What operational challenge defines when a structurally sound satellite becomes classified as long-term debris?

If it cannot be commanded to de-orbit and burn up within a specified timeframe, like 25 years

The transition from an active space object to classified long-term debris hinges on end-of-life management, particularly concerning planetary protection mandates. For an object to avoid being counted as hazardous debris for centuries or millennia, especially in high orbits, agencies often require it to de-orbit and fully disintegrate in the atmosphere within a set period, frequently cited as 25 years. If a satellite is unable to execute the necessary de-orbit burn due to system failure, even if it remains structurally sound or carries unused instruments, its inability to meet this atmospheric passage criterion firmly places it in the category of hazardous, long-term orbital debris.