Morning and evening launches were common before the arrival of the International Space Station. Now, however, the shuttle must be in-plane or "catch up" with the the space station, which means it must launch within five minutes of it passing overhead. Also, the shuttle must now launch during the day because of visual launch requirements for video review. Here is a primer on weather requirements for a shuttle launch:
- After tanking (filling of external fuel tank), countdown will stop if temperature exceeds 99 degrees for more than 30 consecutive minutes.
Wind for tanking
- Will not begin if winds exceed 48 mph for three hours.
Wind for launch
- East northeast and north northwest winds cannot exceed 39 miles per hour.
- South southeast & west southwest winds cannot exceed 23 miles per hour.
- Upper level wind speeds must conform to a wind profile determined 30 minutes before launch and confirmed by several weather balloon launches from Cape Canaveral Air Force Station.
- None at launch site or within flight path.
Lightning for tanking
- Cannot begin if lightning is observed — or will occur over the next three hours — within 5.75 miles from launch pad.
Lightning for launch
- No lightning within 11.5 miles from the pad or planned flight path within 15 minutes before launch.
- No clouds within 11.5 miles of the launch pad. If clouds are present, they may not have been associated with thunderstorms within three hours. Clouds must be thin, and be less than or equal to 25 percent of the sky cover.
- Shuttle may not be launched through cloud layer more than 4,500 feet thick.
- Shuttle may not be launched through any type of cloud layer, which extends to an altitude where temperatures are between 32 degrees and -4 degrees Fahrenheit if this cloud is associated with disturbed (unsettled) weather within 5.75 miles of launch pad.
- Shuttle may not be launched through an opaque cloud, which has become detached from a thunderstorm within three hours before launch or within 5.75 miles of debris clouds that show radar return of light rain.
- Shuttle may not be launched through cumulous clouds with tops extending past 10,000 feet or within 5.75 miles of cloud tops extending into 18,000 feet or above.
- Shuttle cannot be launched through cumulous clouds within 11.5 miles that extend past 23,000 feet or the nearest edge of any cumulonimbus or thunderstorm cloud and associated anvil.
SOURCE: Spaceflight Meteorology Group-Johnson Space Center-Houston Kennedy Space Center