Propagation#

Creating a Propagation#

Propagations can be created using the CLI using satcat create propagation:

satcat create propagation --duration-sec 86400 --timestep-sec 60

Much like screenings, propagations are also asynchronous jobs which are run on Satcat’s servers. They can be submitted using satcat submit propagation [id] and awaited using satcat await propagation [id].

You can also use the --submit flag of create propagation to automatically submit the propagation upon creation if it has been fully configured using the other parameters of create_propagation, and the --wait flag to await completion if submit was also supplied.

CCSDS Orbit Parameter Message (OPM)#

The Satcat SDK supports configuring propagations using the CCSDS Orbit Parameter Message (OPM) file format. This file format allows you to specify your spacecraft’s state vector, covariance, physical quantities such as mass, and optionally any maneuvers that you wish to generate a predictive ephemeris from. For more information on the CCSDS OPM file format, see the CCSDS Orbit Data Messages Blue Book. The Satcat platform references the CCSDS 502.0-B-2 version of the CCSDS Blue Book document.

To create a propagation using an OPM, you can use the --opm flag of satcat create propagation:

satcat create propagation --opm USER_OPM_FILE.txt

Creating a propagation from an OPM file has the following implications:

  • The initial state of the propagation is set to the state vector supplied in the OPM.

  • If a covariance matrix is specified in the OPM, the initial covariance of the propagation is set to the covariance matrix supplied in the OPM.

  • If any maneuvers are specified in the OPM, the maneuvers are added to the propagation.

  • If the spacecraft parameters section is present in the OPM, this information is added to the propagation.

  • If the propagation does not already contain a value for start_time, the epoch of the state vector is set as the propagation’s start_time.

Warning

As per CCSDS 502.0-B-2 3.2.4.9, the spacecraft parameters section must be supplied if the OPM contains maneuvers. Additionally, as per sections 3.2.4.5 & 3.2.4.6, drag and solar radiation pressure forces are only taken into account if the values for drag and SRP coefficient supplied in the OPM are nonzero.

These settings have a large impact on the trajectory of a spacecraft, particularly in low earth orbit. To ensure the fidelity of the resulting predictive ephemeris, the Satcat SDK requires the Spacecraft Parameters section of the OPM, even if the file contains no maneuvers.

Please take care to supply the best possible estimates for the values in the Spacecraft Parameters section when supplying an OPM for propagation.

Screening using Propagations#

The Screening module of the SDK supports using Propagations to screen natively. To use a propagation in a screening based on an OPM, you can use the --opm flag of satcat create screening:

satcat create screening --opm USER_OPM_FILE.txt

This will automatically create a screening and attached propagation (as a primary) configured using the OPM. You may also choose to use the --submit and --wait flags to automatically submit and await completion of both the propagation and screening:

satcat create screening --opm USER_OPM_FILE.txt --submit --wait

# Or, equivalently, using short flags
satcat create screening --opm USER_OPM_FILE.txt -sw