Airbus Defence and Space

COMPONENTS, ENGINEERING TOOLS AND SERVICES

Atomox

At altitudes between 200 km and 700 km, the residual atmosphere consists primarily of atomic oxygen (AO). The orbiting spacecraft motion through this atmospheric AO can generate a flux to the spacecraft surfaces with significant energy of about 5eV. The incident AO can lead to oxidation and erosion of outer spacecraft materials and to degradation of surface properties.

 

The ATOMOX

software was developed to predict the surfaces erosion induced by the impact of atomic oxygen.

Atomox detailed presentation

 

Features / technical details

The ATOMOX software is a 3D geometrical analysis tool for the computation of atomic oxygen (and other species of the residual atmosphere) fluence and resulting material erosion on the outer surfaces of an orbiting spacecraft in LEO. This tool accounts for the 3D spacecraft geometry, the spacecraft attitude, surface material properties (e.g. absorptivity, diffuse / specular reflection) and computes the species fluence for the mission lifetime. The main directional properties of the incident particles are included: motion through the co-rotating atmosphere, shadowing brought by the structure, particles thermal motion and multiple reflections on the external surfaces. Standard atmosphere models can be selected for the computation of the particles number density.

ATOMOX is integrated within SYSTEMA framework, so integrates the basic functionalities:
  • Spacecraft geometry is modelled with simple shapes (rectangles, quadrangles, cylinders, spheres, etc.) hierarchically organised. For geometry definition, a 3D-graphic modeller is available.
  • Definition of spacecraft orbit and pointing requirements is carried out with MISSION module. A complete orbit generator is available in MISSION / ORBIT. The nominal pointing, attitude laws, and mobile parts (e.g. solar array) can be defined within the MISSION / POINTING module. Both modules are completed by means of visualisation of the spacecraft trajectory and attitude.
  • The results along the obit can be visualized with 2D and 3D visualisation tools.

The Monte-Carlo ray-tracing technique is applied to compute the flux of atomic oxygen. Its principle is to simulate the atomic oxygen / spacecraft interactions with enough particles such that statistics on the simulated results will reproduce satisfactorily the macroscopic behaviour. The ray-tracing is linked to an appropriate random numbers generator. The principle is the same for the different types of particles considered by the tool (atoms, molecules, ions). The ray-tracing technique considers emitted points from the surface of the satellite and detects if a given element (mesh) is struck by the ray. This method, particularly well adapted for detecting impacts on small surfaces, avoids the firing of a prohibitive number of rays. Then, the ray is followed by multiple reflections on the satellite surfaces. The main characteristics of the tool are the following :

  • The following environment models can be used to describe the ambient characteristics : MSIS-86, MSIS-90, DTM, IRI-90 and HWM-90.
  • The ambient atmosphere temperature can be handled by the tool : this is performed assuming a Maxwellian isotropic distribution of velocity.
  • Multiple reflections can be taken into account : this is performed using the ray-tracing method by following the successive histories of the rays after reflection. The surface properties are described by the following parameters : absorption coefficient, specularity ratio, accommodation coefficient.

Spinning can be modelled : in this case the ATOMOX tool performs the average of the flux on all the orientation of the spacecraft with respects to the ambient atmosphere.

 

Applications

The ATOMOX is often used to perform prediction of surfaces recession on LEO Airbus Defence and Space spacecraft. The maturity of the tool is good, as the process of surfaces erosion by Atomic Oxygen is well understood and as the materials sensitivity to AO has been measured for most of the space materials.

Moreover dedicated validations have been performed on LDEF spacecraft showing a good agreement between simulation and in-orbit data.

Reference customers

Airbus Defence and Space LEO satellites: SPOT4, SPOT5, Helios, Aladin…