In the news today, Queensland farmer Mr James Stirton spoke of a piece of space junk he found on his property, west of Charleville, and appealed to the space community to identity it. He found the object near a track in November; it was a sphere 54 cm in diameter, weighing 20 kg, and had carbon fibre rope wrapped around it (I'm taking this from the news story online).
ABC Radio in Longreach called me for comment, and this is my working hypothesis for the moment:
The object is a Composite Overwrapped Pressure Vehicle or COPV, basically a titanium lining (titanium resists the heat of re-entry much better than aluminium, a common material in spacecraft) wrapped in fibres of carbon reinforced with epoxy resin or other materials. COPV technology has been around since 1964, and titanium pressure spheres are one of the most common types of space junk to be recognised after re-entry.
I'm assuming, since Mr Stirton found the sphere near an existing track, that its re-entry is more likely to be recent than not. It can be no later than 2007 and no earlier than 1964 (so we're talking just eight years after the launch of Sputnik 1). Certainly debris from missions such as Gemini has been found in Australia, so an early origin is not out of the question.
However, if Mr Stirton is like most people on the land, and I speak from experience having grown up on a property myself, he'd notice something like that on the side of a track pretty quickly! So let's just look at the re-entry data for November 2007, keeping in mind that of course it may be earlier.
According to the Centre for Orbital and Reentry Debris Studies, in November last year there were three predicted re-entries, all upper rocket stages:
1. The Geosynchronous Satellite Launch Vehicle (GSLV, India; launched from Sriharikota)
2. Molniya-M (Russia, launched from Plesetsk)
3. Delta II (USA, launched from Cape Canaveral)
In this age of commercial space, the COPV could have been manufactured anywhere, so examination of the actual object may not in itself be able to identify the source.
But there we go, problem solved! (Dr Space Junk is always happy to help). Mr Stirton reported that he got short shrift from NASA, and this does rather suggest that it may be from a USA military launch - perhaps this narrows it down, perhaps not.
Could I be any happier than I am right now, thinking and writing about orbital debris on a Friday night? No. I could not.