Space environment threats for spacecrafts computer systems

space with sign "DANGER"

Apart from space radiation, space environment makes other threats for spacecraft’s computer systems. Our bodies are accommodated to The Earths environment, the same is with tools and devices invented by mankind, also computers. It is not sure that our toys will work the same in the foreign environment.

Vacuum environment

In space, devices work in an environment with very low pressure – vacuum environment. The elements of the electric circuit of computer systems have to work similar during start or deorbitation (in atmosphere pressure) and during operating in open space. Coils, for example, discharge differently in the atmosphere, than in a vacuum. Capacitors have to have very good sealed dielectric to prevent a change of their capacity. If the circuit contains trapped gas (e.g. inside inaccurate solder), the system can be damaged in a vacuum. Plastic elements may gas-out under vacuum, it may be important for integrated circuit encapsulated in plastic.

Vacuum discharge

In The XVIII century, William Watson observed discharge of electrified body placed in a vacuum environment( actually in very rare gas ). Together with the discharge process, the emission of light was observed. The phenomenon was named “vacuum discharge”. It happens in pressure between 103 and 10-1 Pa and may cause effects on electrical instruments in ascending or returning phase of spacecraft vessel mission. When the vacuum reaches 10-2 Pa, then corona discharge is produced which can damage the spacecraft’s power supply systems.

Thermal environment

Elements of spacecraft’s computer systems usually are designed to work in the thermal environment of The Earth, in range of temperature -15oC – 50oC. Work of semiconductors, capacitors, resistors depends on temperature, they are used in space but designed for The Earth environment. Thermal design has to ensure that spacecraft’s equipment works in an incorrect range of temperature.

Heating and cooling

Depends on its position spacecraft are heating or cooling. When the vessel is on the sunny part of its orbit then it becomes hot, opposite when it is in dark (e.g in planets shadow) it becomes cold, but the temperature of equipment must be stabilized in some range in both cases. Because of the vacuum environment, thermal convection does not happen, and radiation heating is the only way to control spacecraft temperature. Space vessels take thermal energy directly from The Sun, from the radiation of nearby planet and from The Sun radiation reflected from a nearby planet. Spacecrafts release energy by radiation to deep space. The balance between taken and released energy is decisive for vessel temperature.

Space thermal environment
Space thermal environment, Peter Fortescue, Graham Swinerd, John Stark (2011) Spacecraft Systems Engineering 4th Edition.

Atomic oxygen

On LEO orbits density of the atmosphere is very low, but not insignificant. The dominant species on an altitude between 300km-900km is either atomic oxygen or helium. Oxygen is chemical very active, moreover, its relative speed to the vessel is big what makes the aggressive environment and cause spacecraft’s surface erosion, stable formations of oxide, scattering or reflection and chemiluminescent glow. All these effects change the properties of materials and may irreversibly change their optical, mechanical, thermal or electrical characteristics.

space shuttle glow
Effect of interaction between atomic oxygen and spacecraft surface – chemiluminescent glow
STS-062 – Shuttle glow following Columbia from U.S. National Archives’s

Space debris

Meteoroids, micro-meteoroids and ‘space junks’ travel in the area of spacecraft operations. The mass of these elements varies from partial parts of a gram (micro-meteoroids, the dust of aluminium) to millions of tons in case of large meteoroids. Debris collision with spacecraft may have dramatic consequences, even very small particles may cause large damage due to their very high speed. For example, is assumed that particles with size greater than 1mm are a threat for International Space Station. If the probability of collision with ISS is less than one to 10000, then ISS is moved. Smaller particles (mass 10-3g – 10-9g) can penetrate protective coatings, may damage solar arrays, sensitive optical surface and detectors.

Kessler syndrom

In 1978 Donald J. Kessler has publicized article “Collision Frequency of Artificial Satellites: The Creation of a Debris Belt”. The author has predicted that collisions between catalogued space debris will produce a large amount of new debris. Some parts of the new debris would be large enough to be catalogued and would collide again, whats resulting in an exponential growth in the collision rate and debris population. This positive feedback loop in which debris-generating collisions would rendering parts of Earth orbit unusable. Nowadays planned LEO satellite constellations will contain a lot of spacecrafts: Starlink 12000, OneWeb 650, Blue Origin 32361 Such a huge number of satellites will drastically increase the probability of collisions and the fulfilment of the Kessler prophecy.

Summarize

Computer systems and they peripherals may be overheated, overcooled, damaged by uncontrolled electric effects or physically destroyed by impact with external objects. It is important to allow to work system even if some of its parts failures of even completely destroyed.

  1. from Wikipedia

References

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