To end this discussion we would need:
The weight of the or-biter with e.g. a full tank in the payload bay.
(Or how many fuel the SRB's plus SSME with full external tank can lift into orbit.)
The orbital speed of the shuttle (8000 m/s)
The necessary speed for TLI.
The thrust of the OMS.
(Then we can calculate how long the OMS must fire.)
How much fuel per second the OMS burns.
(Then we can calculate weight and remaining fuel after TLI.)
The orbital speed of the lunar orbit.
(Then we can calculate weight and remaining fuel in lunar orbit.)
The necessary speed for TEI.
(Then we can calculate weight and remaining fuel after TEI.)
Finally we can calculate how much fuel it would take to reduce speed before reentry.
Should we have still fuel in the tanks after this calculation we can use this weight for a useful payload in lunar orbit.
Should this weight be only the mass of a camera to take pictures, the whole thing would be more theoretical than practical.
Should this weight be negative we could avoid lunar orbit and do an Apollo 13 style flight. This should need less fuel.
Should the weight of the remaining fuel after an Apollo 13 style flight be still negative we could take one of the "Shuttle" retiring places from the list (theoretical).
/Armin
I did not calculate this, but when I compare the weight of the empty or-biter with the weight of an Apollo capsule and the Saturn V liftoff weight I guess it is not possible.