The projects aims to improve team's existing know-how in the area of small autonomous vehicles, namely planetary rovers, operating in rough environments. Rovers have been consistently included in many exploration missions, and such an option will be even more important in the frame of upcoming, budget-minded smaller missions, carried on by single agencies and research centers to investigate limited areas of Moon or Mars. In such a frame, rovers could really provide significant scientific return. These rovers should be extremely efficient, and the project is intended to investigate optimal architectures for the mechanical and electrical subsystems of these vehicles. The goal is to identify optimized architecture to push up to reasonable edge the performance in terms of mass, power, energy, robustness, reliabiity, all of them concerned with peculiar, already identified specific missions in selected location and coarsely pre-defined path. In short, not a general purpose rover for planetary exploration, while instead an extremely specialized vehicle tuned for the specific soil and environment of a lunar or martian location, i.e. the target of the small mission. Based on consistent previous activities of the team-members, the project will include advanced simulation as well as preliminary prototyping steps, all developed in labs at Sapienza. The findings of the project coming from such a specialized design approach will help the team growth also with respect to other areas of applications for small rovers, as operations in hostile environments and surveillance vehicles.
The general assumption of this project is to design a high-performance vehicle, specifically tailored to an area of a given celestial body, and even more to an identified "small" mission profile. In such an approach, the mechanical design will start first, with the goal to specifically target the mobility on the soil proper to the selected path. Therefore, traction characteristics and vibration damping will be optimized with respect to components' mass and energy/power consumption on one side, and robustness/reliability on the other, leading to an overall lighter and effective vehicle. The idea is to update classical, sound studies (like [1]), in order to couple them with the most recent findings from Moon/Mars exploration and their geological and terra-mechanics results, so to be able to use far more correct data, closer to the true soil parameters, for friction, slope, sliding at the peculiar location. Recent findings in analyzing optimal paths for solar system bodies exploration [2] will be instrumental to this phase. In addition, properties and characteristics of newly available, advanced materials offer clear perspectives to improve older design performance (see [3] as an example). The mastering of advanced multibody simulation approaches to correctly represent vibration envelope [4], and the relevant expertise of the PI in effective vibration damping for space structures [5] will ensure that these aspects could be conveniently tackled and indeed updated with respect to newly adopted materials and configurations. Later on, the tests on the soil analogue carried on with the prototype will allow to conveniently judge design performance. Within such a frame, the experience gained by the team with miniaturized COTS inertial units (also considered for space use, with radiation tests currently carried out in cooperation with ENEA labs) will provide significant measurements of the vibrations for the rovers' mechanical links. Indeed, the mechanical design should be improved thanks to the use of the latter design/simulation/test techniques.
A specific and original contribution of this research will be given by the inclusion - since the beginning of the chassis design - of the requirements for the visual-based navigation system, to assess the maximum level of vibrations that could be tolerated without affecting the quality of the captured images/movies and indeed the accuracy of the navigation solution [6]. In such a way, no additional suspension system would be needed for the camera, indeed simplifying the overall design and having a stiffer system also limiting the effect of flexibility and lever arm's uncertainties in the pointing of the cameras. Again, this is an area where recent technological developments, both in hardware and software, should grant credible improvements.
With respect to the electrical system, the proposed solution deals with a novel design for a regulated bus, supplied as an example by a single high-energy Li-Ion cell. This solution, suggested by availability of battery cells capable to provide the full capacity required for the mission, can be accomplished thanks to a specifically developed high-gain Battery Charge Discharge Regulator (BCDR) [7]. Different possible voltage requirements will be satisfied by means of high-efficiency converters, also in the step-up configuration [8]. Again, advances of low-power command electronics, and mastering of their application, suggests that improvements in efficiency are possible. As for mechanical aspects, the way to benefit from these improvements is to focus on very specific working conditions, with a carefully tuned design, and indeed to subsystems devoted to a peculiar mission, i.e. the "fil rouge" of this proposal.
[1] Yoshida et al. "Slip, Traction Control, and Navigation of a Lunar Rover", Proceedings of the 7th International Symposium on Artificial Intelligence, Robotics and Automation in Space: i-SAIRAS 2003.
[2] [several authors] Studies for H2020 projects targeting Moon/Mars exploration and terrestrial site-replica (2015-18).
[3] https://www.nasa.gov/specials/wheels/
[4] M Sabatini, P Gasbarri, R Monti, GB Palmerini, "Vibration control of a flexible space manipulator during on orbit operations", Acta Astronautica 54 (1), 1-24 (2012).
[5] "Monitoring of a controlled space flexible multibody by means of embedded piezoelectric sensors and cameras synergy", see PI's publication list, entry #2.
[6] M.Carpentiero, M.Sabatini, G.B.Palmerini, "Capabilities of stereo vision systems for future space missions", paper IAC-16-D.1.2.7, 67th International Astronautical Congress, Guadalajara (2016).
[7] M.Macellari, G.B.Palmerini, L.Schirone, "Bidirectional converter for single-cell Li-ion batteries in a small space vehicle", IEEE Aerospace Conference Proceedings (2012).
[8] Schirone, L., Macellari, M., Pellitteri, F., "Predictive dead time controller for GaN-based boost converters", IET Power Electronics, Vol. 10, p. 421-428 (2017).