API Reference — Earth Satellites¶
See Earth Satellites for an introduction to downloading Earth satellite data and computing their positions with Skyfield.
- class skyfield.sgp4lib.EarthSatellite(line1, line2, name=None, ts=None)¶
An Earth satellite loaded from a TLE file and propagated with SGP4.
An earth satellite object is a Skyfield vector function, so you can either call its
at()
method to generate its position in the sky or else use addition and subtraction to combine it with other vectors.Satellite parameters are generally only accurate for a week or two around the epoch of the parameters, the date for which they were generated, which is available as an attribute:
epoch
A Skyfield
Time
giving the exact epoch moment for these satellite orbit parameters.name
Satellite name
When building a satellite, use the arguments
line1
andline2
to provide the two data lines from a TLE file as separate strings. Optionalname
lets you give a name to the satellite, accessible later through thename
attribute.ts
is aTimescale
object, used to generate theepoch
value; if it is not provided, the satellite will use a built inTimescale
object.If you are interested in the catalog entry details, the SGP4 model parameters for a particular satellite can be accessed through its
model
attribute:model.satnum
The unique satellite NORAD catalog number given in the TLE file.
model.classification
Satellite classification, or else
'U'
for “Unknown”model.intldesg
International designator
model.epochyr
Full four-digit year of this element set’s epoch moment.
model.epochdays
Fractional days into the year of the epoch moment.
model.jdsatepoch
Julian date of the epoch (computed from
epochyr
andepochdays
).model.ndot
First time derivative of the mean motion (ignored by SGP4).
model.nddot
Second time derivative of the mean motion (ignored by SGP4).
model.bstar
Ballistic drag coefficient B* in inverse earth radii.
model.ephtype
Ephemeris type (ignored by SGP4 as determination now automatic)
model.elnum
Element number
model.inclo
Inclination in radians.
model.nodeo
Right ascension of ascending node in radians.
model.ecco
Eccentricity.
model.argpo
Argument of perigee in radians.
model.mo
Mean anomaly in radians.
model.no_kozai
Mean motion in radians per minute.
model.revnum
Revolution number at epoch [Revs]
- classmethod from_satrec(satrec, ts)¶
Build an EarthSatellite from a raw sgp4 Satrec object.
This lets you provide raw numeric orbital elements instead of the text of a TLE set. See Build a satellite with a specific gravity model for detais.
- ITRF_position_velocity_error(t)¶
Deprecated: use the TEME and ITRS frame objects instead.
- find_events(topos, t0, t1, altitude_degrees=0.0)¶
Return the times at which the satellite rises, culminates, and sets.
Searches between
t0
andt1
, which should each be a SkyfieldTime
object, for passes of this satellite above the locationtopos
that reach at leastaltitude_degrees
above the horizon.Returns a tuple
(t, events)
whose first element is aTime
array and whose second element is an array of events:0 — Satellite rose above
altitude_degrees
.1 — Satellite culminated and started to descend again.
2 — Satellite fell below
altitude_degrees
.
Note that multiple culminations in a row are possible when, without setting, the satellite reaches a second peak altitude after descending partway down the sky from the first one.
- class skyfield.sgp4lib.TEME¶
The SGP4-specific True Equator Mean Equinox frame of reference.
Described in AIAA 2006-6753 Appendix C. See Coordinates in other reference frames for a guide to using Skyfield reference frames like this one.