Trajectory Prediction of a Model Rocket Falling into the Towing Tank: Experimental Tests versus Numerical Simulations

Abstract

The SpaceX company has introduced a reusable first stage rocket that lands on a floating barge. In the event that the first stage rocket falls off the platform, the investigation of landing location on the seafloor may help to increase the salvage efficiency. This paper deals with the application of experimental and numerical techniques into locating a model rocket freely falling into the towing tank with various initial drop angles. The floor of the towing tank represents the ocean floor with regards to the landing position of the model rocket. The landing position is of interest to recover the fallen rocket. The University of New Orleans Towing Tank facility has been used to release a model first-stage Falcon 9 rocket at initial drop angles from 0° to 90° with a uniform increment of 15°. The landing point distribution at each drop angle is recorded using a landing grid on the bottom of the towing tank. First, a deterministic model based on the Dropped Objects Simulator (DROBS) is used to calculate an ideal landing point, which is compared with the experimental results. It is found that one single simulation by the deterministic model cannot reasonably explain the random landing point distributions observed in the experiment. Therefore, the Monte Carlo method based on a stochastic model is used to numerically consider the effects from various random disturbances. The landing point distribution obtained by stochastic process analysis is close to the experimentally obtained distribution for each drop angle case. The stochastic modeling shows more advantages and advancements in subsequent analysis, such as the calculation of landing velocity/speed. The findings from stochastic modeling of the dropping process is also discussed. Finally, the drop angle is found to significantly affect the trajectory, landing points, and landing speed in both the deterministic and the stochastic model.