According to veteran russian cosmonaut Oleg Kotov, quoted in a New Scientist article the soviet Buran shuttle (1) was much safer than the American shuttle due to fundamental design decisions. Kotov’s comments once again underline the importance to safety of architectural decisions in the early phases of a design.
One example of the inherently safer design was the decision to use the Energya liquid fueled and engined rocket for the booster segment, rather than having engines on the Buran shuttle. This meant no external fuel tank and no insulation problems.
This is a great example of how a simple architectural decision, in this case to strictly allocate mission functions to one flight system segment, can have profound implications for the safety of the system. Another example is the architectural decision not to provide a crew escape for the American shuttle, while Buran provided ejector seat escape even for mid-deck crew positions. One should note that the final American shuttle architecture (the external tank) was the end result of a series of very complex compromises and redesigns forced by budgetary cutbacks and changing government priorities. Whereas the Buran’s architecture, mission and funding was a good deal simpler.
Evaluating risk during conceptual design is usually quite difficult because although hazards maybe apparent their likelihood is extremely difficult (if not impossible) to evaluate. This can lead to conceptual designers building in hazards inadvertently, as was the case with the shuttle program, through a series apparently ‘benign’ architectural tradeoffs. Addressing this problem of uncertainty Nancy Leveson of MIT has developed a method using the hazard mitigation potential of identified architectures as an analog for risk (Leveson & Dulac 2009). For those of you interested in safety during the early architectural design phase, I’d recommend having a read.
1. Buran means snow storm, a very cool name :-).
1. Leveson, N., Dulac, N., Incorporating Safety Risk in Early System Architecture Trade Studies, AIAA Journal of Spacecraft and Rockets, Vol. 46, No. 2, March-April 2009.