Microrockets for Smart Dust

Abstract

This paper details the design and fabrication of millimeter-scale solid propellant rockets for one-time deployment of wireless sensor platforms, known as Smart Dust. Each microrocket assembly is an integrated system, incorporating a combustion chamber, composite propellant grain, nozzle, igniter, and thermoelectric power converter. Solid propellant is advantageous for a millimeter-scale single-use device because of its simple implementation, unlike liquid propellants, which require a more elaborate system of pumps and valves. Therefore the total system volume and complexity are minimized. One type of combustion chamber was fabricated in silicon; however, thermal losses to the silicon sidewalls during combustion through a 1.5 mm 2 cross section of fuel were too high to reliably maintain a burn. Successful combustion was demonstrated in cylindrical alumina ceramic combustion chambers with thermal conductivities five times lower than silicon and cross sections of 1-8 mm 2. Thrusts of 10-15 mN were measured for ceramic rockets weighing under l g, with specific impulses up to 15 s. Silicon nozzles integrated with polysilicon microheaters and thermopiles for thermal power conversion were microfabricated in a single process. Fuel ignition by polysilicon microheaters suspended on a low-stress nitride (LSN) membrane was demonstrated. Microheaters require less than 0.5 W of power to ignite a propellant composed primarily of hydroxyl-terminated polybutadiene (HTPB) with ammonium perchlorate (AP) oxidizer. They are suspended for thermal isolation through bulk post-processing by a backside deep reactive ion etch (DRIE). The etched hole beneath the igniter area also serves as a nozzle through which high-velocity combustion gases exit the rocket. Thermopiles, which generate voltages proportional to hot and cold junction temperature differentials, have been fabricated in the same process as igniters, and span backside DRIE thermal isolation cavities. Ten-junction thermopiles produced a maximum power of 20 µW. With potential temperature differences of hundreds of degrees and a total of 120 thermocouple junctions fabricated on the silicon nozzle chip, hundreds of milliwatts of power could feasibly be produced during the microrocket's flight and used to augment the Smart Dust power supply.

Design, fabrication, and testing of MEMS solid propellant thruster array chip on glass wafer

“…These previous MEMS thruster designs face technological problems due to the complexity of their components, such as valves and moving parts, and due to their chemical residence times. Recently, several MSPTs have been developed [8][9][10][11][12][13]. MSPTs represent the most feasible thruster design for development with current MEMS technology.…”

“…The horizontal type with a two-dimensional shape contains most of the thruster components in one layer, and allows diverse geometry to be realized [9]. The vertical type consists of a stack of several wafers and its fabrication process is more complicated [10][11][12][13]. However, the vertical type is more suitable for producing MSPT thruster arrays.…”

Design and Fabrication of the Harvard Ambulatory Micro-Robot

“…There are multiple potential locomotion modes for microrobots, including crawling [10], rolling, flying [24], jumping [3], gliding [26], slithering, or rockets [22]. This work focuses on ambulation, which has been shown to be robust and efficient on diverse terrain by studies of insect locomotion.…”

Integration of a MEMS based safe arm and fire device

“…Since then, this concept has been applied into many fields by many teams: micropropulsion [1][2][3][4][5][6][7][8][9][10], microinitiation [11,[13][14][15] (in both military and civil domains), gases for actuation (including injection or moving fluid) [12,[16][17][18][19], gases for chemical reaction [21][22][23], welding [24] and switching [25]. In this paper, we propose to explore micropyrotechnics to fabricate a miniature Safe Arm and Fire device (SAF).…”