Weather "outlooks" which are provided by the Range Weather Operations Facility at Cape Canaveral begin at Launch minus 5 days. These include weather trends, and their possible effects on launch day.
For the Space Shuttle, 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.
During the countdown, formal weather briefings occur approximately as follows:
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-0 hr 35 min: Briefing for launch and RTLS
L-0 hr 13 min: Poll all weather constraints
The basic weather parameters 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 will not continue if the temperature exceeds 99 degrees for more than 30 consecutive minutes.
After tanking begins, the countdown shall not be continued nor the Shuttle launched if the temperature is lower than the prescribed minimum value for longer than 30 minutes unless sun, wind 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 36The 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, when the wind direction at the launch pad is between 300 degrees and 060 degrees, the highest wind allowable is 34 knots. When the wind direction is between 150 degrees and 200 degrees, the highest wind allowable is 20 knots. The peak allowable wind speeds are on a descending scale between the directions of 060 degrees and 150 degrees, and an ascending scale between 200 degrees and 300 degrees.
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):
- 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 concurance of the safety director may make an exception after consultation with the Shuttle Weather Officer.
- Launch will not occur if lightning has been detected within 10 nautical miles of the pad or the planned flight path within 30 minutes prior to launch, unless the source of lightning has moved more than 10 nautical miles away from the pad or the flight path.
- The one-minute average of the electric field mill network, used to measure electric fields, shall not exceed -1 or +1 kilovolt per meter within five nautical miles of the launch pad at any time within 15 minutes prior to launch.
The above rule need not apply if the following two conditions are observed to exist:
1. 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.
2. A known source of electric fields such as ground fog or smoke that is occurring near the field mill which has been previously determined and documented to be benign is clearly causing the elevated readings.
KSC Seasonal Altitudes of Temperature Levels in thousands of feet
January July
Temp Low Avg High Temp Low Avg High
-4 F 21 Kft 24 Kft 26 Kft -4 F 23 Kft 27 Kft 29 Kft
14 13 18 21 14 18 21 23
23 9 15 18 23 16 18 20
32 sfc 12 16 32 13 15 18
41 sfc 9 14 41 10 12 15
Clouds: (types known to contain hazardous electric fields)- The Space Shuttle may not be launched if the planned flight path is through a layer of clouds with a thickness of 4,500 feet or greater where the temperature of any part of the layer is between 32 degrees F. and -4 degrees F.
- The Space Shuttle may not be launched if the planned flight path is through a cumulus type cloud with its top between the 41 degrees F. temperature level and 23 degrees F. temperature. Launch may occur if: 1) the cloud is not producing precipitation; 2) the distance from the furthest edge of the cloud top to at least one operating field mill is less than the altitude at the 23 degree F temperature level or 3 nautical miles, whichever is less; 3) field mill readings within five nautical miles of the flight path must be between -100 volts per meter and +1000 volts per meter.
- The Space Shuttle may not be launched through 1) cumulus type clouds with tops higher than the 23 degree F. temperature level; 2) through or within 5 nautical miles of the nearest edge of cumulus type clouds with tops higher than the 14 degree F level; 3) through or within 10 nautical miles of the nearest edge of any cumulonimbus or thunderstorm cloud including nontransparent parts of its anvil; 4) through or within 10 nautical miles of the nearest edge of a nontransparent detached anvil cloud for the first hour after detachment from the parent thunderstorm or cumulonimbus cloud.
- The Space Shuttle may not be launched if the flight path is through any clouds that extend to altitudes at or above the 32 degrees F. level which are associated with disturbed weather producing moderate or greater precipitation within five nautical miles of the flight path.
- The Space Shuttle may not be launched if the flight path will carry the vehicle through a thunderstorm or cumulonimbus debris cloud which is not transparent and less than three hours old. Launch may not occur within five nautical miles of these debris clouds unless: 1) for 15 minutes preceding launch there is at least one working field mill within five nautical miles of the debris cloud; 2) all electric field mill readings are between -1 kilovolt and + 1 kilovolt per meter within five nautical miles of the flight path; 3) no precipitation has been detected or observed.
A "Good Sense Rule" is in effect for launch which states: "Even when constraints are not violated, if any other hazardous conditions exist, the launch weather officer will report the threat to the launch director. The launch director may hold at any time based on the instability of the weather."
CONTINGENCY LANDING WEATHER CRITERIA
Weather conditions for a landing also affect the launch criteria since the possibility exists for a Return To Launch Site abort (RTLS), landings at the Trans-Oceanic Abort Landing Sites (TAL), the Abort Once Around (AOA) sites and the first day Primary Landing Site (PLS). All criteria refer to observed and forecast weather conditions except for first day PLS which is forecast weather only.
- For RTLS, cloud coverage 5/10 or less below 5,000 feet and a visibility of 4 nautical miles or greater is required.
- For AOA, TAL and PLS sites, cloud coverage 5 tenths or less below 8,000 feet and a visibility of five nautical miles.
- With redundant Microwave Landing System capability or weather reconnaissance aircraft, the ceiling and visibility must be 10,000 feet and 7 nautical miles for all sites.
- For RTLS and the TAL sites, no thunderstorms, lightning, or precipitation within 20 nautical miles of the runway, or within 10 nautical miles of the final approach path extending outward to 30 nautical miles from the end of the runway.
- For AOA and PLS sites, no thunderstorms, lightning or precipitation within 30 nautical miles of the runway, or within 20 nautical miles of the final approach path extending to 30 nautical miles from the end of the runway.
- For RTLS and the TAL sites, no detached opaque thunderstorm anvil cloud less than 3 hours old within 15 nautical miles of the runway or within 5 nautical miles of the final approach path extending outward to 30 nautical miles from the end of the runway.
- For AOA and PLS sites, no detached opaque thunderstorm anvil cloud less than 3 hours old within 20 nautical miles of the runway or within 10 nautical miles of the final approach path extending to 30 nautical miles from the end of the runway.
- Crosswind component not to exceed 15 knots. For the TAL, AOA and PLS sites there is a night-time crosswind limit of 12 knots.
- Headwind not to exceed 25 knots.
- Tailwind not to exceed 10 knots average, 15 knots peak.
- Turbulence conditions must be less than or equal to moderate intensity.
KSC END OF MISSION LANDING WEATHER CRITERIA
All criteria refer to observed and forecast weather conditions. All criteria refer to observed and forecast weather conditions except for the 2/10 cloud rule which is required to be observed only. At decision time for the deorbit burn 90 minutes before landing the required conditions must be:
- Cloud coverage of 5/10 or less below 10,000 feet and a visibility of 5 miles or greater is required.
- The peak cross wind cannot be exceed 15 knots, 12 knots at night. If the mission duration is greater than 12 days the limit is 12 knots, day and night.
- Headwind cannot exceed 25 knots.
- Tailwind cannot exceed 10 knots average, 15 knots peak.
- The deorbit burn shall not occur if thunderstorm, lightning, or precipitation activity is forecast within 30 nautical miles of the Shuttle Landing Facility.
- At a range of 30 nautical miles, vertical clearance from the tops of rain showers or thunderstorms must be greater than 2 nautical miles.
- Detached opaque thunderstorm anvils less than three hours old must not be within 20 nautical miles of the Shuttle Landing Facility, or within 10 nautical miles of the flight path when the orbiter is within 30 nautical miles of the runway.
- Scattered cloud layers below 10,000 feet must not exceed 2/10 sky coverage.
- Turbulence must be less than or equal to moderate intensity.
WEATHER INSTRUMENTATION The equipment used by the forecasters to develop the downrange and launch clearance and landing forecasts are:
-Radar: Launch and landing forecasters can access displays from two different radars. One is located at Patrick Air Force Base south of Cocoa Beach. The other is located in Melbourne at the National Weather Service and is a NEXRAD Doppler radar. Each radar provides rain intensity and cloud top information out to a distance as far as 200 nautical miles. The NEXRAD radar can also provide estimates of total rainfall and wind velocities.
-Field Mill Network: Thirty-one advanced field mill sites around KSC and Cape Canaveral Air Station provide data on lightning activity and surface electric fields induced by charge aloft. This data helps forecasters determine when electric charge aloft may be sufficient to create triggered lightning during launch, and to determine when to issue and cancel lightning advisories and warnings.
-Lightning Detection System: Detects and plots cloud to ground lightning strikes within 125 miles of the Kennedy Space Center. Location accuracy is optimum within 30 nautical miles. Locations of strikes are color coded according to time of occurance.
-Lightning Detection And Ranging (LDAR): Plots intracloud, cloud to cloud and cloud to ground lightning in three dimensions within 100 nautical miles of the Kennedy Space Center. Location accuracy is very high within 25 nautical miles. LDAR was developed by NASA-KSC and is currently being transitioned to operational status.
- National Lightning Detection Network: Plots cloud to ground lightning nationwide. Used to help ensure safe transit of the Space Shuttle orbiter atop the Shuttle Carrier Aircraft between Edwards Air Force Base in California and the Kennedy Space Center in Florida. It is also used to assess lightning beyond the 125 mile range of the Lightning Detection System.
-Rawinsonde: A balloon with a tethered instrument package which radios its altitude to the ground together with temperature, dewpoint and humidity, wind speed and direction, and pressure data. Rawinsondes reach altitudes exceeding 100,000 feet.
-Jimsphere balloon: A reflective balloon made of mylar tracked by radar which provides highly accurate information on wind speed and wind direction up to 60,000 feet.
- Doppler Radar Wind Profiler: Measures upper level wind speed and direction over Kennedy Space Center from approximately 10,000 feet to 60,000 feet. The data, received every 5 minutes, is used to ensure the upper winds used to calculate wind loads on the shuttle vehicle have not significantly changed between balloon soundings. If data indicates a possible significant change, another Jimsphere balloon is released.
-Rocketsonde: A 12-foot-tall instrumented rocket is launched on L-1 day which senses and transmits data on temperature, wind speed and direction, wind shear, pressure, and air density at altitudes between 65,000 feet and 370,000 feet. A four-inch in diameter solid rocket motor separates at an altitude of about 5,000 feet, after which an "instrumented dart" coasts to apogee.
-Satellites: Images and data from GOES weather satellites are provided directly to the satellite terminal at USAF Range Weather Opeations and NOAA National Weather Service Spaceflight Meteorology Group in Houston. Also available are the high resolution pictures from polar low earth orbiting spacecraft including both the NOAA polar orbiters and the Defense Meteorological Support Program (DMSP) satellites.
-Meteorological Interactive Data Display System (MIDDS): Integrates for the forecaster diverse weather data on a single visual display satellite images, radar, computer generated graphics of surface and upper air map features, numerical weather models, current weather observations, data from meteorological towers, lightning strikes and field mill information.
- Meteorological towers: 33 wind towers are located on Kennedy Space Center and Cape Canaveral Air Station, including two at each launch pad and three at the Shuttle Landing Facility. In addition to wind, most towers are also instrumented with temperature, and moisture sensors. The 60-foot wind towers at the launch pads and the 33-foot wind towers at the Shuttle Landing Facility are closely monitored for launch and landing criteria. In addition, on the mainland, there is a network of 19 wind towers which extend outward an additional twenty miles. Tower data is important as a tool in short-term forecasting and wind prediction. It also used as an aid in determining the direction and distance a toxic plume would move as a result of a launch mishap.
-Weather Buoys: Instrumented meteorological buoys are anchored 20, 110 and 175 nautical miles East-Northeast of Cape Canaveral. These buoys relay hourly measurements via satellite of temperature, wind speed and direction, barometric pressure, precipitation, sea water temperture, and wave height and period. Buoy data is used in forecasting for launch and landing, the solid rocket booster recovery area for the retrieval ships, and in preparing daily operational forecasts.
-Solid Rocket Booster Retrieval Ships: These vessels radio observed weather conditions and sea state from the booster impact area located up to 150 nautical miles downrange.
-Weather Reconnaissance Aircraft: A T-38 jet and the Shuttle Training Aircraft are flown by a weather support astronaut.
NOTE: The launch weather forecast is prepared by the U.S. Air Force Range Weather Operations Facility at Cape Canaveral. The landing and RTLS forecast is prepared by the NOAA National Weather Servcice Spaceflight Meteorology Group at the Johnson Space Center in Houston.