Distribution A: Approved for public release
REDUCING BLAST DISTANT FOCUSED OVERPRESSURE EFFECTS
Paul Braithwaite, Dan Cheke, Joe Kliger, Brian Liechty, Robert Wardle
Northrop Grumman Innovation Systems; Brigham City, Utah, USA
ABSTRACT
Many factors are considered when evaluating hazards posed by large launch vehicles during takeoff and
early stages of flight. These factors include, but are not limited to: atmospheric conditions, possible failure
scenarios, launch vehicle mass, propellant type and classification, accident-induced overpressure, grain geometries
and burn back profiles, debris generated during a failed launch, local terrain, permanent and transient population,
and so forth. To provide guidance for launch availability of a new all solid propellant launch vehicle, a preliminary
analysis was performed. This analysis predicted the window to safely launch would be unacceptably low and formed
the impetus for additional work to improve product safety and enlarge the launch window.
The product improvement study described in this paper includes modeling and simulation, piecewise full-
scale experimental work, and full-scale validation testing. These efforts culminated in improved product safety and a
substantially increased launch window for the subject vehicle. Comparisons of initial and revised launch availability
predictions provide system-level guidance designed to minimize hazards associated with launch vehicles using large
solid rocket motors (SRM).
INTRODUCTION
Prior to launching rocket-powered launch vehicles, range safety officers perform a careful assessment of
the possible hazards associated with the specific vehicle. This assessment involves consideration of several different
types of hazards including toxicity, debris, and overpressure. Work described in this paper focuses on the
overpressure aspect of launch availability associated with large solid rocket motors (SRM) that are powered using
hazard classification 1.3 solid rocket propellants.
During the past several decades, researchers have carefully studied and characterized the energy released
when hazard class 1.3 propellants are subjected to various insults. The most comprehensive study with the greatest
relevance to SRM fallback was the PIRAT study.
1.
This study was performed by a number of organizations in
response to concerns over launch accidents that resulted in SRM fallback events.
One of the important findings of this study was that hazard classification 1.3 propellants do not detonate on
impact, rather they release their energy through a rapid combustion/deflagration event as flame propagates through
fractured propellant. Even though this reaction is markedly slower than classical shock-to-detonation events, the
energy can be released rapidly enough to generate a shock wave. A depiction of such an event is shown in Figure 1.
Figure 1. Depiction of Combustion-driven Deflagration That Can Occur Through
Damaged Propellant During Solid Rocket Motor Fallback
