Why the station’s waste leaves aboard cargo ships
A space station cannot simply drop a garbage bag overboard: anything released nearby would keep orbiting and could become a collision hazard. Instead, crew members pack discarded food containers, hygiene waste, and other refuse into an uncrewed cargo vehicle after its useful supplies have been unloaded.
Returning that bulky waste to Earth would require a vehicle built to survive reentry and land safely. Many cargo craft are designed for a different job: deliver supplies, then make a controlled descent and be destroyed. Using their empty interior for rubbish makes the trip useful without requiring the station to store trash indefinitely or send it home in a crewed spacecraft.
The vehicle—not a station incinerator—provides the heat
As the loaded craft plunges into the atmosphere, it meets air at enormous speed. Compression and friction heat the vehicle’s exterior; the craft breaks apart and its materials, including the packed waste, are largely consumed in the resulting high-temperature descent. The rubbish is not burned inside the station, and the station does not need a furnace capable of operating in orbit.
Mission planners aim the descent toward a remote ocean area so that any fragments that survive the heating are unlikely to reach populated places. The disposal method therefore depends on both a spacecraft built to be expendable and a carefully chosen reentry path. The same vehicle that ferries supplies up can carry waste away, with Earth’s atmosphere doing the final work.
