The CubeSat Mission FUTURE: a Preliminary Analysis to Validate the On-board Autonomous Orbit Determination
Authors:   Politecnico Di Milano, Milan, Italy, Buonagura Carmine , Borgia Salvatore , Pugliatti Mattia , Morselli Alessandro , Topputo Fancesco , Corradino Filippo , Visconti Pierluigi , Deva Luca , Fedele Alberto , Leccese Giuseppe , Natalucci Silvia 
Published: January 2024

FUTURE is a Low Earth Orbit (LEO) nanosatellite mission that has recently concluded phase A, whose aim is to demonstrate the capability of autonomously determining its orbit exploiting only visual observations, without relying on ranging measurements or on the GNSS (Global Navigation Satellite System) positioning systems. Such approach represents a paradigm shift in how deep-space missions are navigated. Currently, deep-space navigation relies mostly on either radiometric tracking or ground-based orbit determination which requires dedicated antenna networks such as the European Space Tracking Station (ESTRACK) of ESA and the Deep Space Network (DSN) of NASA. While radiometric measurements can provide accurate orbit determination, they require frequent communications with the ground stations, increasing the costs of operations. FUTURE as in-orbit demonstrator could validate this innovative navigation concept with beneficial impacts on beyond-LEO missions: more spacecraft autonomy will reduce spacecraft-ground interactions, minimize the need for operators and ground support, and hence the operations costs.

FUTURE will fly a set of optical sensors on a single satellite and will use the acquired data to feed artificial intelligence algorithms to detect time invariant features of the Earth’s surface, such as lakes and coastlines. These data are then processed on-board to generate positional inputs for the navigation filter which, will finally determine the satellite state in terms of both position and velocity. Furthermore, opportunistic observations with other celestial objects can be carried on concurrently to validate alternative autonomous navigation techniques using different sets of measurements. Being in Earth orbit, it will be possible to assess the orbit determination accuracy achievable with artificial intelligence and filtering techniques by taking as a reference the orbit determination performed by means of GALILEO/GNSS measurements.

This work presents the outcomes of the Phase A study of FUTURE, focusing on the navigation filter preliminary architecture, the on-board navigation performance assessment, as well as relevant mission analysis studies. The paper is organized into three main parts: the first part will thoroughly describe the FUTURE mission and its innovative goals and navigation filter preliminary architecture. In the second part, the considered Sun-synchronous operational orbit will be defined. Coverage analysis will be performed to understand when it is possible to acquire meaningful terrestrial feature images and take advantage of the autonomous navigation algorithm. Maximum eclipse times and flyover times of oceans or polar regions will be determined to understand the worst-case scenario in terms of free filter propagation. The visibility of the Moon and planets throughout the mission will be established to understand the time windows in which opportunistic scenarios can be exploited. Subsequently, some preliminary results of the navigation filter are described. In phase A, a Hybrid Extended Kalman Filter (HEKF) has been employed. As the filter shall operate with different set of range measurement (features and Moon observations) two different operative scenarios are described and analysed. The nominal scenario is represented by the natural features of the planet, through which accuracies of a few meters can be achieved. The opportunistic scenario consists of navigation exploiting the Moon, carried out during periods when the satellite flies over the oceans or polar regions. It will be shown that this scenario is not complementary to the nominal one since extended time periods in which the lunar disk is not visible are present. In addition, the navigation accuracy in this case is much lower, on the order of hundreds of meters.

Finally, some future developments of the navigation filter during phase B are given together with some hints of the potential applications of the proposed technology, in particular how it could enhance autonomous operation and navigation around other planets and moons by exploiting their morphological features and how the opportunistic scenario could be exploited to complement periods during which relevant morphological features are not present on the ground or when the main attractor is in eclipse.

FUTURE is one of the twenty missions funded by ASI under the ALCOR program, aimed at placing Italy in a condition of consolidated leadership in the nano and micro satellite sector. The FUTURE consortium is composed of entities and institutions from Italy. Tyvak International serves as the prime contractor, managing the entire program and providing mission development, system integration and verification, launch coordination, and mission operations support. The DART team at Politecnico di Milano is responsible for the mission analysis and for the design, verification, and validation of the navigation filter solution. ALTEC is in charge of the ground segment design and spacecraft operations. AIKO oversees the development of artificial intelligence-based image processing algorithms. The authors would like to acknowledge the FUTURE team and the support received by ASI.