Launch Criteria for Discovery

Right now the weather for the shuttle launch on Wednesday looks pretty good. I would say the chance of a shower scrubbing the launch is only about 25%.

When I worked in Florida, I covered several shuttle launches. They truly are something to see. TV definitely does not due it justice. Especially a night launch. When you watch on TV they stay zoomed into the shuttle but at the press site you can follow a white plume of smoke and condensed water high into the sky arcing toward the horizon. The shuttle lifts off the pad silently too. At 3.5 miles away, the noise shakes the ground.

The weather rules for launching are in a book several inches think. I had that book and referred to it often back in the 1980's when I covered the launches. Here is a condensed summary of the rules courtesy of NASA's Public Information Office.

Later,
Dan


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Space Shuttle Weather Launch Commit Criteria and KSC End of Mission Weather Landing Criteria


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 forecasts are provided by the U. S. Air Force Range Weather Operations Facility at Cape Canaveral beginning at Launch minus 3 days in coordination with the NOAA National Weather Service Space Flight 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:

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:

a.) the temperature exceeds 99 degrees for more than 30 consecutive minutes.

b.) the 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 for each mission and may be as low as 24 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):

* 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.

Clouds: (types known to contain hazardous electric fields)

* Do not launch if any part of the planned flight path is through a layer of clouds any part of which is within 5 nautical miles is 4,500 feet thick or greater and the temperature of any part of the layer is between 32 degrees F. and -4 degrees F. Launch may occur if the cloud layer is a cirrus-like cloud that has never been associated with convective clouds, is located entirely at temperatures of 5 degrees F. or colder, and shows no evidence of containing water droplets.

* Do not launch through cumulus type clouds with tops higher than the 41 degree F. temperature level. Launch may occur through clouds as cold as 23 degrees F. if the cloud is not producing precipitation, and all field mills within 5 nautical miles of the flight path and at least one field mill within 2 nautical miles of the cloud center read between -100 volts per meter and +500 volts per meter.

* Do not launch 1.) through or within 5 nautical miles of the nearest edge of cumulus type clouds with tops higher than the 14 degree F level; 2) through or within 10 nautical miles of the nearest edge of cumulus clouds with tops higher than the -4 degrees F. level.

* Do not launch if the flight path is through any non-transparent clouds that extend to altitudes at or above the 32 degrees F. level which are associated with disturbed weather producing moderate or greater precipitation, or melting precipitation, within five nautical miles of the flight path.

* Do not launch through an attached anvil cloud. If lightning occurs in the anvil or the associated main cloud, do not launch within 10 nautical miles for the first 30 minutes after lightning is observed, or within 5 nautical miles from 30 minutes to 3 hours after lightning is observed.

* Do not launch if the flight path will carry the vehicle:

a.) through non-transparent parts of a detached anvil for the first three hours after the anvil detaches from the parent cloud, or the first four hours after the last lightning occurs in the detached anvil.

b.) within 10 nautical miles of non-transparent parts of a detached anvil for the first thirty minutes after the time of the last lightning in the parent or anvil cloud before detachment, or the detached anvil after its detachment.

c.) within 5 nautical miles of non-transparent parts of a detached anvil for the first three hours after the time of the last lightning in the parent or anvil cloud before detachment, or the detached anvil after detachment, unless there is a field mill within 5 nautical miles of the detached anvil reading less than 1,000 volts per meter for the last 15 minutes and a maximum radar returns from any part of the detached anvil within 5 nautical miles of the flight path have been less than 10 dBZ (light rain) for 15 minutes.

* Do not launch 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 in the debris cloud (less than 10 dbz by radar) within 5 nautical miles of the flight path.

* Do not launch if the flight path will carry the vehicle through any cumulus cloud that has developed from a smoke plume while the cloud is attached to the plume, or for the first 60 minutes after the cumulus cloud detaches from the smoke plume.

Supporting Table: 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

Range Safety Cloud Ceiling and Visibility constraints:

* Direct visual observation of the Shuttle is required through 8,000 feet. This requirement may be satisfied using optical tracking sites or a forward observer

* For cloud ceilings of any thickness between 6,000 feet and 8,000 feet the following conditions must be met for launch to occur:

a.) the vehicle integrity can be observed without interruption through 6,000 feet.

b.) all required Range Safety instrumentation is functioning properly

c.) the U.S. Air Force 45th Space Wing Commander approves the decision to proceed

* For cloud ceilings between 4,000 feet and 6,000 feet the following conditions must be met for launch to proceed:

a.) the thickness of the clouds must be less than 500 feet

b.) the vehicle integrity can be monitored by the Eastern Range airborne and/or the ground forward observers through 8,000 feet

c.) all required Range Safety instrumentation is functioning properly

d.) the U.S. Air Force 45th Space Wing Commander approves the decision to proceed

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 FLIGHT RULES

Weather criteria for an emergency landing must be considered along with 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). These forecasts are prepared by the NOAA National Weather Service Spaceflight Meteorology Group in Houston and briefed by them to the astronauts, Flight Director and Mission Management Team. All criteria refer to observed and forecast weather conditions except for the first day PLS which is forecast weather only.

* For RTLS with redundant Microwave Landing System (MLS) capability and a weather reconnaissance aircraft, cloud coverage 4/8 or less below 5,000 feet and a visibility of 4 statute miles or greater are required. For AOA and PLS sites, cloud coverage 4/8 or less below 8,000 feet and a visibility of 5 statute miles or greater is required. For TAL sites, cloud coverage 4/8 or less below 5,000 feet and a visibility of 5 statute miles or greater are required.

* For landing on a hard surface runway without redundant Microwave Landing System (MLS) capability all sites require a ceiling not less than 10,000 feet and a visibility of at least 7 statute miles. Landing at night on a lake bed runway may occur if the ceiling is not lower than 15,000 feet and the visibility is 7 miles or greater with at least non-redundant MLS capability .

* For the RTLS site and 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.

* An RTLS rule exception may be made for light precipitation within 20 nautical miles of the runway if the specific criteria listed below are met:

a.) The tops of the clouds containing precipitation do not extend into temperature regions colder than 41 (F.); they have not been colder than 14 (F. ) within 2.5 hours prior to launch; the radar reflectivity is less than 30 dbz at all levels within and below the clouds.

b.) Precipitation covers less than 10% of the area within 20 nautical miles of the runway, or multiple heading alignment circles are clear of showers.

c.) The movement of the showers is observed to be consistent and no additional convective development is forecast.

d.) Touchdown/rollout criteria and associated navigational aids meet the specified prelaunch go/no go requirements.

If showers exceed either parameter of part a.) above, an RTLS landing may still occur if a 2 nautical mile vertical clearance can be maintained from the top of any shower within 10 nautical miles of the approach paths.

* For RTLS and TAL sites, no detached opaque thunderstorm anvils less than three 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 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.

* The RTLS crosswind component may not exceed 15 knots. If the astronaut flying weather reconnaissance in the Shuttle Training Aircraft executes the approach and considers the landing conditions to be acceptable, this limit may be increased to 17 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 FLIGHT RULES

The end of mission landing weather forecast is prepared by the NOAA National Weather Service Spaceflight Meteorology Group in Houston for the astronauts, Flight Director and Mission Management Team. All criteria refer to observed and forecast weather conditions. Decision time for the deorbit burn is 70 - 90 minutes before landing. The weather criteria are:

* Cloud coverage of 4/8 or less below 8,000 feet and a visibility of 5 miles or greater required.

* The peak cross wind cannot exceed 15 knots, 12 knots at night. If the mission duration is greater than 20 days the limit is 12 knots, day and night.

* Headwind cannot exceed 25 knots.

* Tailwind cannot exceed 10 knots average, 15 knots peak.

* No thunderstorm, lightning, or precipitation activity is within 30 nautical miles of the Shuttle Landing Facility.

* 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.

* Turbulence must be less than or equal to moderate intensity.

* Consideration may be given for landing with a "no go" observation and a "go" forecast if at decision time analysis clearly indicates a continuing trend of improving weather conditions, and the forecast states that all weather criteria will be met at landing time.

WEATHER INSTRUMENTATION

The weather equipment used by the forecasters to develop the launch and landing forecasts is:

* Radar: Launch forecasters located at Cape Canaveral Air Station and landing forecasters located in Houston can access displays from two different radar. 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 radial 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 nautical miles of the Kennedy Space Center. Location accuracy is optimum within 30 nautical miles. Locations of strikes are color coded according to time of occurrence.

* Lightning Detection And Ranging (LDAR): Developed by NASA at the Kennedy Space Center, 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 data is important in determining the beginning and end of lightning conditions.

* 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 from the Doppler Radar Wind Profiler 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.

* Satellite Images and Data: Provided directly to the satellite terminal at USAF Range Weather Operations and NOAA National Weather Service Space Flight Meteorology Group in Houston by the geostationary GOES weather satellites. In addition high resolution images are received from spacecraft in low earth orbit including both the NOAA and the Defense Meteorological Support Program (DMSP) polar orbiting satellites.

* Meteorological Interactive Data Display System (MIDDS): Integrates diverse weather data on a single display terminal-- 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.

* Towers: 33 meteorological 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 towers at the launch pads and the 33-foot 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 an important short-term forecasting tool and also helps determine the direction and distance of toxic corridors in the event of a mishap.

* Buoys: Meteorological buoys are anchored 20, 110 and 160 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 temperature, and wave height and period. Buoy data is used for launch, landing, booster retrieval, and daily ground processing forecasts for the Kennedy Space Center and Cape Canaveral Air Station.

* 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.