Researchers say parts of the Moon may be set aside as graveyards for defunct satellites.
Lunar orbits are expected to grow crowded as space agencies expand Moon missions.
Without an atmosphere, old satellites cannot burn up like they do on Earth.
Most will need to be deliberately crash-landed on the surface.
Scientists warn random impacts could damage instruments and historic sites.
High-speed collisions also create dust and vibrations across the lunar surface.
International agencies are proposing designated impact zones or deep craters.
Supporters say this would protect important regions and limit debris spread.
