Electrical equipment in aerospace vehicles has been affected by the complex and harsh environment from the moment it is put into use. It is very difficult to accurately determine the degree of the impact, but it is necessary to correctly estimate the possible impact, and the product is being developed. Strict environmental tests must be passed during the production process.
There are three environmental factors affecting aviation and spacecraft: climatic factors, mechanical factors, chemical and nuclear factors.
- Climatic factors
Climatic factors include temperature, altitude, humidity, rain, mold, salt spray, sand and dust. The working climate of the electrical equipment of aerospace vehicles not only varies widely, but also changes rapidly. When the plane is parked in the cold zone or flying at high altitude, the temperature is as low as -60℃. In summer, the temperature at the airport is around 50℃. In the troposphere below 11km, as the altitude increases, the temperature decreases. In the altitude of 1lkm to nearly 30km, the temperature is -55℃. Continue to rise to 40km, the temperature is 0 ℃, this layer is called the stratosphere. The height of 50~80km is the middle layer, and the temperature is lower than 0℃. For electrical equipment working near aero engines, the ambient temperature is higher than the atmospheric temperature. The temperature difference directly affects the operation of electrical equipment. For example, the allowable maximum output power of the generator is changed, the accuracy of the control electrical equipment is deteriorated, and even it malfunctions.
Atmospheric pressure, density, water content, and oxygen content all change with altitude. When flying at high altitudes, due to the reduced gas density, the heat dissipation conditions of the air-cooled generator become worse, allowing the output power to be significantly reduced. The decrease in water vapor content in the high-altitude atmosphere is the main factor causing the rapid wear of the brushes of the DC motor. The rapid changes in temperature and atmospheric pressure are the main causes of air leakage in sealed relays. Moist air can enter the equipment through a tortuous path, resulting in poor insulation performance. Rain and humidity have similar effects. Mildew significantly reduces the performance of insulating materials and even loses their insulating ability. Salt spray causes severe corrosion of electrical equipment used in naval aircraft. Therefore, not only should salt spray be prevented from entering the electrical equipment, but also the housing materials and surface treatment methods of electrical equipment should be strictly controlled. Sand and dust entering the motor will reduce the insulation performance and accelerate the wear of the bearing. A close-fitting shell structure and seal should be used to prevent the intrusion of sand and dust. The equipment that must open holes should pay attention to the possible impact of the intrusion of sand and dust.
The environment when a spacecraft flies in outer space is called the space flight environment, which can be divided into interplanetary space environment, earth space environment and other planetary space environments in the solar system. The interplanetary space environment is a very high vacuum environment, with continuous solar electromagnetic radiation, explosive high-energy particle radiation, stable solar wind (plasma flow) and interplanetary magnetic field, which are mainly affected by solar activities; in addition, there are High-energy charged particles and micrometeoroids from space. The geospatial environment includes the upper atmosphere, ionosphere and magnetosphere. The density of the upper atmosphere decreases as altitude increases, and is related to atmospheric temperature, which varies with seasons, locations, and solar activity. Starting from 60km from the ground, due to the electromagnetic radiation and particle radiation of the sun, atmospheric molecules ionize to form the ionosphere, and the concentration of electrons also changes at any time. The earth’s magnetic field is similar to the dipole magnetic field. The solar wind shields the earth’s magnetic field in a certain space around the earth to form the earth’s magnetosphere. The disturbance of the solar wind can cause magnetospheric storms and sub-magnetospheric storms. Magnetospheric substorms will produce high-energy plasma of 3~200keV, which can reach the orbital height of a geostationary satellite when injected into the earth. The region of high-energy charged particles with a relatively high density in the magnetosphere is called the Van Allen radiation belt. Other planetary space environments, such as the extremely thin atmosphere on Mercury, have great temperature differences between day and night, reaching 427°C during the day and -173°C at night; the surface pressure of Venus is 90 times that of the earth, the main component is carbon dioxide, and the surface temperature reaches 465-485°C. The space environment has an impact on spacecraft materials and devices. For example, high-energy charged particles can damage solar cells, optical surfaces, organic materials, and semiconductor devices. Ultraviolet radiation reduces the conversion efficiency of solar cells. In a vacuum environment, various materials will lose the dissolved gas inside and the adsorbed gas on the surface, resulting in outgassing of the material, thereby gradually reducing the weight of the material. The low-pressure environment will cause the circuit to produce gas discharge breakdown and cause damage. Under high vacuum conditions, the solid surfaces contact each other and cause adhesion and cold welding, causing the moving parts on the spacecraft to malfunction, thereby accelerating the wear of the bearings, causing the electrical contacts to jam and the solar cell wing panels to be difficult to stretch. The sand erosion of micrometeoroids on the surface of spacecraft also affects optical surfaces and solar cells.
- Mechanical factors
Vibration, shock and acceleration are the main mechanical factors that affect the operation of the equipment. The vibration frequency band produced by aero engine work is quite wide, piston engine is 5~500Hz, jet engine is as high as 2000Hz. The launch of artillery, the take-off and landing of aircraft, aerobatics, etc. will cause great acceleration. Mechanical factors cause deformation of parts, fatigue and damage of materials, breakage of wires, bounce of rotating motor brushes, and malfunction of relays. Electrical equipment must have good anti-vibration strength and anti-vibration stability to ensure that no mechanical resonance occurs. Vibration reduction and isolation measures should be taken when necessary. The weightless working environment of spacecraft electrical equipment and the requirement of aerospace vehicles to work at any position also bring complexity to the structural design of electrical equipment.
- Chemical and nuclear factors
The chemical and nuclear factors encountered by electrical equipment include harmful gases, harmful liquids, electromagnetic radiation and high-energy particle radiation.
Harmful gases such as battery gas, fuel vapor, and ozone. Harmful liquids such as fuel, hydraulic oil and lubricating oil. Electromagnetic radiation includes infrared, ultraviolet, X-ray and y-ray. High-energy particle radiation such as a-rays, β-rays, protons and neutrons. It is necessary to prevent electric sparks from contacting with explosive gas to avoid fire. The equipment itself should not explode, and external explosions should not cause damage to the equipment. Prevent harmful liquids from dripping into the equipment and causing corrosion. It is necessary to fully consider the interference and damage caused by electromagnetic radiation and high-energy particle streams to radio electronic equipment.