A low cost thrust stand for testing of nano-satellite propulsion systems

The miniaturization of electronic components allows implementing complete satellite functions in very compact systems. Not only businesses but also universities, with their typical budget and time constraints, are often involved in the development of nano-satellites as they set off as a cheap and accessible platform for applied space research and education, giving students the opportunity to gain hands-on experience in space hardware. Miniaturized satellites lead to the development of micro-thrusters that provide levels of thrust sometimes lower than a few micro-Newtons. Very sensitive systems, capable of detecting such low forces, are required to test and characterize these small engines. This paper describes a small and low-cost thrust stand designed, manufactured and tested at University of Rome La Sapienza for measuring the thrust produced by micro-thrusters in the micro-to-milli Newton range. The mechanical design is based on a hanging pendulum configuration: a cross-beam rests on a pair of sharp-tip elements (two razor blades) that allow the pendulum to rotate with minimal friction. The cross beam is equipped with a laser, whose beam is projected on a graduated surface one meter distant in order to amplify the reading of the small oscillations caused by the thrust exerted by the micro engine fixed at the bottom of the pendulum arm. A camera records the displacement of the laser beam, which is quantified thanks to a graduated surface and from which the thrust trend is estimated. To avoid any dynamic disturbance arising from physical connection of the pendulum with the static support, the pendulum is built with its own electrical supply and gas feeding system, which is activated by a wireless command. The performed experimental activities proved the thrust stand to be able to measure forces in the order of a few milli-Newtons as well as in the order of 100 micro-Newtons. The results show that even with a limited budget and low cost technology, satisfactory performance, suitable for typical university micro-satellite applications, can be obtained.