Data Fields:
- Data: The GP Data button links to a page which provides the GP data
used to generate the associated prediction.
- NORAD Catalog Number: NORAD Catalog Numbers of the two conjuncting
objects.
- Name: SATCAT names of the two conjuncting objects. Operational
status of each object is shown in brackets, using the standard CelesTrak SATCAT codes.
- Days Since Epoch: The number of days from the epoch of the NORAD GP
or SupGP (green) element set used to produce the prediction until the time of
closest approach for the conjunction.
- TCA (UTC): Time of closest approach.
- Min Range (km): The distance between the two conjuncting objects at
the time of closest approach.
- Relative Speed (km/sec): Relative speed of the two conjuncting
objects at the time of closest approach.
- Max Probability: Given fixed spherical object radii and relative
distance at the time of closest approach (TCA), the projected covariance ellipse
is sized and oriented to produce the maximum probability. For these reports the
ratio of major-to-minor axes of the projected covariance ellipse is set using
radial, in-track, and cross-track values of 100 m, 300 m, 100 m, respectively.
If the combined object radius is greater than the relative distance, the maximum
probability will be one; such occurrences are not addressed here. For more
details on the maximum probability method, see Dr. Sal Alfano's paper titled
"Relating Position Uncertainty to Maximum Conjunction
Probability".
- Dilution Threshold (km): The standard deviation that produces the
maximum probability defines the threshold of dilution. A smaller or larger
standard deviation will produce a smaller probability. In the case of computing
true probability with a smaller standard deviation, the data is of sufficient
quality to associate low probability with low risk. For a larger standard
deviation, this is not the case and the resulting true probability calculation
becomes "diluted." If operating in this dilution region, the recommendation is
to obtain better data and reassess the encounter. If time or resources do not
permit, then the maximum probability should be used in place of the true
probability.
- SGP4 Propagation Errors: A list of objects which were not screened
because their GP data shows they have already decayed (but haven't yet been
reflected in the SATCAT) or will decay prior to the end of the computation
interval.
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