Acceptance Test: A test performed to demonstrate that the hardware is acceptable for its intended use. It also serves as a quality control screen to detect manufacturing, material, or workmanship defects in the flight build and to demonstrate compliance with specified requirements. Note: Acceptance tests are performed on previously qualified hardware to limit loading conditions.
Creep: A time-dependent deformation under load and thermal environments that results in cumulative, permanent deformation.
Detrimental Yielding: Yielding that adversely affects the form, fit, and function, or integrity of the structure.
Discontinuity Area: A local region of a composite or non-metallic structure consisting of thickness changes, built-up plies, dropped plies, chopped fiber or reinforced regions around fittings, joints, or interfaces. In these regions, the stress state and load distribution may be difficult to characterize by analysis. Note: Bonded joints are considered discontinuities.
Factored Load or Stress: The limit load or stress multiplied by the appropriate design or test factor.
Factors of Safety (Safety Factors): Multiplying factors to be applied to limit loads or stresses for purposes of analytical assessment (design factors) or test verification (test factors) of design adequacy in strength or stability.
Failure: Rupture, collapse, excessive deformation, or any other phenomenon resulting in the inability of a structure to sustain specified loads, pressures, and environments or to function as designed.
Fatigue: The cumulative irreversible damage incurred in materials caused by cyclic application of stresses and environments, resulting in degradation of load-carrying capability.
Glass: Composed of any of a large class of materials with highly variable mechanical and optical properties that solidify from the molten state without crystallization and is typically made by fusing silicates with boric oxide, aluminum oxide, or phosphorus pentoxide; generally hard, brittle, and transparent or translucent; an amorphous (non-crystalline) material that is isotropic and elastic.
Habitable Module: A pressurized, life-supporting enclosure or module that is normally intended to support life without the need for spacesuits or a special breathing apparatus. The enclosure may be one that is continuously inhabited, or one that is used for crew transfer or crew-accessible stowage, as long as life support is a requirement for the design. Single mission or multi-mission designs are included.
Limit Load: The maximum anticipated load, or combination of loads that a structure may experience during its design service life under all expected conditions of operation.
Margin of Safety (MS): MS = [Allowable Load (Yield or Ultimate)/Limit Load*Factor of Safety (Yield or Ultimate)] - 1. Note: Load may refer to force, stress, or strain.
Maximum Design Pressure (MDP): The highest possible operating pressure considering maximum temperature, maximum relief pressure, maximum regulator pressure, and, where applicable, transient pressure excursions. MDP for human-rated hardware is a two-failure tolerant pressure; i.e., MDP will not be exceeded for any combination of two credible failures that will affect pressure. For all other hardware, MDP is equivalent to MEOP.
Maximum Expected Operating Pressure (MEOP): The maximum pressure which pressurized hardware is expected to experience during its service life, in association with its applicable operating environments. MEOP includes the effects of temperature, transient peaks, vehicle acceleration, and relief valve tolerance.
Pressure Vessel: A container designed primarily for storing pressurized gases or liquids and that:
- (1) Contains stored energy of 19,309 Joules (14,240 ft-lb) or greater, based on adiabatic expansion of a perfect gas; or
- (2) Will experience a maximum design pressure greater than 689.5 kiloPascal (kPa) absolute (100 pounds per square inch absolute (psia)); or
- (3) Contains a pressurized fluid in excess of 103.4 kPa absolute (15 psia), which will create a safety hazard, if released.
Pressurized Component: A component in a pressurized system, other than a pressure vessel, pressurized structure, or special pressurized equipment that is designed largely by the internal pressure. Examples are lines, fittings, gauges, valves, bellows, and hoses.
Pressurized Structures: Structures designed to carry both internal pressure loads and vehicle structural loads. The main propellant tank of a launch vehicle is a typical example.
NASA-STD-5001B W/CHANGE 3
Proof Test: A test performed on flight hardware to screen for defects in workmanship and material quality, and to verify structural integrity. Note: Proof tests are performed at a load or pressure in excess of limit load or MDP but below the yield strength of the hardware. Proof tests are performed on each flight unit for structures whose strength is workmanship or fabrication dependent. Proof tests are also used to screen for initial flaws in fracture critical items.
Proof Test Factor: A multiplying factor to be applied to the limit load or MDP to define the proof test load or pressure.
Protoflight Hardware: Hardware that is qualified using a protoflight verification approach.
Protoflight Test: A test performed on flight or flight-like hardware (i.e., is built with same drawings, materials and processes as the flight unit) to demonstrate that the design meets structural integrity requirements. The test is performed at loads or pressure in excess of limit load or maximum design pressure but below the yield strength of the structure. When performed on flight structure, the test also verifies the workmanship and material quality of the flight build. Note: Protoflight tests combine elements of prototype and acceptance test programs.
Protoflight Test Factor: A multiplying factor to be applied to limit load or MDP to define the protoflight test load or pressure.
Prototype Hardwire: Hardwire of a new design that is produced from the same drawings and using the same materials, tooling, manufacturing processes, inspection methods, and personnel competency levels as will be used for the flight hardwire. Note: Prototype hardwire is dedicated test hardwire that is not intended to be used as a flight unit. Prototype Test: A test conducted using prototype hardwate to demonstrate that all structural integrity requirements have been met. Note: Prototype testing is performed at load levels sufficient to demonstrate that the test article will not fail at ultimate design loads.
Qualification Test: A test performed to qualify the hardware design for flight. Note: Qualification tests are conducted on a flight-quality structure at load levels sufficient to demonstrate that all structural design requirements have been met. Both protoflight and prototype tests are considered qualification tests.
Qualification Test Factor: A multiplying factor to be applied to the limit load or MDP to define the qualification test load or pressure.
NASA-STD-5001B W/CHANGE 3
Safety Critical: A classification for structures, components, procedures, etc., whose failure to perform as designed or produce the intended results would pose a threat of serious personal injury or loss of life.
Service Life: All significant loading cycles or events during the period beginning with manufacture of a component and ending with completion of its specified use. Testing, transportation, lift-off, ascent, on-orbit operations, descent, landing, and post-landing events are to be considered.
Service Life Factor (Life Factor): A multiplying factor to be applied to the maximum expected number of load cycles in the service life to determine the design adequacy in fatigue or fracture.
Special Pressurized Equipment: A piece of equipment that meets the pressure vessel definition, but which is not feasible or cost effective to comply with the requirements applicable to pressure vessels. Included are batteries, heat pipes, cryostats, and sealed containers.
Structural Softgoods: Straps, fabrics, inflatable structures, gossamer structures, and other similar structures that carry structural loads.
Threaded Fastening System (Fastening System): An assembled combination of a fastener, an internally threaded part, such as a nut or an insert, and also the region of all parts clamped between them, including washers, compressed by the fastener preload.
Ultimate Design Load: The product of the ultimate factor of safety and the limit load.
Ultimate Strength: The maximum load or stress that a structure or material can withstand without incurring failure.
Unfactored Load or Stress: The limit load or stress before application of any design or test factors.
Verification: Any combination of test or analysis used to demonstrate that the hardware meets the defined requirements. Workmanship Verification: Any test or inspection, including visual, dimensional, and non-destructive evaluation, performed to demonstrate the adequacy of the flight build. Tests performed to demonstrate workmanship may be static or dynamic.
Yield Design Load: The product of the yield factor of safety and the limit load.
Yield Strength: The maximum load or stress that a structure or material can withstand without incurring detrimental yielding.