with the description of '537 patent, both thrusters in that propulsion system use a common fuel, Hydrazine. The bipropellant thruster uses the liquid oxidizer, N.sub.2 O.sub.4, as the second propellant.
The SCAT thruster uses the same oxidizer to both cool the thruster chamber, whereby the oxidizer is transformed to a gaseous phase, and, in the gaseous phase, as the second propellant for the bipropellant mode of operation. In its construction, the SCAT thruster contains two connected reaction chambers. Liquid propellant fuel, such as hydrazine, is fed into the first chamber where it reacts with a catalyst and enters the gaseous phase in an exothermic reaction, thereby heating the chamber walls, and the reaction propellant gas is propelled by the reaction into a second chamber. Liquid propellent oxidizer is fedlonger operational life in comparison to other engines, all other factors being equal, an additional advantage to the engine.
The SCAT thruster is noted as having dual mode capability. It is shown to operate in a bipropellant mode and, alternately in a monopropellent mode. It is now realized that a simple SCAT bi-modal thruster can operate in either a bipropellant mode and achieve an I.sub.SP of over 315 seconds, or, alternatively, can operate in a monopropellant mode and achieve an I.sub.SP of about 225 seconds.
The SCAT thruster is described in the two cited patents as useful for station keeping/changing and attitude control functions of the propulsion system, and the patents thereby propose the SCAT thruster as a substitute for the monopropellant RCS thrusters in the single fuel rocket propulsion