A. Apologies if this is addressed previously on TrekBBS. B. I usually hate in-universe conjecture, but was watching an ep last night with now you see 'em, now you don't, spheres at the rears of the nacelles. So I thought I'd ask if the contuinity-crazed among us have any explanations. I have none other than modelmakers or Jeffries thought they looked better (debatable). But do YOU have any conjecture as to what they are and why they sem to be so jettisonable and replacable?