OrbitPy

This package contain set of modules to compute mission-data of satellites. It can be used to perform the following calculations:

1. Generation of satellite orbits from constellation specifications.

2. Computation of propagated satellite state (position and velocity) data.

3. Generation of grid points at a (user-defined or auto) angular resolution over region of interest.

4. Grid Coverage: Computation of satellite access intervals over given set of grid points (grid-coverage) for the length of the mission.

    i. With consideration of satellite/sensor pointing (orientation) directions.
    ii. With consideration of sensor field-of-view (FOV) and field-of-regard (FOR).
   

5. Pointing-options Coverage: Computation of coverage in which set of pointing-options of the satellite/instrument are specified and accessed ground-locations (intersection of the pointing-axis with the Earth's surface) is calculated.

6. Pointing-options with Grid Coverage: Grid Coverage calculated for different satellite/instrument orientations.

7. Specular Coverage: Calculation of specular points and grid points inside the specular regions. Several source (transmitter) satellites may be specified, and the receiver satellite/sensor orientation and FOV is taken into consideration.

8. Computation of inter-satellite communication (line-of-sight) time intervals.

9. Computation of ground-station contact time intervals.

10. Computation of satellite eclipse time-intervals.

11. (Under dev) Sensor pixel-array projection to simulated Level-2 satellite imagery.

The orbitpy package is built on top of the propcov package available in the propcov folder. Please refer to the README.MD file within the propcov folder for description of the respective package.

Install

Requires: Unix-like operating system, python 3.8, pip, gcc-11, make, cmake

It is recommended to carry out the installation in a conda environment. Instructions are available in the README file of the InstruPy package.

1. Install the instrupy package (dependency).

2. Run make from the main repo directory.

   All the below dependencies are automatically installed. If any errors are encountered please check that the following dependencies are installed. Install the dependencies separately and then run make.

   • numpy
   • pandas
   • scipy
   • sphinx
   • sphinx_rtd_theme==0.5.2
   • propcov

3. Run make runtest. This runs all the tests and can be used to verify the package.

4. Find the documentation in: /docs/_build/html/index.html#

In order to uninstall run make bare in the terminal.

---

NOTE

The OrbitPy installation automatically installs the package propcov which consists of python binding of C++ classes which provide the functionality for orbit propagation, coverage calculations and sensor pixel-array projection. The python bound C++ objects are implemented in OrbitPy.

The make runtest does not run the tests of the propcov library. Please see the README.MD in the propcov folder on how to run it's tests.

Documentation of the propcov library is available in the Word document propcov/docs/propcov-cpp.docx.

Mac users have reported errors in the installation of propcov. This mostly relates to the environmental setup in which wrong C++ compiler is selected for compilation. Please see the README.MD in the propcov for debug information.

Directory structure

├───docs (sphinx documentation)
├───orbitpy (folder with the source files)
├───propcov (propcov package)
├───TBD (To be determined, temporary folder with old files)
└───tests (folder with test scripts)
    ├───test_coveragecalculator (tests of the coveragecalculator module)
    ├───test_data (reference test checkpoint data)
    ├───util (util folder with supporting scripts for tests)
    └───validation (validation tests)
        ├───GMAT (GMAT reference data)
        └───STK (STK reference data)
            ├───test_coveragecalculator_GridCoverage_with_STK
            └───test_propagation_with_STK

License and Copyright

Copyright 2022 Bay Area Environmental Research Institute

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Credits and Acknowledgments

This work has been funded by grants from the National Aeronautics and Space Administration (NASA) Earth Science Technology Office (ESTO) through the Advanced Information Systems Technology (AIST) Program.

OrbitPy uses:

• GMAT2020a gmatutil source (https://sourceforge.net/p/gmat/git/ci/GMAT-R2020a/tree/src/gmatutil/)
• Pybind11 (https://pybind11.readthedocs.io/en/stable/basics.html)
• JSON for Modern C++ (https://github.com/nlohmann/json)
• GoogleTest (https://github.com/google/googletest)

Questions?

Please contact Vinay ([email protected])

Developer Tasks

Restructuring notes

• Need to account for spacecraft bus orientation in coverage calculations
• Use datetime module for storing time and time-delta
• Think about how to represent large volumes of output data (propagation, coverage). Currently it is in the form of files, and file I/O operations are performed. Should we also offer other options?
• Tag grid points with 'target ids' (similar to indices)
• How to ensure unique identifiers for satellties, instruments, grid points, etc?
• Using Quaternion to represent orientation instead of Euler angles.

OrbitPy

• SGP4 Propagator validation tests with STK (or another s/w)
• Incorporate artificial image synthesis involving the propcov classes DiscretizedSensor, Projector and the orbitpy SensorPixelProjection module. Add python-tests.
• Search for ‘Vinay’ and ‘TODO’ over all the files

Propcov-cpp

• Explore the orbit interpolation functions.
• Make a C++ SystemTestDriver
• Add unconventional sensor FOV geometry shapes GTests for GMATCustomSensor and DSPIPCustomSensor class.
• Rename TATCException to PropcovCppException
• Add GTests for Spacecraft, CoverageChecker, NadirPointingAttitude and other classes. (There are in total 26 propcov-cpp active classes, of which currently there are GTests ofr 15 of these classes. Some tests in the tests/tests-cpp/old folder can be rewritten into the GTest format.)
• Consider avoiding virtual functions since it has runtime costs associated with it??

Debug Tips

Errors in the propcov-cpp classes are sometime not visible (i.e. not displayed) when the propcov package is installed. The package installation can happen, but import will not work. In such cases run make from propcov-cpp -> tests, and debug any errors.