Thanks to prolonged weather issues in Florida, Space Shuttle Atlantis landed about a week ago at Edwards AFB in California, rather than its preferred location at Kennedy Space Center. In order to get the shuttle back to Florida, a ferry flight is required. Those ferry flights are taking place now. The process is very interesting and suffice it to say, weather plays the biggest role in getting the shuttle back to FL. It actually takes 4 flights and a couple of days to get the shuttle back to KSC on the back of a modified Boeing 747 used by NASA for just this purpose. The shuttle will be making a stop pretty close to the Mid-South on it's return trip - landing at Columbus AFB, Columbus, MS, shortly after 1:30pm this afternoon. Posted on a NASA Ferry Flight blog, here's a portion of what Ferry Ops Manager Don McCormack had to say about weather impacts to the flight plan:
...the Orbiter has a very restrictive set of atmospheric/weather requirements. We must, at all cost, avoid rain in flight. Flying through rain will damage the Orbiter's thermal protection system and result in a costly and long delay before the Orbiter's next flight. We also try very hard to avoid exposing the Orbiter to severe weather on the ground, which could also cause damage. The Orbiter cannot be exposed to temperatures less than 15 F either in flight or on the ground and the Orbiter cannot fly at an altitude where the pressure is less than 8 psia. These requirements typically limit our altitude to an 11,000 to 16,000 ft range [typically, commercial jets cruise at 30,000-39,000 feet]. So, the SCA/Orbiter route is largely driven by the bases that are available and the weather en route.
In addition, the SCA [Shuttle Carrier Aircraft, the modified 747] has a very limited range when ferrying the Orbiter. That range depends primarily on the weight of the Orbiter and the air temperature. Winds are also a factor. The heavier the Orbiter is, the less fuel we can load into the SCA, pure and simple. Without going into a lot of technical details, hotter air is less dense air and that too significantly impacts the performance of the aircraft.