Space environment

Perturbations is a Systema application that delivers analysis of environmental perturbations caused by solar pressure and air drag generated by atmosphere remains at low altitudes. It plays a key role in the spacecraft analysis process by modelling external forces acting on the spacecraft throughout its mission.

Solar pressure

The solar pressure module computes the force generated by incident sunlight photons impacting spacecraft surfaces. Solar radiation pressure is defined as the vector difference between the incident and reflected momentum flux.

Sun radiation incident on the satellite's surfaces produces a radiation pressure, or force per unit area, equal to the vector difference between the incident and reflected momentum flux.

The major factors determining the radiation pressure are:

• The intensity, spectral and spatial distribution of solar radiation
• The geometry of the satellite
• The optical properties of the satellite surfaces

Solar pressure allows to account for the induced forces and torques using a state-of-the-art analytical ray tracing algorithm. This enables precise evaluation of spacecraft dynamic response to solar influence under various mission conditions.

Air drag

In low-Earth orbit, a satellite moves through the residual atmosphere and experiences aerodynamic forces. These forces result from the interaction of the atmosphere molecules with the satellite's surfaces.

The air drag module computes perturbing forces, torques and thermal fluxes resulting from the interaction of the atmosphere particles with the satellite's surfaces.

Air drag depends on several key parameters:

• The satellite velocity
• The atmospheric constituents, their density and their kinetic temperature
• The motion of the atmosphere
• The geometry of the satellite
• The orientation of the satellite w.r.t. the incoming flow
• The surface characteristics and temperature

This force is usually modelled by assuming that it acts in a direction opposite to the spacecraft's velocity vector relative to the ambient atmosphere. The results are computed using a modified Maxellian model for Particle/Wall Interaction. This tool enhances scenario specification, supports accurate simulation of perturbing forces, and helps engineers anticipate design impacts early in the mission planning phase.

Debris is a Systema application designed to predict the risk of spacecraft equipment or structural failure due to space debris. With the continuous growth of orbital debris, the potential for mission-critical damage increases, driving the need for numerical tools to support MMOD (MicroMeteoroid and Orbital Debris) risk assessment methodologies.

Larger on-orbit objects are tracked, and orbit change manoeuvres can be performed to avoid potential collisions. However, for non-trackable debris, spacecraft must rely on shielding or other risk mitigation strategies to minimise the chances of impact. To support the spacecraft design and analysis process, Debris offers engineers a reliable tool to model and assess the risk of impact and inform protective design decisions.

The prevention of critical damage to sensitive surfaces, which could compromise mission objectives and spacecraft lifetime, is a growing concern among satellite design engineers. To optimise the positioning of critical elements and maximise overall performance efficiency, it is essential to have a comprehensive understanding and quantitative characterisation of MMOD impact risk.

Debris is designed to provide engineers with a practical tool for evaluating the probability of no-penetration (PNP) of selected elements within the spacecraft geometry. The simulation process is engineered to be compatible with repeated trade-off analysis between different spacecraft configurations.

MMOD risk assessment via Debris includes:

• Computation of the number of direct impacts on an element
• Computation of the number of penetrations on an element
• Computation of damaged area on an element
• Computation of the PNP of an element

These features support engineering decisions and ensure spacecraft modelling accounts for structural vulnerabilities and debris exposure in a quantifiable way.

Plumflow is a module included in the Systema-Plume suite that computes the flow field generated by thrusters operating in a vacuum. It models a wide range of plume characteristics, including:

• Chemical composition of the gas in the chamber and in the plume
• Physical properties of the gas: viscosity, heat capacity, g, species diameter
• If necessary, description of the non-gaseous phase : particles or droplets
• Properties of the plume along the streamlines (velocity, density, pressures…)
• Characteristics of the engine (thrust, mass flow rate…)

The software applies multiple advanced methods:

• This calculation involves a large panel of different methods:
  • The computation of the chemical composition and physical properties is performed under assumption of thermodynamic equilibrium
  • The computation of the flow inside the engine and its expansion in the surrounding space uses the method of characteristics or navier-stokes equation resolution. These programs perform the simulation of the boundary layer expansion at the nozzle lip
  • The extension of the flow-field beyond the navier-stokes and the method of characteristics computational domain uses the source-flow method, considering the expansion as isotropic
  • Other methods can be used to handle more specific problems like direct simulation Monte-Carlo at the nozzle lip or droplets propagation

These capabilities enable comprehensive simulation of thruster behaviour and plume evolution under space conditions, contributing to accurate spacecraft modelling and engineering analyses.

The image below shows the pressure distribution on the solar array of an observation satellite alongside the thruster flow field in vacuum.

GTD is a Systema application dedicated to radio-frequency (RF) analysis based on the geometrical theory of diffraction (GTD). It plays a crucial role in the spacecraft design and analysis process by modelling antenna behaviour and interactions within complex satellite structures.

The radio frequency (RF) analysis of satellites is an essential step to ensure a successful mission. For directive antennae, the satellite structure and nearby payloads may often be neglected, but for low-gain and omnidirectional antennae, the structure can substantially influence radiation characteristics.

For these types of antennae, it is critical to compute the interfered antenna pattern when mounted on a satellite structure. GTD provides this capability, enhancing the accuracy of simulation and antenna design.

In addition to the antenna pattern, this software enables the calculation of antenna-to-antenna coupling due to structural effects, which is important for optimal antenna positioning and electromagnetic compatibility (EMC) analysis. It also allows field computation on physical and virtual spacecraft surfaces.

The RF analysis is based on GTD, which assumes high-frequency wave behaviour. Ray tracing is performed in two modes:

• Backward ray tracing: calculates ray paths from the observation point, using known source position and geometry
• Forward ray tracing: emits rays from the source in all directions and tracks their full propagation

The software supports:

• Multiple reflected and diffracted rays per surface (up to two per ray)
• Curved and planar surface analysis
• Creeping ray effects on planar surfaces

For antenna coupling, GTD determines:

1. Coupling ray paths using ray tracing which determines the coupling ray paths
2. Coupling value calculated by field propagation along the rays using a complex or RSS field summation

GTD helps engineers with result visualisation, RF System analysis such as early interaction issue detection, antenna placement optimisation, and antenna pattern prediction. It is a valuable tool for designing high-performance communication systems under realistic space mission constraints.