Any reason(s) in particular that you're certain that Horcrux-creation would have detrimental effects significant enough that Voldemort would create only one, maximum? I assume it must have some detrimental effects, because otherwise, given a Rational Dark Lord armed with a time-turner, we'd be looking at Horcruxes proliferating as fast as he can make them. Tens or hundreds or thousands of horcruxes, one on every muggle device launched into or out of orbit, if he could manage it.

I notice that you seem to take for granted the existence of "souls" in MoR, which is far from certain. Actually I would rate the possibility as decidedly uncertain, since if souls and their attendant afterlife existed, it'd put quite a dent in the entire motivation for Harry's "conquer death and achieve immortality for everyone" program. And as prasannak noted, Harry has raised the alternate hypothesis that horcrux creation is less soul-fragmentation and more mind-uploading: "Maybe he found some way of duplicating the power of the Resurrection Stone, only he loaded it in advance with a complete copy of his brain state. Or something like that." (Chapter 39)

edit:

And I just remembered a brief exchange between Quirrell and Harry in chapter 46, which (to me, at least) hints at the existence of more than one horcrux. Quirrell asks Harry, hypothetically speaking, where he would choose to "lose something where no one would ever find it again." (I assumed he was being all ironic again and was talking about horcruxes.) Harry reeled off a list of about 5 possible hiding places, to which Quirrell responds "All excellent suggestions... But tell me, Mr. Potter, why those exact five? ...There is an interesting pattern to them.... One might say it sounds like something of a riddle." (Riddle? Irony overload.)

It just dawned on me that those 5 hiding places could only be clues to a riddle (the riddle of where Voldemort chose to hide all his horcruxes) if they didn't encompass the complete set of all horcrux hiding places, meaning that there are probably more than 5. Additionally, those 5 hiding places would only be good "clues" if they were themselves correct hiding places, from which further hiding places could be extrapolated based on some sort of shared similarity.