An ordinary motor will face a series of severe challenges in a vacuum environment. Without special design and treatment, it is likely to fail within a short period. Simply put, an ordinary motor cannot be used directly in a vacuum environment.
The main reasons and potential consequences are as follows:
Heat Dissipation Problem (The Most Critical Issue)
In Earth's Atmosphere: The motor generates heat during operation. Ordinary motors dissipate heat primarily through three methods:
Convection: Surrounding air flow carries heat away (this is the primary method).
Conduction: Heat is transferred to the mounting structure via the motor base.
Radiation: Heat is radiated outward as infrared radiation (accounts for a very small proportion at normal temperatures).
In a Vacuum: There is no air, so convective heat transfer completely fails. Heat dissipation can only rely on conduction and radiation.
Conduction becomes crucial but requires extremely large-area, tight contact between the motor and the mounting structure, along with the use of highly thermally conductive materials (e.g., thermal grease). This is very difficult to achieve perfectly in engineering.
Radiation is very inefficient at low temperatures.
Consequence: The motor will overheat drastically, causing internal temperatures to far exceed design limits. This can lead to melting of the insulation, demagnetization of permanent magnets, evaporation or solidification of bearing lubricant, and ultimately result in motor burnout or seizure.
Lubrication Problem
Ordinary Lubricants: Most greases or lubricating oils used in ordinary motors will, in a vacuum environment:
Rapidly Evaporate/Sublime: The boiling point is extremely low in a vacuum, causing liquid lubricants to rapidly turn into gas and evaporate, leading to dry running of the bearings.
Contaminate the Environment: The evaporated oil vapor can condense on nearby precision equipment, such as optical lenses or sensor surfaces, causing permanent contamination and functional failure. This is absolutely unacceptable for spacecraft.
Consequence: The bearings wear out or seize due to lack of lubrication in a short time, causing the motor to stop rotating.
Corona Discharge and Arcing (Especially Dangerous for High-Voltage Motors)
In Earth's Atmosphere: Air has a certain dielectric strength, preventing discharge between electrodes below a certain voltage.
In a Vacuum: Vacuum itself is an excellent insulator, but its insulating capability is closely related to electrode material and surface finish. In a vacuum, insulation between electrodes no longer relies on a medium but on the vacuum itself.
The problem is: At high voltages, motor windings—especially at points with minor insulation defects or sharp points—can cause residual gas molecules to ionize, easily leading to corona discharge or vacuum arcing.
Consequence: Continuous discharge can severely erode and damage the insulation material, eventually causing winding short circuits and motor failure.
Material Outgassing
Problem: Many materials used in the manufacturing of ordinary motors (such as plastics, paints, adhesives, ordinary wire insulation, etc.) absorb and dissolve gas molecules from the air. In a vacuum environment, these gases are slowly released, a process known as "outgassing."
Consequence: Similar to lubricant evaporation, these released gases can contaminate the entire vacuum system, which is fatal for scientific experiments requiring ultra-high vacuum or for space telescopes.
So, What Motors Are Used in Vacuum Environments?
To solve the above problems, engineers have developed motors specifically designed for vacuum environments. The main solutions include:
Special Heat Dissipation Design:
Strengthen conduction paths using highly thermally conductive metals (like copper) for components or heat sinks.
Design dedicated connection cooling plates with internal coolant to forcibly remove heat.
Increase the motor's operating temperature class using higher-grade insulation materials (e.g., Class H, Class C).
Vacuum Lubrication Technology:
Use solid lubricants such as molybdenum disulfide, PTFE, or graphite.
Use full ceramic bearings or specially treated metal bearings.
Vacuum-Compatible Materials and Insulation:
Select all structural materials with low outgassing rates.
Use special vacuum-compatible impregnating varnishes and potting materials for windings.
For high-voltage motors, special consideration must be given to insulation structure and processes to prevent corona discharge.
Therefore, if you need to use a motor in a vacuum environment (such as in space equipment, vacuum coating machines, particle accelerators, etc.), you must select a vacuum motor specifically designed and certified for vacuum use, and cannot directly use an ordinary motor.
