On August 19, International Space Station (ISS) astronaut Chris Cassidy reported an unidentified object floating past the window. The last time an ISS crewmember spotted something unusual out the window, it was small frozen flakes from a serious ammonia leak that spawned rapid mobilization of an unscheduled extravehicular activity. This time the object was much larger: the cover from an antenna, broken off the Zvezda module, lazily floating past the docked Progress cargo vessel.

Space debris the size of the cover (exact size unknown, but visually quite substantial) would normally initiate contingency measures to avoid a collision. However, the danger of space debris is rooted in its velocity, which in low Earth orbit is around 7 km/s – much faster than a speeding bullet. Objects released from ISS, however, start with the same velocity as the station, therefore their velocity relative to the station is quite low and not particularly dangerous.

The cover could pose more of a problem as it drifts away from the station, potentially crossing paths with other spacecraft that could be endangered. It will not remain a problem for long, however. Due to ISS’ low altitude orbit, atmospheric drag will sooner or later pull the cover out of orbit and it will burn up on reentry. For a comparable situation, one can look at the November 2008 EVA in which astronaut Heidemarie Stefanyshyn-Piper lost hold of a 14 kg tool bag. The bag drifted away and ultimately reentered the atmosphere the following August. It was monitored the entire time by the US Air Force Joint Operation Space Center (JSpOC) and was not observed to collide with anything.

There is no word at this time as to whether the Zvezda antenna requires repairs or what caused the cover to detach from the station.

Below is a video of the cover drifting past Cassidy’s window: