GNSS/INS/Star Tracker Integration for Real-Time On-Board Autonomous Orbit and Attitude Determination in LEO, MEO, GEO and Beyond

In our previous studies, we demonstrated that Global Navigation Satellite System (GNSS) signals can be processed, not only in Low Earth Orbit (LEO), but also in higher earth orbits, up to the Moon. In order to maximize the GNSSbased navigation performance, we implemented an adaptive orbital filter, which fuses the GNSS observations with a model of the spacecraft dynamics, achieving a navigation accuracy of approximately 100 meters, at Moon altitude. In this paper, we take a step forward and we investigate the design of an advanced multisensor solution that, in addition to combining GNSS with an orbital forces model, also adds the integration of an Inertial Navigation System (INS) and of a Star Tracker, in order to provide a versatile, real-time, on-board, autonomous orbit and attitude determination in different space mission scenarios, from LEO to GEO and beyond. First, we describe the designed architecture of the integrated system, then its implementation, and finally we report its achieved navigation performance for different altitudes up to the Moon, showing that the synergistic integration of the different sensors, can overcome their individual drawbacks and provide a better navigation performance than either could achieve individually.

GNSS/INS/Star Tracker Integrated Navigation System for Earth-Moon Transfer Orbit

Cyril Botteron, Vincenzo Capuano, Pierre-André Farine, Jérôme Leclère, Jia Tian, Yanguang Wang

Over the last few years, new Global Navigation Satellite System (GNSS) applications have emerged that go far beyond the original objectives of GNSS which was providing position, velocity and timing (PVT) services for land, maritime, and air applications. Indeed, today, GNSS is used in Low Earth Orbit (LEO) for a wide range of applications such as real-time navigation, formation flying, precise time synchronization, orbit determination and atmospheric profiling. GNSS, in fact, can maximize the autonomy of a spacecraft and reduce the burden and costs of network operations. For this reason, there is a strong interest to also use GNSS for High Earth Orbit or Highly Elliptical Orbit (HEO) missions. However, the use of GNSS for HEO up to Moon altitudes is still new, and terrestrial GNSS receivers have not been designed to cope with the space environment which affects considerably the GNSS receiver performance and the GNSS solution (e.g. navigation solution). The goal of our research is therefore to develop a proof of concept of a spaceborne GNSS receiver for Earth-Moon transfer orbits, assisted by Inertial Navigation System (INS), a Star Tracker and an orbital forces model to increase the navigation accuracy and to achieve the required sensitivity.

2014

GNSS-based Orbital Filter for Earth Moon Transfer Orbits

Cyril Botteron, Vincenzo Capuano, Pierre-André Farine

Cambridge University Press2015

GNSS-Based Navigation for Lunar Missions

Vincenzo Capuano

Numerous applications, not only Earth-based, but also space-based, have strengthened the interest of the international scientific community in using Global Navigation Satellite Systems (GNSSs) as navigation systems for space missions that require good accuracy and low operating costs. Indeed, already used in Low Earth Orbits (LEOs), GNSS based-navigation GNSS-based navigation systems can maximize the autonomy of a spacecraft while reducing the costs of ground operations, allowing for budget-limited missions of micro- and nanosatellites. This is why GNSS is also very attractive for applications in higher Earth orbits up to the Moon, such as in Moon Transfer Orbits (MTOs). However, while GNSS receivers have already been exploited with success for LEOs, their use in higher Earth orbits above the GNSS constellation is extremely challenging, particularly on the way from the Earth to the Moon, characterized by weaker signals with wider gain variability, larger dynamic ranges resulting in higher Doppler and Doppler rates, critically lower satellite signal availability, and poorer satellite-to-user geometry. In this context, the first research objective and achievement of this PhD research is a feasibility study of GNSS as an autonomous navigation system to reach the Moon, and the determination of the requirements for the design of a code-based GNSS receiver for such a mission. The most efficient combinations of signals transmitted by the GPS, Galileo, and combined GPS-Galileo constellations have been identified by analyzing the theoretical achievable signal acquisition and tracking sensitivities, the resultant constellation availability, the pseudorange error factors, and the geometry error factor and accordingly the achievable navigation performance The results show that GNSS signals can be tracked up to Moon altitude, but not with the current GNSS receiver technology for terrestrial use. The second research objective and achievement is the design and implementation of a GNSS receiver proof-of-concept capable of providing GNSS observations onboard a space vehicle orbiting up to Moon altitude. This research work describes the hardware architecture, the high-sensitivity acquisition and tracking modules and the standalone single-epoch navigation performance of the developed GPS L1 C/A hard-ware receiver, named the WeakHEO receiver. Although they can still be collected, GNSS observations at Moon altitude, if not filtered, but simply used to compute a single-epoch least-squares solution, lead to a very coarse navigation accuracy, on the order of 1 to 10 km, depending on the number and type of signals successfully processed. Therefore, the third and main research objective and achievement is the design and implementation of a GNSS-based orbital filter (OF) determination unit, based on an extended Kalman filter (EKF) and an orbital forces model, able to significantly improve the achievable navigation performance and also to aid acquisition and tracking modules of the GNSS receiver. Simulation results of the OF performance when processing simulated GPS and Galileo observations, but also real GPS L1 C/A observations provided by the WeakHEO receiver (when connected in a hardware in the loop configuration to a full constellation GNSS radio frequency signal simulator), show a positioning accuracy at Moon altitude of a few hundred meters.

EPFL2016

GNSS-Based Navigation for Lunar Missions

Vincenzo Capuano

EPFL2016