"Earth is a small town with many neighborhoods in a very big universe." The quote of the American Astronaut Ronald John Garan Jr. perfectly summarizes the universal and enduring mankind's interest in exploring the unknown, discovering new worlds, pushing the boundaries of scientific and technical limits further and beyond. More than a half century ago, during a speech delivered at Rice University in Houston, President John F. Kennedy claimed the Moon as the new frontier for the human space exploration. The outstanding achievements of the Apollo mission pushed the research in space across the second part of the last century with new goals, as the permanent presence of the human in space. The evolutionary space program built up around that promise was, to say the least, challenging and involved the development of several revolutionary elements. Due to the significant economic effort required by the Apollo mission, only two elements were realized: the Space Shuttle on one side and the Skylab space station on the other. While the Shuttle remained operative until 2011, Skylab was short-lived and disposed after about six years. Only by joining forces with other international partners, NASA was able to realize a long lasting permanent outpost orbiting around Earth, i.e. the International Space Station (ISS). But again, due to the considerable efforts dedicated to build up the ISS and to keep the Space Shuttle operative, the space race suffered a second setback. Until 2007, when the international community drew up a new visionary program. Moon exploration stepped again into the spotlight to extend and sustain human activities beyond Low Earth Orbit (LEO) towards Mars. The new era of space exploration has begun with the intent of expanding the frontiers of knowledge, capability, and opportunities in space. One of the first milestones is represented by the settlement of the so-called Lunar Orbital Platform-Gateway (LOP-G) by the mid 2020's. The Gateway will serve as a manned outpost in the lunar vicinity to support activities on and around the Moon while also servicing as technological and operational testbed to open the frontier for human exploration of Mars, thanks to the exploitation of key technologies, such as high-power electric propulsion. To sustain the LOP-G and its future visiting crews, the Orion spacecraft is currently under development. However, the usability of the Gateway could be extended if new transportation systems would be available to support the station transferring additional supplies and equipment. In compliance with the current plans to efficiently reduce the number of development and validation economic efforts by designing and exploiting same elements for multiple missions, a reusable, high-power electric space tug, i.e. the Lunar Space Tug (LST), is proposed in this Thesis to support the replenishment of the LOP-G. This innovative transportation system should be flexible enough to be adopted in different phases of the Gateway lifetime and for evolving needs. The LST should be in charge of recovering cargo modules released in Earth proximity and transfer them up to the Gateway performing a low-thrust transfer, before return to its operational orbit, ready for the next delivery mission, envisioning a closed-loop mission profile. A tailored multi-input/multi-output design tool has been developed to obtain the preliminary and detailed design, at component level, of the LST spacecraft for several propulsion subsystem architectures. The impact of adopting this technology on the platform design is investigated with respect to several thruster working points and case studies, each one characterized by different refurbishment needs. Then, the optimal LST configuration able to support the Gateway crew for different resupply needs is selected, performing a trade-off analysis among the design solutions that comply with all mission and system constraints previously defined in order to minimize the spacecraft mass, propellant consumption and overall mission cost. From an operational viewpoint, the LST should significantly rely on the Automated Rendezvous and Docking (ARVD) technology, which has been identified as crucial for the transition of space missions from geocentric architectures to self-sustainable, autonomy and independent. At this end, new Guidance Navigation and Control (GNC) algorithms shall be investigated to allow ARVD maneuvers to become reliable routine. In particular, the control problem encapsulates safety restrictions and performance specification that shall be properly addressed verifying the effectiveness and real-time implementability of innovative control strategies. Thus, a 6 Degrees-of-Freedom (DoF) orbital simulator has been developed to simulate the rotational and translational dynamics of the LST and its target vehicles in both Earth orbit and Lunar proximity. Moreover, to reproduce a realistic simulation environment, uncertainty and disturbance affecting the spacecraft dynamics during the maneuver have been modeled and included in the simulator. For attitude and orbital control, three different Model Predictive Control (MPC) algorithms have been implemented and their performance evaluated in the presence of disturbance and parametric uncertainty. In particular, a sampling-based stochastic MPC algorithm is proposed and the typical binding computational effort required by these type of stochastic algorithms, especially when running on low-performing hardware, has been overcome shifting the intensive computations to the offline phase, thus greatly reducing the online computational cost. To complete the algorithms verification process, all three MPC strategies have been experimentally validated exploiting spacecraft mock-up and running the algorithms on the on-board micro-controller, demonstrating their effectiveness and real-time computational applicability.
A Comprehensive Modeling Framework for Integrated Mission Analysis and Design of a Reusable Electric Space Tug / Mammarella, Martina. - (2019 Feb 11).
|Titolo:||A Comprehensive Modeling Framework for Integrated Mission Analysis and Design of a Reusable Electric Space Tug|
|Data di pubblicazione:||11-feb-2019|
|Appare nelle tipologie:||8.1 Doctoral thesis Polito|