MEMS-based satellite thruster using water as propellant

1. Project Overview & Objectives

The primary goal is to develop a compact, safe, and cost-effective propulsion system for small satellites (such as CubeSats and NanoSats) that uses water as a propellant. The system should provide precise attitude control, orbital maintenance, and de-orbit capabilities. Using water eliminates the need for hazardous propellants, which simplifies handling and reduces launch costs. The system design should be modular, low-power, and scalable to accommodate various mission requirements.

2. System Design & Components

A complete water-based MEMS thruster system consists of several integrated components:

- Propellant Tank: This tank stores deionized water. Its design must consider the zero-gravity environment and include a propellant management device (PMD)—such as a sponge or capillary vanes—to ensure water is always available at the outlet.

- MEMS Thruster Chip: The core of the system, this chip is fabricated on a silicon wafer and contains microcomponents like a vaporization chamber and a micro-nozzle. An integrated electrical resistor acts as a heater.

- Power & Control Unit: This unit regulates the power supplied to the thruster chip's heater. It receives commands from the satellite's main computer to pulse the thruster, controlling thrust levels and durations with high precision.

- Thermal Control System: Critical to preventing water from freezing in space, this system includes heaters and insulation to maintain the propellant at a safe temperature.

3. Working Principle

The thruster operates based on vaporization

- Vaporization (Resistojet): A small amount of water is fed into the vaporization chamber. The integrated micro-heater quickly boils the water, turning it into superheated steam, which is then expelled through the micro-nozzle to generate thrust. This process can be precisely controlled by modulating the power to the heater.

4. Fabrication & Assembly

The fabrication of the MEMS thruster chip is a highly specialized process involving micromachining techniques adapted from the semiconductor industry, including photolithography, etching, and thin-film deposition. Multiple silicon wafers are bonded together to form the complete chip. The final thruster module consists of the MEMS chip, propellant tank, and control electronics, all integrated into a compact unit suitable for a CubeSat's standard form factor.

5. Testing & Validation

Rigorous testing is essential to qualify the system for space flight, including:

- Thrust Measurement: Testing the thruster's performance (thrust and specific impulse) in a vacuum chamber.
 
- Endurance & Reliability: Running the thruster through extended test cycles to ensure long-term reliability.
 
- Thermal Vacuum Testing: Simulating the extreme temperatures and vacuum of space to verify the thermal control system and prevent water from freezing.
 
- Vibration Testing: Ensuring the thruster can withstand the intense forces experienced during a rocket launch.