To be “absolutely safe” a system, product, device or material should never cause or have the potential to cause an accident; a goal practically impossible to achieve. In the realization and operation of systems the term “safety” is generally used to mean “acceptable risk level”, not “absolute safety”.
Acceptable risk level is not the same as personal acceptance of risk, but it refers to risk acceptability by stakeholders’ community or by society in a broad sense. Acceptable risk levels vary from system to system, and evolve with time due to socio-economic changes and technological advancement. Implementing proven best-practices at status-of-art is a prerequisite for achieving an acceptable risk level, or in other words to make a system “safe”. Best-practices are traditionally established by government regulations and norms, and/or by industrial standards. Without such reference the term “safety” or “acceptable risk” becomes meaningless. In other words compliance with regulations, norms and standards represent the “safety yardstick” of a system.
In the development of a space system, safety is achieved through a combination of requirements that go under the names of ‘fault tolerance’ and ‘fault avoidance’, plus by introducing capabilities helpful in case of emergency.
Fault tolerance, consists in the designed-in characteristics that maintains prescribed functions or services to users despite the existence of faults. Fault tolerance is implemented for example by redundancies and barriers. Instead fault avoidance, consists in reducing the probability of a fault by increasing the reliability of individual items (design margins, worst case design, materials selection, use of hi-rel components, de-rating, quality control, testing, etc.). Fault avoidance techniques applied in design are also called “design for minimum risk“: essentially the achievement of increased likelihood that a required function is available, through the use of proven technical standards.
Sometimes technical standards are seen as separate from safety standards just because the relevant technical authorities resides in different groups. As a matter of fact a large number of requirements in technical standards used in space systems development are aimed to safety.
As human spaceflight transition from government sole activity to a variety of commercial and mixed operations, the need arises for industry to develop a notion of safety as their collective responsibility and common strategic goal for business growth. It is the best interest of industry to cooperate among themselves and with regulators at developing, adopting, and enforcing safety and technical standards.
A large body of knowledge exists that has been accumulated in government space programs. It can be reviewed, adapted and re-used, or simply adopted. It should be noted that such standards are discipline oriented and not configuration specific. They can be applied to a variety of systems development from orbital and suborbital vehicles to payloads and station modules. An inventory of such standards was already proposed in recent times by NASA as recommended practices to companies involved in the Crew Commercial Program [CCT-STD-1140 “In the course of over forty years of human space flight, NASA has developed a working knowledge and body of standards that seek to guide both the design and the evaluation of safe designs for space systems”].
Those standards, plus a safety standard drafted by IAASS on the basis of heritage safety requirements used in the NSTS and ISS programs, could be used as initial reference from which to initiate a wider review by all those interested to cooperate to the development of commercial human spaceflight standards.