39
Debris impact analysis and mapping results for the
rocket vehicle ALV
aBstract
A risk analysis of the ATK ALV X1 vehicle was
developed by the American company ACTA to
support the NASA space agency Wallops Flight
Facility located in Virginia. This particular risk
analysis obtained results of the probability of im-
pact of fragments of this vehicle that could collide
with a B747 aircraft that could be flying over the
space test area. The ATK ALV X1 was launched
successfully but left its nominal flight path tra-
jectory after 27 seconds, and for safety purposes,
the flight termination system (FTS) was activated
by destroying the vehicle and throwing into space
the fragments that endanger air transport. Once
again, in space history, ACTA contributes to pu-
blic and transportation safety in this manner.
Key words: ATK, ALV, ACTA, NASA, WFF, risk,
trajectory, debris, analysis, impact, aircraft, B747,
FTS, fragments
resumen
Un análisis de riesgo del vehículo espacial ATK
ALV X1 fue desarrollado por la compañía
norteamericana ACTA para dar soporte a la agencia
espacial NASA Wallops Flight Facility, localizado
en Virginia. Este análisis de riesgo en particular,
obtuvo resultados de probabilidades de impacto
de fragmentos o escombros de dicho vehículo que
podría impactar sobre aviones B747 que podrían
estar sobrevolando el área de prueba espacial. El
ATK ALV X1 despegó con éxito, pero salió de
su trayectoria de vuelo después de 27 segundos,
y por seguridad, el sistema de terminación de
vuelo (FTS) fue activado destruyendo al vehículo
y lanzando al espacio los fragmentos que ponen
en peligro al transporte aéreo. Una vez más, en la
historia espacial, ACTA contribuye a la seguridad
del público y transporte en este sentido.
Palabras clave: ATK, ALV, ACTA, NASA, WFF,
probabilidad, impacto, peligro, aviones, B747,
FTS, seguridad, riesgo, trayectoria, escombros,
fragmentos, análisis
L A. A
1 Universidad de San Martín de Porres
Lima - Perú
larriolag@usmp.pe
Análisis de impacto de escombros y resultados de mapeo para el
vehículo rocket ALV
Recibido: febrero 09 de 2018 | Revisado: abril 26 de 2018 | Aceptado: mayo 11 de 2018
https:// doi.org/ 10.24265/campus.2018.v23n25.03
| C | L, | V. XXIII | N. 25 | PP. - | - | | -
40
Introduction
ACTA was asked to provide additional
support to ATK (Alliant Techsystems) and
NASA-WFF (Wallops Flight Facility) in
preparation for the forthcoming launch
of the ALV X1 vehicle. e two areas of
support were: (1) updating the toxic risk
database due to a change in the trajectory
and (2) provide an analysis of the risks to
the aircraft from debris resulting from a
vehicle breakup.
e purpose of the ATK ALV X1
vehicle was to carry two payloads. e
HY-BOLT (Hypersonic Boundary Layer
Transition) and SOAREX (Suborbital
Aerodynamic Reentry Experiment). e
rst was designed to cross the atmosphere
and evaluate the boundary layer as
described by Schetz, J. and Bowersox,
R. (2011). e second to characterize a
new vehicle for re-entry and innovative
self-orientation as described by Eterno,
J. (1989). e vehicle was designed to
reach a height of 400 km and a speed
of approximately 8,500 km / h (Mach
number of 8). At this point, the payloads
should have been ejected.
For this mission, NASA and ATK hired
ACTA to conduct a risk analysis of debris
impact on airplanes in order to prevent
areas of risk and to take the necessary
measures to protect air transport.
However, on August 28, 2008, ATK
ALV X1 was launched successfully but
the ascent lasted only about 27 seconds,
and immediately the vehicle began to
turn o course, which is why the ight
termination system (FTS) was activated
to nish the mission. e results of the
risk analysis that ACTA carried out prior
to the launch, served to support, and
in that sense, prevent disasters due to
debris impacts on aircraft ying over the
spacecraft’s ight area.
Discussion
Two fragment lists were used for the
risk analysis using a program named
RRAT. e rst list contained Stage 2
debris assuming and explosive failure
im the Star 37 Stage 2 solid rocket
motor as described by Eterno, J. (1989).
is debris list started at the Stage II
ignition time of 73 seconds and adjusted
at 10 seconds intervals of ight. e
second debris list contained a complete
fragment list for Stage 1 ight. In this
list, the number of fragments in the
Stage 2avionics section due to a Stage 1
explosion was not reduced as it was for
Stage 2 failures. ATK pointed out that
they have a rather massive aluminum
plate above the Stage 2 attitude control
system (ACS), dened by Larson, and
Wertz, (1992) that shields the avionics
pallet and avionics section from direct
impact from fragments ejected from a
failure/explosion in the lower part of the
vehicle.
No malfunction turns were used
in the analysis because of the limited
time to perform the work. Cross-range
dispersions due to guidance uncertainties
were provided to ACTA in form of a
plot that had results from a Monte Carlo
analysis (2000 trajectories) of guidance
and performance variation (Figure 1).
L A. A
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41
Figure 1. IIP Plots of the Outcome of Many
Random Trajectories from the Uncertainty
in Guidance and Performance.
Figure 2 shows the impact probability
contours for a B747 aircraft ying along a
contour. e primary source for the cross-
range extent of the contours is the fragment
velocities as described by Nelson, Larson,
and Arriola, (2007). No malfunction
turns were used in the analysis because
of the limited time and the cross-range
dispersions due to guidance uncertainties
were not included either.
e impact probability contours
extend downrange approximately 887
NM from the launch pad to the 1x10
-7
contour level.
Figure 2. Aircraft (B747) Debris Impact
Probability Contours Using No Cross-Range
Guidance and Performance Uncertainty or
Malfunction Turn Contribution
e impact probability contours
during second stage would normally
drop o, but this vehicle has a very slow
IIP (instantaneous impact point) rate
during second stage which produces
longer dwell times. Consequently, the
higher probability contours persist until
the end of ight.
To see if the addition of cross-range
uncertainty would change the results,
two more plots were prepared: one with
a 5 nm one-sigma cross-range variation
at burnout and the second with a 10 nm
cross-range variation. ese two numbers
were based on the likely dispersions
estimated from the Monte Carlo results
in Figure 1. ACTA developed a metric
body axis data le (MBOD) for input to
RRAT as described by Nelson, Larson,
and Arriola, (2007) to capture the
cross-range uncertainty in the form of
covariance matrices due to guidance and
performance error. Figure 3 and Figure
4 show how 5 nm and 10 nm (1σ)
cross range guidance and performance
uncertainties aect the impact probability
contours.
Figure 3. Aircraft (B747) Debris Impact
Probability Contours Using 5 nm (1σ)
Cross-Range Guidance and Performance
Uncertainty
D ALV
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42
Figure 4. Aircraft (B747) Debris Impact
Probability Contours Using 10 nm (1σ)
Cross-Range Guidance and Performance
Uncertainty
Comparing Figure 2, Figure 3 and
Figure 4, we nd very little dierence in
the dispersions. us, we conclude that
the dispersion due to fragment velocity
dominates. In addition, all three gures
have high probability contours all the
way to the end of ight. Consequently,
it can be concluded that with this debris
list, these high failure probabilities and a
low accelerating 2
nd
stage, the contours
will persist to the impact region.
Conclusion
Two critiques of the approach
depicted in the charts above have
been made, suggesting these results
are over-conservative. e results are
approximated by assuming aircraft are
ying “along a contour” (or equivalently
around a grid cell at that point) for the
entire duration that debris is a hazard
at that altitude. A rst critique is that
aircraft quickly pass through the region,
so are not exposed to the entire duration
of debris. While it is true that most
aircraft passing through a given location
will be exposed to lower risk, a previous
study has demonstrated that these results
are only slightly conservative compared
to an aircraft with the worst-case ight
path (time and direction) through the
point. However, there is currently non
procedure to prohibit only specic ight
paths (with the resolution necessary
to discriminate this), so it is necessary
to prohibit all ights through points
exceeding the criterion. Secondly, the
method assumes that an aircraft is present,
when in fact, there are few ights, and
therefore one should consider the density
of aircraft. is could be correct when the
consideration is collective risk. However,
the aircraft keep-out region is dened in
order that individual risk is below the
acceptable risk criterion.
References
Schetz, J. & Bowersox R. (2011).
Boundary Layer Analysis, USA:
American Institute of Aeronautics
and Astronautics
Eterno, J. (1989). Ball Aerospace System
Group, CO, USA.
Larson, W., Wertz, J. (1992). Space
Mission Analysis and Design.
Torrance, USA: Microcosm
Nelson, A., Larson, E., Arriola, L. (2007).
Determining Buer Zones for
Experimental Permits. Torrance,
USA: ACTA
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