Radiation transfer thrusters for low thrust applications

A thruster assembly for low thrust applications and use with a propellant which may be heated in order to obtain a higher specific impulse which increases the life of a propulsion system, the thruster assembly comprising:

• (a) a heating filament and power source controllably connected thereto;
• (b) a heater cavity having an inner surface coated with a refractory material which at elevated temperatures has a high emissivity property and a low vapor pressure;
• (c) a supporting structure for the heating filament, the structure supporting the filament entirely within the heater cavity in a manner such that the filament is separate from the heater walls and radiation shielding means comprising a plurality of discs mounted about said supporting structure and at least some of said discs having substantially cylindrical reflectors attached to the outer periphery thereof and extending toward said heating filament;
• (d) a propellant guiding structure surrounding the heater cavity and having at least one propellant passageway therein, the propellant guiding structure physically isolating said heating filament from said propellant;
• (e) a nozzle;
• (f) an insert in the nozzle at the throat portion of the nozzle, the insert separated from the remainder of the nozzle by a gap having a separating means therein;
• (g) the propellant guiding structure having an inner portion, the inner portion cooperating with the nozzle insert and the heater cavity to form an inner zone, whereby the inner zone has a higher temperature than the remaining fuel passageway and the inner zone further provides the thermal insulation to reduce loss of heat of the ambient environment (space) and a supporting structure to which the thruster assembly is mounted;
• (h) the fuel guiding structure having a heat sinking capability whereby the filament may be switched on or off when the propellant is not flowing through the passageway;
• and
• (i) the heating sinking capability further constructed to permit sufficient heat to be transferred to the fluid, thereby permitting the fluid to be heated in order to obtain said high specific impulse to be used as a propellant at times when the filament is switched off, provided that the average amount of energy supplied by the filament over a period of time during which the filament has been placed at an elevated temperature is greater than the amount of heat energy necessary to heat the propellant passing through the propellant passageway during that period of time.

A thruster assembly comprising:

• (a) a housing;
• (b) a heating filament mounted on a supporting structure to thereby form a heating subassembly and radiation shielding means comprising a plurality of discs mounted about said supporting structure and at least some of said discs having substantially cylindrical reflectors attached to the outer periphery thereof and extending toward said heating filament;
• (c) said subassembly being detachably mounted in an opening defined in said housing;
• (d) said opening leading to a heater cavity defined by walls which, in assembly, surround said heating filament in spaced relation thereto;
• said heating filament being entirely contained in said hear cavity;
• (e) propellant supply means leading to expansion nozzle means;
• (f) said propellant supply means and said expansion nozzle means being isolated from said heater cavity and said heating filament being completely isolated from said propellant;
• whereby
• (g) said propellant is heated by energy transfer through walls, said heater cavity, said propellant supply means and said expansion nozzle means being surrounded by shield means mounted in said housing and comprising a plurality of shells substantially concentrically mounted within said housing and concentric shielding members substantially concentrically mounted between said shells.