Space simulation chambers

The extreme environmental conditions to which space equipment are exposed throughout their working life demand that the highest standards possible be met in terms of materials and system reliability. The only way of assuring an astronaut's life is by conducting very thorough and detailed testing processes. The main aim of such exhaustive testing is to minimize the risks since the cost of a medium size satellite is calculated at hundreds of millions of euros.

What does "space simulation" mean?

The physical simulation of the satellite as a whole should approximate its actual working conditions, as much as is feasibly possible:

In space, far from the earth's surface, the pressure is around 1.10ֿ¹³ mbar and the temperature about 4º K, only taking the radiation temperature into account since space is virtually opaque in the optical sense. The space around the earth also receives radiation from the sun, the earth and the rest of the celestial bodies. At a height of 150km and 60º above the earth's equator, solar radiation has an intensity of about 1.4kW/m2, the solar radiation reflected on the earth about 0.39kW/m2 and the radiation generated by the earth's own temperature 0.26kW/m2. The solar light spectral distribution and its reflection on the earth correspond to that of a black body at 6000k whilst the earth's natural radiation corresponds to that of a black body at 260k. Direct solar radiation may be considered constant in any weather conditions but the earth's natural radiation and the solar radiation reflected in it vary with the meteorological situation (cloud presence or not) as well as with the latitude and height over the entire surface. Finally other electromagnetic radiation present in space and particle flows without intense charges and variable speeds are added to these visible and infrared radiations.

The simulation of such complex and environmentally variable conditions is technologically non-viable therefore the space simulation chambers are usually restricted to the vacuum simulation up to 1. 10ֿ¹³ mbar, cold and visible and infrared radiation (-180ºC/+150ºC)

What is a simulation chamber?

A chamber is constructed of 4 basic operating blocks or subsystems:

Test chamber

This is the vacuum chamber's outer body. It is manufactured in welded stainless steel allowing high vacuum levels (1.10ֿ⁷ mbar) in its interior. It also has a door, used for the entrance and exit of the equipment to be analysed, the test instrumentation and personnel.

Vacuum subsystem

This is used to achieve high vacuum levels in the inner chamber by means of a combination of a preliminary vacuum set as well as a high vacuum set comprising of cryogenic and turbo molecular pumps.

Thermal subsystem

This is made up of a series of cryogenic shrouds, covering all the inner chamber walls, visually appearing opaque. They produce a capacity homothetic to that of the inner chamber. The range of test temperatures is obtained using a thermal control unit, recycling a thermal fluid suitable for the entire range of temperatures. The cooling is achieved using thermal exchange with liquid nitrogen (LN2) and the heating by means of an exchanger with electrical resistances.

Control subsystem

Complex architecture of the control system, with various net worked PLCs, touch screen for localised control and PCs for the supervisory system and data gathering.

How does it operate?

Space simulation is carried out using different tests, each one to study different parameters of importance in the development of a new satellite. The thermal tests include cycles such as tests in a state of equilibrium or a stationary state. The thermal cycles are used to confirm the suitability of the parts and of the component as a whole whilst the thermal tests are used to test the validity of the thermal behaviour of the instrument. The tests allow its thermal expansion, heat coefficients, contraction and weak points to be determined as well as simulating and calculating the effects of solar light, low temperatures and the resulting damage to the material.

• Vacuum thermal tests: Here high vacuum conditions and temperature cycles between -180º C and + 150ºC are combined. These are usually used in the structural defect analysis in materials under the effects of thermal fatigue and degasification.
• Thermal balanced tests: Solar radiation is simulated in high vacuum conditions above the component being analysed with the aim of determining the distribution and temperature gradients established in working conditions.
• Resistance to solar radiation and infrared tests
• Mechanical tests: measurements of mechanical parameters such as tension and deformation in different states of the structural parts. For said studies photogrammetry is used amongst other types of technology

Thermal vacuum chambers are designed for the qualification and acceptance tests of spacecrafts, sub systems and equipment under environmental conditions simulating those encountered during the spacecraft's effective life in orbit.

The main parameters simulated by these chambers are:

• - Vacuum
• - Space cold sink effects