readOEM: Read an Orbital Ephemeris Message file

In asteRisk: Computation of Satellite Position

Read an Orbital Ephemeris Message file

Description

OEM (Orbital Ephemeris Message) is one of the three standard file formats defined by the CCSDS for transferring spacecraft orbit information. OEM files contain the position and velocity of a given object at multiple times (epochs). They can also contain optionally acceleration values, covariance matrixes that indicate the uncertainty of the provided state vectors and other additional information. This function reads OEM files, retrieving also the optional fields.

Usage

readOEM(filename)

Arguments

filename

Path to the OEM file.

Value

A list with two elements. The first element, named header, is a list with the following elements:

OMVersion	Version of the OEM format used in the file
creationDate	Date of creation of the file
creator	Individual or organization that generated the file

The second element is named dataBlocks, and it contains one element for each ephemeris data block found in the OEM file. Each of these elements is a list with the following elements that provide information about the ephemerides of object (note that some elements are not mandatory and therefore might not be present in all OEM files; in these cases, their value is set to NULL):

objectName	Name of the object
objectID	Object identifier for the object. Frequently, although not always, the identifier has the format YYYY-NNNPPP, where YYYY is the year of launch, NNN is the three-digit serial number specifying the launch number during year YYYY and PPP is a part specifier comprising 1 to 3 capital letters that indicate the part of the object put into space during the launch.
referenceFrame	Frame of reference in which ephemerides are provided.
refFrameEpoch	Epoch for the frame of reference, for cases where it is not intrinsic to the frame itself, such as TEME.
centerName	Name of the center of coordinates. For example, a celestial body, the barycenter of the entire Solar System or even other spacecraft.
timeSystem	Time system used for the ephemerides, covariance matrixes and all other time fields of the data block.
startTime	Start time of the time span covered by the ephemerides and covariance matrixes in this data block.
endTime	End time of the time span covered by the ephemerides and covariance matrixes in this data block.
usableStartTime	Start time of the usable time span covered by the ephemerides and covariance matrixes in this data block.
usableEndTime	End time of the usable time span covered by the ephemerides and covariance matrixes in this data block.
interpolationMethod	Recommended interpolation method to calculate ephemerides at epochs between those directly given in the data block.
interpolationOrder	Recommended interpolation degree to calculate ephemerides at epochs between those directly given in the data block.
mass	Mass in kg of the object.
dragArea	Effective area of the object subjected to drag, in square meters.
dragCoefficient	Drag coefficient of the object.
solarRadArea	Effective area of the object subjected to solar radiation pressure, in square meters.
solarRadCoefficient	Solar radiation pressure coefficient of the object.
ephemerides	Data frame with the 7 or 10 columns providing the ephemerides for the object. The 1st column provides the epochs for each ephemeris; columns 2 to 4 provide the X, Y and Z components of position (in km), and columns 5 to 7 provide the X, Y and Z components of velocity (in km/s). Columns 8 to 10 are optional, and if present provide the X, Y and Z components of acceleration (in km/s2)
covarianceMatrixes	List where each element is a 3-element list that provides a covariance matrix for this data block. Each of the 3-element lists corresponding to a covariance matrix contains the following elements: epoch Epoch of the navigation solution related to this covariance matrix. referenceFrame Reference frame for the covariance matrix. Frequently this is the same as for the ephemerides. In order to facilitate interpretation of the covariance matrix, conversion to a perifocal frame of reference might be advisable. covarianceMatrix Covariance matrix that provides information about the uncertainties of position and velocities. This is a symmetric 6x6 matrix where the values in the diagonal are the squared standard deviations of each variable, and the other values are covariances between 2 variables (those corresponding to the row and column of each value). The rows and columns correspond to the following variables, in the specified order: X position, Y position, Z position, X velocity, Y velocity and Z velocity.

References

https://public.ccsds.org/Pubs/502x0b2c1e2.pdf https://spotthestation.nasa.gov/trajectory_data.cfm

Examples

# The file testOEM.txt provided with the package includes ephemerides data
# for the ISS publicly available

testOEM_ISS <- readOEM(paste0(path.package("asteRisk"), "/testOEM.txt"))
testOEM_ISS$header
testOEM_ISS$dataBlocks[[1]]$objectName
head(testOEM_ISS$dataBlocks[[1]]$ephemerides)

asteRisk documentation built on Jan. 14, 2023, 5:07 p.m.