2012 International Conference on Lightning Protection (ICLP), Vienna, Austria
Summary of 2011 Direct and Nearby Lightning
Strikes to Launch Complex 39B, Kennedy Space
Center, Florida
C.T. Mata, A. G. Mata
ESC
Kennedy Space Center, FL, USA
Carlos.T.Mata@nasa.gov, Angel.G.Mata@nasa.gov
Abstract— A Lightning Protection System (LPS) was designed
and built at Launch Complex 39B (LC39B), at the Kennedy
Space Center (KSC), Florida in 2009. This LPS was instrumented
with comprehensive meteorological and lightning data
acquisition systems that were deployed from late 2010 until mid
2011. The first direct strikes to the LPS were recorded in March
of 2011, when a limited number of sensors had been activated.
The lightning instrumentation system detected a total of 70
nearby strokes and 19 direct strokes to the LPS, in 2011, 2 of the
19 direct strokes to the LPS had two simultaneous ground
attachment points (in both instances one channel terminated on
the LPS and the other on the nearby ground). In addition to the
70 nearby strokes, some more distant nearby strokes where
captured on video records for which limited data were acquired.
Instrumentation deployment chronological milestones, a
summary of lightning strikes (direct and nearby), high speed
video frames, downconductor currents, and dH/dt and dE/dt
typical waveforms for direct and nearby strokes are presented in
this paper.
Keywords-Lightning Protection System; LC39B; KSC, Data
Acquisition System, Lightning Instrumentation System.
I.
INTRODUCTION
The installation of the meteorological and lightning
instrumentation systems at Launch Complex 39B (LC39B)
started in February 2011 and March 2011 and were completed
in September 2011 and May 2011, respectively. The triggering
thresholds of the lightning instrumentation were adjusted based
on previous test runs at the International Center for Lightning
Research and Testing, (ICLRT), Camp Blanding, Florida, in
which the same instrumentation was tested in 2009 and 2010.
During the previous to last Space Shuttle mission, STS-134, the
triggering thresholds of the system were reduced in an attempt
to make the LC39B lightning instrumentation trigger from
strikes at Launch Complex 39A (LC39A), where Endeavor was
being prepared to launch. The thresholds were lowered from
March 10, 2011, until shortly after the STS-134 launch on May
16, 2011. A few storms passed through the launch pad areas
and many images of nearby strikes were captured with some
limited number of usable waveforms. Note that the dynamic
range of the measurements was not changed, so the majority of
the waveforms for distant nearby strikes had very poor
resolution. Shortly before the roll out of the last Space Shuttle
mission, Atlantis, STS-135, May 31 2011, a trigger signal from
the LC39A lightning instrumentation system was connected as
an input trigger to the LC39B lightning instrumentation system
(June 21, 2011), in an attempt to increase the LC39B lightning
instrumentation triggering capabilities and reduce the number
of triggers from nearby events to both launch pads. This trigger
signal from LC39A to LC39B was left in place even after
Atlantis launched in July 8, 2011. The lightning
instrumentation system at LC39B helped determine the
location of LC39A nearby strikes during some storms prior to
launch and even a strike within the LC39A perimeter the day
before launch, preventing a potential launch scrub that would
have delayed the mission and resulted in additional costs.
II. INSTRUMENTATION OVERVIEW AND SETUP
Reference [1] and [2] describe the LC39B weather
instrumentation, which is composed of two data acquisition
(DAQ) systems, Lightning and Meteorological, both running
24/7. The lightning protection system (LPS) consists of a
catenary wire system (at about 181 meters above ground level)
with nine downconductors connected to ground, supported by
three insulators installed atop three towers in a triangular
configuration. Field sensors’ signals are digitized and
transmitted, via fiber optics, to centralized transient recorders
located in the Pad Termination Connection Room (PTCR). All
the LPS instrumentation, including the digitizers, transient
recorders, and computers, are battery backed up.
A. Lightning Instrumentation
This is an event driven, 100 megasamples per second
sampling system, which includes six synchronized high-speed
video cameras installed atop each of the LPS towers (two per
tower) and one remote high-speed video camera installed about
five kilometers southwest of LC39B atop the Vehicle
Assembly Building (VAB)). There are a total of nine current
sensors installed at ground level on each of the nine
downconductors; four dH/dt, 3-axis measurement stations; and
five dE/dt stations composed of two antennas each. The
electromagnetic sensors are all installed at ground level with
elevations ranging from 5.9 to 7.4 meters height referred to the
North American Vertical Datum of 1988 (NAVD88). All these
signals are recorded using three synchronized transient
recorders (HBM GENESIS 16t). Fig. 1 shows an overview of
the lightning instrumentation system installed at LC39B.
Figure 1. Panoramic view of LC39B, at the KSC, Florida, showing the
lightning protection system and the architecture of the lightning
instrumentation system.
Window triggering and an OR gate are used to trigger the
LC39B lightning instrumentation system from any of the thirty
one ground level sensors (9 downconductor currents, 12 dH/dt,
10 dE/dt). Additionally a TTL signal from the LC39A lightning
instrumentation system is also an input to the OR gate. After a
qualified trigger is received, the signal of all the ground level
sensors is recorded on a 30 millisecond time window with 50%
pre-trigger sampling at 100 megasamples per second. The
seven high speed video cameras record up to 455 frames with
312.5 microsecond exposure (up to 142.1 milliseconds of video
at 3,200 frames per second) with a 1280x800 resolution, also
with 50% pre-trigger. The VAB camera has been operational
since spring of 2012.
B. Meteorological Instrumentation
The meteorological instrumentation is a 24/7, 1 sample per
second, system, which provides air temperature, relative
humidity, wind direction, and wind speed at four different
altitudes (40.2, 78.3, 116.4 and 139.3 meters), on each of the
four levels (A, B, C, and D) of the LC39B LPS towers. In
addition, there are two rain gauge stations (at ground level) that
measure rain precipitation and accumulation, adding for a total
of 26 meteorological sensors. Fig. 2 shows an overview of the
meteorological instrumentation system architecture installed at
LC39B.
The meteorological data is displayed on the KSC internal
television system (OTV), showing the one-minute running
average of all the measurements in addition to the maximum
wind gust and wind direction over the last minute.
Additionally, the meteorological data will be transmitted (fall
of 2012) to the 45th Weather Squadron (WS), Cape Canaveral
Air Force Station (CCAFS), Florida, to support weather related
launch decisions.
Figure 2. Panoramic view of the LC39B, at the KSC, Florida, showing the
architecture of the LC39B meteorological instrumentation depicting a typical
lightning protection tower and the sensors’ locations.
III.
CHRONOLOGICAL MILESTONES
The weather instrumentation (lightning and meteorological)
of LC39B has been incrementally increasing after the LC39B
LPS was built. Table I shows the milestones of the deployment
of these DAQ systems.
TABLE I.
LIST OF CHRONOLOGICAL MILESTONES OF THE LC39B
WEATHER INSTRUMENTATION SYSTEM FROM ITS CONCEPTUAL DESIGN.
Action
Conceptual Design
Construction
Instrumentation Enclosure fabrication, testing and
installation
DAQ installed
All (4) Tower 1 meteorological stations active
All (9) downconductors instrumentation, towers 2 &
3 meteorological stations (8) and 2 (out of 6) high
speed video cameras active
First and last nearby lightning strike recorded (2011)
First and last direct lightning strike recorded (2011)
Time
2007
2008-2009
2010
January 2011
February 2011
March 2011
Mar. 30th &
Oct. 10th
Mar. 31th &
Aug. 14th
4 (out of 6) high speed camera and all (12) magnetic
April 2011
field measurements active
All (6) high speed video cameras and all (10) electric
May 2011
field measurementsa active
Meteorological data shown on OTV, additional
trigger signal from LC39A and additional
June 2011
(temporary) high speed video camera in Launch
Control Center (LCC)
1 (out of 2) rain stations active
August 2011
All (2) rain stations active
September 2011
VAB camera installation
March 2012
Meteorological data sent to 45th WS (expected)
October 2012
a. From May until July there were some electric field measurements troubleshooting, so, limited dE/dt
measurements are available for this period.
IV. ACQUIRED LIGHTNING DATA
The lightning instrumentation system was active from midMarch of 2011 and it triggered on 14 different days acquiring a
total of 48 lightning flashes with 89 return strokes. These
flashes are organized between direct and nearby. The latter are
also grouped between close nearby (within LC39B perimeter)
and nearby, referring to all the strikes with attachment points
outside the LC39B perimeter. Fig. 3 shows colored tear drops,
yellow (for negative) and blue (for positive) to indicate the
locations of all the direct and close nearby strikes acquired by
the LC39B LPS during 2011.
B. Close nearby (within the LC39B perimeter fence): There
were 3 nearby lightning flashes, with a total of 6 return
strokes, striking within the LC39B perimeter:
• 1 four-stroke flash striking the perimeter fence (all
three subsequent strokes following the path of the first
stroke).
•
2 single-stroke flashes (one negative and one positive)
terminating on the ground.
C. Nearby: The lightning instrumentation system captured
40 nearby (outside the LC39B perimeter fence) lightning
flashes with a total of 64 return strokes:
• 2 nearby subsequent strokes, whose first strokes
attached to the LPS.
•
26 presumed single-stroke flashes (due to the limited
range of the LC9B lightning instrumentation system it
is not possible to label these as single-stroke flashes).
•
14 multiple-stroke flashes (minimum of 2 return
strokes and maximum of 6 return strokes and). Note
that due to the limited range of the LC39B lightning
instrumentation system it is likely some of the
subsequent strokes were not captured.
V.
Figure 3. Satellite view of the LC39B indicating the location of the three
lightning towers, 1-3. Yellow lines show the projection to ground of the
catenary wire system and downconductors. The red circle delimits a 1
kilometer square area centered in the pad. Colored tear drops, yellow for
negative and blue for positive, indicate the location of only the direct and
close nearby strikes to the LC39B, additionally the strike location for the two
return strokes with multiple simultaneous attachment points is shown outside
of the LC39B perimeter.
A. Direct: The LPS has been struck directly by 8 negative
lightning flashes with a total of 19 return strokes:
• 5 flashes attached to the towers.
•
3 flashes attached to the catenary wire system or
downconductors.
•
3 single-stroke flashes.
•
5 multiple-stroke flashes (minimum of 2 return strokes
and maximum of 8 return strokes).
•
Only one multiple-stroke (3) flash had all subsequent
return strokes terminating at the same location as the
first return stroke.
•
2 return strokes had two simultaneous attachment
points, direct (tower) and nearby outside the pad
perimeter.
STATISTICS
From late March until December of 2011, the LC39B was
struck by downward lightning strikes as observed in high speed
cameras videos. A total of 11 flashes terminated within the
LC39B perimeter fence (out of 48 flashes detected by the
LC39B lightning instrumentation system, or about 23%) which
has an area of approximately 1 km2, see Fig. 3. About 55% of
these flashes (6 of 11) had multiple return strokes and 33% of
the multiple-stroke flashes (2 of 6) had all the return strokes (4
and 3) terminating at the same location.
One of these flashes was a positive (single-stroke) flash
representing 9% (1 of 11) of all the flashes detected by the
LC39B lightning instrumentation system within an area of 1
km2. Consequently, the estimated ground flash density for
LC39B during 2011 was 11 flashes/km2/year with 9% of
positive flashes. Furthermore, the 2011 estimated ground stroke
density for LC39B was 25 strokes/km2/year with 4% positive
strokes. Within this area, about 73% of the flashes (8 of 11)
and 76% of the strokes (19 of 25) attached directly to the LPS
and 18% (2 of 11) of these flashes had multiple simultaneous
attachment points, with one branch attaching directly to one of
the LPS towers and a second branch attaching to ground
(outside of the LC39B perimeter).
These results seem to contradict the predictions of the
LC39B LPS Monte Carlo simulations previously run [1] and
[3], where over a period of 10,000 years, using a ground flash
density of 17 flashes/km2/year (with 5% of positive flashes),
26% of the flashes struck the LPS and 74% struck ground in
the vicinity of the LC39B within an area of approximately 1
km2.
About 63% of the direct flashes were multiple-stroke
flashes (5 of 8) and only 20% of them (1 of 5) had all of its
return strokes (3) terminating at the same location.
Each of the three towers of the LC39B LPS was struck
directly by lightning at least once, with tower 1 being impacted
by 2 flashes (10 return strokes), tower 2 by 4 flashes (4 return
strokes) and tower 3 by the first return stroke (with the largest
measured peak current of 2011) of a three-stroke flash with the
2nd return stroke striking tower 2 and the ground
(simultaneously) and the 3rd return stroke striking ground at the
same location as the 2nd return stroke. Tower 2 was the only
tower struck twice with direct strikes and simultaneous nearby
strikes outside the LC39B perimeter fence (about 560 and 615
meters east and south-east of tower 2).
terminal of tower 1 and provide a short electrical path to
ground. The other portion of the incident current flows through
the rest of the LPS to ground, also with a dependency on the
shortest electrical distance of each of the remaining
downconductors. The largest measured currents to ground, as
expected, flow through the downconductors closer to the strike
location.
From the downconductors measured currents to ground,
considering only direct strikes to the LPS:
1.
The median peak current, calculated as the
algebraic sum of downconductor currents to ground,
was 29.1 kA for 16 return strokes (excluding a direct
stroke
which
saturated
two
downconductor
measurements and strokes with simultaneous ground
attachment points).
2.
Rise-times, 10% to 90%, were between 1 and 6 µs,
with an arithmetic mean of 2.9 µs.
3.
The minimum, arithmetic mean and maximum inter
stroke time intervals from:
•
11 subsequent return strokes (direct strikes to the
LPS) were 23, 84 and 180 ms.
•
14 subsequent return strokes (direct and nearby
strikes within the LC39B perimeter, about 1 km2
area) were 17, 71 and 180 ms.
•
38 subsequent return strokes (direct and nearby
strikes detected by LC39B LPS) were 1.5, 116 and
389 ms.
VI. SELECTED WAVEFORMS
A representative set of waveforms comprised of the LC39B
LPS 9 downconductor currents, 12 dH/dt, 10 dE/dt are included
for two selected cases, direct and nearby strikes to the LC39B
LPS. Additionally, salient data from the U.S. National
Lightning Detection Network (NLDN) and the Cloud-toGround Surveillance System (CGLSS) is presented for these
events [4] and [5].
A. Direct Lightning Strikes
Recorded downconductors’ currents show a consistent
incident current division mainly into two portions defined by 1)
the shortest electrical distance between the strike location to
ground and 2) the rest of the LPS. Such current division is
depicted in Fig. 4 where a direct strike to tower 1 (see Fig. 5) is
illustrated. The measured downconductors’ currents are shown
in Fig. 6 and in this case, the shortest electrical distance
between the lightning strike and ground is through
downconductors 1 and 2, which are connected to the air strike
Figure 4. LC39B LPS current distribution scheme due to a direct strike (to
tower 1). Colored arrows (red and blue), indicate the division of the incident
current into two main groups.
Figure 5. First return stroke of a negative lightning three-stroke flash striking
tower 1 of the LC39B LPS on August 14 of 2012 at 21:10:15.7870656 (UTC).
Rate of change of the magnetic and electric fields measured
at LC39B are shown in Fig. 7 and Fig. 8, respectively. Larger
rate of change of fields are also observed on the closer stations
to the strike location.
A direct comparison between the LC39B LPS calculated
current to ground and strike location with the information
provided by CGLSS and NLDN, for a direct strike to Tower 1
on 8/14/2011 at 21:10:15.787065 UTC, reveals the following:
1.
The LC39B lightning instrumentation measured a
peak current to ground of -54.4 kA, 10%-90% risetime of 6.04 µs, transferring 7.75 Coulombs to ground
in 1 ms.
2.
CGLSS reported a peak current of -34.1 kA (37%
peak current underestimation) with a location error of
68 meters southwest of tower 1.
3.
NLDN reported a peak current of -39.8 kA (27%
peak current underestimation) with a location error of
700 meters southeast of tower 1.
Figure 6. LC39B LPS downconductors measured currents to ground for the direct strike to tower 1 on August 14 of 2011 at 21:10:15.7870656 (UTC).
Figure 7. LC39B measured dH/dt for the direct lightning strike to tower 1 on August 14 of 2011 at 21:10:15.7870656 (UTC).
Figure 8. LC39B measured dE/dt for the direct lightning strike to tower 1 on August 14 of 2011 at 21:10:15.7870656 (UTC).
During 2011, it was found that both systems, CGLSS and
NLDN, underestimate the peak current by 10-40% compared to
the LC39B LPS measured currents to ground. Additionally the
minimum, mean and maximum absolute location errors
calculated for all the (19) direct strokes to the LC39B LPS
were 51, 190 and 467 meters for CGLSS (12 samples) and 133,
572 and 1,714 meters for NLDN (14 samples) [4] and
“unpublished” [5].
group, is made of the downconductor(s) within close proximity
to the imaginary line, in which no significant current flow is
observed. A high speed video camera frame, corresponding to
the return stroke of nearby strike presented in this section is
shown in Fig. 10.
It is worth noting the availability of meteorological data,
not included in this manuscript, for all the recorded lightning
events of the LC39B LPS during 2011.
B. Nearby Lightning Strikes
For nearby strikes, the current distribution among the LPS
downconductors is conceptually different than for direct strikes
and it can be seen as currents flowing from the strike location
into the LPS through the closest downconductors and then
leaving the LPS through the downconductors farther away
from the strike location. The current distribution can be
visualized by defining three groups of downconductors
identified by an imaginary line that goes perpendicular to the
azimuth of the strike location, see Fig. 9.
Figure 9. LC39B LPS current flow scheme due to a nearby strike. Colored
arrows (red, blue and green) indicate the three different current flow groups
and brown dashed lines illustrate the imaginary lines indicating the azituth of
the lightning strike location and its perpendicular line referenced to the center
of the path.
The first group is made of all the downconductors between
the strike and the imaginary line, which allows current to flow
into the LPS. The second group is made of all the
downconductors past the imaginary line, which allows the
current to flow out of the LPS. The third, and less obvious
Even though a thorough analysis of nearby strikes has not
been completed at the present time, corresponding
downconductors’ current data show a tendency to balance the
flow of current for both, previously referred, first and second
groups. The arithmetic sum of all currents to ground result in
the displacement current through the LPS. As expected, closer
nearby strikes seem to result on currents to ground with higher
frequency components (see Fig. 11) than farther away nearby
strikes.
Similar to the direct strike, the larger rate of change of the
magnetic and electric fields are observed closer to the strike
location, see Fig. 12 and Fig 13.
A direct comparison between the LC39B lightning
instrumentation system detected strike location and the
information provided by CGLSS and NLDN reveal that for the
nearby negative single-stroke flash striking 473 meters NorthNorthwest of the LC39B center (within the LC39B perimeter
fence) on 8/14/2011 at 21:05:44.080012 UTC, CGLSS reported
strike location error was 122 meters NLDN reported strike
location error was 364 meters. The peak current reported by
both, CGLSS and NLDN for this event were -15.8 kA and 18.4 kA, respectively. Note that the LC39B lightning
instrumentation automated capability to estimate the nearby
stroke peak currents is still under development and it is
expected to be completed by 2013.
Figure 10. Nearby single-stroke negative flash striking withing the LC39B
perimeter fence on August 14 of 2012 at 21:05:44.0800717 (UTC).
Figure 11. LC39B LPS downconductors measured currents to ground for the nearby lightning strike within the pad perimeter on August 14 of 2011 at
21:05:44.0800717 (UTC).
Figure 12. LC39B LPS measured dH/dt for the nearby lightning strike within the pad perimeter on August 14 of 2011 at 21:05:44.0800717 (UTC).
Figure 13. LC39B LPS measured dE/dt for the nearby lightning strike within the pad perimeter on August 14 of 2011 at 21:05:44.0800717 (UTC).
VII. CONCLUSIONS
After less than one year of deployment, the new lightning
instrumentation system at LC39B has shown significant
improvements over the previous lightning instrumentation
system used at KSC. The instrumentation system has proven to
be extremely reliable and accurate, capturing a series of
astonishing images and set of waveforms for typical and
unusual lightning strikes. There is an increased interest to
potentially deploy similar systems throughout KSC and
CCAFS, in which case, in the future, there may be a
comprehensive an integrated lightning observation system with
synchronized lightning instrumentation over an area of several
square kilometers where ground-truth data will be acquired.
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[4]
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