ET asked:

>The thing I don't understand is the presumed proximity to Earth in
>both orbital radius and plane.

The assumptions are that the depleted decelleration stage is something that is big, heavily eroded by micrometeors and highly radioactive. The command vehicle (payload) would contain a machine intelligence that would prefer not to be near something that was pouring out radiation. There is the additional assumption that the command vehicle has a modest propulsion system, e.g. chemical or low thrust electric. This means that the decelleration stage can't be too far away.

>Also, how old would you guess an object would be. If it's old
>enough how could one tell the difference?

It would be millions of years old and so beat up that you could not tell it was an artifact until you got a very close look at it. It probably would have been originally shaped like a big umbrella (a paraboloid) or a cone but would now look like a big ball of shredded metal (the comparison is what the Titanic looked like before it sank and what it looks like now). The decelleration stage would probably be made out of high carbon steel (iron and carbon are easy to find in space).

>Mathilde could've been a masive artifact that had accumulated
>debris and regolith and we'd never be the wiser without some
>serious excavation.

I don't think the decelleration stage would accumulate regolith because it wouldn't have much gravity. It's surface would be shredded metal. It would have the spectral signature of an iron asteroid (they're common). It might be a bit shinier than your run-of-the-mill iron-nickle asteroid and have a higher spin rate.

>Do you have anything written up on this idea?

No, I haven't. I could write up a little note about it for the "Journal of the British Interplanetary Society" (JBIS). However doing so would be pointless since the idea would get lost in the background noise (this is becoming true with most aerospace related papers). Again, the big problem with using a JIMO type vehicle for this search is NOT letting people know that it is a hunt for ET. Lots of people would oppose a garden variety NEO search, prefering the money spent on their own pet projects. Once the word got out that the hidden agenda was "searching for ET", the opponents would use the "giggle factor" to zero out funding. The project would have to be sold as an Earth defense scheme against asteroid collision.

Gary