Magnets have magnetic curves. When the magnet generates thrust, there must be unused magnetic curves gathered around it. The collision of these magnetic curves will generate excess heat. The magnet will lose its magnetism when the Curie temperature is exceeded. I want it to generate enough thrust. The power of the spacecraft requires very huge magnets. Because the hardness of the magnets that can be used in the universe is very brittle, it is very difficult to produce such a large magnet. Even if it is produced, it is very difficult to install such a large magnet.
Nuclear energy is A clean energy source, but its continuous use requires a large amount of coolant. The universe cannot obtain this type of coolant. Therefore, the current technology cannot use it in spacecraft.
The use of solar energy seems feasible, but when it cannot enter sunlight. , energy cannot be obtained,, and storage of solar energy requires huge batteries, which will increase the weight of the spacecraft, so solar energy is generally used as an auxiliary energy source to maintain the operation of electronic instruments in the universe.