Range Safety Assessment

Project Description and Significance

The Aerosciences and Compressible Fluid Mechanics Department at Sandia performs a range of safety and dispersion analyses for Sandia's rocket-system and reentry-vehicle flight tests, and for rocket systems and flight tests launched from Sandia facilities as a service to external organizations. Such analyses quantify (a) the standard dispersion about a nominal trajectory, (b) the types and probabilities of failure occurrence, (c) the effects of these failures on the vehicle's trajectory, (d) the hardware ground-impact statistics, (e) and the expectations for casualty and damage caused by hardware impact.

Although we have successfully performed range safety and dispersion analyses for over 30 years, there is increasing concern both within and outside Sandia about safety procedures and lack of formal documentation. To improve the quality of our analyses, we are integrating probabilistic risk-assessment (PRA) approaches into flight safety analyses.

Sandia's Contribution

There are six steps in the procedure used to quantify the risks associated with a specific flight test.

Analyze failure modes and probabilities. A detailed systems analysis is performed by the Reliability Assessment Department to determine possible failure modes and their associated probabilities. Any previous failures in flight vehicles are analyzed.
Determine effects of failures on flight behavior. Various system failures are grouped by their effects on the flight behavior of the vehicle. Those failures that would result in a mission failure, but would not cause a deviation of the vehicle from its planned flight path, are not included.
Make perturbed trajectory simulations. For each group of failures, six-degree-of-freedom Monte Carlo* trajectory simulations are made from the time of failure until a destruct action is taken by the range safety officer or the vehicle begins to break up. *(Monte Carlo simulation consists of running a computer code multiple times, using input parameters that vary between runs. The parameters are usually randomly selected from a pre-defined statistical distribution. This method propagates uncertainty in the values for model input parameters to provide a distribution of possible model outputs that represent the range of output uncertainty.)
Develop destruct/debris model. Debris models are developed on the basis of the vehicle's structural characteristics and the characteristics of the flight termination system. Thermal demise of pieces during reentry is considered when desired.
Conduct debris-trajectory simulations. Monte Carlo trajectory simulations of each of the debris pieces are conducted to ground impact.
Generate probability density function for the casualty expectation. The ground impacts of the Monte Carlo trajectory simulations are used to generate a statistical footprint, a probability density function (PDF). This PDF is then combined with map and demographic data to calculate probabilities of impact within keep-out zones and the probability of injury to people, the casualty expectation.

As worldwide civil space-related activities intensify and the number of launches and recoveries at a greater array of launch sites grows, there will be increasing demand for the launch agency to satisfy more stringent requirements to ensure the safety of people and assets adjacent to the launch and recovery areas, and to the flight corridors. While it is impossible to ensure absolute safety, risk minimization will become essential, and the remaining risks must meet acceptable standards.

Sandia's research in this area is unique and will contribute to creating a much enhanced risk analysis tool for all rocket testing activities. Today's safety- conscious environment makes it important to extend risk-assessment capabilities and codes beyond those that currently exist for U.S. test ranges. Sandia's work is intended to provide enhancements such as:

Addressing launch sites and specific missions in ways that are adaptable to most space technology and manufacturing flights.
Describing the multiple-degree-of-freedom motion of the complex multistage launch platforms and recovery payloads, their guidance and control systems, or their descent and landing systems.
Considering the effects of statistical variations in vehicle aerodynamics, atmospheric conditions, hardware and software reliability, and flight-sequencing scenarios on trajectory behavior.
Meeting modern standards for documentation and code quality control.
Applying rigorous, defensible, mathematical, probabilistic risk-assessment technology coupled to the complete dynamic equations of motion.

Future Work

Our current capability to perform range-safety risk assessments is very labor-intensive. More needs to be done to automate the procedures, to link the different code modules, and to more fully integrate PRA technology. The overall analysis procedure can be improved and streamlined.

For further information, contact:

Walter H. Rutledge
Sandia National Laboratories, MS-0825
Albuquerque, NM 87185-0825
Phone: (505) 844-6548
e-mail: whrutle@sandia.gov

Submitted October 1996
Layout design by Wanda Mar.