Iris Rover Thermal & Structural Simulation

Astrobotic & Carnegie Mellon Joint Project, Spring and Summer 2019

For this ANSYS study simulation, I worked with the thermal team in order to simulate early stage temperature and collision conditions on the lunar surface for the Iris Rover, projected to launch in 2022. The rover's thermal design is simulated under conditions to ensure survivability on the lunar surface during the lunar day via its route on the moon. The battery trade study simulates important conditions of external radiation and internal heat flux effects on the top panel and inside of the rover body. The space-radiation study simulates the estimated heat loss to space from the rover. The structural study simulates deformation or failure on the wheels when colliding with surrounding lunar rocks.

Iris rover (in yellow) traveling after arrival on the lunar surface from the lander (in red)

Thermal radiation from sun and regolith simulation

For this simulation, the outside of the rover is modeled via expected thermal conditions, including radiation from the sun and radiation from the regolith to regulate heat exchange. Other thermal conditions include internal heat generation from the radiator. The heat flux is also modeled at the top panel, as that is the solar panel reflecting the most of the solar radiation from penetrating the inside, holding the battery and electronics. Since the rover is expected to drive over regolith between 50-90 degrees Celsius, we used a worst case scenario of 120 degrees Celsius. During surface operations, the rover power duty cycle must be properly managed in order to avoid overheating and therefore malfunction. Hence, the simulations will help determine the layers of MLI (multi-layer insulation) of emissivity 0.7 to sustain both hot-biased surface operation and cold-biased spaceflight.

Radiation conditions on the lunar rover and battery under ambient regolith temperature

Steady state temperature change on rover under direct radiation on the regolith

Steady state heat flux on rover from radiation on the regolith

From the combination of thermal radiation and heat flux, we found that there was an average heat flux of 174.38 W/m^2, a relatively high rate of heat exchange. From prior analysis, MLI uniformly blankets all sides of the rover's inner sections, so the team determined that around 20-30 layers of MLI would sufficiently regulate the temperatures during surface operation under solar angles of 30-45 degrees.

Thermal radiation from rover into space simulation

For this simulation, the rover is modeled in steady state conditions on the regolith. This simulation isolates total heat loss to the environment from the rover with insulation installed. The simulation results below show the thermal radiation from the rover to space. We can gauge the total heat flux, temperature change, and directional heat flux resulting from heat loss to space in order to determine the additional MLI layers to add to sustain survivability.

Total heat flux from rover to space

Temperature loss from the rover to space

Directional heat flux from rover when sun is angled toward one side

Structural Analysis from lunar rock collision

For this simulation, we looked at max deformation if the rover were to get pinned on a lunar rock, inflicting damage to the back wheels. FEA was performed to see total stress and deformation under collision. The wheels were modeled as fixed to the rover at this condition, with the bottom surface of the wheels experiencing an external load. The wheels in the model below are simplified. The wheels of the physical model are grooved, to be able to traverse through lunar sand and small rocks. Since the material of the wheels are carbon fiber, we expect that normal collisions would not greatly damage the wheels. The simulation below shows an exaggerated deformation, however, as expected the stress and deformation is relatively small.

Total stress concentration along the back wheels at inflicted point

Total deformation along the back wheels at inflicted point