That was a great read, thank you! It has this tidbit:
> STS-93 carried the heaviest payload the shuttle ever launched; the Chandra X-ray observatory (formerly known as the Advanced X-ray Astronomy Facility or AXAF) and it IUS booster.
Why would such a heavy payload have been launched on Columbia, which famously was the heaviest orbiter and thus never visited the ISS?
Columbia had slightly more space in the payload bay due to her airlock being internal and not taking up cargo bay space. Other shuttles had to have an external airlock fitted in the payload bay as needed which made them unable to fit AXAF. IIRC the airlock requirement was as a back-up in case there were deployment issues.
Again, if my memory serves, Columbia's internal airlock however is what made it unable to dock with the ISS. It was the only shuttle that retained that configuration. It's also part of the reason it was heavier, along with it being the initial airframe and built heavier than the subsequent ones.
OV-099 Challenger was renumbered from STA-099 (Structural Test Article), it was not originally built to be flown.
OV-099 as a number actually doesn't make sense, because the numbering scheme (OV-XYY) in full reads: Orbiter Vehicle, Series X, Vehicle YY.
Series 1 is the original (and only) line of flightworthy Space Shuttle Orbiters including Enterprise, Vehicle number is given in sequence within a series starting from 01.
So OV-101 (Enterprise's) reads Orbiter Vehicle, Series 1, Vehicle 01. OV-102 (Columbia's) reads likewise Vehicle 02, and so on.
OV-099 (Challenger's) reads Orbiter Vehicle, Series 0, Vehicle 99 which makes absolutely no sense.
But in the context of this thread we're discussing how heavy the airframe is. Wouldn't OV-99 be lacking the airframe lightening enhancements that OV-103 and later enjoyed?
If we really want to get particular there was OV-098, Pathfinder, though being made of wood it obviously was never meant for more than fitment testing. Oddly though it did get the OV designation, not the STA designation.
Mockups that were particularly detailed and well-preserved (OV-098 Pathfinder) or appreciated (OV-095 SAIL) were given honorary Orbiter Vehicle designations.
