Utilities

pyRTX.utilities.export_formatted(accelerations, epochs, filename, units=None)[source]

Export acceleration data to formatted text file with epoch timestamps.

Writes acceleration vectors and their corresponding epochs to a CSV file with descriptive header. The output format is suitable for reading by orbit determination software or data analysis tools.

Parameters:

  • accelerations (ndarray, shape (N, 3)) – Array of 3-component acceleration vectors. Each row is [ax, ay, az] at one time step. Must be 2D array with exactly 3 columns.

  • epochs (ndarray, shape (N,)) – Array of epoch times corresponding to each acceleration vector. Should be in seconds past J2000 (SPICE ephemeris time format).

  • filename (str) – Path to output file. Typically uses .txt or .csv extension.

  • units (str or None, default None) – Optional string describing the units of the acceleration data (e.g., ‘km/s^2’, ‘m/s^2’). Will be added to file header if provided.

Returns:

Data is written to file at specified filename.

Return type:

None

Raises:

ValueError – If accelerations is not shape (N, 3) or if the number of epochs doesn’t match the number of acceleration vectors.

Notes

Output file format: - CSV format with comma delimiters - Header line with format description and optional units - Data columns: Epoch, X, Y, Z - One row per time step

The file header contains: - Description of data format - Column definitions (Epoch in seconds past J2000, X, Y, Z components) - Units information if provided

Example output file: .. code-block:

# Acceleration file. Columns: Epoch (seconds past J2000), X, Y, Z. Units: km/s^2
0.000000000000000000e+00,1.234567890123456789e-08,2.345678901234567890e-08,3.456789012345678901e-08
6.000000000000000000e+01,1.234567890123456789e-08,2.345678901234567890e-08,3.456789012345678901e-08
...

The output can be read back using:

data = np.loadtxt(filename, delimiter=',')
epochs = data[:, 0]
accelerations = data[:, 1:4]

Examples

>>> epochs = np.array([0.0, 60.0, 120.0])
>>> accels = np.array([[1e-8, 2e-8, 3e-8],
...                    [1.1e-8, 2.1e-8, 3.1e-8],
...                    [1.2e-8, 2.2e-8, 3.2e-8]])
>>> export_formatted(accels, epochs, 'output.txt', units='km/s^2')

See also

export_exac

Export to GEODYN EXAC binary format

numpy.savetxt

Underlying function for text output

pyRTX.utilities.export_exac(satelliteID, data, tstep, startTime, endTime, outFileName)[source]

Export acceleration data to GEODYN EXAC (External Accelerations) file format.

GEODYN is NASA’s precision orbit determination software. The EXAC format is a Fortran-formatted binary file used to provide time-varying external accelerations (such as solar radiation pressure) to the orbit propagator.

Parameters:

  • satelliteID (int) – Satellite identifier code used in GEODYN processing.

  • data (ndarray, shape (N, 3)) – Acceleration data to be written, in km/s². Each row is [ax, ay, az] at one time step.

  • tstep (int or float) – Time step between data records in seconds (e.g., 60 for 1-minute data).

  • startTime (datetime.datetime) – Start time of the data series. Must include date and time information down to microseconds.

  • endTime (datetime.datetime) – End time of the data series. Must be consistent with len(data) and tstep.

  • outFileName (str) – Path to output EXAC file. Typically uses .exac or .bin extension.

Returns:

Data is written to binary file at outFileName.

Return type:

None

Notes

EXAC File Structure:

  • Master header record: Control parameters and file type identifier

  • Satellite-specific header: Satellite ID, time step, start/end times

  • Data records: Time stamp + 3D acceleration vector + padding zeros

Time Format:

  • Stored as YYMMDDHHMMSSμμμμμμ (year-month-day-hour-minute-second-microsecond)

  • Year uses 2-digit format (YY)

Coordinate System:

  • Accelerations should be in the same reference frame as the GEODYN orbit integration (typically J2000 or ICRF)

Units:

  • Accelerations: km/s²

  • Time step: seconds

This format is used for high-precision orbit determination where external non-gravitational forces (solar pressure, atmospheric drag, etc.) need to be accurately modeled.

Requires scipy.io.FortranFile for binary I/O operations.

pyRTX.utilities.to_datetime(epoch)[source]

Converts a SPICE epoch to a Python datetime object.

Parameters:

epoch (float) – The SPICE ephemeris time in seconds past J2000.

Returns:

The corresponding datetime object.

Return type:

datetime.datetime

pyRTX.utilities.getScPosVel(spacecraft, center, epochs, frame)[source]

Retrieves the position and velocity of a spacecraft.

Parameters:

  • spacecraft (str) – The name of the spacecraft.

  • center (str) – The name of the center of motion.

  • epochs (list of float) – A list of SPICE ephemeris times.

  • frame (str) – The reference frame.

Returns:

A tuple containing two numpy arrays: the position vectors and the velocity vectors.

Return type:

tuple