
MISS_DISTANCERELATIVE_SPEED

RELATIVE_POSITION_R

RELATIVE_POSITION_T

Page 0

CDM_ID:XXXXXXXXX

2015-07-04T12:00:00.000000
JSPOC
STARLINK-61
000012345_conj_000054321_202
2067143221_06514372256137
2015-07-04T12:00:00.000000
437

15031

43.2, -574

43.2, -574

ANNEX C: 19 SDS CDM FIELDS EXPLAINEDRELATIVE_POSITION_N

The N component of Object
2’s position relative to
Object 1 in an RTN
coordinate frame in meters
The R component of Object
2’s velocity relative to
Object 1’s velocity in an
RTN coordinate frame inmeters/second
The T component of Object
2’s velocity relative to
Object 1’s velocity in an
RTN coordinate frame inmeters/second
The N component of Object
2’s velocity relative to
Object 1’s velocity in an
RTN coordinate frame inmeter/second
If applicable, theprobability of collision(PoC) calculated by 18
SPCS from values of 0.0 to
1.0
The method utilized to
calculate probability ofcollision
The screening mode usedby the 18 SPCS to predictthe conjunction containedin the CDM. Options
include stand-off radius,
ellipsoid and covariance
The data used by 18 SPCS
to generate the CDM

43.2, -574

OBJECT

The object for which themetadata applies for

OBJECT 1
OBJECT 2

OBJECT_DESIGNATOR

The SCC or NORAD CAT ID
for the object
The satellite catalog used
for the object
The common name for theobjectThe International
Designator for the object ina YYYY-DDDXXX format
notating the year and dayof launch followed by atleast one capital letter to

25544

RELATIVE_VELOCITY_R

RELATIVE_VELOCITY_T

RELATIVE_VELOCITY_N

COLLISION_PROBABILITYCOLLISION_PROBABILITY_METHODCOMMENT Screening Option

COMMENT Screened with

CATALOG_NAMEOBJECT_NAME
INTERNATIONAL_DESIGNATOR

Page 1-36.3, 41.7, 12971.8-36.3, 41.7, 12971.8-36.3, 41.7, 12971.8

0.000003656957

FOSTER-1992

Stand-Off, Ellipsoid, Covarianceinertial state vector
unknown state vector type

SATCATSTARLINK-61, COSMOS 1408 DEB
1998-067A

ANNEX C: 19 SDS CDM FIELDS EXPLAINEDOBJECT_TYPE
OPERATOR_CONTACT_POSITIONOPERATOR_ORGANIZATIONOPERATOR_PHONEOPERATOR_EMAILEPHEMERIS_NAME

COVARIANCE_METHODMANEUVERABLE
REF_FRAMEGRAVITY_MODELATMOSPHERIC_MODEL

N_BODY_PERTURBATIONSPage 2discern between objects ofthe same launch
Category of type of object
The contact position of theowner/operator of theobject. Space-Track willplace a URL for a query thatwill lead to thisinformation
The organization of theowner/operator of theobject
The phone number of theowner/operator of theobject. Space-Track willplace a URL for a query thatwill lead to thisinformation
The e-mail of theowner/operator of theobject. Space-Track willplace a URL for a query thatwill lead to thisinformation
The name of the ephemeris
utilized if the data source isephemeris
The method of whichcovariance is calculated.
When covariance cannot becalculated, default values
may be used. Caution
should be used when using
default values whencalculating PoC
The maneuver capability ofthe object
Name of the reference
frame for the provided
state vectors
The name of the gravity
model used for
propagation
The name of theatmospheric model used
for propagation
The gravitational
perturbation models used
in a comma separated
formatPAYLOAD, ROCKET BODY,
DEBRIS, UNKNOWN, OTHER

SpaceX, Iridium, CNESNONE
MEME_25544_ISS_1651200_oper__unclassified.txt
CALCULATEDDEFAULT

YES, NO, N/A
ITRF

EGM-96: 36D 360

JBH09

MOON,SUNANNEX C: 19 SDS CDM FIELDS EXPLAINEDSOLAR_RAD_PRESSURE

EARTH_TIDESINTRACK_THRUSTCOMMENT Covariance Scale Factor
COMMENT Exclusion Volume
Radius

TIME_LASTOB_STARTTIME_LASTOB_END

RECOMMENDED_OD_SPAN

ACTUAL_OD_SPAN

OBS_AVAILALBEOBS_USEDRESIDUALS_ACCEPTEDWEIGHTED_RMS

Page 3

Indicates whether solar
radiation pressure wasused during the Orbit
Determination (OD) of theobjectIndicates whether solid
Earth and ocean tides wereused in the OD of object
Indicates whether in-track
thrust modeling was used
for the OD and propagationof the object
The scale that covariance ismultiplied by
The radius of a sphere inmeters to create a sphericalvolume representative of
the object and used in the
PoC calculation
The time in UTC of the startof the timespan that
contains observations usedin the OD. This time will
start at the latest accepted
observation
The time in UTC of the endof the timespan that
contains observations usedin the OD. This time willend at the most recent
accepted observation
The recommended timespan for the OD of theobject in days
The actual time span usedin the OD of the object indays
Total amount ofobservations available for
the OD of the object
Actual number ofobservations used in the
OD of the object
The percentage of residuals
accepted in the OD of theobject
The weighted Root Mean
Square (RMS) of theresiduals from a batch leastsquares

YES
NO

YES
NO
YES
NO
1.000000
5.0000002015-07-04T12:00:00.000000

2015-07-04T12:00:00.000000

2.76

2.76

57

57

99.3

1.446

ANNEX C: 19 SDS CDM FIELDS EXPLAINEDCOMMENT Apogee Altitude
COMMENT Perigee Altitude
COMMENT Inclination
COMMENT Operator Hard Body
Radius

AREA_PC
CD_AREA_OVER_MASS

CR_AREA_OVER_MASS

THRUST_ACCELERATION

SEDR

X
Y
Z
X_DOT
Y_DOT
Z_DOT
COMMENT DCP Density Forecast
Uncertainty

Page 4

The apogee of the object inkm
The perigee of the object in
km
The inclination of theobject in deg
If input by anowner/operator, the Hard
Body Radius of the object
in meters
The area of the object usedin the PoC calculation in m2
The object’s CD•A/m usedin the propagation of thevector and covariance to
TCA in m2/kg
The object’s CR•A/m usedin the propagation of thevector and covariance to
TCA in m2/kg
The object’s acceleration in
the In-track or R direction(RTN) used for propagating
the state vector andcovariance until TCA in
m/s2
The average amount ofenergy being removed
from an object’s orbit due
to atmospheric drag in
W/kg
Object position vector X
component in km
Object position vector Y
component in km
Object position vector Z
component in km
Object velocity vector X
component in km/s
Object velocity vector Y
component in km/s
Object velocity vector Z
component in km/s
The dynamic considers
parameter (DCP) 1-sigma
uncertainty of the relative
atmospheric density for the
specified object (given as asimple ratio). This is theuncertainty of the average

460
437
60.7
0.00

2.26420.161615504658

0

0
0.634

0.020492

1670.352554-6834.579872-1430.950837
2.780391335
2.808606433-5.751722603
2.143370310000000E-01

ANNEX C: 19 SDS CDM FIELDS EXPLAINEDCOMMENT DCP Sensitivity Vector
RTN Pos

DCP Sensitivity Vector RTN Vel

CR_R
CT_R
CT_T
CN_R
CN_T
CN_N
CRDOT_R
CRDOT_T
CRDOT_N
CRDOT_RDOT
CTDOT_R
CTDOT_T
CTDOT_N

Page 5

atmospheric density
exerting drag on the object,
relative to the nominal(measured) atmosphericdensity
The DCP position
sensitivity vector
expressed in the object’sradial-transverse-normal(RTN) reference frame inmeters. This sensitivity
vector relates changes in
the object’s TCA position
vector to variations inrelative atmosphericdensity
The DCP velocity
sensitivity vector relateschanges in the object’s TCA
inertial velocity vector tovariations in relative
atmospheric density and isin meters/sec
Object covariance matrix[1,1] in m2
Object covariance matrix[2,1] in m2
Object covariance matrix[2,2] in m2
Object covariance matrix[3,1] in m2
Object covariance matrix[3,2] in m2
Object covariance matrix[3,3] in m2
Object covariance matrix[4,1] in m2/s
Object covariance matrix[4,2] in m2/s
Object covariance matrix[4,3] in m2/s
Object covariance matrix[4,4] in m2/s2
Object covariance matrix[5,1] in m2/s
Object covariance matrix[5,2] in m2/s
Object covariance matrix[5,3] in m2/s

-7.345809012167026E+02
3.865957136169006E+05-1.456925086066596E+02-2.195009966872100E+02
2.630946954519584E-01
3.265607422364180E-01

ANNEX C: 19 SDS CDM FIELDS EXPLAINEDCTDOT_RDOT
CTDOT_TDOT
CNDOT_R
CNDOT_T
CNDOT_N
CNDOT_RDOT
CNDOT_TDOT
CNDOT_NDOT
CDRG_R
CDRG_T
CDRG_N
CDRG_RDOT
CDRG_TDOTCDRG_NDOT
CDRG_DRG
CSRP_R
CSRP_T
CSRP_N
CSRP_RDOT
CSRP_TDOTCSRP_NDOTCSRP_DRG
CSRP_SRP

Page 6

Object covariance matrix[5,4] in m2/s2
Object covariance matrix[5,5] in m2/s2
Object covariance matrix[6,1] in m2/s
Object covariance matrix[6,2] in m2/s
Object covariance matrix[6,3] in m2/s
Object covariance matrix[6,4] in m2/s2
Object covariance matrix[6,5] in m2/s2
Object covariance matrix[6,6] in m2/s2
Object covariance matrix[7,1] in m3/kg
Object covariance matrix[7,2] in m3/kg
Object covariance matrix[7,3] in m3/kg
Object covariance matrix[7,4] in m3/(kg*s)
Object covariance matrix[7,5] in m3/(kg*s)
Object covariance matrix[7,6] in m3/(kg*s)
Object covariance matrix[7,7] in m4/kg2
Object covariance matrix[8,1] in m3/kg
Object covariance matrix[8,2] in m3/kg
Object covariance matrix[8,3] in m3/kg
Object covariance matrix[8,4] in m3/(kg*s)
Object covariance matrix[8,5] in m3/(kg*s)
Object covariance matrix[8,6] in m3/(kg*s)
Object covariance matrix[8,7] in m4/kg2
Object covariance matrix[8,8] in m4/kg2