Conference 7.286::space

778.0. "Experiments point to possible easing of launch rules (Shuttle/KSC)" by PRAGMA::GRIFFIN (Dave Griffin) Tue Jan 28 1992 20:09

1/27/92

Jim Cast
NASA Headquarters, Washington, D.C.

H. Keith Henry
Langley Research Center, Hampton, Va.

Jim Sahli
Marshall Space Flight Center, Huntsville, Ala.

George Diller
Kennedy Space Center, Fla.

Capt. Ken Warren
USAF 45th Space Wing, Fla.


RELEASE: 92-

        This month, NASA began its final phase of "field mill" flight tests to
study launch-related weather at its Florida launch site. "Field mills" are
instruments that detect the presence of electric charges in the atmosphere.

        Results from earlier flights demonstrated that present weather rules
fully protect space launch vehicles from triggered lightning hazards.  However,
there is strong evidence that a number of rules are overly conservative and
potentially, could delay launches under weather conditions that do not pose any
real lightning threats.

        A NASA Learjet from Langley Research Center, Hampton, Va., has been
flown in the vicinity of NASA Kennedy Space Center, Fla., and USAF launch
facilities at Cape Canaveral, Fla., collecting meteorological data and
atmospheric electric field strength data.  Seasonal data has been taken for two
summer seasons and one previous winter season.  The flight test series just
underway, the last in the series, is planned for 8 weeks.

        "In a limited number of cases to date," said William Bihner, NASA
Airborne Field Mill Program Manager, "the weather was in violation of launch
commit criteria as written, but we did not measure an electrical hazard aloft.
It looks very promising that by the conclusion of the program we will be able
to recommend changes to present launch commit criteria that will maintain
launch safety while reducing launch restrictions."

        The set of criteria most likely to be relaxed are those that govern
launches through or near cumulus clouds, large puffy clouds that appear most
often in the spring and summer.  The next best candidate for relaxation are
those associated with layered clouds, seen most often in the winter.  The
layered cloud phenomena has the greatest impact on Space Shuttle and other
rocket launches from the Kennedy center and the USAF Eastern Test Range.

        There are six natural and triggered lightning constraints that can
delay a launch.  Flight data was collected for each.  The first rule prohibits
a launch within 10 nautical miles of any type of lightning 30 minutes prior to
launch.  The second prohibits a launch through or near cumulus clouds,
depending upon the combination of distance and temperature at the cloud top.
The remaining rules deal with the intensity of the electric field as measured
at the surface, the presence or absence of vertically continuous layers of
clouds and the presence of disturbed weather (moderate or greater
precipitation) or debris clouds associated with a thunderstorm.

        Safely opening the launch window even a little in the thunderstorm-
prevalent Central Florida area could result in a significant reduction of
lightning-related launch delays.  Electrically charged clouds, believed to be
lightning conducive, pass over the Cape Canaveral area more than 100 days each
year, especially from May to September.

        A lightning strike to a vehicle can be triggered when the vehicle
passes near a thunderstorm or even through an electric field left from a
decaying thunderstorm.  Components in the rocket or its payload can be damaged
by the strike.

        A change in lightning rules will not occur immediately, Bihner said.
Enough data must be collected to be considered statistically significant and
the conclusions must be scientifically validated, then Air Force and NASA
officials will have to approve changes, he said.  The process will be slow and
deliberate because safety is involved, he added.

        Funding for the joint NASA-Air Force Airborne Field Mill Program is
provided by the NASA Headquarters Office of Space Flight, Washington, D.C. and
the USAF Space Systems Division, Los Angeles.

        Participants in the field mill program are drawn from the USAF 45th
Space Wing and three NASA centers.  The Marshall Space Flight Center,
Huntsville, Ala., designed and fabricated the onboard electric field sensors
and is responsible for data processing, archiving and analysis.  Langley is
providing the aircraft and all flight support.  Kennedy is providing real-time
weather data, aircraft guidance and real-time ground station support during
data gathering flights.  The aircraft is controlled from and data collected at
the 45th Space Wing's Range Operations Control Center.