Session: 15-01-01: ASME International Undergraduate Research and Design Exposition

Paper Number: 100662

100662 - Variable Range Torsional Pendulum Thrust Balance for Electric Propulsion Testing 

Efficient means of propulsion are required for enabling satellites to perform station keeping burns for the duration of a long mission, and for enabling deep space exploration missions up to the edges of our solar system. Electric propulsion methods are of particular interest as they have high specific impulses. However, most of these propulsion devices produce thrust values in the range of micronewtons to millinewtons. Research in developing these systems requires a thrust balance that can record values on these orders of magnitude. Electric Propulsion R&D is often out of reach for undergraduates whose colleges do not have active research groups working in this area. Measuring thrust values on the scale of micronewtons is a cost-prohibitive barrier of entry. To overcome this challenge and begin conducting research in this field, a low-cost thrust balance has been designed and developed. 

The setup consists of a torsional pendulum balance, inspired by the Cavendish experiment, on which an ion thruster can be mounted and placed in a vacuum chamber. An aluminum bar is suspended using a steel wire. The thruster and a counter weight is mounted to either end of the aluminum bar. Upon firing, the thruster applies a force off-center from the center of mass of the pendulum arm, resulting in a torque that rotates the bar and twists the wire. The steel wire imparts a restoring torque until the system reaches a steady state. Using a magnetic encoder and a microcontroller, the angular displacement of the bar is recorded. Since the torsion constant of the wire is known, the total restoring torque can be calculated. From this value, the thrust at the end of the bar is measured. A key feature of this torsion pendulum balance is that the thrust range it is measuring can be varied- from micronewtons to millinewtons to newtons. This is done by replacing the torsion-providing wire against which a thruster acts. Using permanent magnets for a preliminary test of this system, the resolution of the thrust measurement device was found to be approximately 38 micronewtons. Thus, the thrust imparted by ion thrusters on the scale of millinewtons can be measured. The resolution can be reduced further by improving the accuracy of recording the angular displacement of the arm, and by using a different suspending wire.

The goals of this research project were achieved with a $300 budget, and electric propulsion devices that will be developed in the future at Rose-Hulman Institute of Technology can be tested with this test stand.

Presenting Author: Ishaan Mishra Rose-Hulman Institute of Technology

Presenting Author Biography: Ishaan Mishra is a sophomore physics and computational science major at Rose-Hulman Institute of Technology minoring in aerospace engineering. His primary research areas include computational plasma physics and accelerator physics. He plans on pursuing a graduate degree in plasma propulsion to enable exploration of the Solar System at realistic time scales.

Authors:

Ishaan Mishra Rose-Hulman Institute of Technology
Jacob Consalvi Rose-Hulman Institute of Technology