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Performance tests in the 100-hr range have been conducted for 100-/zlb thruster modules at average specific impulses ranging from 577 to 1135 sec. Three new thruster configurations--bipolar self neutralizing, linear slit, and high-voltage thick needle--have been investigated. A 50-/zlb bipolar module has been run for two 50-hr tests at specific impulses of 700 and 800 sec. A complete micro thruster flight system is being developed for yaw control of a synchronous satellite. One thruster module for this system has accumulated 1500-hr operation (820 hr continuous) in the 800-sec specific impulse range with no degradation. Direct transverse thrust measurements of an electrostatically deflected colloid beam were taken to demonstrate thrust vector control capability. Up to 40-jiilb transverse force was measured for 129-jLilb total thrust. Nomenclature IN= needle current, amp /sp = specific impulse, sec m = mass flow rate, kg/sec q/m = particle charge/mass, coul/kg q/m = average charge/mass, coul/kg T = thrust, /db VN = needle voltage, kv V xtr = extractor voltage, kv r] = beam efficiency Introduction r ¥ 1 HE heavy particle or colloid thruster produces thrust -•-basically in the same fashion as an ion engine, i.e., by electrostatic acceleration of positively charged particles. The neutralization of either beam can be accomplished by the injection of electrons. The similarity stops here. The charged beam in an ion engine consists of a single fixed specific charge and a small number of neutrals; the colloid beam contains charged multimolecular or heavy particles having a narrow velocity dispersion. Its spread in specific charge (q/m) is peaked about an average value which may be shifted over three decades, from less than 200 to over 300,000 coul/kg. For comparison, q/m = 720,000 coul/kg for cesium. It is this ability to vary the position of the peak of the q/m distribution, and therefore the I sp of the heavy particle thruster, which allows mission parameters to be optimized. The colloid thruster concepts described herein have evolved from eight years of joint research and development efforts between the Aero Propulsion Laboratory at Wright-Patterson Air Force Base and TRW Systems. This work has been devoted primarily to developing 1) optimum performance capillary dimensions and geometry, 2) a suitable highperformance propellant, and 3) adequate diagnostic techniques for thruster analysis. In the primary design to be discussed, a capillary tube (Fig.

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