A search of the archive turned up nada on this subject.
Why does the space shuttle orbit the earth with its top-side facing the earth? Is it possible to turn it over?
My guess: Until they’re getting ready to land, there’s no reason to maintain any particular attitude in relation to the Earth. Perhaps they want the heatshields sunward when they come to the dayside.
The sun rises and sets on the shuttle approx. every 90 minutes. That causes many hundred degree temp shifts in a very short period of time. The bottom of the shuttle has the thickest heat proofing. So, the Space Shuttle isn’t top side towards Earth, it’s bottom side towards sun. Also, the radiators are in the bay doors, and facing them towards the Earth is much more efficient than any other direction. That’s why they open the bay doors soon after ‘parking.’
–Tim
Plus there aren’t any down-facing windows on the shuttle. If the crew wants to see where they are at the moment, they need only look out at the earth “above” them. (I doubt they have any technical reason to do this, but it might make them feel better.)
(It sure beats Roddenberry’s Enterprise always flying around planets sideways.)
This is just one of the shuttle’s orientations. This Shuttle orientation is called “-ZLV”, which means the minus z axis of the Space Shuttle (which goes through the top of the Shuttle) is pointed in the “local vertical” (LV) direction.
One reason for this is the EarhKAM mounted on the top of the shuttle. The EarthKAM camera will only be taking pictures of the Earth when the Shuttle is in this orientation…upside down.
Actually, according to mission control, the shuttle normally flies upside down so that the radar equipoment on board can look at Earth (presumably for mapping, navigation, and/or communications purposes). The information can be found here, most of the way down the page:
http://spaceflight.nasa.gov/feedback/expert/answer/MCC/sts-99/02_20_13_35_24.html
Homer, I’m almost certain what you say about the bay doors being open is correct, but the heat-proofing on the bottom of the shuttle would not protect it from the sun’s heat; it’s made to protect from frictional (conductive) heat in the atmosphere, not from radiative heat as much. Any surface that helps to reflect away the heat (which I assume both top and bottom will do) should keep down the total heat in the shuttle.
(Of course, the unstated reason is simple, if sentimental: it’s hard for the astronauts to look at home when the windows are pointing toward space. I would want to be looking homeward. 
LL
Just a nit, Laz, but I think there is some benefit to having your best insulated side toward the sun. No, the thermal tiles won’t keep the shuttle cool forever, but they will slow down the transfer of heat to/from the rest of the ship.
So it’s a little added benefit to the “upside-down” orientation.
Okay, so I looked smart at the time, but I was basically quoting this month’s issue of Popular Science verbatim.
This same exact question is in their FYI section this month.
Heh heh.
–Tim
Hmm… reminds me of the old Apollo days, they used to slowly rotate the ship on its longitudinal axis, to evenly distribute heat absorption. The sides of the ship would spend equal time in light (heat) and darkness (cooling). They called it “the rotisserie method.”