An example of Phased Mission System (PMS) 

A phased-mission of an ideal space application

- a space application whose mission alternates operational phases as Launch, Planet, Scientific Observations 1 and Scientific Observations 2 with Hibernation phases, typically entered to maintain a low level of activity during periods of navigation
- the next phase to be performed is to be chosen at the time the preceding phase ends. For instance, a secondary goal could be sacrificed if there are few available resources: these resources should be better held in a spare state in order to guarantee a reliable execution of the main goal of the mission
- operational phases have stringent dependability requirements

PMS equipped with:

- 4 redundant identical processors
- depending on the phase, some of the processors can be kept as spares

Fault hypothesis:

- processors fail and are repaired independently from each other; the repair occurs with a rate m
- processors fail with phase-dependent rates: lLaunch=lPlanet=lSc.Obs1=10-5, lHiber=10-6 and lSc.Obs2=10-4
- the activation of a cold spare may succeed or fail, with probability c and 1-c, respectively

Dependability measures of interest:

- probability that the system succesfully completes its mission, that is the reliability of the PMS at the end of the mission time

Model of the system in DEEM: Phase Net (PhN) and System Net (SN):

Obtained results:

This file was generated Fri Sep 9 15:23:33 2005
 

STUDY_NAME: scenario_1

STUDY_variables_setting:
Time    8.853600e+04
'lambda_LP    '[1e-7, 1e-3, *10]
'mu    '[1e-5, 1e-2, *10]

_____________________________________________________________________________

'REW_MEASURE_NAME: Reliability
'REW_FUNCTION: IF(mark(Fail)=0)THEN(1)ELSE(0)
'ANALYSIS_TYPE: ISTANTANEOUS
'
'lambda_LP/mu    1.000000e-05    1.000000e-04    1.000000e-03    1.000000e-02    
1.000000e-07    9.991043e-01    9.996496e-01    9.997213e-01    9.997292e-01    
1.000000e-06    9.883220e-01    9.984909e-01    9.996039e-01    9.996907e-01    
1.000000e-05    6.147312e-01    9.495937e-01    9.975957e-01    9.992435e-01    
1.000000e-04    3.604473e-05    6.076581e-02    9.022252e-01    9.888153e-01    
1.000000e-03    3.628080e-44    1.117069e-32    5.567967e-08    5.263088e-01

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