Developing Safety-critical Software Requirements for Commercial Reusable Launch Vehicles

A number of inventors and entrepreneurs are currently attempting to develop and commercially operate reusable launch vehicles to carry voluntary participants into space. To reduce the risk to the public in the operation of these vehicles, a launch vehicle operator typically performs analyses to identify safety measures and develop safety requirements. The focus of these safety efforts has historically been to develop and implement safety requirements for hardware systems and subsystems. However, software and computing systems are increasingly being used in launch vehicles to control or monitor safety-critical systems, compute or transmit safety-critical data, and detect and mitigate faults. Therefore, identifying the hazards, assessing the risks, and implementing valid safety requirements for these software elements are becoming critical to public safety. This paper presents lessons learned from the failure of space vehicle systems that can be applied to the development of safety-critical software requirements for commercial reusable launch vehicles. The paper also describes a software system safety process recommended by the Federal Aviation Administration (FAA) for developing safety requirements to reduce the risks from the use of software in reusable launch vehicle operations.