NASA is monitoring a piece of debris from a defunct Russian satellite that could make a close approach tomorrow to the International Space Station and space shuttle Atlantis. This sort of thing does happen pretty often, but this space encounter is tinged with a special degree of concern because it’s the last time garbage might imperil a shuttle.

Mission managers are studying the debris to determine its size and trajectory, according to

Space junk threatens the station fairly often — two weeks ago, a big piece of junk narrowly missed the station and forced the six-member crew to scramble into a Soyuz rocket for possible escape. Managers had practically zero warning of that piece of space junk, which officials later said was probably the largest object to ever approach the station.

This most recent piece of junk is from the Cold War era satellite COSMOS 375, which was deliberately destroyed on Oct. 30, 1970, shortly after its launch. COSMOS was part of a Russian program to repel space-based attacks.

It is one of more than 500,000 pieces of debris in Earth’s orbit that are tracked by the U.S. Strategic Command. NASA and others have proposed a wide range of solutions for clearing the free-flying objects, but none have been attempted yet.