readTLE {asteRisk}

Read a TLE file

Description

TLE (Two-/Three- Line Element) is a standard structured text file format for representing orbital state vectors. This function reads a TLE file containing one or more TLEs. The TLE file can contain either Two Line Elements or Three Line Elements, but all the TLE in a single file must be of the same type. The two lines of a Two Line Element contain all the ephemeris information. The additional line in a Three Line Element is optional, and contains just the satellite name. For a detailed description of the TLE format, see https://celestrak.com/columns/v04n03/#FAQ01.

Usage

readTLE(filename, maxTLEs=NULL)

Arguments

filename

Path to the TLE file. Alternatively, an URL pointing to a TLE file.

maxTLEs

Maximum number of TLEs to read, starting from the beginning of the file. By default, all TLEs present in the file are read.

Value

A list with the following elements that define the orbital state vector of the satellite (or, if the file contained multiple TLE, a nested list, where each element of the top level list represents an orbital state vector, and comprises the following elements):

NORADcatalogNumber

NORAD Catalog Number, also known as Satellite Catalog Number, assigned by United States Space Command to each artificial object orbiting Earth

classificationLevel

Classification level of the information for the orbiting object. Can be unclassified, classified, secret or unknown

internationalDesignator

International Designator, also known as COSPAR ID, of the object. It consists of the launch year, separated by a hyphen from a three-digit number indicating the launch number for that year and a set of one to three letters indicating the piece for a launch with multiple pieces.

launchYear

The launch year of the object

launchNumber

The launch number of the object during its launch year

launchPiece

The piece for the launch of the object, if it was a launch with multiple pieces

dateTime

Date time string to which the orbital state vector corresponds

elementNumber

Element number for the object. In principle, every time a new TLE is generated for an object, the element number is incremented, and therefore element numbers could be used to assess if all the TLEs for a certain object are available. However, in practice it is observed that this is not always the case, with some numbers skipped and some numbers repeated.

inclination

Mean orbital inclination of the satellite in degrees. This is the angle between the orbital plane of the satellite and the equatorial plane

ascension

Mean longitude of the ascending node of the satellite at epoch, also known as right ascension of the ascending node, in degrees. This is the angle between the direction of the ascending node (the point where the satellite crosses the equatorial plane moving north) and the direction of the First Point of Aries (which indicates the location of the vernal equinox)

eccentricity

Mean eccentricity of the orbit of the object. Eccentricity is a measurement of how much the orbit deviates from a circular shape, with 0 indicating a perfectly circular orbit and 1 indicating an extreme case of parabolic trajectory

perigeeArgument

Mean argument of the perigee of the object in degrees. This is the angle between the direction of the ascending node and the direction of the perigee (the point of the orbit at which the object is closest to the Earth)

meanAnomaly

Mean anomaly of the orbit of the object in degrees. This indicates where the satellite is along its orbital path. It is provided as the angle between the direction of the perigee and the hypothetical point where the object would be if it was moving in a circular orbit with the same period as its true orbit after the same amount of time since it last crossed the perigee had ellapsed. Therefore, 0 denotes that the object is at the perigee

meanMotion

Mean motion of the satellite at epoch in revolutions/day

meanMotionDerivative

First time derivative of the mean motion of the satellite in revolutions/day^2^

meanMotionSecondDerivative

Second time derivative of the mean motion of the satellite in revolutions/day^3^.

Bstar

Drag coefficient of the satellite in units of (earth radii)^-1^. Bstar is an adjusted value of the ballistic coefficient of the satellite, and it indicates how susceptible it is to atmospheric drag.

ephemerisType

Source for the ephemeris (orbital state vector). Most commonly, it is distributed data obtained by combaining multiple observations with the SGP4/SDP4 models

epochRevolutionNumber

Number of full orbital revolutions completed by the object

objectName

Name of the object, retrieved from the first line of the TLE if a Three Line Element was provided

References

https://celestrak.org/columns/v04n03/#FAQ01 http://www.celestrak.org/publications/aiaa/2006-6753/AIAA-2006-6753.pdf

Examples

# The file testTLE.txt provided with the package includes 29 TLE covering a
# variety of satellites, extracted from Revisiting Space Track Report #3

test_TLEs <- readTLE(paste0(path.package("asteRisk"), "/testTLE.txt"))
test_TLEs