Cool read indeed. The pathfinder test of rotating the orbiter to the right angle is interesting. They have a test load of some concrete slabs on there, but that can't be equal to the weight of the real orbiter... or can it?
The density of normal concrete is 2400 kg/m3(150 lb/ft3) and the density of lightweight concrete is 1750 kg/m3(109lb/ft3) as per the Engineering Handbook. New York: CRC Press, 1996.
On page Atlantis weight is given as 167,219lbs with a loads of 125,023lbs on the 2 aft attach points and 42,193lbs on the front attach point in the X-axis. With a load distribution from front to aft of: 25.23%/74.77%.
I'm not sure if those 2 large cement slabs and the associated ironwork of the pathfinder rig, would equate to the weight of Atlantis or not. The document doesn't spell out the pathfinder rig weight(so far as I saw). I will defer any estimation of the combined weight of the pathfinder's ironwork and concrete slabs to other NSF'ers that have greater experience in such estimations.
A ditty on Orbiter Vehicle weights:
Atlantis benefited from lessons learned in the construction and testing of Enterprise, Columbia and Challenger. At rollout, its weight was some 6,974 pounds less than Columbia. The experience gained during the Orbiter assembly process also enabled Atlantis to be completed with a 49.5 percent reduction in man hours (compared to Columbia). Much of this decrease can be attributed to the greater use of thermal protection blankets on the upper orbiter body instead of tiles. During the construction of Discovery and Atlantis, NASA opted to have the various contractors manufacture a set of 'structural spares' to facilitate the repair of an Orbiter if one was damaged during an accident. This contract was valued at $389 million and consisted of a spare aft-fuselage, mid-fuselage, forward fuselage halves, vertical tail and rudder, wings, elevons and a body flap. These spares were later assembled into the orbiter Endeavour. Atlantis was shipped to California to undergo upgrades and modifications. These modifications include a drag chute, new plumbing lines that configure the orbiter for extended duration, more than 800 new heat protection tiles and blankets and new insulation for the main landing gear doors, structural mods to the Atlantis airframe. Altogether, 165 modifications were made to Atlantis over the 20 months it spent in Palmdale, California.
Empty Weight was 155,400 lbs at rollout and 175,111 lbs with main engines installed. This was about 2,889 pounds lighter than Columbia OV-101 Enterprise
149,574lbs-150,876lbs as equipped for CIFT/ALT* OV-102-Columbia
-Empty Weight was 158,289 lbs at rollout and 178,000 lbs with main engines installedOV-103 Discovery
At rollout, it weighed 6,870 pounds less than Columbia(calculated=151,419lbs.171130 with SSME's).OV-104 Atlantis
151,315 lbs at rollout and 171,000 lbs with main engines installed. OV-105-Endeavour
- Empty Weight was 151,205 lbs at rollout and 172,000 lbs with main engines installed.
* Only weight data located was from the CIFT(Captive Inert Flight Tests)and ALT(Approach Landing Tests) from Jun. 18, 1977 through Oct. 26, 1977. Enterprise's weigh ranged from a low of149,574 lbs upon landing ALT-1-Aug 12, 1977 and ALT-2-Sept 13, 1977 to a high recorded landing weight of 150,876 lbs after the completion of ALT-4 on Oct. 12, 1977. http://upload.wikimedia.org/wikipedia/commons/5/5f/Enterprise_Diary.pdf