Mission Abort Research Articles

State-based mission abort policies for multistate systems

Most of the previous research on optimal mission abort policies was devoted to binary systems that can be only in two states, i.e., operable or failure. However, a wide class of engineering systems is characterized by more than one operable state. Thus, it can be reasonable to terminate a mission and initiate a rescue procedure that can save, e.g., costly or safety-critical systems when a system had deteriorated to a certain extent. A system operates in a random environment modeled by a renewal process of shocks. With each shock, the state of a system can deteriorate with certain probabilities that can eventually result in the total failure. The bivariate constrained probability-wise and cost-wise optimization problems are formulated and the necessary relationships for solving them are derived. The detailed illustrative numerical example is discussed.

Mission Abort Policy for Systems with Observable States of Standby Components.

For some critical applications, successfully accomplishing the mission or surviving the system through aborting the mission and performing a rescue procedure in the event of certain deterioration condition being satisfied are both pivotal. This has motivated considerable studies on mission abort policies (MAPs) to mitigate the risk of system loss in the past several years, especially for standby systems that use one or multiple standby sparing components to continue the mission when the online component fails, improving the mission success probability. The existing MAPs are mainly based on the number of failed online components ignoring the status of the standby components. This article makes contributions by modeling standby systems subject to MAPs that depend not only on the number of failed online components but also on the number of available standby components remaining. Further, dynamic MAPs considering another additional factor, the time elapsed from the mission beginning in the event of the mission abort decision making, are investigated. The solution methodology encompasses an event-transition based numerical algorithm for evaluating the mission success probability and system survival probability of standby systems subject to the considered MAPs. Examples are provided to demonstrate the benefit of considering the state of standby components and elapsed operation time in obtaining more flexible MAPs.

Dynamic mission abort policy for systems operating in a controllable environment with self-healing mechanism

Catastrophic failures of safety-critical systems could result in significant economic losses and damage. To improve the survival probability of safety-critical systems, self-healing mechanism is usually considered in the design stage and mission abort may be conducted if the failure risk becomes too high. We investigate the optimal mission abort policies for systems subject to a controllable shock process with self-healing mechanism. Minor failure and catastrophic failures are two competing failure modes of the system. Imperfect repair is carried out when a minor failure occurs and the external shock process is renewed after the imperfect repair. Mission abort decisions are considered based on the time in mission and the number of experienced minor failures. The optimal mission abort problem is formulated within the framework of stochastic dynamic programming to minimize the expected total cost of mission failure, system failure and imperfect repair. The structural properties of the optimal policy are investigated using the optimal stopping theory and a case study is presented to illustrate the obtained results.

Mission abort and rescue for multistate systems operating under the Poisson process of shocks

The paper discusses mission abort and rescue strategies for multistate systems with different levels of performance. A system operates in a random environment modeled by the non-homogeneous Poisson process of shocks. With each shock, the state of a system stochastically deteriorates gradually moving to the state of a total failure. To prevent this event and to increase a system survival probability, a mission can be aborted and a rescue procedure can be activated. The number of experienced shocks is a decision parameter for the corresponding optimization problem that aims at maximizing the mission success probability subject to providing the desired level of survival probability. A detailed numerical example illustrates our findings.

Optimal aborting rule in multi-attempt missions performed by multicomponent systems

When the risk of a system's failure during a mission increases with time, it may be reasonable to abort a mission and to attempt it again after the corresponding rescue procedures. This risk can increase with time either when a system's lifetime is characterized by the increasing failure rate, or due to a hostile environment. In this paper, a random environment is modeled by the point process of shocks. Each shock increases the failure probability, thus exhibiting the aging effect. We generalize some recent results reported in the literature to the multi-attempt case when each of statistically identical system's components can independently complete a mission. The corresponding probabilistic model is developed and the tradeoff between a mission success probability and the expected number of lost components is discussed. The problem of minimization of the overall expected operational losses is formulated. Different types of abort policies have been compared in the detailed illustrative example. It was shown that the smallest expected operational losses can be achieved when the mission abort rule depends on the number of an attempt and on the number of components starting this attempt.

Optimal mission abort policies for multistate systems

All previous research on optimal mission abort policies was devoted to binary systems that can be only in two states, i.e., operable or failed. This paper considers mission abort and rescue strategies for multistate systems that, apart from a completely operable state and the state of a total failure, can operate in intermediate states with different levels of performance. A system operates in a random environment modeled by a renewal process of shocks. With each shock, the state of a system can deteriorate with certain probabilities that can eventually result in the total failure. Therefore, in order to increase system's survival probability, a mission can be aborted and a rescue procedure can be activated. The trade-off between the mission success probability and the system's survival probability is studied and an optimal number of shocks for initiating the abort procedure is defined by solving the corresponding optimization problem. The detailed numerical example illustrates our findings.

Mission abort policy optimization for series systems with overlapping primary and rescue subsystems operating in a random environment

This work considers a system consisting of two overlapping subsets of components. Availability of all components composing the subsets is required for performing the primary mission (PM) and the rescue procedure (RP) respectively. The system is exposed to random shocks during its operation. The components’ resistance to shocks deteriorates with the number of experienced shocks. Failure of any component from the PM subset results in the mission failure. To enhance the system's survivability, the PM can be aborted upon occurrence of the nth shock without waiting for the PM failure. In the case of PM failure or abortion, the RP is activated. If, at least one component from the RP subset does not survive all shocks occurring until completion of the RP, the system is lost. The choice of n should balance the mission success probability and the system survival probability. An algorithm for obtaining these metrics as functions of n is suggested and an example of analyzing the tradeoff between them is given. An example of obtaining the optimal mission abort policies is provided.

Optimal Abort Rules for Multiattempt Missions.

Many real-world systems use mission aborts to enhance their survivability. Specifically, a mission can be aborted when a certain malfunction condition is met and a risk of a system loss in the case of a mission continuation becomes too high. Usually, the rescue or recovery procedure is initiated upon the mission abort. Previous works have discussed a setting when only one attempt to complete a mission is allowed and this attempt can be aborted. However, missions with a possibility of multiple attempts can occur in different real-world settings when accomplishing a mission is really important and the cost-related and the time-wise restrictions for this are not very severe. The probabilistic model for the multiattempt case is suggested and the tradeoff between the overall mission success probability (MSP) and a system loss probability is discussed. The corresponding optimization problems are formulated. For the considered illustrative example, a detailed sensitivity analysis is performed that shows specifically that even when the system's survival is not so important, mission aborting can be used to maximize the multiattempt MSP.

Gamma process based optimal mission abort policy

Various safety-critical systems such as aircrafts, submarines and space stations are required to perform missions continually in harsh environment. To enhance the survivability of such systems, a mission can be aborted when the mission completion becomes problematic and a rescue procedure is immediately initiated. This paper investigates the optimal mission abort policy based on a two-stage Gamma process which can be separated into normal and defective stages. Degradation-based abort policy where a mission is aborted if the system degradation level is higher than a threshold and duration-based abort policy where a mission is aborted if the duration in defective stage is larger than a threshold are considered. The mission success probability and system survivability under these two policies are evaluated and the optimal mission abort thresholds balancing the tradeoff between the mission success probability and system survivability are investigated. A numerical example on an unmanned aerial vehicle (UAV) is presented to illustrate the applicability of the proposed abort policies.

Designing Mission Abort Strategies Based on Early-Warning Information: Application to UAV

The mission abort is an effective action to reduce the risk of casualties and enhance the survivability of mission-based systems such as aircrafts, submarines, and unmanned aerial vehicles (UAVs). A main task in real operations is to strive for balance between the mission reliability and the system survivability via elaborate mission abort plans. In this paper, we design the optimal mission abort policies based on the information of early-warning signals, which indicates the possible forthcoming fatal malfunction. Depending on the acquisition time of such information, the operator may immediately abort the mission, or ignore the information and continue the task. Within the framework of a constant mission duration, we carry out an economic analysis for the above problem. The optimal abort decision that minimizes the expected total economic loss is investigated. We further extend the proposed model to the scenario of a random mission duration and derive the corresponding optimal abort decisions. A case study on a UAV executing power-grid inspection missions is used to illustrate the applicability of the abort policies.

Optimal mission abort policy for systems subject to random shocks based on virtual age process

Safety critical systems such as aircrafts, submarines and space stations are required to perform various missions. To enhance the survivability of such systems, a mission can be aborted when a certain malfunction or incident condition is satisfied and a rescue procedure should be activated. This paper develops a novel mission abort policy for systems experiencing both internal failure and external shocks. Failure process of the system can be divided into two stages from new to the initialization of a defect, and from that to failure. Motivated by the virtual age concept, the impact of external shocks is characterized by random virtual age increment in the two stages. We consider a policy where a mission is aborted if the duration in defective state is larger than a given threshold. Under the stochastic failure model and mission abort policy, mission success probability and system survivability are evaluated and the optimal abort threshold balancing the tradeoff between the system survivability and the mission success probability is investigated. A numerical example on a cooling system in chemical reactors is given to illustrate the applicability of the abort policy.

Influence of failure propagation on mission abort policy in heterogeneous warm standby systems

In many life-critical applications (e.g., spacecraft, aircrafts and chemical reactors), accomplishing a specified mission or aborting mission objectives in the case of certain condition being met to survive the system are both crucial. While conventional reliability models have typically focused only on evaluating the mission success probability, few of recent research addressed effects of mission aborts and studied system survivability. However, these works fail to consider propagated failures that can make significant contributions to the mission failure and may affect the optimal mission abort policy adopted for the system. In this paper, we suggest a numerical method for addressing effects of failure propagations in analyzing the mission success probability (MSP) and system survivability (SS) of 1-out-of-N warm standby systems subject to mission abort. The system may be heterogeneous, composed of components with different standby modes, and different performance and failure time distribution parameters. Both the activation sequence of those heterogeneous components and the adopted mission abort policy can affect the system performance metrics greatly. Therefore, we make further contributions by formulating and solving optimization problems that find the optimal mission abort policy for systems with any given component activation sequence or the optimal combination of mission abort policy and component activation sequence, maximizing the MSP while satisfying a desired SS level. Examples are provided to demonstrate influence of propagated failures on system performance and optimization solutions. Examples also show that the optimal abort policy determined can achieve a good balance between MSP and SS taking into account failure propagation.

Optimal mission abort policy for partially repairable heterogeneous systems

To enhance survivability of many real-world critical systems (e.g., aircrafts, human space flight systems and dangerous technological processes), mission abort procedures are often utilized in practice. In such cases, in order to improve survivability, a rescue or recovery procedure is initiated. In this paper, we first develop a methodology for obtaining the mission success probability (MSP) and the system survival probability (SSP) for heterogeneous systems with major and minor failures. A major failure is non-repairable and results in a failure of a mission, whereas a minor failure is minimally repaired. We consider a policy where a mission is aborted and a rescue procedure is activated if the mth minimal repair occurs before time ξ since the start of a mission. We demonstrate the tradeoff between the SSP and the MSP that should be balanced by the proper choice of the decision variables m and ξ. A detailed illustrative example is presented.

Mission abort policy balancing the uncompleted mission penalty and system loss risk

Mission abort policy is an effective tool for enhancing survivability of many real-world systems when a failure during a mission results in a substantial economic loss. When continuation of a mission is associated with high risks, its primary task can be aborted and a rescue procedure can be initiated to enhance survivability, and therefore, to decrease losses. When the uncompleted tasks for the aborted mission are associated with monetary losses, the tradeoff between the possible losses associated with the uncompleted mission and with the system failure should be balanced. In this paper, we develop a methodology for evaluating the expected uncompleted fraction of a mission and survivability of systems experiencing both internal failures and external shocks. We consider a policy when a mission is aborted and a rescue procedure is activated if the mth shock occurs before time ξ since the mission start. Then we demonstrate the tradeoff between the probability of a system loss and the expected uncompleted fraction of a mission and formulate the corresponding problem of the optimal choice of the decision variables m and ξ. An illustrative example of a mission performed by an unmanned aerial vehicle is presented.

Optimal mission abort policy with multiple shock number thresholds

At many instances, it is important to keep a system from being destroyed or “lost” at a cost of not completing its mission. Therefore, to enhance survivability of many real-world critical systems (e.g. aircrafts and human space flight systems), mission abort procedures are often utilized in practice. In this article, in order to suggest an optimal abort policy, we first develop a methodology for obtaining the mission success probability and survivability of system experiencing both internal failures and external shocks. Each shock increases degradation in a system, and therefore, the number of experienced shocks can be considered as a decision parameter. We divide the mission time into a number of adjacent intervals and suggest a policy when a mission is aborted (and a rescue procedure is activated) if the number of shocks exceeds the value predetermined for each interval. We demonstrate the trade-off between system survivability and mission success probability that should be balanced by the proper choice of the mission abort policy. An illustrative example of a mission performed by an unmanned aerial vehicle is presented.

Co-optimization of state dependent loading and mission abort policy in heterogeneous warm standby systems

This paper models and optimizes a 1-out-of-N: G heterogeneous warm standby system subject to state-dependent component loading and mission abort policies. For circumstances where a system's survival may have a higher priority than continuing a specified mission due to cost or safety reasons, when a certain incident or malfunction condition is met based on a predefined decision rule, the mission objective is aborted and a rescue procedure is performed for system survival. The mission abort policy implemented can affect the system performance significantly. In addition, load levels of system components affect their performances (e.g., productivity) and time-to-failure distributions, and further affect the overall system performance. This paper makes new contributions by formulating and solving a co-optimization problem that finds the optimal combination of mission abort and component loading policies, maximizing the mission success probability while providing a desired level of system survivability. As demonstrated through examples, the co-optimization results can facilitate optimal decisions on effective and safe operations management of warm standby systems.

Optimal Mission Abort Policy for Systems Operating in a Random Environment.

Many real-world critical systems, e.g., aircrafts, manned space flight systems, and submarines, utilize mission aborts to enhance their survivability. Specifically, a mission can be aborted when a certain malfunction condition is met and a rescue or recovery procedure is then initiated. For systems exposed to external impacts, the malfunctions are often caused by the consequences of these impacts. Traditional system reliability models typically cannot address a possibility of mission aborts. Therefore, in this article, we first develop the corresponding methodology for modeling and evaluation of the mission success probability and survivability of systems experiencing both internal failures and external shocks. We consider a policy when a mission is aborted and a rescue procedure is activated upon occurrence of the mth shock. We demonstrate the tradeoff between the system survivability and the mission success probability that should be balanced by the proper choice of the decision variable m. A detailed illustrative example of a mission performed by an unmanned aerial vehicle is presented.

Optimal mission abort policy for systems in a random environment with variable shock rate

To enhance survivability of many real-world critical systems (e.g., aircrafts and human space flight systems), mission abort procedures are often utilized in practice. Specifically, the mission objectives of these systems can be aborted in cases where a certain malfunction condition is met or some obstacles/ hazards occur. Then a rescue or recovery procedure is initiated to enhance survivability. Traditional system reliability models typically cannot address the effects of mission aborts, and thus are not applicable to analyzing systems subject to mission abort requirements. In this paper, we first develop a methodology to model and evaluate mission success probability (MSP) and survivability of systems experiencing both internal failures and external shocks. We consider a policy when a mission is aborted and a rescue procedure is activated if the m-th shock occurs before time ξ since the start of a mission. We demonstrate the tradeoff between system survivability and MSP that should be balanced by the proper choice of the decision variables m and ξ. An illustrative example of a mission performed by an unmanned aerial vehicle is presented.

Human exploration of near earth asteroids: Mission analysis for chemical and electric propulsion

This paper presents a mission analysis comparison of human missions to asteroids using two distinct architectures. The objective is to determine if either architecture can reduce launch mass with respect to the other, while not sacrificing other performance metrics such as mission duration. One architecture relies on chemical propulsion, the traditional workhorse of space exploration. The second combines chemical and electric propulsion into a hybrid architecture that attempts to utilize the strengths of each, namely the short flight times of chemical propulsion and the propellant efficiency of electric propulsion. The architectures are thoroughly detailed, and accessibility of the known asteroid population is determined for both. The most accessible asteroids are discussed in detail. Aspects such as mission abort scenarios and vehicle reusability are also discussed. Ultimately, it is determined that launch mass can be greatly reduced with the hybrid architecture, without a notable increase in mission duration. This demonstrates that significant performance improvements can be introduced to the next step of human space exploration with realistic electric propulsion system capabilities. This leads to immediate cost savings for human exploration and simultaneously opens a path of technology development that leads to technologies enabling access to even further destinations in the future.

A new aerodynamic decoupled frequential FDIR methodology for satellite actuator faults

SUMMARYThis paper presents new results regarding the development of a supervision scheme for a nonlinear satellite model. The main issue concerns the handling of frequency faults affecting the reaction wheels of a spacecraft attitude control system, that is, how to detect and isolate faults, how to determine the different frequencies characterising these faults through spectral analysis and lastly, how to prevent propagation into failures with potential mission abortion as a consequence. Thus, this work investigates the design of a scheme for fault detection, isolation and control reconfiguration applied to the reaction wheels of a spacecraft attitude control, based on the satellite model. This scheme is classifiable as active fault tolerant control. As the study focuses on a general satellite nonlinear model, where aerodynamic and gravitational disturbances, as well as measurement errors, are present, the robustness of the suggested strategy is achieved by exploiting an explicit disturbance decoupling method via a nonlinear geometric approach. To achieve accurate fault diagnosis, aerodynamic disturbance decoupling represents the key point because the aerodynamic model is often uncertain. Moreover, an improvement of the nonlinear geometric approach is presented, to realise both aerodynamic and manoeuvre decoupled fault diagnosis. To the best authors’ knowledge, this is the first works presenting a methodology for frequency fault diagnosis, which is based on the nonlinear geometric approach for fault and disturbance decoupling. The obtained results demonstrate that the proposed methodology can achieve better performances with respect to traditional fault detection and isolation schemes. Copyright © 2013 John Wiley & Sons, Ltd.