 In this video, we will describe in more detail the satellite payload and present the information needed to perform a reliability block diagram. This technique is part of the risk identification and analysis activities required to develop this case study. Remember, you are participating in a project to design an Earth observation satellite, to take detailed images of a chosen part of the world. Our customer has some requirements regarding safety and dependability. One of the dependability requirements specifies that the reliability target of the satellite is 0.5 during the operational lifespan of 10 years. We suggest doing a reliability block diagram to evaluate the satellite reliability during this operational lifespan. A reliability block diagram is a method that uses blocks for representing different components and showing how the reliability contributes to the success or failure of a complex system. These blocks can be connected in a parallel or series configuration. A parallel connection is used to show redundancy. This means that all components must fail for the path to fail. But if you have a serious path, just one failure is enough to cause the entire path to fail. And finally, knowing the failure rates of each component and the system configuration, we can calculate the reliability of the overall system. Now we will describe the configuration of the different units that are present in our satellite payload. But first, we must explain the two existing types of redundancy. We can have passive redundancy, which means that the redundant unit is off and only goes on if the main unit fails. We can also have active redundancy, which means that all units are working at the same time. For instance, an active redundancy 5 over 6 indicates that we have 6 units but only 5 need to be in operation for the system to work properly. It is important to note that failure rates can be expressed in fit. Fit means failure in time. One fit is equivalent to 10 power minus 9 failures per hour. Also, not all units are required to work continuously. This is known as operational rate. For instance, an operational rate of 10% means that the unit is only on 10% of the time. All this information has to be taken into account when calculating the reliability of each unit. The payload contains the following units. A telescope with a failure rate of 20 feet and connected in a serious path. A camera cover with a failure rate of 10 feet connected in a serious path and with an operational rate of 1%. Two payload interface units with a failure rate of 1,500 feet and active redundancy of 1 over 2. Five camera channels with a failure rate of 2000 feet each, an active redundancy of 5 over 5 and 10% operational rate. A compression and memory unit with a failure rate of 500 feet and an active redundancy of 5 over 6. Finally, three X-band transmission with a failure rate of 2000 feet and active redundancy of 3 over 3 and an operational rate of 3%. When it is not mentioned, we assume an operational rate of 100%. To calculate the reliability, you have to remember the following aspects. An operational distribution is frequently used to model reliability of electronic components. If lambda, if the failure rate, then we can calculate the reliability of each component with the following equation. But if the component has an operational rate R different to 100%, the calculation changes because we have different failure rates when the component is on and when it is off. We know the failure rates when the component is on. For electronic equipment, we can assume lambda off is equal to lambda on divided by 10. And now, the reliability of the component can be calculated as follows. We know that our operational life duration T is 10 years. But we have to express this time in hours like all the failure rates. So T would be 87,600 hours. Finally, to calculate the reliability of the fault unit, we have to consider the type of configuration. For active redundancy 1 among n, we have the following equation. Where r i is the reliability of each component and n is the number of units in parallel. Now you have all the information you need to carry out the reliability block diagram of the payload.