Development of the Propulsion System for a Moon Drone Vehicle Demonstrator

Moon Drone is a candidate element of the HERACLES mission, an international robotic sample return mission on the Moon. It is requested to support a rover mission scouting the surrounding environment. Possible utilization scenarios are, for instance: exploration of deep craters, support for rover path planning, perform scientific observation and others. An ESA TRP study lead by Thales Alenia Space with partners GMV, Brno University of Technology and T4i (supported by the University of Padova) has been started to solidly establish the technical feasibility, as well as to early-validate the proposed concept through a prototype to demonstrate the key functions that can enable the Drone mission. The straight-line trajectory mission baseline consists in the following four main phases: vertical lift-off, hovering with horizontal translation from the rover to the target point, hovering with horizontal translation from the target point back to the rover, descent and landing. T4i is in charge of the development of all the thrusters, which have to provide both the main displacements and the attitude control of the Drone. The propulsion system is required to use non-toxic propellants that are safe to handle on ground in order to get on an early demonstration at low budget. Monopropellant hydrogen peroxide has been selected thanks to its moderately high performance, green characteristics, good availability and relatively simple use thanks to catalytic decomposition and non-exotic moderate high temperature chamber materials. The tight schedule has been defined exploiting the significant experience accumulated with hydrogen peroxide over the last 6 years by T4i/UNIPD, including thousands of tests performed up to now in monopropellant, liquid and hybrid bipropellant mode. After a trade-off between several possibilities performed by TAS with T4i/UNIPD support, the design proceeded with a configuration composed by a single throttleable main thruster aided by 4 small thrusters for attitude control. All the thrusters will be fed by the same tank, which is pressurized by nitrogen. The 4 small thrusters work with a bang-bang control with on-off solenoid valves. Instead, the main thruster has a continuous regulating cavitating pintle flow control valve driven by a stepper motor in feedback, a development from a previous one already developed for a hybrid rocket. The rearranged flow control valve differs from the older version for the valve body that has been optimized and reduced consistently in weight. All the motors will be integrated in the Drone demonstrator aimed to perform flight testing on Earth. The testing of the entire Drone demonstrator is expected to be performed at the end of the program. The rapid pace of the program confirmed that the use of green propellants can dramatically reduce costs and provide higher flexibility during development compared to legacy toxic propellant solutions.