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JPL together with Goddard and a private company called Busek Company Inc. developed a new type of propulsion system known as micronewton thrusters for the LISA mission (which has since had a name change and a rescoping). The goal of these small thrusters is to maintain the position of a spacecraft from small external disturbances such as solar winds and radiation pressure. They were to be used on the LISA mission to have the spacecraft precisely follow the freely floating, mirrored, test masses inside of the spacecraft, the positions of which were to be measured by interferometry. My questions are:

  1. What is the expected lifetime of the micronewton thrusters?
  2. What is the propulsion method employed; i.e. chemical, electric, etc.?
  3. Have they been flight tested yet?
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The test masses, along with the thrusters, are part of the Disturbance Reduction System (DRS). They are electrostatic colloid thrusters. From "The Space Technology-7 Disturbance Reduction System" (James R. O'Donnell Jr., Oscar C. Hsu, John Hanson, Vlad Hruby; 2004):

Each DRS colloidal thruster consists of a set of emitters and electrodes that generate thrust by ejecting and electrostatically accelerating nanometer-sized, positively charged propellant droplets (colloids) (Fig. 6). The emitters are held at a positive variable voltage by a beam voltage source typically operating at 6kV. The extractor electrode located near the emitters is supplied by a variable voltage, nominally ranging between 1.5kV to 2.5kV below the emitter voltage. The extractor electrode asserts an electrostatic force on the fluid to form the so-called Taylor cone at the tip of each emitter. The cone tip transits into a cylindrical jet, some tens of nanometers in diameter, which ultimately breaks into a fine spray.

After passing through the extractor, the spray is further accelerated as it flows through an accelerator electrode, which is held at a lower potential than the extractor electrode and negative with respect to the neutralizer cathode to prevent neutralizer electrons from flowing back into the thruster.

Figure 6 Colloidal Thruster Schematic

The Colloid MicroNewton Thrusters, along with new Gravitational Reference Sensors, are being flight tested on this mission. I have not run across a mention of their expected lifetime.

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