Rocket thrust measuring device

Designing a Thrust Stand for CubeSat Propulsion Testing

Accurate thrust measurement is essential for characterising spacecraft propulsion systems, especially for the growing class of small satellites. During my third year at the University of Southampton, in collaboration with Dawn Aerospace, I designed, built, and tested a thrust stand capable of measuring the performance of a low-thrust chemical propulsion system for CubeSats.

The propulsion system under investigation was CubeDrive, a compact chemical propulsion module designed for CubeSats from 3U to 24U platforms. The system uses a green bipropellant combination of nitrous oxide (N₂O) and propylene (C₃H₆) and produces thrust on the order of 1 N, enabling manoeuvres such as orbit changes, station-keeping, and attitude control.

To characterise the thruster’s performance, a pendulum-based thrust balance was developed. The stand consists of a suspended platform supported by stainless-steel flexures, with the thruster mounted on the moving platform. When the thruster fires, the generated force causes a small displacement that is measured using a precision load cell. The system was designed to operate inside a vacuum chamber, ensuring testing conditions representative of the space environment.

A key challenge in measuring low levels of thrust is achieving sufficient sensitivity while maintaining mechanical stability. The design therefore prioritised a high-stiffness load cell and flexure system, allowing the thrust stand to capture rapid thrust events while minimising measurement noise. Calibration was performed using known weights traceable to NIST standards, ensuring measurement accuracy and repeatability.

The resulting performance of the apparatus was exceptional. The thrust stand demonstrated a measurement uncertainty of approximately 35 mN across the entire calibrated range, corresponding to 3–4% uncertainty for most of the measured thrust levels, and achieved a resolution of 1.9 mN peak-to-peak within a 0–10 Hz bandwidth. These figures place the instrument among the highest-performing thrust measurement systems reported in the literature for low-thrust chemical propulsion, where comparable systems often struggle to achieve similar resolution and stability simultaneously.

Testing was carried out in the David Fearn Electric Propulsion Laboratory vacuum facility at the University of Southampton. Multiple hot-fire tests were conducted, demonstrating the stand’s ability to measure thrust transients, quasi-steady thrust profiles, and impulse bits from the CubeDrive propulsion system.