So you want to land a space shuttle at the Kennedy Space Center? How tough can that be?
NASA has extremely strict rules about the weather conditions for landing a space shuttle.
Mission controllers must project forward for 90 minutes, the time from deorbit burn to landing.
Mission Control cannot give the shuttle "go" for deorbit if the cloud cover at the landing site is below 8,000 feet and exceeds 25 percent coverage.
There can be no lightning, thunderstorms or precipitation within 30 nautical miles of the shuttle landing facility. Crosswinds cannot exceed 15 knots, head winds cannot exceed 25 knots, and tailwinds cannot exceed 10 knots.
That's a pretty tough demand in Florida, where afternoon thunderstorms are the norm rather than the exception during the summer.
Flight director Norm Knight, who leads the flight team for Atlantis' return, said, "If I can get them home today, I will get them home."
Eleven shuttle flights have been extended by bad weather, for scientific exploration and for other reasons. The record holder for delays is STS-113, a flight by the Space Shuttle Endeavor in December 2002, which stayed four days longer than planned because of bad weather at the Kennedy Space Center. Mission Control wistfully played "I'll be home for Christmas" as a wake up song for the crew of that mission one morning.
If the shuttle lands at Edwards Air Force Base in California, that means a week's delay in processing the orbiter for its next flight, and an additional cost of $1.7 million for transportation and additional staffing.
Atlantis is scheduled to fly STS-122 in early December and has no wiggle room. It takes several months to get a mission ready. That flight has an eight-day launch window.
When it is time to return to Earth, the orbiter rotates tail-first to fire its orbital maneuvering system engines. This firing is called the deorbit burn. Terminal ignition occurs usually about an hour before landing. The burn lasts three to four minutes and slows the shuttle by about 200 miles an hour -- not much, compared with its total speed of 17,500 mph but just enough to lower it from orbit.
Daylight is not required for landing. At the end of the mission, the shuttle uses Earth's atmosphere as a brake to decelerate from orbital velocity to a safe landing at 220 mph, dissipating all the energy it gained on its way into orbit.
This flight, STS-117, is coming home from a successful 14-day mission
The crew installed a new set of solar panels -- which the Russians believe prompted last week's computer failure, though NASA says there is no proof of that.
Atlantis' crew carried out four spacewalks, including a spectacular unrehearsed fix of a torn piece of insulation near the shuttle's tail. Atlantis also provided stability control for the ISS when the Russian computers failed, causing NASA to consider ordering the three-member crew of the space station to return to Earth, a drastic move that would have had serious consequences for the space program. The station computers came back online in time to prevent that, though engineers are still trying to figure out why they crashed in the first place.
The next flight is STS-118, which is scheduled to launch August 9 and is another flight to finish construction of the space station. Its crew includes Barbara Morgan, the first teacher to make it into space.