Examples

As described in the Run section, OrbitPy functionalities can be accessed by either invoking the bin/run_mission.py script on a JSON file describing the mission specifications or the modules be imported into a python script and used to configure a simulation situation. Examples are available in the examples folder which illustrate both the approaches. The examples are briefly described below.

Simple Mission 1

This example available in the folder examples/simple_mission_1 is based on configuring the mission in a JSON file. It has been described in the Execution with a JSON mission specifications file section.

Planet SkySat

This example is configured in the MissionSpecs.json file in the examples/planet_skysat folder. It can be executed from the repo directory using the command: python bin/run_mission.py examples/planet_skysat/

Skysat-C1 to Skysat-C6 (of the 21 available) are modeled along with their optical instrument. The instrument is modeled as a Matrix imager (spectral information configured to the blue band). Please see the InstruPy repository for references from which the instrument was built (examples/passive_scanner_model/skysat_camera). The imager has 3 adjacent CMOS chips. A scene size of 9.25kmX6.6km is considered.

The maneuvering of the satellites to 28 roll angles is modeled as set of pointing options, with each pointing-option placed under a separate instrument mode. The roll angles are chosen so that the corresponding swaths are adjacent to each other and they cover a span of -10deg to +10deg. The POINTING OPTIONS COVERAGE type of coverage calculation is implemented. At each time-step of propagation, the lat/lon coordinates of the ground points at the intersection of the instrument pointing-axis and the Earths surface are output.

The output file structure is as follows:

│   MissionSpecs.json (Mission configuration file)
│
├───comm (intersatellite contact periods)
│       ...
│
├───sat0 (SkySat-C1)
│       access_instru0_mode0.csv (access events corresponding to mode-0, i.e. pointing at 0 deg roll)
│       access_instru0_mode1.csv
│       access_instru0_mode2.csv
│       ...
│       datametrics_instru0_mode0.csv (data-metrics corresponding to the access events of mode-0)
│       datametrics_instru0_mode1.csv
│       datametrics_instru0_mode2.csv
│       ...
│       state_cartesian.csv (Cartesian orbit data)
│       state_keplerian.csv (Keplerian orbit data)
│
├───sat1 (SkySat-C2)
│       ...
│
├───sat2 (SkySat-C3)
│       ...
│
├───sat3 (SkySat-C4)
│       ...
│
├───sat4 (SkySat-C5)
│       ...
│
└───sat5 (SkySat-C6)
        ...

SAR Constellation

This example (available in examples/sar_constellation/) was developed for the DSHIELD project. The example is built by importing the relevant modules from the OrbitPy library. It simulates 3 satellites carrying L,P band SAR instruments. The coverage calculations is done differently in this example since:

The grid consisted of more then 1.5 million points, and coupled with the requirement to run the simulation at 1 second time-step, the resulting computational load (runtime and data-size) was huge.
The SARs were configured to operate at fixed swath. Fixed swath implies that irrespective of the illuminated swath (which is determined by the sensor cross-track FOV, which here is determined by the antenna beamwidth), the processed swath size is fixed. Hence coverage calculations using the sensor FOV would have yielded erroneous results. (Illuminated swath > fixed swath).

For detailed description please refer the dshield_mission.py script. The script can be executed from the repo directory with the command python examples/sar_constellation/dshield_mission.py.

Landsat-8, SeaHawk-1, (hypothetical) SeaHawk-2

The examples in the folders landsat_seahawk_1 and landsat_seahawk_2 execute the same missions.

The first folder contains a MissionSpecs.json file which has the mission configuration which can be executed from the repo directory using the command: python bin/run_mission.py examples/landsat_seahawk_1/

In the second folder a python script configures the mission using modules imported from OrbitPy. It can be executed from the repo directory using the command python examples/landsat_seahawk_2/landsat_seahawk.py

In the first method the execution produces satellite propagation, coverage, datametrics, eclipse periods and intersatellite communication periods. In the second method the script is built to produce only the propagation, coverage and datametrics.

The example simulates SeaHawks with different modes of operation with each mode as a pointing-option (i.e. a different satellite orientation). The instruments of the satellites (TIRS, OLI and HawkEye are modeled) and corresponding data-metrics calculated for access-events over the mission duration. Since the instruments have a narrow FOV in the along-track direction, and if these FOV were considered, the coverage calculations would need to done with very small propagation step-size. Hence a sceneFOV is defined which has a larger along-track dimension (cross-track dimension is same as the instrument FOV). For detailed description of the mission please refer the landsat_seahawk.py script.