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Agents

Use the Agents table to add Templated and Peripheral Agents to your Scenario. Templated Agents are full digital twins, instances of the templates defined in your Agent Branches. Peripheral Agents are simple entities such as Ground Targets; their position and velocity are propagated, but they have no modeling of Power, Thermal, etc.

Templated Agents​

Templated Agents are full Digital Twins. Digital Twins are instantiated from a specific branch of an Agent Template repository. The initial state used to differentiate Agent Templates currently includes Target assignments and an initial orbit. You may instantiate atTwin from any branch you have read access to. Note: Celestial Targets are not agents and are created at the Agent Template level, since they require no initial state specification.

To add a Templated Agent to your Scenario, click the "+" button at the bottom of the Agents table. After selecting "Templated" as the Agent Type, choose the Repository and Branch where the desired Agent is defined. To fully differentiate your Tempated Agent, you will need to complete its Target Mapping and Initial Orbit, although the former can be completed after saving the agent.

Target and Target Group Mapping​

The abstract Targets and Target Groups defined in each Agent Branch must now be resolved to Agents and Agent Groups in the scenario.

Resolve each Target to an Agent using the interface. Similarly, resolve each Target Group to an Agent Group. Agents and Agent Groups can each be used multiple times in the mapping. Note that Ground Targets may only be resolved to Peripheral Ground Agents and Space Targets may only be resolved to Peripheral Space Agents or Spacecraft Digital Twins. You can save the Agent without completing the mapping, which will allow for all Agents and Agent Groups to be created and then subsequently mapped. However, the mapping must be completed for all Templated Agents prior to simulation.

If an Agent is mapped to an Agent Group that contains it, it will ignore itself and use all other Agents to populate the Target Group.

Defining Initial Orbits​

Sedaro provides four ways of defining the initial orbit of an agent. The orbit is simulated in the same way, regardless of the means of definition.

Position & Velocity​

Specify the initial position and velocity of your spacecraft in J2000 Earth-Centered Inertial (ECI) coordinates. In the ECI reference frame, the xy-plane is coincident with Earth's mean equator. The z-axis and the x-axis are aligned with celestial North and the vernal equinox as they were at 12:00 Terrestrial time on January 1, 2000.

Orbital Elements​

Define your initial orbit using Keplerian orbital elements using the J2000 ECI frame as the frame of reference. After defining the semimajor axis, inclination, and eccentricity, the form will update to determine what additional elements are required to fully define the initial state of your orbit. A brief description of the orbital elements follows.

The semi-major axis and eccentricity (e) define the shape of the orbit as a conic section. Sedaro supports circular (e = 0), elliptical (0 < e < 1), parabolic (e = 1), and hyperbolic (e > 1) orbits.

Inclination is the (positive) tilt angle of the orbital plane relative to the xy-plane.

For inclined orbits, specify the Right Ascension of the Ascending Node (RAAN) relative to the ECI x-axis (vernal equinox on January 1, 2000). This is the (positive) angle between the x-axis and where the orbit passes from below to above the xy-plane (the ascending node).

For eccentric orbits, specify the true anomaly, the positive angular displacement (in the orbit direction) of the spacecraft from perigee.

For inclined eccentric orbits, specify the argument of perigee, the (positive) angle in the orbital plane between the ascending node and the location of perigee.

For equatorial orbits, RAAN and argument of perigee are undefined, as orbit lies in the xy-plane. In this case, define the true longitude of perigee, which is the (positive) angle between the x-axis and perigee.

For circular orbits, the argument of perigee and true anomaly are undefined. For equatorial circular orbits, specify the true longitude, which is the (positive) angle in the xy-plane between the x-axis and location of the spacecraft. For inclined circular orbits, specify the argument of latitude, which is the (positive) angle between the ascending node and the spacecraft.

Reference Orbit​

Several common types of orbit can defined as a reference orbit, which requires fewer inputs from the user. The available reference orbits are as follows:

  • Polar Circular - Provides global coverage, which is often valuable for Earth observation and communications missions. Define this orbit by its altitude, RAAN, and argument of latitude.
  • Equatorial Circular Orbit - Provides reduced launch vehicle requirements and a consistent groundtrack. Define this orbit by its altitude and true longitude.
  • Sun-synchronous Circular - Sun-synchronous orbits provide nearly constant orbit geometry relative to the Sun and is often useful for imaging, weather, and other remote sensing missions. Define this orbit by its altitude and true anomaly and by the desired Mean Local (solar) Time.
  • Geostationary - Provides a constant position relative to the Earth's surface, which is valuable to communications, weather, and navigation missions. Define this orbit by its longitude (earth-fixed).
  • Geostationary Transfer - A Hohmann transfer orbit typically used to transfer between an equatorial low earth orbit (LEO) and geostationary orbit. Therefore, the apogee altitude is geostationary orbit altitude (about 35,786km). Define this orbit by its perigee altitude, true longitude of perigee (recall that this is an equatorial orbit), and true anomaly.
  • International Space Station - The International Space Station (ISS) orbit is nearly circular with an altitude of about 410km and inclination of about 51.6 degrees. Many small satellites are deployed from the ISS or from launch vehicles resupplying the station. Define this orbit using the RAAN and true anomaly.
Two-Line Element​

A TLE encodes a list of orbital elements for a given epoch. The US Air Force tracks objects in orbit and provides regularly updated TLEs to the public. Sedaro propagates your input TLE forward or backward to the start time of your mission and uses this state to set the initial conditions for orbit propagation. Both two- and three- line formats are supported.

Peripheral Agents​

Peripheral agents are simple targets. Only their position and velocity are modeled during a simulation. To add a Peripheral Agent, click the "+" button at the bottom of the Agents table. After choosing "Peripheral" as the Agent type, choose a subtype of Ground Target or Space Target.

Ground Targets are propagated on the surface of the Earth at their defined latitude, longitude, and altitude. Latitude and altitude inputs are geodetic, which is typical for terrestrial latitude and altitude. Negative altitudes are not allowed. If your desired target location is below mean sea level (MSL), set altitude to zero. This is unlikely to impact simulation accuracy, and you can account for the impact of negative altitude when setting target-based conditions for your ConOps (e.g. setting a minimum elevation constraint based on the geometry of local terrain or other obstructions).

Space Targets are propagated based on their given initial orbit using the same propagator as a Templated Agent. The orbits of Space Targets are defined in the same way as for Templated Agents.