Conceptual Design of an Interplanetary Mission for a Small-Sats constellation to support Martian Rovers’ Navigation

The explorations of Mars began in the 1960s and, since then, the efforts aimed at deepening our understanding of the Red Planet have steadily increased. The future promises a growing number of missions primarily dedicated to conducting comprehensive geological studies with the ultimate goal of searching for traces of life on the Martian surface. These missions will also aim at identifying and exploring valuable resources while testing innovative technologies that could prove essential for future human missions. Rovers on the surface are valuable elements to improve the knowledge of the planet. However, they have limited movements due to the impossibility to have a real time guide, at the moment possible only with commands from ground. To increase the velocity of movements over the surface, supports to their navigation should be added. While landmarking from spacecraft in orbit and instruments onboard the rover are the state of the art that is improved mission-by-mission in the last years, a pioneering hypothesis is to think about a GNSS-like constellation as way to increase the performance of localization of a rover. In this thesis, a conceptual design of a constellation of small satellites equipped with elements similar to GNSS receiver and related antenna and orbiting Mars is conducted. This constellation serves to provide a GNSS service to support the navigation of Martian rovers in future missions, with the main objectives of improving navigation accuracy and making it independent from the need for constant monitoring by mission control centers on Earth. After having outlined the objectives and mission’s high level requirements, the architecture and the instrumentation of the GPS system on Earth has been studied to gain the know-how and the fundamental aspects, which will then have to be implemented within the Martian GNSS system. Through the use of the STK software a trade-off analysis on different mission geometries is conducted to define the optimal orbits and position of the spacecraft in the constellation. This geometry is designed to ensure coverage of the band that extends between -30 degrees and +30 degrees of latitude, an area of particular relevance for upcoming missions to Mars. Once the constellation’s configuration is established, it is faced the critical question of the allocation of the essential functions that the Control Segment must perform. These functions are allocated to four larger satellites orbiting in a Martian aerostationary orbit. Subsequently, the communication architecture, which involves the User Segment, the Space Segment and the Control Segment is built. The latter plays a fundamental role for the correct operation of the GPS-like system and also involves the stations of the Deep Space Network and the Master Control Stations located on Earth in addition to the four aerostationary satellites. Finally, a discussion on the advantages, drawbacks, criticalities and complexities related to the provision of a highly precise navigation service based on GNSS-like constellation on Mars is proposed. High accuracy presupposes an accurate knowledge of the ephemeris and time of GPS satellites, which require updates from Earth and are inevitably subject to delays caused by the distance between Mars and the Earth.