THE SMART PROCESS
The SMART process encompasses all the activities (analyses, modelling, test…) set up in the frame of a project (product to develop) to meet the specified SMART performances.
Those activities, generally specified in a set of standards, are tailored and amended as necessary to cope with the needs and defined in a SMART Plan.
It is essential to implement this process in the early stages of product design. ‘Prevention is better than cure’
THE SMART STANDARDS
There are many standards defining the activities of the SMART process. These standards are domain-oriented : nuclear, space, aeronautics, automotive… with common engineering techniques dedicated to each domain objectives, different from one domain to the next.
In the aeronautical sector, for an aircraft, safety is the top requirement (safety first !) and the operational availability referred to as ‘operational-reliability’ is optimized (the aircraft is ready for the next flight in time).
In the nuclear sector, the objective is to maintain and manage production within the safety barriers (safety levels).
In the space sector, safety is mandatory on the ground during the launch preparation (propellant control…). In orbit, priority is given to reliability, mainly because a space vehicle is non-repairable, over the mission time with space debris mitigation up to disposal.
The space sector refers to the ECSS (European Cooperation for Space Standardization) system with ECSS-Q-ST-30 (Dependability) and ECSS-Q-ST-40 (Safety)
THE NOTIONS
RELIABILITY is the ability of a system to achieve :
- a specified mission (Functions and Performances)
- under given conditions
- Over a given time
AVAILABILITY is the ability of a system to achieve :
- a specified mission (Functions and Performances)
- under given conditions
- AT a given time
MAINTAINABILITY is ability of the system to recover :
- a specified operational state (nominal or degraded service)
- under given conditions and with specifed recovery means
- Within a given time (Repair time)
SAFETY
SAFETY is the ability of a system to prevent People from any danger, also to Properties and the Environnement.
RELIABILITY and SAFETY are based on the same techniques but aimed at different objectives : Reliability refers to the mission whereas Safety relates to the integrity of people, properties and the environment.
TESTABILITY is the ability of a system to be tested :
- checking essential and healthy characteristics to guarantee the reliability of the system
- in defined operating modes
- internally (BIT Built-InTest diagnosis) or externally (availability of pertinent parameters)
- at a given time
THE METHODS
Numerous methods are used to support SMART process.
They relate to :
The analyses : most of them are either top-down analyses (e.g. Fault tree) or bottom-up analyses (e.g. FMEA)
RELIABILITY
- Reliability prediction (P)
- FMEA/FMECA (Failure Modes Effects Criticality Analysis)
- HSIA (incl in FMEA) (HW SW Interface Analysis)
- Contingency Analysis
- Fault Tree
- Common Cause Analysis
- WCA (Unit level) (Worst Case Analysis)
- PSA (Unit level) (Parts Stress Analysis)
- Zonal Analysis (incl in FMEA)
- FDIR (Failure Detection Isolation and Recovery)
AVAILABILITY
- Availability prediction (P)
MAINTAINABILITY
- Maintainability prediction (P)
SAFETY
- Hazard Analysis
- SAFETY Risk Assessment (P)
- Warning Time Analysis
- Caution and warning Analysis
- Common Cause Analysis
- Fault Tree
- Human error analysis
- FMECA
- Zonal Analysis
Modelling : from simple ones (e.g. mathematical model representing the active redundancy 1 out of 2) to complex ones (e.g. MBSE : Model-Based System Engineering et MBSA : Model-Based Safety Assessment), the modelling techniques make it possible to automate the analyses and to guarantee the consistency of the analyses with the system configuration.
Tests :
There are different kinds of tests aiming at reliability and safety characterization :
- Screening : to demonstrate that the early defects have been eliminated from a batch of parts
- Reliability : to demonstrate a failure rate or a probability of success at elementary level
- Functional : to demonstrate the ability of the product to perform the specified functions
- Lifetime : to demonstrate the appropriate margin versus wear-out phenomenon
- Radiation : to demonstrate an SEU (Single Event Upset) rate or a safety margin towards cumulated radiation dose
- Characterisation : to assess the margins of the product key characteristics
- Maintainability : to assess the capability for a LRU (Line replaceable unit) to be replaced
- Safety : to demonstrate specific safety characteristics (e.g. Burst test to demonstrate the safety factor of a pressurized vessel)
THE TOOLS
A lot of tools are dedicated to SMART analyses and modelling. These tools are generally specific to the domains on which they are applied. In some cases they could be mandatory (e.g. certification).
They relate to :
- the analyses (e.g. prediction, FMEA…)
- the modelling (e.g. Monte Carlo simulation)
- the tests
Nevertheless, for simple analyses, ‘simple’ tools are sufficient.
TRENDS & INNOVATIONS
- ‘New Space’, this new paradigm aims at democratizing the access to space through cost reduction for design and manufacturing mainly based on a selective approach, ‘Light as possible, Deep as necessary’.
- MBSE (Model-Based System Engineering) et MBSA (Model-Based Safety Assessment) the objective of which is to use the breakthrough of numerical simulation to analyze / simulate the failures in order to assess the system behaviour.
- Operational feedback or in-service feedback may constitute an asset to select the effort to be put on critical items, to avoid to repeat errors and to implement best practices.
- REUSE, reuse of parts, reuse of elements and now even reuse of space vehicle (after re entry) allow to reduce the cost and open a new window on space.
- DISPOSAL and DEBRIS : space debris can no longer be ignored. The design of space vehicles shall implement (by law or by regulatory requirements) provisions to avoid to create debris in-orbit and to integrate capacity for safe disposal at the end of life. (e.g. French Space Operations Act)