Significance and Use
4.1 Flight crew safety is a complex and all-encompassing goal of human spaceflight. The entire spacecraft is designed to get the flight crew safely to and from their Low Earth Orbit (LEO) destination. In the spirit of Specification F3479, Failure Tolerance for Occupant Safety of Suborbital Vehicles, failure tolerance, or an equivalent means of control where failure tolerance is impractical, is the primary control for prevention of catastrophic hazards that cannot be eliminated from the design. This is true for all hazards which may result in a catastrophic event. The spacecraft can be also be designed with increased levels of failure tolerance to enhance the likelihood of mission success.
4.2 This guide is focused upon the design and operational capabilities necessary to support flight crew survivability when failure tolerance has been exhausted. For example, a spacecraft may have three mission computers that perform identical functions. Typical rules that govern the flight operations might allow continuation of the mission after the first failure. Following the second failure, a mission abort is likely using the single remaining mission computer to return the spacecraft to safety. Should this third computer fail, emergency systems are available to assist the return of the flight crew to safety when possible, and it is those systems that are the focus of this guide. Note that for each emergency situation described herein, a set of emergency procedures and the equipment to implement them will be available in order for the crew to survive.
4.3 LEO missions are divided into pre-launch, ascent, orbit, reentry, and landing. Note that there are separate, additional considerations for transport of humans beyond LEO and for missions having crewed durations in LEO of greater than approximately 30 days which are not within the scope of this guide.
Scope
1.1 The purpose of this guide is to provide guidance for current and developing space flight operators who intend to fly humans on spacecraft. The occupants include the crew and spaceflight participants in the orbital vehicles. This guide is targeted primarily toward ground launched, Low Earth Orbit (LEO) spacecraft which provide transportation from the surface to orbit followed by subsequent rendezvous with an orbital complex or short-duration free flight orbit operations, and safe return to Earth’s surface. As used in the guide, LEO is an approximate circular orbit within ~2000 km of Earth’s surface. Longer duration spaceflight (>approximately two weeks) aboard an orbital space station poses unique design and medical constraints which are not specifically addressed in this guide.
1.2 The methods in this guide are best practices. Having prior positive performing systems may be a basis for compliance to this guide.
1.2.1 This is a non-comprehensive subset of best safety practices for crew survivability of catastrophic hazards for which all failure tolerance has been exhausted. This is further elaborated upon in 1.5 and 4.2.
1.3 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.4 Each spacecraft will present its own set of safety hazards that the user of this standard is expected to analyze and implement survivability options where practical. Also, note that safety is an inherent characteristic of a system, not the product of a few key post-hazard mitigation features. History has shown that a safe and successful spaceflight system is built and operated to the highest possible standards of design robustness, manufacturing quality, inspection, test, and operation, including maintenance and sustaining engineering. The addition of the design features and capabilities as recommended in this guide cannot and is not intended to make up for deficiencies in these basics. It is the responsibility of the user of this standard to establish appropriate safety, survivability, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For example, with regard to survivability, certain operators will likely require additional crew survivability capabilities be provided prior to permitting their space vehicle to fly a crew.
1.5 This standard does not purport to address all of the safety or survivability design concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, survivability, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
