Looking at the pre-loss-of-OV-102 plans for then-future shuttle flights (at least according to the document found and scanned by @OrganicMarble and posted as part of this answer, which was drawn up [the document, not the post] while Columbia was in orbit on STS-107), one quickly notices something odd about Columbia’s planned flight manifest. Unlike Discovery, Atlantis, and Endeavour, which were booked solid with a rapid-fire sequence of ISS-component-and/or-crew-delivery flights out through 2010, Columbia had only three flights in the pipeline:
- A single ISS servicing mission (STS-118) in November 2003 (the only time the oldest orbiter was ever planned to visit the ISS);1
- A Hubble servicing mission (STS-123) in November 2004;2
- and, finally, five years and one day later, in November 2009, STS-144, a mission to retrieve the HST and bring it back to Earth (almost certainly to go on display in the Smithsonian).
The lack, on Columbia’s part, of the rapid-fire ISS flights which made up the entirety of the other three orbiters’ planned flight manifests is understandable, given that Columbia was the least-suitable orbiter, by far, for ISS flights (being the oldest, and, thus, heaviest, and, thus, most-marginal-for-high-inclination-flights-[such-as-those-to-the-ISS] orbiter, and the only one to still have its airlock mounted in the orbiter’s middeck, rather than being equipped with the payload-bay-mounted airlock-and-docking-adapter assembly needed for docking with the ISS), but I’m having trouble seeing why Columbia, not being encumbered with a heavy ISS flight schedule, couldn’t launch other payloads in the meantime,3 or do more SCIENCE!!! missions,4 unless they needed four or five years to modify Columbia for STS-144, which stretches the bounds of credibility well past the breaking point.
So why the massive gap?
1: STS-118 was eventually flown, much later, by Endeavour in August 2007.
2: Following the loss of Columbia, the fifth HST servicing mission was initially cancelled, but was later resurrected, and flown by Atlantis in May 2005, as STS-125.
3: You know, like it was already doing, and like all the other orbiters had also been doing prior to being put on ISS-assembly duty...
4: Like how Columbia had been the Spacelab workhorse orbiter in the 1990s, until NASA suddenly decided to retire the Spacelab modules.