Curious story in AFP yesterday:
Full story here – Click the image above for a large view of the object.
Me thinks it is from either of these spacecraft:
The Vostok had a whole ring of spherical tanks, and maybe and old piece of space junk from one of the old service modules finally came home.
Only the main sphere is kept in re-entry, everything else is discarded.
Though given the trajectory when the service package is jettisoned, and because Vostok flight was in the early 1960’s, it seems doubtful such objects would remain in orbit, though possible if they “skipped” off the atmosphere after jettison.
Another candidate is the Soyuz, still in use today:
Under the shroud of the instrumentation support module there are a number of spherical tanks, as seen in this diagram:
UPDATE:Well I was half right, it is a tank from a Russian spacecraft. Niels shows an example from Argentina:
The tank is from a Salyut 7 – Kosmos 1686 spacecraft. It is made of titanium and was used to store helium.
Roy Spencer thinks it is a hydrazine tank:
Probably a standard interchangeable tank used on many spacecraft. Russians tend to reuse a lot of technology.