SPACE ENVIRONMENT: VACUUM
Space is popular for its near-vacuum characteristic. However, along with this environment are potential issues with the satellite:
Out-gassing
From Earth's surface to space, pressure drops very significantly. This change of pressure can cause trapped gasses to be released, and these can re-condense to cause contamination or degradation of certain materials. While this is usually not a big issue, it can still affect delicate sensors and chips.
The concern on out-gassing is heightened when there are people involved, such as in the case of the ISS. A satellite bound for an ISS orbit stays in ISS for a certain duration (usually about a month). Since there are people living in the ISS, the released gasses can cause threat to their health.
Cold Welding
Moving parts in satellites such as deployment mechanisms entail challenges not only in the aspect of launch (vibrations and shock) but also in terms of successful operations (deployment). In vacuum, cold welding occurs – a phenomena where metal components with very little separation in between them fuse together – and impacts moving parts. A popular case of cold welding is the high-gain antenna of Galileo.
Movements such as cyclically opening and closing contacts or oscillations due to vibration can cause degradation or wear of surfaces. On the ground, surfaces kept being re-oxidized, so adhesion is not prominent. However, in vacuum, oxides are broken irreversibly, so the ‘protective layer’ goes away leading to cold welding.
Heat Transfer
Heat transfer in space is limited to radiation and conduction. Without a good thermal design, a satellite may absorb all the radiated heat to its surface and transfer them to the internal components, or drop its temperature and be dead cold. High power devices, having higher tendency to get hotter in space, can also impact its surrounding components. As such, thermal simulations and analysis are often conducted to understand and accommodate thermal effects.
Moving parts in satellites such as deployment mechanisms entail challenges not only in the aspect of launch (vibrations and shock) but also in terms of successful operations (deployment). In vacuum, cold welding occurs – a phenomena where metal components with very little separation in between them fuse together – and impacts moving parts. A popular case of cold welding is the high-gain antenna of Galileo.
Movements such as cyclically opening and closing contacts or oscillations due to vibration can cause degradation or wear of surfaces. On the ground, surfaces kept being re-oxidized, so adhesion is not prominent. However, in vacuum, oxides are broken irreversibly, so the ‘protective layer’ goes away leading to cold welding.
Heat Transfer
Heat transfer in space is limited to radiation and conduction. Without a good thermal design, a satellite may absorb all the radiated heat to its surface and transfer them to the internal components, or drop its temperature and be dead cold. High power devices, having higher tendency to get hotter in space, can also impact its surrounding components. As such, thermal simulations and analysis are often conducted to understand and accommodate thermal effects.
Another potential issue in vacuum is the arcing caused by the low pressure and the presence of high electric fields. This cause potentially damage a satellite, so mitigations should also be considered.
References:
Understanding Space: An Introduction to Astronautics, 2nd edition, Jerry Jon Sellers, McGraw Hill, USA 2004
Spacecraft Systems Engineering, 3rd edition
Assessment of Cold Welding Between Separable Contact Surfaces Due to Impact and Fretting Under Vacuum, 2009
Spacecraft Systems Engineering, 3rd edition
Assessment of Cold Welding Between Separable Contact Surfaces Due to Impact and Fretting Under Vacuum, 2009
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