Creating a Space Simulation
Most GNSS receivers on the market are restricted to 1,000 knots and/or 18,000 m, but the SatGen Software has no such limitations. It can simulate any speed and altitude (by standard, up to the geostationary orbit, but higher altitudes are available upon request). This makes SatGen 4 suitable for simulating space scenarios, such as rocket launches, CubeSat deployments, satellites, space probes, etc.
Orbital Trajectory
The built-in Orbital Trajectory feature is designed for all orbital simulations, except equatorial orbits, such as geostationary. Using the built-in feature is recommended over generating orbits with the popular SGP4 propagator and importing them into SatGen as NMEA files.
Getting Started
- Make sure that you are connected to the Internet.
- Connect the security dongle to your computer.
Wait for the dongle to activate and the light on it to become red.
- Open the SatGen 4 software.
Create the Orbital Trajectory
- Click on Map in the Toolbar.
- Select Orbital Trajectory as the Routing Mode.
- Enter the relevant configuration for your trajectory in the Orbital Trajectory configurator.
- Start (UTC) - Enter the start Date and Time of the trajectory.
- Simulation Length - Enter the required duration of the simulation.
- Height - Enter the required height for the trajectory.
- Inclination - Enter the required angle between the Equator and the orbital plane.
You can select to configure additional parameters for Keplerian elements of the trajectory by selecting Advanced as the Mode and configuring the relevant parameters.
- Click Generate.
- View the generated trajectory in Map Mode.
- If you need to edit the trajectory, click the Options tab under Route to view the trajectory configuration and make further edits.
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When using Two Line Element (TLE) Parameters, we recommend you define the following optional parameters in Advanced Mode:
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Generate the Simulation
- Go to the Create tab
- Set the format to correspond with the LabSat unit you want to use to replay the scenario.
- Choose a file save location and file name.
- Select available constellations and frequencies for the scenario, as well as the quantisation and hardware attenuation.
- When you are happy with the configuration of the output format, click the Create file button to make SatGen generate the GNSS scenario file. If you need to create multiple scenarios and simulations, we recommend that you use the queue. Click on the Add to queue button to make SatGen send the file to the generation queue. (The file generation will be paused until you are finished configuring all your scenarios, and manually start the file generation.)
| Note: SatGen does not simulate atmospheric drag, solar pressure, Sun and Moon pull, nor any other advanced effects; the satellite position may be marginally different from the position calculated by the SGP4 algorithm (the gold standard for TLE simulations). |
NMEA Trajectory
This method is only for space scenarios that cannot be simulated using the Orbital Trajectory feature.
To run a space simulation, you must first create an NMEA file containing the relevant data and trajectory for your simulation. See guidelines below. You can then load this NMEA file into SatGen 4 to create a scenario file for the simulation. After loading the NMEA file, select the appropriate datum in the Options (usually WGS84) and select the True Horizon elevation mask to continuously calculate where the horizon will appear when observed from each trajectory point and increase the number of visible satellites accordingly.
| Note: User-defined script trajectories are defined in a local coordinate system. Due to this, script trajectories aren’t suitable for space and long-distance scenario simulations. |
For space simulations, the trajectory must be precise and smooth. Some popular implementations of orbit algorithms, such as SGP4, have numerical instabilities that will result in a jerky trajectory. Jerky trajectories will get rejected by receivers when simulated.
The NMEA trajectory file must include the following data:
- A sample rate of 1 to 10 Hz (1 Hz recommended).
- Latitude and Longitude values with a minimum of 6 decimal places, for example, 1234.123456.
- An altitude value with a minimum of 3 decimal places, for example, 123456.123.
You can use higher sample rates for the NMEA trajectory files if required. However, you must state the Latitude, Longitude and Altitude values with a higher number of decimal places to avoid sudden jumps due to low resolution of latitude/longitude.
| Note: Sudden jumps in the position, which are unrealistic for a GNSS receiver's real usage, can result in the receiver being unable to maintain the satellite lock throughout the simulated scenario. |
Example of NMEA lines that can be simulated with SatGen 4:
$GPGGA,113000.00,4835.905512038,S,14233.294281653,W,8,16,,416363.7170844,M,,,,*27
$GPGGA,113001.00,4837.279673975,S,14228.068010021,W,8,16,,416374.2386976,M,,,,*2A
$GPGGA,113002.00,4838.649496295,S,14222.836804354,W,8,16,,416384.7328093,M,,,,*24
$GPGGA,113003.00,4840.014971686,S,14217.600671875,W,8,16,,416395.1993741,M,,,,*2B
To simplify the creation process of the NMEA files, SatGen 4 does not enforce the 79-character NMEA line length limit and does not verify the checksum.
Getting Started
- Make sure that you are connected to the Internet.
- Connect the security dongle to your computer.
Wait for the dongle to activate and the light on it to become red.
- Open the SatGen 4 software.
Import the NMEA File
- Click on the Import button.
- Select NMEA File in the panel on the left-hand side.
- Adjust the import settings if necessary.
- Click Import.
SatGen 4 will import your NMEA file and plot the trajectory/route on the map.
| Note: SatGen 4 was originally designed for local driving scenarios and will only give a 2D representation that is not accurate for trajectories such as orbits. When SatGen 4 creates a space simulation, the speed and position graphs in the software will not correctly represent the trajectory loaded or produced by the simulation engine. |
Generate the Simulation
- Go to the Create tab
- Set the format to correspond with the LabSat unit you want to use to replay the scenario.
- Choose a file save location and file name.
- You can also select available constellations and frequencies in the scenario, as well as the scenario quantisation and hardware attenuation.
- When you are happy with the configuration of the output format, click the Create file button to make SatGen generate the GNSS scenario file. If you need to create multiple scenarios and simulations, we recommend that you use the queue. Click on the Add to queue button to make SatGen send the file to the generation queue. (The file generation will be paused until you are finished configuring all your scenarios and manually start the file generation.)