We present processing (green and sintered), part shrinkage and warping, microstructural characterization, and mechanical properties of Si3N4 made by fused deposition of ceramics (FDC), using optical microscopy, scanning electron microscopy, and X‐ray diffraction. The mechanical properties (fracture strength, fracture toughness, and Weibull modulus) are also reported. Proper FDC build parameters resulted in dense, homogeneous, near‐net‐shape Si3N4, with microstructures and mechanical properties similar to conventionally processed material. Mechanical properties are shown to be isotropic, while there is some degree of microstructural texturing (preferred β‐Si3N4 grain orientation) in sintered components.

The tensile creep of an in situ reinforced silicon nitride is described in terms of the rheological behavior of the thin intergranular film present in this liquid-phase sintered silicon nitride. The high stress exponents and apparent activation energies (at constant stress) can be explained assuming non-Newtonian flow behavior of the film during grain boundary sliding. Time-to-failure is related to the minimum creep rate, even for samples which fail by slow crack growth. In addition, the primary creep region and the relaxation effects observed on unloading are described in terms of grain boundary sliding modified by the presence of a grain boundary phase with a lower elastic modulus than silicon nitride.

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The objective o f the NASA JPL Space Technology 7 -Disturbance Reduction System (ST7-DRS) mission is to demonstrate: (I) test mass trajectory control that deviates from purely gravitational trajectory by less than 3~1 0 . '~ ~n / s e c~/ H z~~~ [l+(V3 mHz)*] over a frequency range from 1 mHz to 30 mHz and (2) spacecraft position control within l O n m / H~~.~ over the same frequency range. To achieve these objectives, two technologies must be advanced and tightly integrated. These technologies are the Gravitational Reference Sensors (GRS) being developed by Stanford University and the Colloid Micro-Thruster (CMT) propulsion system in development at Busek Co. Inc. The DRS system will he integrated by JPL and fly on an ESA spacecraft called the LISA Pathfmder. This paper reports on the progress in the propulsion technology area.The 1O:l dynamic thrust range, the continuous thrust adjustability and noise requirements represent unique challenges that require significant advances in several technology areas, including extremely precise propellant flow control (