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.
What is a TLE checksum?
Every TLE 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
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 TLEs have checksums?
Yes, Space-Track.org has updated its code to include checksums for all
current and historical TLEs/3LEs including over 8 Million TLEs/3LEs that
did not previously include one. This provides users with better data
integrity and rudimentary error checking.
Why do all TLEs/3LEs 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 Space-Track.org?
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,
USSTRATCOM catalogs and publishes a number of these objects on Space-Track.org.
For these objects, Country Code & Launch Site values are both UNKN ("Unknown");
The International Designator format in the catalog is YYYY-000A and in TLEs 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.
What changed with Radar Cross Section (RCS) and why?
Did RCS values change?
What timezone is all date/time data in?
USSTRATCOM 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.
Why did USSTRATCOM revising radar cross section (RCS) information published on Space-Track.org?
USSTRATCOM 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).
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.
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 USSTRATCOM at email@example.com for more information on SSA Sharing Agreements.
When did this change take effect?
The system switched to full-time scaled values on 18 Aug 14.
Do satellite owners/operators and other interested parties have opportunities
to influence the implementation process?
USSTRATCOM and JFCC Space will accept feedback throughout the transition process.
Contact firstname.lastname@example.org to provide feedback on Space-Track.org, or email@example.com
for information about how to become a formal partner with USSTRATCOM.
What's new on the site?
Why is there a satellite catalog entry for object number , but no orbital data for that object or TLEs for that object?
All date/time data is stored, delivered, and displayed in UTC
What is the minimum size of objects that are maintained in the satellite catalog?
The answer from our data provider:
"JFCC SPACE cannot post elsets for every man-made object orbiting the earth on www.Space-Track.org.
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 the JSpOC can collect enough information to post a TLE
- Gaps in sensor coverage
Regardless whether an object's elset/TLE is posted on the website or not,
JFCC SPACE screens all objects at least daily and notifies the operator
if that object is predicted to approach another object."
10 centimeter diameter or "softball size" is the typical minimum size object that current sensors can track and the JSpOC maintains in the catalog.
Why does the JSpOC switch elsets after a launch?
The answer from our data provider:
Why have I not heard a response back from the JSpOC after reporting a mis-tagged object to firstname.lastname@example.org?
"After a launch, the JSpOC 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 the JSpOC and sensor network to track the other objects.
Once all objects are catalogued, they will not be renamed until the
JSpOC 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.
The JSpOC 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 Space-Track.org website until after
identification, which could take hours or possibly days after a launch."
The answer from our data provider:
How does the data provider come up with space object's common name?
"Positively identifying all objects after launch
is challenging and may result in accidental misidentification of some objects.
As years pass on, it becomes increasingly difficult to move
historical data within the JSpOC system. The JSpOC has to
validate all possible mis-tagging and receive clarification
from multiple sources, i.e. signals, RCS data, etc. While the
JSpOC 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 the JSpOC data
before the JSpOC 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.
The JSpOC 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."
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.
What criteria are used to determine whether an orbiting object should receive a catalogue number and International Designation?
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.
There are three primary considerations when deciding to catalog an orbiting object:
I noticed a TLE with an epoch a few days in the future. Aren't TLEs supposed to be timing off the LAST ascending node pass prior to the current observations?
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).
TLEs can contain future epochs.
What is the JSpOC's reporting criteria for conjunction
data messages (CDMs) in the following orbital regimes:
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.
Low Earth Orbit (LEO), Medium Earth Orbit
(MEO), Highly Elliptical Orbit (HEO), and Deep Space (DS)?