Astrodynamics-Project-Propagator

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The objective of this project is the development of an orbital propagator in the Matlab environment. This propagator should provide a realistic approxi- mation of spacecraft trajectories around the Earth. Eventually, the predictions of your propagator should be compared against the real trajectory of a satellite in low Earth orbit.

Authors: Antoine Montuzet, Arnaud Saison
Academic year: 2022-2023
Course: AERO0024-1 Astrodynamics

(Credits: ASCII Art by Shanaka Dias from https://www.asciiart.eu/animals/reptiles/alligators)

User Guide

System requirements

• MATLAB R2022a or later
• Aerospace Toolbox
• Warning: some of the codes can take up to several minutes to run.

Others:

• The S3L propagator is required to be placed in a folder named S3Lprop_v1_21.
• The SGP4 analytical propagator as provided by S3L must be placed that same folder.
• The file structure should not be changed

Project

Each question of the project is answered in a separate file:

• Propagator01_Saison_Montuzet.m = simple two-body problem for ISS orbit for 24 hours
• Propagator02_Saison_Montuzet.m = two-body with J2 perturbation for ISS orbit for 24 hours
• Propagator03_Saison_Montuzet.m = two-body with J2 and drag for ISS orbit for 24 hours
• Propagator04_Saison_Montuzet.m = two-body with J2 and drag for HST orbit for 24 hours, and SGP4 abalytical propagator

Each file has a corresponding paramters file with the same number identifier.

Propagator

The propagator requires a parameters structure as generated by processParam.m, which requires itself an input paramters structure. No processing should be done before using processParam.m. The parameters file must contain:

• Options for perturbations
  • par.ENABLE_J2 = {1,0} enables/disables J2 perturbation
  • par.ENABLE_DRAG = {1,0} enables/disables drag perturbation using Harris-Priester
• TLE has 2 different modes, both work with only one object to propagate:
  • Give one TLE (three line element) that is used as initial orbit for propgation.
    • par.TLE.L0 = line 0 the TLE
    • par.TLE.L1 = line 1 the TLE
    • par.TLE.L2 = line 2 the TLE
  • Give TLEs in bulk for same object. Initial TLE is used for propagation, followings are plotted for comparison. There should be a txt file containing all TLEs (three line elements).
    • par.BULKTLES_FILENAME = [char vector (uses '', NOT ""), whitout extension name] file containing all TLEs without additional lines at the end, exactly as download from Space-Track.org
• In order to use SGP4, an additional, specially formatted TLE (two line element in this case) is required.
  • par.SGP4TLE_FILENAME = [char vector (uses '', NOT ""), whitout extension name] file containing one TLE
  • par.SGP4_ECI_MODE = {1,0} enables/diables use of tle2eci.m file that is provided by S3L and does not work properly. Can be used for comparison, but orbit will be incorrect.
• Drag parameters
  • par.prop.MASS = [kg] mass of object
  • par.prop.CD = [-] drag coefficient of the object
  • par.prop.A = [m^2] object area
  • par.prop.n = Harris-Priester value for inclination of orbit
• Solver parameters
  • par.SOLVER = {ODE45, ODE78, ODE113} solver used for propagation
  • par.N_STEP = [nb] number of step in the simulation
  • par.T_END = [s] number of seconds in the simulation
  • par.REL_TOL = [-] relative tolerance
  • par.ABS_TOL = [-] absolute tolerance
• par.DEBUG = {1,0} enable/diasable additional command window outputs
• Print to PDF feature
  • par.PRINT_PDF = {1,0} enable/disable printing figures to PDF in the specified figures folder (WARNING: printing figures to PDF requires about 1 second per figure)
  • par.PDF_FOLDER = [char vector (uses '', NOT "")] folder in which PDF figures are saved

Project strucure and functionalities

Structure:

• data/
  • bulkISSTLEs.txt several ISS TLEs
  • ISSTLE.txt TLE (two lines) of the ISS for SGP4
  • ISSTLE.txt HST (two lines) of the HST for SGP4
  • coast.mat coast outlines
  • planetaryData.m all astronomical data (R_earth, mu, J2, ...)
• figures/ contains all output figures (folder name can be changed in parameters file)
• propagator/
  • matlab/
    • anaDragPertu.m analytical formulas for drag
    • anaNoPertu.m analytical formulas without perturbations
    • anaOblPertu.m analytical formulas for J2
    • diffEq.m differential equation
    • ECI2ECEF2LLA2OE.m all frame transformations
    • ECI2kepl.m calls ijk2keplerian for all time steps
    • getLatestTLE.m uses Celestrack API to get latest TLE of object
    • harris_priester.m calculates the density depending on position and altitude
    • mean2trueAnomaly.m converts mean anomaly to true anomaly
    • processBulkTLEs.m processes several TLEs in txt file
    • processParam.m processes and groups parameters and TLE
    • processTLE.m parses and converts text TLE to orbital elements, utc time, and orbital elements
    • propagator.m solves the equation of motion with solvers
  • python/
  • S3Lprop_v1_21/ contains all S3L propagator files WARNING: FOLDER MUST BE PLACED THERE AND HAVE THIS PRECISE NAME
    • tle2eci/tle2eci.p-m m and p file for tle2eci provided by S3L
• utils/
  • angleDiscon.m allows representation between 0 and 360° without cutting plot on screen
  • betterYLim.m centers data and limits to bounds
  • dispKeplerian.m displays keplerian elements in command window
  • dispLine.m diplays a horizontal line in the command window
  • dispParam.m displays parameters as output by processParam in the command window
  • errorComparison.m plots ECI and LLA errors
  • fig2pdf.m automatically converts figure to pdf
  • grdtrk.m customized ground track function as provided in project statement
  • plot_3D.m represents solution in 3D
  • plotConstant.m detects if data for a plot is almost cst
  • plotDayLines.m plots vertical line at each day
  • plotOE.m plots all the orbital elements
  • plotOrbit.m plots ground track and altitude
  • xticksCustomDate.m plots hours on minor grid
• convergenceStudy.m convergence study script
• Propagator01_Saison_Montuzet.m
• Propagator02_Saison_Montuzet.m
• Propagator03_Saison_Montuzet.m
• Propagator04_Saison_Montuzet.m
• uncertaintyStudy visualization of uncertainty on $\mu$