ISO 23020:2021 pdf free download – Space systems一Determination of test methods to characterize material or component properties required for break-up models used for Earth re- entry.
New regulations require unmanned spacecraft and launch vehicle orbital stages, called space bodies in this document, to be designed and manufactured in such way that fragments generated during Earth re-entry cannot cause casualties, damage to property or environmental pollution on the ground (see Iso 24113).
Space bodies are submitted to high aero-thermodynamic fluxes, pressures and shear stresses that lead to their disintegration into fragments that can potentially reach ground after a re-entry. These fragments are generated by the effect of aero-thermal loads seen by components that constitute a space body. The assessment of the fragmentation and subsequent survivability of the fragments in terms of size and trajectory is based on simulation.
The methodology to determine the size of the debris is based on an idealized two-step process, called fragmentation and survivability.
— Fragmentation
Based on the knowledge of the orbital (ballistic) trajectory of the space body and the knowledge of its design, the computation of temperature and stresses determine the most probable failure locations that will generate sub components. The breakup fragments prior to re-entry are termed debris.
— Survivability
The objective is then to determine if debris can survive (no completely burned), and then if the final size and energy when touching down the Earth are in accordance with the international regulation. The computation of the final size and energy of the debris is based on generic geometry definition, homogenized properties and on the knowledge of their trajectories.
For both fragmentation and survivability, suitable thermal response models require a range of material properties for a full characterization of the material response.
Thermal tests used to determine material properties need to be well defined and shared between spacecraft manufacturers and regulation authorities.
There are a range of relevant spacecraft materials, from metals, organic and ceramics to composite materials.
As a result, the material or component properties used in break-up models is an essential model input. Objects that separate during the ascent phase and impact the ground are addressed in ISO 14620-2.
Assessment, mitigating and control of potential risks created by the re-enter of objects from the orbit are addressed in ISO 27875.
4.3 Type of tests
Elementary thermal tests can characterize basic properties, such as thermal conductivity, specific heat capacity and chemical effects inclusive of melt and pyrolysis. These bulk properties are independent of the surface state or any surface interactions with the environmental gas.
In order to produce a reasonable prediction of the survivability of an object during the re-entry, it is necessary to take into account mass and energy transfer occurring between the object surface and the environmental gas. Surface properties and characteristics, such as emissivity, catalicity of the object, shall be measured in representative atmosphere.
The available data is often restricted to a temperature domain, which is generally well below the real or predicted temperature, met by the debris during the terminal re-entry phase.
Technological tests (complementary to elementary tests) are consequently required to extend the domain temperature in a more relevant surface state so that surface mass and energy transfer are ideally well captured.
These technological tests can be divided in two types.
The first type is radiative (generally in the infrared wavelength domain), where a furnace may be used to expose one face of the material sample to highly calibrated pure radiative heat flux in air at ambient pressure or in vacuum. This allows capturing of the material emissivity, the roughness and some chemical effects that contribute to the surface mass and energy transfer. Convective flow effects on the surface phenomena in such a test set-up are not assessed.
The second method to generate high temperature and pseudo flight representative aerothermal loads consists in the use of plasma wind tunnel facilities. These facilities can capture effects such as the material chemical catalicity to the recombination of air molecules at the surface, and the thermomechanical flow effects on the material.