NASA's Weather Criteria
		-for Space Shuttle Launch and End of Mission Landing The following article is an in-depth look at the weather criteria for launching and landing Space Shuttles and expendable rockets. It is broken into four categories: Launch Criteria Contingency Flight Rules KSC End of Mission Landing Flight Rules Weather Instrumentation The launch weather guidelines involving the Space Shuttle and expendable rockets are similar in many areas, but a distinction is made for the individual characteristics of each. The criteria are broadly conservative and assure avoidance of possibly adverse conditions. They are reviewed for each launch. For the Space Shuttle, weather "outlooks" provided by the U. S. Air Force Range Weather Operations Facility at Cape Canaveral begin at Launch minus 5 days in coordination with the NOAA National Weather Service Spaceflight Meteorology Group (SMG) at the Johnson Space Center in Houston. These include weather trends and their possible effects on launch day. A formal prelaunch weather briefing is held on Launch minus 1 day which is a specific weather briefing for all areas of Space Shuttle launch operations. Launch weather forecasts, ground operations forecasts, and launch weather briefings for the Mission Management Team and the Space Shuttle Launch Director are prepared by the Range Weather Operations Facility. Forecasts which apply after launch are prepared by SMG. These include all emergency landing forecasts and the end of mission forecasts briefed by SMG to the astronauts, the Flight Director and Mission Management Team. During the countdown, formal weather briefings occur approximately as follows (where "L-" equals "Launch minus":) L-24 hr 0 min: Briefing for Flight Director and astronauts L-21 hr 0 min: Briefing for removal of Rotating Service Structure L-9 hr 00 min: Briefing for external tank fuel loading L-4 hr 30 min: Briefing for Space Shuttle Launch Director L-3 hr 55 min: Briefing for astronauts L-2 hr 10 min: Briefing for Flight Director L-0 hr 35 min: Briefing for launch and RTLS L-0 hr 13 min: Poll all weather constraints The basic weather launch commit criteria on the pad at liftoff must be: Temperature: Prior to external tank propellant loading, tanking will not begin if the 24 hour average temperature has been below 41 degrees. After tanking begins, the countdown shall not be continued nor the Shuttle launched if: Temperature exceeds 99 degrees for more than 30 consecutive minutes. Temperature is lower than the prescribed minimum value for longer than 30 minutes unless sun angle, wind, temperature and relative humidity conditions permit recovery. The minimum temperature limit in degrees F. is specified by the table below and is a function of the five minute average of temperature, wind and humidity. The table becomes applicable when the observed temperature reaches 48 degrees. In no case may the Space Shuttle be launched if the temperature is 35 degrees or colder. Wind Speed Relative Humidity (kts) 0-64% 65-74% 75-79% 80-89% 90-100% 0 - 1 48 47 46 45 44 2 47 46 45 44 43 3 41 41 41 40 39 4 39 39 39 39 38 5 - 7 38 38 38 38 38 8 - 14 37 37 37 37 37 >14 36 36 36 36 36 The above table can be used to determine when conditions are again acceptable for launch if parameters have been out of limits for thirty minutes or less. If longer than thirty minutes, a mathematical recovery formula of the environmental conditions is used to determine if a return to acceptable parameters has been achieved. Launch conditions have been reached if the formula reaches a positive value. Wind: Tanking will not begin if the wind is observed or forecast to exceed 42 knots for the next three hour period. For launch the wind constraints at the launch pad will vary slightly for each mission. The peak wind speed allowable is 30 knots. However, when the wind direction is between 100 degrees and 260 degrees, the peak speed varies and may be as low as 21 knots. The upper atmosphere wind profile must conform to either one of two wind loading programs developed by the Johnson Space Center. This profile is determined by a series of Jimsphere wind balloon releases from Cape Canaveral Air Station. A final recommendation is made by the JSC Launch Systems Evaluation Advisory Team (LSEAT) to the KSC launch director at Launch minus 30 minutes. The Space Shuttle will not be launched within 30 minutes of the time a determination has been made that the upper wind profile will adversely affect the performance of the launch vehicle. A downrange weather advisory shall be issued by the Shuttle Weather Officer to the Mission Management Team for their consideration if the wind in the solid rocket booster recovery area is forecast to exceed 26 knots during retrieval operations. Seas in excess of Sea State 5 (8-13 feet) may also be a factor considered by the Mission Management Team. Precipitation: None at the launch pad or within the flight path. Lightning (and electric fields with triggering potential): Lightning is a giant spark. A single stroke of lightning can heat the air around it to 30,000 degrees Celsius (54,000 degrees Farhenheit)! This extreme heating causes the air to expand at an explosive rate. The expansion creates a shock wave that turns into a booming sound wave, better known as thunder. Thus the name thunderstorm. Image & caption courtesy of Windows to the Universe Copyright 1998, The Regents of the Univ. of Michigan Click for full size version (27K JPG) Tanking will not begin if there is forecast to be greater than a 20% chance of lightning within five nautical miles of the launch pad during the first hour of tanking. The launch director with the concurrence of the safety director may make an exception after consultation with the Shuttle Weather Officer. Do not launch if lightning has been detected within 10 nautical miles of the pad or the planned flight path within 30 minutes prior to launch. Launch may occur if the source of lightning has moved more than 10 nautical miles away from the pad or the flight path and a field mill, used to measure electric fields, is located within 5 nautical miles of the lightning flash. The one-minute average of the electric field mill network may not exceed -1 or +1 kilovolt per meter within five nautical miles of the launch pad or the lightning flash at any time within 15 minutes prior to launch. This field mill criteria becomes -1.5 or + 1.5 kilovolts per meter if there are no clouds within 10 nautical miles of the flight path except those which are transparent. Also excepted are clouds with tops below the 41 degrees F. temperature level that have not have been previously associated with a thunderstorm, or associated with convective clouds having tops above the 14 degrees F. temperature level during the last three hours. Do not launch when lightning is observed and the cloud which produced the lightning is within 10 nautical miles of the flight path. Launch may not occur until 30 minutes has elapsed since the lightning flash, or the cloud has moved more than 10 nautical miles away.

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