TrueTwin Technology

TrueTwin enables high fidelity simulation of entire space missions. This encompasses all relevant physical entities, the software components deployed within them, and the environmental effects that impact them. This article describes the TrueTwin architecture, and how TrueTwin capabilities can be used to effectively simulate your own missions.

Concepts

TrueTwin Satellites represent discrete spacecraft participating in simulated mission segments. Each TrueTwin Satellite may act as a direct digital twin of a real spacecraft or represent planned capabilities yet to be launched on orbit.

TrueTwin Satellites are deployed using integrated software models that represent logical software and hardware components operating within a satellite system. Satellites may also incorporate user-provided software and hardware components collocated in an ACP environment or remotely connected from locations anywhere in the world.

In all deployment models, TrueTwin Satellites operate real flight software. It is architecturally just another model operating within a virtual satellite, which happens to control other components. Users may decide to use Antaris SatOS flight software to fill this role, but any other flight software solution may also be integrated into a simulation.

TrueTwin Ground Stations offer communications capabilities to TrueTwin Satellites using RF or optical infrastructure. Each Ground Station may be defined to represent real world capabilities, or simply provide some potential capability.

TrueTwin Scenarios describe the overall scope and content of a simulation. Scenarios act as a simulation runtime that hosts all elements in the same universe of existence so they can carry out a relevant mission segment.

TrueTwin Scenarios may represent a future mission segment that has yet to happen, or a segment that has occurred in the past. This allows users to better diagnose anomalies, evaluate alternate onboard schedules, or simply explore mission solutions.

Scenarios may be executed in realtime or in accelerated time. Realtime scenarios are typically used to perform distributed simulations with some hardware in the loop. Accelerated time is used when all elements are deployed using pure software models in a collocated environment, and operator interaction is not desired.

Satellite Simulation

TrueTwin Satellites directly represent real satellite systems, abstracting subsystems and components such that software-based models may be easily configured to represent real world elements. The same abstraction enables users to dynamically incorporate distributed hardware and software components into a common simulation. This powerful satellite virtualization capability enables users to execute simulations at any point in a mission lifecycle with whatever level of fidelity is desired.

System Design

The TrueTwin Satellite architecture is comprised of three primary layers:

Flight Software operates within a TrueTwin Satellite in a semiautonomous mode, receiving commands over a simulated TT&C link while also handling automated onboard operations. Antaris SatOS is integrated natively into TrueTwin and can be used through the entire mission lifecycle, including the operational phase. Users may also decide to integrate other flight software solutions.

Space Vehicle systems are abstracted through a set of carefully-designed APIs exposed to the onboard flight software. These elements are all simulated within physical space connected to a common structure. This is a critical aspect of TrueTwin, as any operations carried out by an individual actuator such as a reaction wheel will accurately affect the space vehicle, and will also affect measurements through relevant sensors such as angular rates from an IMU and power draw from a battery.

Space Environment represents elements like celestial bodies (Earth, Sun, Moon), physical forces (drag, gravity), and even other orbiting objects. Just as an explicit actuator operation will have a physical impact on a space vehicle, so will the models operating within the space environment. For example, the spacecraft attitude and its position relative to the Sun will influence the output of the solar panels.

Sensors & Actuators

Below is a description of the simulated bus sensors and actuators within a TrueTwin Satellite. Note that much of the configuration is provided automatically through the bus configured from the device catalog.

Name	Config	Notes
Coarse Sun Sensor	* Field of view * Orientation * Measurement bias * Measurement noise * Scale factor	Configuration values provided per sensor
Magnetometer	* Orientation * Measurement bias * Measurement noise * Scale factor	Configuration values provided per sensor
Star Tracker	* Measurement noise * Rate error modeling * Sun and Earth Keep-out triggers	Configuration values provided per sensor
IMU	* Orientation * Gyro and Accelerometer noise * Measurement bias * Scale factor
GNSS	* Refresh Rate * Latency * Acquisition Time * Position, Velocity, and Time Noise
Torque Rod	* Orientation * Dipole	Configuration values provided per actuator
Reaction Wheel	* Wheel layout (3- or 4-wheel orientation) * Maximum speed * Maximum momentum * Maximum torque * Static/dynamic imbalances	Configuration values applied per wheel
Thruster	* Location * Orientation * Maximum thrust * Nozzle area * ISP * Propellant consumption

Power

TrueTwin Satellites contain a complete power system. This includes power generation via solar panels, storage within battery packs, and distribution to simulated devices.

Power generated through solar panels is configured using the following inputs:

• Total panel area

• Charging efficiency

• Panel orientation

Onboard power storage relies on configurable battery packs. A satellite may contain a configurable number of cells, each with its own defined storage capacity.

Power consumption is configured per component with static voltage and current parameters. The power status of each component can be toggled during TrueTwin simulations.

Reaction wheel power consumption is modeled based on the current speed of each wheel.

Environmental Models

Below is a description of the models configured within the space environment that have an effect on the simulated space vehicle independently of any flight software control path:

Name	Configuration
Celestial Body Gravity	N/A
Earth Magnetic Field	N/A
Atmospheric Drag	* Surface area * Drag coefficient
Solar Radiation Pressure	* Surface area * Reflection coefficient
Gravity Gradient Torque	* Moment of inertia * Center of mass

Orbit Propagation

TrueTwin simulation uses a high-fidelity orbit propagation method to propagate satellite orbits. This is not configurable by end users.

Distributed Simulation

TrueTwin supports engineers in the development of satellites using physically distributed systems. This enables a variety of simulation modes across individual bus components, vendor-provided simulators, payload devices, and more. The TrueTwin architecture allows this wherever a common network is available, typically facilitated through secure tunneling over the public internet or through a private corporate network.

Bus Components

Any bus component described in the TrueTwin Satellite System Design may be connected to a simulation remotely. This capability is typically used in support of the integration of a specific hardware component a flight software solution.

Payload Devices

Payload devices are further generalized than bus components, as the operation of a given payload is more open ended. Integration of any payload is governed by an SDK, which is available in the SatOS-Payload-SDK repository.