Help Documentation

Overview's Application Programming Interface (API) allows users to access data on this site programmatically using custom, stable URLs with configurable parameters. This API conforms to the general principles of a design called Representational State Transfer or "REST" and is identical to the data returned in the site's Graphical User Interface (GUI).
If you are going to develop scripts that query our API and believe that developing/testing them could violate our API guidelines, please Contact Us to request access to our test server. This will enable you to develop your scripts against the same API without affecting the production server.
API Use Guidelines
API Throttling:

Space-track throttles API use in order to maintain consistent performance for all users. To avoid error messages, please limit your query frequency.

Limit API queries to less than 30 requests per 1 minute(s) / 300 requests per 1 hour(s)
To prevent excess bandwidth costs, please do not exceed the following data retrieval rates for your automated scripts:
Type Frequency Details
CDM  3 / day Once every 8 hours for all constellation Conjunction Data Messages (CDM)
CDM  1 / hour Once every hour for a specific conjunction event (Note: The 18 SDS will continue to send Close Approach (CA) emails to satellite owners/operators)
TLE  1 / hour Once every hour for TLEs. Please randomly choose a minute for this query that is not at the top or bottom of the hour.
SATCAT  1 / day Once per day after 1700 (UTC) for SATCAT data
BOXSCORE  1 / day Once per day after 1700 (UTC) for Box Score data
60-DAY DECAY  1 / week Once per week, on Wednesdays after 1700 (UTC), for 60-Day Decay data

With great power comes great responsibility...
The API Query Builder tool allows users a great amount of power and flexibility in creating queries. Your space-track account may be suspended if you violate the usage policy by querying data too often or by running queries that negatively impact the performance of the website. Repeat offenders may have their account suspended permanently.

If your account has been suspended you should receive instructions from us on what you need to do in order to have your account re-instated.

We're here to help...
We realize that it can sometimes be challenging to use our API to craft an efficient query to retrieve the data that you're looking for. Rest assured that we're here to help you! If you Contact Us and tell us what you are trying to accomplish, we can help you customize your queries to meet your needs.

Please login to view this content.

Please login to view this content.
What is Alpha-5?
Alpha-5 is an object numbering schema that alters the Two-line Element Set (TLE) format to replace the 1st digit of the 5-digit object number with an alphanumeric character, making it possible to represent 240,000 more numbers without widening the fixed-width format. It is a stop-gap measure that enables continued use of the TLE format for objects with an object_number of up to 339,999 for certain legacy systems. In order to achieve this, the Alpha-5 format replaces the first character of an object number over 99,999 with a letter. A is 10, B is 11, C is 12, and so on. For clarity, the “I” and “O” characters are not used in Alpha-5.
More information about Alpha-5 can be found on the TLE page here:

Note: encourages all users to use extensible formats, such as JSON, XML, or CSV. These formats are capable of handling 9-digit numbers, and will not use the Alpha-5 numbering schema.
How can I get Alpha-5 from Space-track?
To get just Alpha-5 formatted TLE’s from space-track, request ephemerides using the TLE format for objects with a number between 100,000 and 339,999 using the GP and GP_History API classes.
How can I avoid breaking my software that doesn't support Alpha-5?
If your software cannot process alphabetical characters in the catalog number section of the TLE, you can eliminate the Alpha-5 range from your query by adding /NORAD_CAT_ID/<100000/ to filter them out like in this example:
Can I get Alpha-5 values for other formats?
Alpha-5 is designed as a TLE-specific format for the GP and GP_History API classes. Only the TLE and 3LE formats will show this Alpha-5 designator in lines 1 and 2. All other formats are capable of handling object numbers up to 999,999,999. Users can only query the API using numbers in NORAD_CAT_ID. Even though TLE/3LE will support Alpha-5 format on output in lines 1 and 2, users need to specify NORAD_CAT_ID integer values to return specific objects. The API will not support filtering on Alpha-5 values or ranges like /NORAD_CAT_ID/T0000--V9999/ We encourage users to switch to formats other than the legacy fixed width TLE/3LE that are highly extensible (XML, KVN, JSON).
Why will the tle, tle_latest, and tle_publish API classes be deprecated?
We found that the conflating API classes of data with the names of the various formats for the same data was confusing. With 9-digit catalog numbers on the horizon, we need new API classes that will efficiently handle all General Perturbations elsets: they are GP and GP_History.

The new GP classes are designed to accommodate the expanded satellite catalog’s 9-digit identifiers. Users can return ephemerides for any publicly available object in the catalog using the CCSDS's flexible Orbit Mean-Elements Message (OMM) format in canonical XML/KVN, JSON, CSV, or HTML. All 5 of these formats use the same keywords and definitions for OMM as provided in the Orbit Data Messages (ODM) CCSDS Recommended Standard 502.0-B-3.

The general perturbations (GP) class is an efficient listing of the newest SGP4 keplerian element set for each man-made earth-orbiting object tracked by the 18th Space Defense Squadron so users can propagate the most up-to-date orbit. GP_History has the complete set of historical ephemerides, totaling over 138 Million elsets.

We will deprecate the OMM and TLE API classes at some point in the future, but not the OMM and TLE formats. Ephemerides for all objects will continue to be available with GP and GP_History classes in the following formats: OMM Standard XML, OMM Standard KVN, JSON, CSV, and HTML. Only currently available catalog number ranges below 100,000 will continue to be available in the legacy fixed-width TLE or 3LE format because TLE/3LE formats lack support for numbers above 99,999. We also plan to support any future Space Force formats that the 18th Space Defense Squadron may send us.

For example, the newest elset for the International Space station will be available in TLE format using this API query:
(note that objects > 99,999 are not available in TLE/3LE format)

The newest elsets for the ISS, NAVSTAR 77, and NAVSTAR 78 in OMM (KVN) format are:
The last 30 days of elsets for the ISS in OMM (XML) format is:
We encourage you to review all the options and new metadata fields for querying the gp and gp_history classes on our API help page: and recommend that developers migrate their software to use the OMM standard (displayed in /class/gp/ as the /format/xml/) for all GP ephemerides because, again, legacy fixed-width TLE or 3LE format lacks support for numbers above 99,999.
What will replace the tle, tle_latest, and tle_publish classes?
The use case for tle_latest is fulfilled by the GP class, an efficient listing of the newest element set for each object tracked by 18 SDS. Over 75% of space-track users queried tle_latest and specified /ORDINAL/1/, so we simplified the gp class to deliver just the newest elset.

The use case for the omm and tle classes will change to gp_history class which uses the very same elements or "predicates" as the GP class and provides access to our database of over 138 million historical elsets.

The use case for the tle_publish class will be the same gp_history class and use the CREATION_DATE field (also currently in GP class) to differentiate when the ephemerides was published to
What are analyst objects?
Analyst objects are on-orbit objects that are tracked by the U.S. Space Surveillance Network (SSN) with insufficient fidelity for publication in the public satellite catalog (SATCAT). The lack of fidelity may be due to infrequent tracking, cross-tagging (observation association with closely-spaced objects), or inability to associate the object with a known launch. For current statistics on the total number of objects tracked by the SSN, to include the number of active payloads, analyst objects and debris, visit Space-Track's login page.

The 18th Space Defense Squadron (18 SDS) is responsible for analyzing tracking data from the SSN to maintain the SATCAT, and creating and updating analyst objects as new satellites launch and new objects are found. The analyst range, which is denoted by a satellite number from 80,000-89,999, is used like an analytical sandbox, where Orbital Analysts (OA) can create, change, and update objects until they have sufficient data and information to transition them to the public SATCAT. Consequently, analyst numbers can be constantly reused for different objects.
What are well-tracked analyst objects of unknown origin?
A "well-tracked analyst" object is an object in orbit with uncertain origin. Historically, USSPACECOM has not published these in the SATCAT due to the absence of critical data points such as launch date or launch country. In order to better manage congestion caused by space debris to enhance spaceflight safety, USSPACECOM now shares positional data (in the form of ELSETs) for these well-tracked analyst objects with registered Space-Track users.
What is the criteria for well-tracked?
Well-tracked objects are generally objects that have been consistently tracked by the SSN for longer than six months that don't frequently cross-tag with other objects.
Why is USSPACECOM releasing this data?
Publishing information on objects of unknown origin will help enhance spaceflight safety, prevent potentially catastrophic orbital collisions, and increase international cooperation in space.
Will this list be updated?
Yes, this list will be periodically updated as more analyst objects that meet well-tracked criteria are identified.
How will I know if an object moves from the analyst object range to the SATCAT?
USSPACECOM will not typically announce movement of objects from the analyst object range to the SATCAT; newly cataloged objects may or may not have been objects tracked in the analyst range.
How do I know if the analyst object is a payload, rocket body (R/B) or piece of debris?
Analyst objects that meet well-tracked criteria are generally debris objects, as is the majority of the space catalog. If the object type is known, it will be provided when and if the object is entered into the space catalog.
How will the international designator be formatted in the TLEs for well-tracked analyst objects if you don't know what launch they are associated with?
The international designator may be blank, replaced with the digit zero, or in some cases, there may be a partial international designator.
Why did you add period, apogee, perigee, and semi-major axis to the TLE and TLE_latest API classes and how do you calculate them?
We added semi-major axis, period, apogee, and perigee to the TLE and TLE_latest API classes so that users can filter their queries by these values, download only the data they need, and decrease the amount of the site's bandwidth that they use. Now, all the orbital elements in the satellite catalog (SATCAT) are available in the TLE class. However, the value of the same element (e.g. apogee) may not match exactly.

Every ELSET already displays a value for the object's mean motion ("n") and eccentricity ("e"), so we derive these additional four values using the following calculations:

  • period = 1440/n
  • Using mu, the standard gravitational parameter for the earth (398600.4418),
    semi-major axis "a" = (mu/(n*2*pi/(24*3600))^2)^(1/3)
  • Using semi-major axis "a", eccentricity "e", and the Earth's radius in km,
    apogee = (a * (1 + e))- 6378.135
    perigee = (a * (1 - e))- 6378.135
What is a TLE checksum?
A checksum is rudimentary means of detecting errors which may have been introduced during data transmission or storage. In TLEs and 3LEs, the last digit on line 1 and line 2 is a simple modulo-10 checksum. To calculate it, add the values of the numbers in the first 68 characters on each line—ignoring all letters, spaces, periods, and plus signs—and assign a value of 1 to all minus signs. The checksum is the last digit of that sum (the “ones” place) and is appended in the 69th character position.
Do all ELSETs have checksums?
Yes, has updated its code to include checksums for all current and historical ELSETs including over 8 Million ELSETs that did not previously include one. This provides users with better data integrity and rudimentary error checking.
Why do all ELSETs have a constant element number of 999?
To eliminate confusion caused by reusing element numbers after 999 has been reached. For example, object number 11 has used the same element numbers over 15 times throughout its life cycle.
What is a "well-tracked object" and how do I recognize it on
A "well-tracked object" is an object in orbit with uncertainty surrounding its origin. In order to better manage congestion caused by space debris and enhance spaceflight safety, USSPACECOM catalogs and publishes a number of these objects on For these objects, Country Code & Launch Site values are both UNKN ("Unknown"); The International Designator format in the catalog is YYYY-000A and in ELSETs is YY000A (year cataloged, '000' Launch #, & next alpha in sequence, e.g. 2014-000B, 2014-000C, etc.); The Launch Date is 1 January of the year that the object is cataloged.
RCS - What changed with Radar Cross Section (RCS) and why? Did RCS values change?
USSPACECOM has added scaling of RCS values to the SATCAT. Until 18 Aug 14, there was a dual-feed of both current values (RCSVALUE) & scaled values (RCS_SIZE). RCS_SIZE has 3 values: Small (< 0.1m2), Medium (0.1m2 – 1m2), & Large (>1m2). Space-Track began showing only scaled values on 18 August 2014 (with RCSVALUE showing a static value of 0 in satcat, satcat_debut, & decay classes). There is no change to CDM spaceflight safety notification info or procedures.
RCS - Why did USSPACECOM revise the RCS information published on
USSPACECOM simplified the process of reporting RCS information on space objects. The Conjunction Data Message (CDM) provides spaceflight safety information (including RCS) in a single product. Previously, users used two products, a Conjunction Summary Message (CSM) and the Satellite Catalog (SATCAT).
RCS - Will there be any change to current spaceflight safety information or procedures?
No. The Conjunction Data Message (CDM), which is sent to owner/operators to warn of a potential collision, contains the actual RCS to assist satellite owners/operators in spaceflight safety decision-making.
RCS - My organization was using RCS values. Is there a way to still receive that information?
Yes. Formal SSA sharing partners can receive additional information. Contact USSPACECOM at for more information on SSA Sharing Agreements.
RCS - When did this change take effect?
The system switched to full-time scaled values on 18 Aug 14.
What timezone is all date/time data in?
All date/time data is stored, delivered, and displayed in UTC.
What's new on the site?
Please engage us on our social media sites: facebook or twitter.
Why is there a satellite catalog entry for object number [12345], but no (or less timely) orbital data or ELSETs for that object?
The answer from our data provider:
"S4S will provide periodic updates which may not include elsets and timely orbital data for every man-made object orbiting the earth on

Reasons include but are not limited to:
- National security reasons
- Some objects are too small for the sensors to consistently track
- Some objects decay before S4S can collect enough information to post a TLE
- Gaps in sensor coverage

Regardless of whether or not an object's ELSET and orbital data are posted on the website, S4S screens all objects at least daily and notifies the operator if that object is predicted to approach another object."
What is the minimum size of objects that are maintained in the satellite catalog?
10 centimeter diameter or "softball size" is the typical minimum size object that current sensors can track and 18 SDS maintains in the catalog.
Why does 18 SDS switch ELSets after a launch?
The answer from our data provider:
"After a launch, 18 SDS has a time requirement to identify objects from the launch.

For a multi-payload launch, typically the payloads are bunched together, making separation difficult, while the rocket body is generally drifting away and is easier to produce an elset. This elset is then used as a basis for 18 SDS and sensor network to track the other objects.

Once all objects are catalogued, they will not be renamed until the 18 SDS receives positive identification. At that point, once all payloads are known, the sensor network requires listing the payloads first before any rocket body or other launch debris. 18 SDS recognizes this can be frustrating for users; however, the sensor network takes priority. The only way to solve this is to not send the ELSets to the website until after identification, which could take hours or possibly days after a launch."
Why have I not heard a response back from 18 SDS after reporting a mis-tagged object to ?
The answer from our data provider:
"Positively identifying all objects after launch is challenging and may result in accidental mis-identification of some objects.

As years pass on, it becomes increasingly difficult to move historical data within the 18 SDS system. 18 SDS has to validate all possible mis-tagging and receive clarification from multiple sources, i.e. signals, RCS data, etc. While 18 SDS may be aware of the error, multiple users of the official data would have to be notified, and on occasion, might have to initiate changes to their system to line-up with 18 SDS data before 18 SDS can initiate the change. Depending how much time has passed since launch, it may take a while to move all the appropriate data into the correct object.

18 SDS appreciates all notifications of possible mis-tagging, but please realize their primary focus is tracking objects for collision avoidance so the extra duty of cross checking mis-tagging reports can be placed at a lower priority at times."
How does the data provider come up with a space object's common name?
Typically, the owner/operator reports the common name to our data provider. If our system already has a similar name, our data provider will adapt it.

If our data provider is not told what the common name is, he/she will get the name from either the launch team or open sources. Some common names may be abbreviated or truncated due to character limitations in that data field.
What criteria are used to determine whether an orbiting object should receive a catalogue number and International Designation?
There are three primary considerations when deciding to catalog an orbiting object:
We must be able to determine who it belongs to, what launch it correlates to, and the object must be able to to be maintained (tracked well).
I noticed a ELSET with an epoch a few days in the future. Aren't ELSETs supposed to be timing off the LAST ascending node pass prior to the current observations?
ELSETs can contain future epochs.

About 20 satellites are categorized as "multi-day objects" because their period is so large. Consequently, our data provider propagates the epoch into the future based on perigee to enable better tracking by available sensors when the object finally comes back into view.

An example is Object 10370 with a 5683.23 minute period.
What is 18 SDS's reporting criteria for conjunction data messages (CDMs) in the following orbital regimes:
Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Highly Elliptical Orbit (HEO), and Deep Space (DS)?
See the Spaceflight Safety Handbook for Operators for the most current information.

For further information on orbital mechanics see: link

Point in the orbit where an Earth satellite is farthest from the Earth. Units are kilometers. link
Argument of Perigee (Degrees)
The angle between the ascending node and the orbit's point of closest approach to the earth (perigee). link
B* Drag Term
Also called the radiation pressure coefficient. Units are earth radii^-1. The last two characters define an applicable power of 10. link
Catalog Change Report
Report that details the changes (launches, additions, decays and updates) to the satellite catalog (SATCAT). Now parts 4 & 5 of the SSR
Catalog Number
Sequential number assigned by the US Space Force as objects are cataloged. Synonyms: Satellite Catalog Number, NORAD_CAT_ID, and OBJECT_NUMBER. link
Celestial Equator
It is a projection of the terrestrial equator out into space. link
Sum of all of the characters in the data line, modulo 10. link
Common Name
Also known as OBJECT_NAME, this is simply the name associated with the satellite. link
Complete Data Files
See: link
Conjunction Assessment (CA)
The process of predicting and reporting the close approaches between Resident Space Object (RSOs) or between launch vehicles and RSOs. link
Conjunction Data Message (CDM)
CCSDS Recommended Standard message format for exchanging spacecraft conjunction information between originators of Conjunction Assessments (CAs) and satellite owner/operators and other authorized parties.
Conjunction Summary Message (CSM) - DEPRECATED
The CSM is a fixed-format ASCII formatted message which contains information about a predicted conjunction between space objects.
The nation or group that has responsibility for an object
Current Catalog Files
See: link
Any object with the string 'DEB' or 'COOLANT' or 'SHROUD' or 'WESTFORD NEEDLES' in the SATCAT object common name. link
The lessening of the eccentricity of the elliptical orbit of an artificial satellite. link
Decay Date
Date object reentered the earth's atmosphere in YYYY-MM-DD format. link
Decay Message Types
SATCAT - Historical.
Decay Entry - Historical.
TIP Message - Prediction.
60day Decay - Prediction.
A constant defining the shape of the orbit (0=circular, Less than 1=elliptical). link
Element Number
The ELSET number is a running count of all ELSETs generated by 18 SDS for this object. link
Element Set (ELSET)
See: Two Line Element set.
Element Set Epoch
The first two digits ('13') indicate the year. Add 1900 for years >= 57, and 2000 for all others. The remainder of the field ('236.56031392') is the Julian day of the year. link
The specific time at which the position of a satellite is defined. link
The unique identifying number of the source file for a particular object's data - higher numbers are more recent uploads.
First Derivative of the Mean Motion
Is the daily rate of change in the number of revolutions the object completes each day, divided by 2. Units are revolutions/day. link
Geosynchronous Report
Report generated using search parameters of satellite period between 1430-1450 minutes. link
Inclination - Orbital Inclination (Degrees)
The angle between the equator and the orbit plane.
INTLDES - International Designator
Also known as COSPAR designation or NSSDC ID, this is one format for uniquely identifying an object. link
Latest Data
Displays the latest ELSET for the object. link
Latest ELSET
Displays the last 5 ELSETs for the object. link
Launch Date
Date object was launched in YYYY-MM-DD format. See: link
Launch Number
A three-letter code representing the sequential identifier of a piece in a launch.
Launch Site
See: link
Laser Clearinghouse (LCH)
An organization within S4S that supports safe and responsible laser activities consistent with the needs of national defense. See: link
Mean Anomaly (degrees)
The angle, measured from perigee, of the satellite location in the orbit referenced to a circular orbit with radius equal to the semi-major axis. link
Mean Equinox
The direction to the equinox at a particular epoch, with the effect of nutation subtracted. link
Message Epoch
The UTC time that 18 SDS generated a message.
New Registered User Application
On-line application submitted in order to obtain a user account on link
Object ID
The CCSDS's name for International Designator.
Object Number - Catalog Number
Synonyms: Satellite Catalog Number, NORAD_CAT_ID, Object Number
Orbit Mean-Elements Message (OMM)
An approved international standard for a mathematical representation of a satellite’s mean orbit IAW CCSDS 502.0-B-2 Orbit Data Messages Blue Book.
Orbital Data Request (ODR)
The ODR is the form submitted by requesters asking for SSA services or information. link
Orbital Data Request Process
The procedures used by users to request Space Situational Awareness (SSA) advanced services support. link
Orbit Inclination (Degrees)
The angle between the equator and the orbit plane. link
Owner/Operator (O/O)
The designated control center or agency that is the focal point for operational control of a satellite payload, and/or vehicle, and/or ground site. The owner/operator interfaces with USSPACECOM and/or S4S and is generally the location where the operations center is located for a given space system.
Any object not classified in the SATCAT as a rocket body or debris is considered a payload. link
Point in the orbit where an Earth satellite is closest to the Earth. Units are kilometers. link
The number of minutes an object takes to make one full orbit. link
In the Decay class, lower PRECEDENCE values indicate more recent data. link
Predicted Decay Location
In the TIP class, LAT / LON values show the location above which an object is predicted to arrive at 10km altitude during its descent, not the predicted Earth impact location.
Predicted Decay Time
The time that an object is predicted to reach its decay location. Format: GMT Date (YYYY-MM-DD, HH:MM:SS) +/- XX Hours.
Radar Cross Section (RCS)
A measure of how detectable an object is by radar, measured in square meters. We do not provide numeric RCS values unless you have a valid requirement to see them. If you have a requirement for these values, please submit an Orbital Data Request (ODR) to get permission for RCS values. See our help page at link
Recent Satellite Decays
A listing of recent satellite decays on link
Revolution Number at Epoch
The number of orbits the object has completed at Epoch Time. link
Right Ascension (or Longitude) of Ascending Node (degrees)
Is the angle of the ascending node measured EAST of the vernal equinox along the celestial equator. link
Rocket Body
The propulsion unit(s) used to deploy satellites into orbit. These are cataloged differently from standard debris because they can have mechanisms or fuel on board that can affect the orbital behavior of the rocket body even after long periods of time. Rocket bodies are also constructed to endure high temperatures and stresses associated with launch so they have a greater probability of surviving reentry and require closer attention than most debris. Rocket Bodies are any object which contains the strings 'R/B' or 'AKM' (Apogee Kick Motor) or 'PKM' (Perigee Kick Motor) but not 'DEB' (Debris) in the SATCAT object common name. link
The Space Forces - Space is the Space Force Service component to United States Space Command and is responsible for executing continuous, integrated space operations to deliver theater and global effects in support of national and combatant commander objectives. Additionally, the S4S commander conducts joint space operations on behalf of USSPACECOM commander through Combined Joint Force Space Component Commander (CJFSCC) authorities. link | link
Any object in orbit around the Earth. Used interchangeably with 'resident space object'. However, commonly and mistakenly used to mean payload. Both a piece of debris and the moon are satellites.(SI 534-03)
Satellite Box Score
Accounting of man-made objects that have been or are in orbit by country. (SI 534-03) link
Satellite Catalog Number
Sequential number assigned by the US Space Force as objects are cataloged. Synonyms: Catalog Number, NORAD_CAT_ID, and OBJECT_NUMBER. link
Satellite Catalog (SATCAT)
A catalog of satellite positional data maintained by 18 SDS.(SI 534-03) link
Satellite Situation Report
Listing of those satellites (objects) currently in orbit and those which have previously orbited the Earth. Some objects are too small or too far from the Earth's surface to be detected; therefore, the Satellite Situation Report does not include all man-made objects orbiting the Earth. link
Second Derivative of the Mean Motion
Measures the second time derivative in daily mean motion. link
A deactivated website. Its file sharing functionality was added to in 2014.
The website that provides unclassified SSA services and information. is managed, maintained and administered by S4S. link
The area above the lowest altitude that permits a vehicle to orbit the Earth without entering the earth's atmosphere. That altitude is approximately 100 kilometers (62 miles). link
Space Surveillance Data
Data derived from the observation of space and activities occurring in space. link
Space Weather
The conditions and phenomena in space and specifically in the near-Earth environment that may affect space assets or space operations. link
SI 534-03
USSTRATCOM Strategic Instruction (SI) 534-03, Sharing Space Situational Awareness (SSA) Information, 18 January 2013. Establishes standard guidance for providing unclassified SSA information to United States Government (USG) agencies (including organizations supporting the USG under contract) and non-USG entities.
Tracking and Impact Prediction (TIP) Message
Projected satellite reentry predictions for objects which have the potential for generating debris which could pose a hazard to people or property on Earth. link and link
Two Line Element set (TLE)
A mathematical representation of a satellite’s mean orbit. See: link
Three Line Format
Same as a TLE except the first line contains the satellite common name. link
User Agreement
The terms and conditions a potential user must agree to and abide by in order to obtain access to link
Vernal Equinox
The point on the celestial sphere at which the Sun passes from south to north of the celestial equator each year. link
AKM Apogee Kick Motor
DD Day
DEB Debris
DoD Department of Defense
ELSET Element Set
GMT Greenwich Mean Time
HH Hour
S4S Space Forces - Space
MM Month or Minutes
PKM Perigee Kick Motor
RCS Radar Cross Section
SATCAT Satellite Catalog
SS Seconds
SSA Space Situational Awareness
TBA "To Be Announced" in the future.
TBD "To Be Determined" or unknown
TIP Tracking and Impact Prediction
TLE Two Line Element set
USG United States Government
USSTRATCOM United States Strategic Command
USSPACECOM United States Space Command
1 25544U 98067A   04236.56031392  .00020137  00000-0  16538-3 0  9993
2 25544  51.6335 344.7760 0007976 126.2523 325.9359 15.70406856328906
1234567890123456789012345678901234567890123456789012345678901234567890   reference number line
         1         2         3         4         5         6         7

Line 0
Columns Example Description
1-24 ISS (ZARYA) The common name for the object based on information from the Satellite Catalog.
Line 1
Columns Example Description
1 1 Line Number
3-7 25544 Satellite Catalog Number
8 U Elset Classification
10-17 98067A International Designator
19-32 04236.56031392 Element Set Epoch (UTC) *Note: spaces are acceptable in columns 21 & 22
34-43 .00020137 1st Derivative of the Mean Motion with respect to Time
45-52 00000-0 2nd Derivative of the Mean Motion with respect to Time (decimal point assumed)
54-61 16538-3 B* Drag Term
63 0 Element Set Type
65-68 999 Element Number
69 3 Checksum
Line 2
Columns Example Description
1 2 Line Number
3-7 25544 Satellite Catalog Number
9-16 51.6335 Orbit Inclination (degrees)
18-25 344.7760 Right Ascension of Ascending Node (degrees)
27-33 0007976 Eccentricity (decimal point assumed)
35-42 126.2523 Argument of Perigee (degrees)
44-51 325.9359 Mean Anomaly (degrees)
53-63 15.70406856 Mean Motion (revolutions/day)
64-68 32890 Revolution Number at Epoch
69 6 Checksum
Back to top
Satellite Catalog Number

example: 25544

  • The catalog number assigned to the object by the US Space Force.
  • Numbers are assigned sequentially as objects are cataloged.
  • Object numbers less than 10000 are always aligned to the right, and padded with zeros or spaces to the left.

The security classification of the element set. All objects on this site will have a classification of 'U' (unclassified).

International Designator

example: 98067A

This is another format for identifying an object.

  • The first two characters designate the launch year of the object.
  • The next 3 characters indicate the launch number, starting from the beginning of the year.
    This particular launch was the 67th launch of 1998.
  • The remainder of the field (1 to 3 characters) indicates the piece of the launch. Piece 'A' is usually the payload.
Element Set Epoch

example: 04236.56031392

  • The first two digits ('04') indicate the year. Add 1900 for years >= 57, and 2000 for all others.
  • The remainder of the field ('236.56031392') is the day of the year.
  • Spaces or numbers are acceptable in day of the year. (e.g. '236' or '006' or ' 6').
1st Derivative of the Mean Motion

example: .00020137

"+", "-" or " " (space) are acceptable in the 34th character position on Line 1, and indicate positive or negative value for 1st Derivative of the Mean Motion. A space implies a positive value.


The checksum is the sum of all characters in the data line, modulo 10. In this formula, the following non-numeric characters are assigned the indicated values:

  • Blanks, periods, letters, '+' signs -> 0
  • '-' signs -> 1
Back to top

Alpha-5 is a stopgap object numbering schema from the United States Space Force that increases the satellite catalog’s capacity to display up to 339,999 objects in the GP/GP_History API classes using legacy fixed-width Two and Three Line Element Set (TLE/3LE) formats.

Replacing the 1st digit of the 5-digit object number with an alphanumeric character makes it possible to represent 240,000 more numbers. Objects less than 100,000 are unaffected by Alpha-5, as are users who download elsets from the GP and GP_History API classes in other formats like XML, JSON, KVN, and CSV. In order to preserve legacy operations that depend on 5-digit integers, our legacy API Classes tle, tle_latest, and tle_publish will not change to Alpha-5.

Only capital letters and numbers are used in Alpha-5. The letters “I” and “O” are omitted to avoid confusion with the numbers “1” and “0”.


Some example object numbers in Alpha-5 format, as they would be seen in the TLE:

100000 => A0000 148493 => E8493
182931 => J2931 234018 => P4018
301928 => W1928 339999 => Z9999

Even though TLE/3LE will support Alpha-5 format on output in lines 1 and 2, users need to specify NORAD_CAT_ID integer values to return specific objects. The API will not support filtering on Alpha-5 values or ranges like /NORAD_CAT_ID/T0000--V9999/.

Alpha-5 Propagator

If your propagation software cannot process alphabetical characters in the catalog number section of the TLE, you can eliminate the Alpha-5 range from your query by adding /NORAD_CAT_ID/<100000/ to filter them out as displayed in this example:

The latest SGP4 propagator, Version 8.0, is compatible with the new Alpha-5 format shown in this graphic and is available at

Alpha 5 TLE Graphic
Full Alpha-5 Numbering
A => 10 J => 18 S => 26
B => 11 K => 19 T => 27
C => 12 L => 20 U => 28
D => 13 M => 21 V => 29
E => 14 N => 22 W => 30
F => 15 P => 23 X => 31
G => 16 Q => 24 Y => 32
H => 17 R => 25 Z => 33
Future Use
While this schema extends the usability of the TLE format, encourages users to switch to a more extensible format, such as XML, KVN, or JSON. These formats handle the ever-increasing size of the catalog, regardless of object number size.
Back to top

As the United States government agency responsible for Space Situational Awareness (SSA) information, United States Space Command (USSPACECOM), is committed to promoting a safe, stable, sustainable, and secure space environment through SSA information sharing. As more countries, companies, and non-governmental organizations field space capabilities and benefit from the use of space systems, it is in our collective interest to act responsibly and to enhance overall spaceflight safety. To achieve effective SSA, USSPACECOM seeks to increase cooperation and collaboration with partners and space-faring entities through the exchange of SSA data and provision of SSA services.

The Space Forces - Space (S4S) - Combined Joint Force Space Component Commander (CJFSCC) provides SSA services through this website and the 18th Space Defense Squadron (18 SDS), located at Vandenberg Space Force Base, California. There are three levels of SSA services: basic, emergency, and advanced.

  Basic Services
  Basic SSA Information

USSPACECOM provides space surveillance data to registered users through this public website, 18 SDS routinely updates the website with positional data on more than 16,000 satellites in orbit around the Earth. Users can build customized API queries to pull specific data from historical records, and automate the retrieval of new data.

Available products: Required from customer:
  Redistribution of Basic SSA Information

USSPACECOM has provided express blanket approval for transfer/redistribution of basic SSA data and services accessed via conditioned on appropriate citation. Publications of analysis based on USSPACECOM data also require appropriate citations.

Basic SSA data are Two-Line Elements (TLEs) and Orbital Mean-element Messages (OMMs); SATCAT; and Satellite Decay and Reentry Data.

Basic SSA data can be found on the Home panel:

  Emergency Services
18 SDS provides emergency services to customers with specific needs, such those who operate satellites.
  Anomaly Resolution

Anomaly Resolution consists of actions taken by an owner/operator in response to a launch or on-orbit anomaly or non-nominal condition affecting a spacecraft bus, telemetry subsystem or communications payload, onboard sensor(s), or any other operating payload or subsystem.

Available products:
  • Special Perturbation (SP) state vectors
  • Unclassified imagery analysis, if available and approved for release
Required from customer:
  Basic Emergency Conjunction Assessment (On-Orbit)

On-Orbit Conjunction Assessment (CA) is the process for determining the point and time of closest approach of two tracked orbiting objects. 18 SDS screens all active satellites against the satellite catalog several times per day to identify close approaches. If a close approach meets emergency reportable criteria, 18 SDS will notify the satellite's owner/operator by email and through's Operator Panel. This service is provided at no cost to promote spaceflight safety, and does not require an SSA Sharing Agreement or an ODR.

Available products: Required from customer:
  • Contact and provide:
    • Contact information: email addresses and phone number(s)
    • usernames
    • The catalog number(s) and name(s) of the satellites you own or operate
  Basic Emergency Collision Avoidance (On-Orbit)

If a satellite owner/operator receives a close approach notification email from 18 SDS, the owner/operator may submit their proposed maneuver plan and ephemeris for screening against the space catalog. Results that meet emergency reportable criteria will be provided. Collision avoidance is the responsibility of the satellite owner/operator, but 18 SDS will support their collision avoidance efforts by screening their predictive ephemeris and providing results in the Conjunction Data Message (CDM) format.

Available products: Required from customer:
  Advanced Services
Advanced services are available to all entities who sign an SSA Sharing Agreement with USSPACECOM.
  Launch Conjunction Assessment

Launch Conjunction Assessment (CA) identifies potential conjunctions that may result in a collision between launching objects and on-orbit objects. Using information provided by the customer prior to launch, via the Form 22 , 18 SDS screens the launch vehicle against the space catalog and provides conjunction information for each associated launch time. Screening begins at an altitude of 150km or greater and continues through the duration of the launch trajectory provided by customer. The Launch CA screening results identify periods during the launch window which may put the rocket and payload at increased risk for collision.

Available products:
  • Launch CA screening results: summary of predicted conjunction time windows, including:
    • Time of launch
    • Catalog number and common name of the conjuncting object
    • Mission Elapsed Time (MET) after liftoff (in seconds) of the predicted close approach
    • Predicted overall miss distance (in km) for the close approach at the MET
Required from customer:
  Launch Early Orbit Determination

Early Orbit Determination (EODET) is the process by which the Space Surveillance Network (SSN) tracks a launch and/or separation of an object and sends observation data to 18 SDS for the calculation of initial orbit(s), entry into the space catalog, identification and naming of the object(s), and continual generation of element sets. 18 SDS uses information provided by the launch entity or satellite owner/operator to inform the tracking, cataloging, and identification process.

Available products/services: Required from customer:
  Early Orbit Conjunction Assessment

Early Orbit Conjunction Assessment (CA) includes the screening of owner/operator-provided ephemeris against the satellite catalog to facilitate the safe maneuvering of a newly launched object into its final orbit. Expanded screening volumes and propagation are used to identify possible close approaches. Operators may provide more than one ephemeris file for each maneuver to allow analysis of multiple scenarios.

Available products: Required from customer:
  Advanced Conjunction Assessment (On-Orbit)

Advanced On-Orbit CA uses expanded screening volumes and propagation to provide more results than Basic Emergency CA.

Available products: Required from customer:
  Advanced Collision Avoidance (On-Orbit)

Advanced Collision Avoidance may be provided to assist owners/operators in relocating a satellite, or to avoid self-identified close approaches. Both situations allow an owner/operator to submit maneuver and non-maneuver ephemeris for expanded screening against the satellite catalog.

Available products: Required from customer:
  Disposal/End-of-Life Support

Disposal/End-of-Life Support consists of planning for proper upper stage disposal and spacecraft end-of-life operations. If provided maneuver planning and on-orbit Information, 18 SDS may support a satellite owner/operator’s plans for disposing of an object by providing conjunction assessment and collision avoidance using expanded screening volumes and propagation.

Available products: Required from customer:
  Deorbit and Reentry Support

Deorbit and Reentry Support includes reentry assessment, reentry confirmation, and assistance in deorbit operations. Reentry assessments are predictions of the time and location where an uncontrolled object will reenter the atmosphere (not where the object will impact the ground). If a satellite owner/operator decides to perform the controlled deorbit of a satellite or rocket stage and provides relevant on-orbit information, 18 SDS will provide related conjunction assessment and collision avoidance support using expanded screening volumes and propagation, and confirmation of reentry after the owner/operator’s deorbit procedures are performed.

Available products: Required from customer:
  SSA Sharing Agreement
USSPACECOM/J5 Strategy, Plans, and Policy negotiates SSA Sharing Agreements. The SSA Sharing Agreement establishes the parameters within which data will be exchanged by both signing parties to facilitate ongoing cooperation and advance spaceflight safety. All members of the space community, including satellite operators, launching agencies, commercial service providers, and research/academic institutions, are welcome to contact for more information on the agreement process. U.S. government (USG) organizations and their contractors have implied agreements and do not need to pursue additional documentation with USSPACECOM.

  Orbital Data Request

All customers (non-U.S. government, commercial, and USG) should request advanced services using the Orbital Data Request (ODR) form. To submit an ODR, follow the directions on page 1 of the form and send it to

18 SDS’s SSA Sharing Team processes all requests, which undergo security, legal, and resource assessments before the final 18 SDS authority approves or disapproves the request. In the event of disapproval, the SSA Sharing Team will work with the customer to revise their request for reconsideration. If a request is approved by 18 SDS, but the customer is non-USG and does not have an SSA Sharing Agreement, the request will be forwarded to USSPACECOM for further review.

After approval, the SSA Sharing Team will provide an estimate of when the data will be delivered, or when the ongoing service will be initiated. In some situations this will take more time than others, but the customer will be notified accordingly. ODRs are valid for one year from the date of approval.

Customers may request information not included in standard services, but this will lengthen the review process and the time required to deliver the data or service, if the request is approved.

  Register Your Satellite/Payload with 18 SDS

Whether you are putting your first satellite on orbit, or adding to an existing constellation, we encourage you to register your asset with 18 SDS so that we can plan for optimal tracking and identification, and provide you with conjunction assessment services as soon as possible. As soon as you register, a member of 18 SDS will contact you to discuss the details of your mission and coordinate conjunction assessment and other required support.

  Communicating and Coordinating with 18 SDS

Due to the dynamic nature of space operations, 18 SDS relies on information from operators, launching agencies, and the overall space community to maintain space situational awareness. Even if you do not require direct support from 18 SDS, we welcome the following information:

Maintaining spaceflight safety and space situational awareness is a cooperative activity and responsibility. The information you provide advances these goals and ensures equal access to space for all global users. If you have questions about USSPACECOM services or suggestions on how we can improve any aspect of our SSA Sharing process, we encourage you to contact the 18 SDS SSA Sharing Team at

  U.S. Government Entities and Contractors

USG entities and their contractors may be eligible to receive additional data and services not listed above depending on their mission requirements and security clearance. For more information, please email

  Frequently Asked Questions
  What do you do with the information provided in the R-15 form?
The information in the R-15 form is the basis for 18 SDS’s launch planning. The Launch Team uses the launch sequence and orbital parameters to determine what sensors can track the launch and how soon the first element set(s) will be available. The spacecraft parameters help our Analysts decide how the objects will be maintained in the space catalog. The R-15 also informs how our Analysts will name the objects, and who 18 SDS will contact with conjunction assessment warnings.

  Can I submit the R-15 if I don’t have all of the information?
Yes. 18 SDS understands that different portions of a launch mission are managed by different entities, and appreciates any portion of the information you can provide to

  If I don’t have an SSA Sharing Agreement can I submit an ODR?
Yes. We highly encourage you to sign an SSA Sharing Agreement, but if your agreement is in negotiations or delayed for any reason, you can submit an ODR, which will be sent to USSPACECOM for final decision.

  How long does it take an ODR to be approved?
ODRs are usually approved in 30 days, but this can increase or decrease depending on the complexity and classification of the requested data.

  I’m a satellite operator who receives CDMs. Do I need to submit an ODR to share these with other organizations?
No. Each satellite organization may designate a Primary Representative who can manage access to CDMs for their constellation. For more information, contact

  My organization just launched a satellite, but it hasn’t been identified in the catalog. What can I do?
If you can correlate your satellite to an unnamed object in the catalog (e.g. Object A or Object B) send the identification to If you receive telemetry from your satellite, please send a two-line element set or ephemeris to

  Key Contacts

18 SDS SSA Sharing Team
Please direct all initial inquiries to 18 SDS SSA Sharing Team. The SSA Sharing Team will respond to your inquiry, or put you in contact with the appropriate 18 SDS personnel.
Phone: +1-805-606-2675 or DSN 276-2675

19 SDS Orbital Safety Team
Please contact 19 SDS Orbital Safety Team for routine conjunction assessment support. They are manned 24 hours a day, 7 days a week.
Phone: +1-540-284-3999 or DSN 284-3999

  Data Examples

Form Use to: Format
Satellite Registration Form Register your asset with 18 SDS for optimal identification, tracking, and conjunction assessment services. docx
Orbital Data Request Request all advanced services docx    pdf
Form 22 Provide detailed parameters on launch collision avoidance requirements docx
R-15 Form Provide detailed parameters on an upcoming launch and/or satellites to achieve orbit docx
Early Orbit Maneuver Plan List maneuver schedule and screening requirements for satellite(s) as they transfer from spacecraft separation to final orbit xlsx

× LCH is not available outside of normal duty hours (M-F 0800-1700 PST).
During normal duty hours please contact LCH at (805) 605-4763 / (805) 606-7410.
Please email for further information or coordination.
For EMERGENCY actions, please contact (805) 605-3514 to request on-call support.
"The Laser Clearinghouse mission is to provide the mission capabilities for supporting safe and responsible laser activities consistent with the needs of national defense"
- United States Strategic Command Instruction 534-12

LCH Contact Information

Please read the following terms and conditions of the User Agreement carefully! This website permits access to U.S. Government space situational awareness information to approved users only. To obtain access, all users must abide by the following terms and conditions:

The User agrees not to transfer any data or technical information received from this website, or other U.S. Government source, including the analysis of data, to any other entity without prior express approval. See, 10 USC 2274(c)(2).

The User agrees to pay an amount that may be charged. The present U.S. Government policy is not to charge for website access. The website will provide notification should this policy change. See, 10 USC 2274(c)(1).

The User agrees to hold harmless the U.S. Government, any agencies and instrumentalities thereof, and any individuals, firms, corporations, and other persons acting for the United States. Such shall be immune from any suit in any court for any cause of action arising from the provision or receipt of space situational awareness services or information, whether or not provided in accordance with 10 USC 2274, or any related action or omission. See, 10 USC 2274 (g).

The User agrees he or she will only enter this site utilizing his or her own username and password. The User agrees not to share, assign or transfer his or her username or password to another. Each individual user or entity is required to obtain a separate account. See, 10 USC 2274(c)(3).

The User agrees to provide a valid and working email address at registration and for the duration of Account usage. This ensures effective communication with and delivery of services to the User. As part of the registration process, the User will be asked to provide and verify his/her email address.

The User agrees these terms and conditions shall be governed by and construed in accordance with U.S. Federal law.

Approved access must be renewed periodically. The U.S. Government may unilaterally terminate this agreement for any reason.

The agreed upon terms and conditions above do not alter in any way those of any other written agreement with the U.S. Government for space situational awareness services and information. The U.S. Government reserves the right to change or modify these terms and conditions at any time, and without prior notification.





Current as of 1 August 2019.

Web Site Privacy and Security Notices, Web Site Disclaimer, and Accessibility Statement

Thank you for visiting this web site and reviewing its privacy and security notices.

Web Site Privacy Notice

Cookie technology may be used to enhance your experience while accessing this web site. At no time is private information you have provided – whether stored in cookies (persistent) or elsewhere – shared with third parties that have no right to that information. If you do not wish to have persistent cookies stored on your machine, you can turn them off in your browser. However, this may impact some of your functionality while visiting certain web sites.

Below are examples of what we do with your information when reading or downloading information from this Web site.

We may collect and store information for statistical purposes. For example, we may count the number of visitors to the different pages of our Web site to help make them more useful to visitors. This information does not identify you personally. We collect and store the following information about your visit automatically:

  • The Internet domain (for example, "" if you use a private Internet access account, or "" if you connect from a university's domain) and IP address (an IP address is a number that is automatically assigned to your computer whenever you are surfing the Web) from which you access the web site;
  • The type of browser and operating system used to access our site;
  • The date and time you access our site;
  • The pages you visit; and
  • If you visited this web site from a link on another Web site, the address of that Web site.

Similar information is gathered for anonymous ftp, remote account login, or for other comparable types of connections.

The information that you provide to administrators of this web site will be used only for its intended purpose, except as required by law, or if pertinent to judicial or governmental investigations or proceedings.

When Sending Us E-Mail

By sending us an electronic mail (e-mail) message, you may be sending us personal information such as your name, address, and e-mail address. We may store your name, address, and e-mail address of the requester in order to respond to your request or otherwise resolve the subject matter of the e-mail. Under certain limited circumstances, we may be required by law to disclose the information you submit.

Remember that e-mail is not necessarily secure against interception. If your communication is sensitive, or includes personal information such as your Social Security number, you should consider sending it by postal mail instead.

When Registering

Information collected through questionnaires, feedback forms, or other means, enables us to determine visitors' interests, with the goal of providing better service to our visitors.

Regardless of the information being transmitted, we will protect all such information consistent with the principles of the Federal Records Act, the Privacy Act, and as applicable, the Freedom of Information Act.

Web Site Security

For site security purposes and to ensure that this web-based service remains available to all users, this computer system employs software programs that monitor network traffic to identify unauthorized attempts to upload or change information, or otherwise cause damage. Anyone using this system expressly consents to such monitoring and is advised that if such monitoring reveals evidence of possible abuse or criminal activity, such evidence may be provided to appropriate law enforcement officials. Unauthorized attempts to upload or change information are strictly prohibited and may be punishable by law, including the Computer Fraud and Abuse Act of 1986 and the National Information Infrastructure Protection Act of 1996.

For detailed questions regarding the satellite data, ephemeris, or decay information presented on this website, please email the data provider (18th Space Defense Squadron) at

For permission to redistribute space-track data, information outside of what space-track provides, requests for launch support, and requests for Conjunction Assessment, please submit an Orbital Data Request.

For problems with Laser Clearinghouse procedures or documents, please contact the LCH team.

For problems with website functionality, please email