Commit
to Launch: Space Shuttle Weather Launch Commit Criteria
The
launch weather guidelines involving the Space Shuttle and expendable
rockets are similar in many areas, but distinctions are made for the
individual characteristics of each. The criteria are broadly
conservative to assure avoidance of possible adverse conditions. The
criteria are reviewed for each launch. Weather outlooks, which are
provided by the Cape Canaveral Range Forecast Facility begin at
Launch-minus-5-days. The outlooks include weather trends and their
possible effects on launch day.
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 as follows:
Temperature
Prior to external tank propellant loading, tanking will not begin if
the 24-hour average temperature has been below 41 degrees F. After
tanking begins, the countdown will not continue if the temperature
exceeds 99 degrees F 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°F. In no case may the Space Shuttle be
launched if the temperature is 35°F or colder.
Wind
Speed Relative Humidity
Knots |
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 |
06 |
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 30
minutes or less. If longer than 30 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 speed is 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 Force 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.
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 next three
hours.
Launch
will not occur if lightning has been detected within 10 nautical
miles of the pad or the planned flight path within 15 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 launch pad. If
clouds are present they may not have been previously associated with
a thunderstorm, or associated with convective clouds having tops
greater than the -4 degrees F. temperature level (approximately
23,000 feet) during the last three hours. The clouds must be thin
optically transparent clouds, or a cloud cover less than or equal to
25% of the sky with tops below or equal to the 41 degrees F.
temperature level (approximately 10,000 feet).
2. It
can be determined that abnormal readings are the result of smoke,
fog, or a maritime inversion associated with an onshore or
alongshore wind present over the electric field mills, causing those
mills located near the ocean to be elevated with a positive polarity
between 1 and 1.5 kilovolts per meter.
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. This frequently corresponds to the altitudes between
approximately 13,000 feet and 23,000 feet.
The
Space Shuttle may not be launched if the planned flight path is
through any cloud type that extends to an altitude where the
temperature is between 32 degrees and -4 degrees F. if this is
associated with disturbed weather within five nautical miles of the
flight path. (Again, this may correspond to the region between
approximately 13,000 feet and 23,000 feet altitude.)
The
Space Shuttle may not be launched through an opaque cloud which has
become detached from a thunderstorm within three hours before
launch, or within 5 nautical miles of thunderstorm debris clouds not
able to be monitored by the field mill network, or producing a radar
return showing light rain.
The
Space Shuttle may not be launched through cumulus type clouds with
tops extending into a temperature 41 degrees F. or colder (located
at approximately 10,000 feet), or within 5 nautical miles of clouds
with tops extending higher than the 14 degree F. temperature level
(located at approximately 18,000 feet).
The
Space Shuttle may not be launched through or within 10 nautical
miles of cumulus type clouds with tops extending higher than the -4
degree F. temperature level (approximately 23,000 feet), or of the
nearest edge of any cumulonimbus or thunderstorm cloud including its
associated anvil.