I want to know how many have been to space (they don't have to have returned.)
Actual Minifigures In Space
There have been a number of videos posted from the ISS mission, where we can clearly see one of the astronauts (Satoshi Furukawa) on the station holding a model with some minifigures:
On the Gallery Pages they list out "Working and living in space - This is the LEGO models shown in the videos"
In the shots there are there are at least 7, if not 8 minifigs (assuming that each hair and face is part of a complete minifig, rather than having the bodies reused for the shots):
This appears to be the first time actual articulated minifigs have officially gone to space.
A Romanian named Oaida Raul sent the Lego Shuttle [bs:3367] up on a weather balloon to "the edge of space" on 31 December 2011, but hasn't released actual figures of the altitude reached:
Two Canadian Students sent a Minifigure up to the stratosphere in January 2012, high enough to see the curvature of the earth, which can be seen reported on the Toronto Star's pages:
Before then the closest thing to a minifig officially sent to space are the three custom built aluminium Minifigure statues that went up on the JUNO space craft this year:
This wired article concludes:
LEGOSpace.com's insistence on not supporting deep-linking fails me, but if you go to the Education Blog and scroll to Thursday, August 04, 2011
Pictures of Minifigures
Prior to these two missions, previous missions have been promoted as sending Minifigures to space when in fact what they actually contained were pictures of minifigures:
When in reality what happened was:
Since 2010 there have been Lego sets on the ISS but no mention of minifigs officially manning the outpost.
according to this NASA-article: at least 3 - the minifigs of galileo galilei, the god jupiter and his wife juno.
Actually, I think the correct answer to that is "none".
So this leaves us with the three custom-built aluminium minifigs of the JUNO spacecraft, but considering these as minifigs is a bit of a stretch. To me, these are but statues of minifigs, not real ones. They aren't even yellow!