Atlantis is roughly halfway home to Kennedy Space Center. The shuttle orbiter and its carrier 747 aircraft landed at Lackland Air Force Base in San Antonio, Texas, about 10:10 a.m. EDT.
The third leg of the ferry flight is expected to depart Lackland around noon Eastern time for Columbus Air Force Base in Mississippi, a two-hour trip. Columbus is about 60 miles south of Tupelo, Miss., and 130 miles west of Birmingham, Ala.So far, NASA says a return to Kennedy Space Center is expected no earlier than 6 p.m.
Keep refreshing this page for the latest flight plans. And here's a couple more ways to track the journey:
-- Click the aircraft's tail number here: NASA911.
-- Sign up for text alerts using the black box on the right side of this page.
San Antonio was the second stop in Atlantis' cross-country trip home from Edwards Air Force Base in California, which began Monday.
The first stop was in west Texas, at Biggs Army Airfield in El Paso. The piggyback spacecraft and jumbo jet left there around 8:40 a.m. EDT. today. The journey's first two legs totaled about 1,200 miles, or about half the distance between Edwards and KSC, depending on the route taken.
Ever wonder how NASA picks its layover locations for the orbiter and Shuttle Carrier Aircraft, or SCA?
Don McCormack, ferry operations manager, offered this interesting explanation on a NASA blog:
First of all, we start with a list of airfields (about 20), primarily military bases that are on an approved list of airfields to be used during a ferry mission.
Each of these bases has agreed to accommodate an SCA/Orbiter landing and each has personnel trained to do so.
There is a very specific set of requirements that must be satisfied by each base. These requirements include providing security for the Orbiter, providing a safe place to park an Orbiter that still has highly toxic commodities on board, has ground support equipment that can reach the Orbiter on top of the SCA if it is required, and not least of all, is willing to accept the disruption to normal operations that is caused when we arrive. In addition, if the ferry stop is overnight, the base also arranges for transportation and lodging of the ferry team.
Second, 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. So, the SCA/Orbiter route is largely driven by the bases that are available and the weather en route.
In addition, the SCA 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.
Finally, hardware issues can also impact our route selection by causing delays. During delays, the weather changes and often times so does the route.
So, there are many factors that drive the route we take with weather being the big one. And as everyone can understand, predicting the weather is not an exact science. That's the biggest reason that it's often the morning of the flight before we can say, with certainty, where we're going.
IMAGE: The space shuttle Atlantis rode piggyback Monday atop a modified 747 as they flew over Las Cruces, N.M., from Edwards Air Force Base in California. Credit: AP Photo/Las Cruces Sun-News, Norm Dettlaff. Maps of ferry flight destinations from FlightAware.
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