October 4, 1995
KSC Release No. 100-95
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.
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 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, 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 lightning is observed within five nautical miles of the launch pad or is
forecast to occur during the first hour of tanking.
- 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 CRITERIA
Weather conditions for a landing also affect the launch criteria since the possibility exists
for a Return To Launch Site abort (RTLS) at the Kennedy Space Center or for emergency
landings at other off-site locations.
The landing criteria for the Trans-Oceanic Abort Sites (TAL), and the Abort Once Around
(AOA) sites of Edwards Air Force Base, and White Sands Space Harbor are:
- Cloud coverage 5 tenths or less below 8,000 feet with a clear line of sight to the end of the
runway.
- For AOA, 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.
- 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 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 RTLS, a ceiling of 5,000 feet and a visibility of 4 nautical miles or greater is required.
- Visibility for the TAL sites and AOA, 5 statute miles or greater where microwave landing
system (MLS) instrument landing capability is available; otherwise 7 statute miles.
- Crosswind component for Return to Launch Site (RTLS) not to exceed 15 knots. For Abort
Once Around (AOA) and Trans-Oceanic (TAL) contingency landing sites the night-time crosswind
limit is 12 knots.
- Headwind not to exceed 25 knots
- Tailwind not to exceed 10 knots average, 15 knots peak
- Sun angle on final approach not within 10 degrees in azimuth and 0 to 20 degrees in elevation
KSC END OF MISSION LANDING WEATHER CRITERIA
At decision time for the deorbit burn 90 minutes before landing:
- The visibility must be observed and forecast to be 5 nautical miles or greater.
- Headwind not to exceed 25 knots
- Tailwind not to exceed 10 knots average, 15 knots peak
- The peak cross wind shall not be observed or forecast to exceed 15 knots, 12 knots at night. If
the mission duration is greater than 12 days the limit is 12 knots, day or night.
- An observed or forecast cloud ceiling must be 10,000 feet or higher.
- Observed scattered cloud layers below 10,000 feet must not exceed 2/10 sky coverage.
- At a range of 30 nautical miles, vertical clearance from the tops of rain showers or
thunderstorms must be greater than 2 nautical miles.
- The deorbit burn shall not occur if thunderstorm, lightning, or precipitation activity is observed
or forecast within 30 nautical miles of the Shuttle Landing Facility.
- Detached opaque thunderstorm anvils less than three hours old must not be observed or forecast
to 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.
WEATHER INSTRUMENTATION
The equipment used by the forecaster to develop the downrange and launch
clearance forecast are:
-Radar: The color weather radar display is located at the Cape Canaveral Forecast Facility. The
antenna is located on Patrick Air Force Base in Cocoa Beach. Echo returns and information
about rain intensity and cloud tops may be observed up to a distance of 200 nautical miles. Also
available to the Shuttle Weather Officer is a display of the National Weather Service doppler
weather radar located in Melbourne.
-Field Mill Network: Thirty-one advanced field mill sites around KSC and Cape Canaveral Air
Station provide a contour map of electric fields and lightning activity. This tool assists the
forecaster in determining that the lightning avoidance criteria are met.
-Lightning Detection System: Plots cloud to ground lightning strikes within 125 miles of the
Range Weather Facility.
-Lightning Detection And Ranging (LDAR): A new system developed by NASA undergoing
evaluation, LDAR is a three dimensional system that plots intracloud, cloud to cloud and cloud to
ground lightning with high demonstrated accuracy within 25 nautical miles but recording lightning
events up to 100 nautical miles distant from Cape Canaveral.
-Rawinsonde: A balloon with a tethered instrument package which radios to the ground its
altitude with weather data on temperature, dewpoint and humidity, wind speed and direction, and
pressure. A rawinsonde may reach an altitude as high as 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.
-Rocketsonde: On L-1 day, a 12-foot-tall instrumented rocket is launched. It returns data on
temperature, wind speed and direction, wind shear, pressure, and air density at the altitude region
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 in the Range Weather
Facility by the GOES weather satellites, and also 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 on a
single visual display the satellite images, computer generated graphics of surface and upper air
map features, and current weather observations. The system will also display or plot and contour
various meteorological parameters, and can display any selected current National Weather Service
radar picture.
-Wind towers: A total of 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 sensors. The 60-foot
wind towers at the launch pads and the 10-meter 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 and are used as a tool in
short-term forecasting.
-Instrumented Weather Buoys: Anchored East-Northeast of Cape Canaveral, two
meteorological buoys are stationed at distances of 25 nautical miles and 110 nautical miles.
Offshore weather conditions may be influencing onshore weather. These ocean weather buoys
relay hourly reports by satellite and are received at the Range Weather Facility. Measurements
include air temperature, wind speed and direction, barometric pressure, precipitation, sea water
temperature, and the wave height with period.
-Solid Rocket Booster Retrieval Ships: These vessels radio observed weather conditions and sea
state from the booster impact area located approximately 160 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
Space Flight Meteorology Group at the Johnson Space Center in Houston.
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