Robot Propulsion in an Asteroid's Microgravity Environment

Traditional robots that move using wheels or legs won’t work in an asteroid’s microgravity environment (1/100th to 1/100,000th that of Earth) because of lack of friction and low escape velocity. The goal of this project was to build a robot propulsion system that can work in microgravity by using cold gas (CG) propulsion. Another goal was to simulate microgravity using Helium balloons and then test the robot propulsion system in microgravity.

A robot propulsion system using cold gas propulsion was successfully built and tested using commonly available materials, including a 16g high pressure CO2 cartridge (853 psi, $1.50/each), a regulator (nozzle), a linear actuator and an Arduino controller. The mass flow rate and exhaust velocity of the system were calculated using the choked flow equation and calculators on the NASA GRC site. The mass flow rate was calculated to be: 0.012Kg/s and the exhaust velocity was: 556.8 m/s. Using these values and the rocket equation it was calculated that the robot would generate a thrust of 6.5N. During testing, the robot generated an actual thrust of 5.6N with an impulse duration of 0.5 seconds. The main sources of error were measurement errors due to lack of accurate measuring devices and quality of the CO2 cartridge.

A microgravity system was also simulated using Helium balloons which reduced gravitational acceleration to as low as 1.25 m/s2 (1/8th that of Earth). While even lower values of gravitational acceleration were possible, the large size (diameter 28”+) and lightness of the balloons made them very prone to air disturbance creating unintended thrust vectors.

Robot propulsion was tested in both regular gravity and microgravity environments. The robot performed predictably in regular gravity and the measurements were in line with the model. However, in microgravity the results were mixed. The high speed of the robot (> 3m/s) caused the Helium balloons to generate significant air drag which significantly affected the results, especially when the coefficient of friction between the robot and the surface was low. Increasing the coefficient of friction reduced the effect of air drag and the robot behaved more predictably, i.e. it had higher speed and traveled a longer distance in microgravity vs regular gravity.

Overall, the results demonstrated that cold gas propulsion can be used for robot propulsion in microgravity with predictable results, but Helium balloons are not suited for use with high thrust propulsion like cold gas propulsion due to the effects of air drag. Low thrust propulsion mechanisms like hopping and ion thrust engines may be more suitable for Helium balloon simulated microgravity.