Purdue University Graduate School

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posted on 2022-12-07, 21:53 authored by Katherine L F GasawayKatherine L F Gasaway

As the small satellite market has grown from a niche of the space economy to a full commercial force,  microthrusters remain an area of significant growth in the space industry as new technologies mature. The \textit{Film-Evaporation Microelectricalmechanical Tunable Array} (FEMTA) is one such device. FEMTA is \textit{microelectricalmechanical system} (MEMS) device that harnesses the microcapillary action of water and vacuum boiling to generate thrust. The water propellant is not chemically altered at all by the process; it is simply evaporated. This technology has been tested in relevant laboratory environments, and a suborbital flight opportunity in 2023 as a payload on a Blue Origin New Shepard rocket  will grant FEMTA a demonstration in a space environment. The flight will provide 150 seconds of weightlessness at the zenith of the suborbital flight path before the booster returns to land. During weightlessness, the experiment will be exposed to the ambient environment allowing for a full capability test of the thruster. The experiment is meant to demonstrate the propellant management system for FEMTA in 0G and measure the thrust produced by a FEMTA thruster.

The propellant management system portion of the experiment consists of an oversized version of the subsystem intended for use in the thruster. The propellant management system uses a hydrofluoroether to inflate a diaphragm to ensure constant wetting of the propellant tank exit and nozzle inlet. The experiment will take tank pressure data and flow sensor data to understand the system's behavior. The system is duplicated for redundancy and to double the possible data. This system requires further testing before being prepared for launch, vibrational testing, thermal testing, and vacuum testing. 

The 0G thrust experiment and plume analysis portion of the experiment consists of numerical modeling and a novel thrust measurement approach. \textit{Direct Simulation Monte Carlo} (DSMC) is being applied to understand the pressure, density, and temperature distributions of the plume of water vapor produced by the FEMTA thruster. The FEMTA nozzle environment is challenging to simulate with computational fluid dynamics  or DSMC due to chaotic transient effects and because both the continuum and molecular regimes must be considered. The current analysis consisted of a two-dimensional model and investigated the effect of meniscus location and contact angle on thrust generated.

It is not possible to use traditional thrust measurement devices (sensitive torsional thrust stands or microsensors intended for use on small satellites) for microthrusters on a rocket booster. Two  novel approaches for performing thrust measurement in the range of 100 microNewtons have been investigated. The first approach ionizes the FEMTA thruster plume and analyzes the plasma by optical emission spectroscopy. The theory states that the relative intensity of a given wavelength observed correlates to the density of the species in the plasma. The density of water would be directly correlated to the thrust generated by FEMTA during the experiment, as more water is evaporated as thrust is increased. This method is no longer being considered for the suborbital experiment but did yield promising results. 

The second approach employs a d'Arsonval meter, a photo-interrupt, and an Arduino controller. The d'Arsonval meter consists of a stationary permanent magnet with a moving coil and a pointer. Increasing the voltage in the coil causes a torque on the system due to the magnetic field induced by the permanent magnet. This torque causes a deflection of the pointer that is proportional to the voltage applied. The flag of the sensor will be placed in the path of the gas jet from the thruster. The force caused by the jet pressure will move the flag. An Arduino controller will vary the voltage to hold the flag in place. As the mass flow rate increases, the reaction force required to hold the flag in place will increase. This sensor can be calibrated using an analog cold gas system that passes various gases (air nitrogen, argon, etc.) through an orifice nozzle at mass flow rates that are set by a mass flow rate controller. DSMC analysis has been performed to understand the flow field and flow properties and how they directly relate to the force experienced by the flag sensor. 

An undergraduate course has supported parts of the work described in this dissertation. This course has applied the Vertically Integrated Projects approach to project-based learning. This method and its results were analyzed and lessons learned as well as a blueprint for future application of this method to other small satellite projects are discussed.




Degree Type

  • Doctor of Philosophy


  • Aeronautics and Astronautics

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Alina Alexeenko

Additional Committee Member 2

Stephen Heister

Additional Committee Member 3

Alexey Shashurin

Additional Committee Member 4

Timothée Poupoint