"Definitions Gas: Gas@ for the purpose of this ARP@ shall be defined as the gaseous product (s) resulting from the decomposition@ dissociation@ or combustion of liquid or solid mono or bi-propellants. Where other gases such as heated N2@ H2@ H2O (stem)@ etc.@ which may have similar physical and/or chemical properties as the defined ""gas""@ are used to effect testing economies@ they may be considered as being included in this ARP. Linear Actuator: For the purpose of this ARP@ a linear actuator shall be considered to be any gas powered device@ generally consisting of a piston and cylinder@ which in its energy converting stage changes gas energy to a directions (push and/or pull type) mechanical power. Vane Actuator: For the purpose of this ARP a vane actuator shall be considered to be any gas powered device@ generally consisting of a rotating shaft@ with one or more vanes@ enclosed in a housing@ which provides an inlet and outlet port. In its energy converting stage the vane actuator changes gas energy to rotary mechanical power with general less than one complete revolution. Exclusions: To be considered in the development of the ""gas actuator"" but not a part or this ARP@ are such devices as the servo control valve@ speed reducer@ output conversion devices@ servo loop feedback mechanisms@ and dynamic characteristics of the driven load. Design Considerations Life: This ARP will generally define the life requirements of ""gas actuators"" for three broad categories of flight vehicles. Long Range Air Breathing Vehicles ?C The actuators for this type vehicle generally will have both a long operational and ground checkout Life. Manned Re-entry Vehicles ?CActuators for this type vehicle generally will have a moderately long operational life@ but will be significantly less than their ground checkout life. Single Use Vehicles ?C Actuators for this type vehicle have a long ground checkout life with a short operational life may range from a few seconds to several hours. Environment and Performance: This ARP will be confined to discussing the environments and gas temperatures most likely to be encountered@ listing some of the performance parameters without numerically defining them@ and to specifying tests to show compliance with the performance and reliability requirements under the expected environmental conditions. This ARP will not define a specific ""gas actuator""."