Initial Orbit Determination (Least Squares Method)

Version 3.1.0 (96.2 MB) by Meysam Mahooti
Initial orbit determination applying the Least Squares method
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Updated 29 Feb 2024

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1) In test_LSQ_GEOS3, we define global variables: const (astronomical and mathematical constants), CS (unnormalized gravity field coefficients), AuxParam (struct that represents model parameters and time for orbit propagator), eopdata (Earth orientation parameters), PC (planetary coefficients for JPL ephemerides computation).
2) Download Earth orientation parameters from the following link (if it is out of date).
https://celestrak.org/SpaceData/EOP-All.txt
3) Earth orientation parameters are read from EOP-All.txt.
4) Observations are read from GEOS3.txt, and biases from table 4-4 of the book “Fundamentals of Astrodynamics and Applications, 4th Edition, 2013,” are subtracted. Then measurement noises are set from table 4-4. After that, the station ecef position is calculated using Position.m, and two sets of observations (azimuth, elevation, and range) are selected. Afterward, LTC matrix (transformation from Greenwich meridian system to local tangent coordinates) is computed by LTCMatrix.m, and the initial guess of the satellite state vector at the epoch (first measurement’s time) is found by Elements.m and State.m.
5) The Least Squares’ initial parameters and parameters for orbit propagator (AuxParam.Mjd_UTC = Mjd_UTC; AuxParam.n = 20; AuxParam.m = 20; AuxParam.sun = 1; AuxParam.moon = 1; AuxParam.planets = 1;) are set.
6) The epoch’s state vector is propagated to the times of all measurements in an iterative procedure and corrected at each stage. Then epoch’s state vector is converted from the TOD to the ECI coordinate system and compared with the true state vector.
Please note that numerical integration is done in TOD coordinate system. So, only Earth rotation is considered in Accel.m and VarEqn.m.
References:
O. Montenbruck, E. Gill, "Satellite Orbits: Models, Methods, and Applications," Springer Verlag, Heidelberg, 2005.
D. Vallado, "Fundamentals of Astrodynamics and Applications," 4th Edition, 2013.
https://celestrak.org/software/vallado/matlab.zip
https://ssd.jpl.nasa.gov/planets/eph_export.html

Cite As

Meysam Mahooti (2024). Initial Orbit Determination (Least Squares Method) (https://www.mathworks.com/matlabcentral/fileexchange/55626-initial-orbit-determination-least-squares-method), MATLAB Central File Exchange. Retrieved .

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Initial Orbit Determination (Least Squares Method)

Version Published Release Notes
3.1.0

It was revised to decrease CPU usage.
3.0.0

test_LSQ_GEOS3.m was modified.
2.2.2

test_LSQ_GEOS3.m was modified.
2.2.1

It was revised on 2022-10-25.
2.2.0

test_LSQ_GEOS3.m was modified.
2.1.2

It was revised on 2022-10-23.
2.1.1.0

The test_LSQ_GEOS3.m file has been updated, and documentation has been provided.
2.1.0.0

Shampine-Gordon integrator is replaced by Radau IIA integrator
2.0.0.0

The DE430 full matrix is added.
1.1.1.1

Revised on March 16, 2020.
1.1.1.0

Documentation is added.
1.1.0.0

ECI to ECEF transformation is updated based on IAU 2006 Resolution.
1.0.0.0

The image is added.

Revised on 2016-11-21.