NetSat—Challenges and lessons learned of a formation of 4 nano-satellites

Abstract

The objective of the NetSat mission was to develop underlying technologies for small satellite formation flying and to demonstrate it at the level of four nano-satellites in three-dimensional configurations. Thus, base technologies, such as orbit determination, attitude determination and control, inter-satellite communication, and multi-satellite operations were studied and implemented on a 3U CubeSat platform. Technological challenges concerned in particular the precision 3-axis attitude control system in combination with an electric continuous low-thrust propulsion system. Different control approaches for efficient transitions between various formation topologies were analyzed, taking the limitations of the hardware platform (propellant mass, thrust level, power budget, attitude control capabilities) as well as external orbit perturbations into account and allowing for distributed control of multi-satellite formations. In a research program of over 15 years, the essential technologies for formations of small satellites were realized subsequently and then tested in orbit on multiple missions. On this basis, NetSat was launched on 28. September 2020 on a Soyuz rocket into a circular orbit of an altitude of 575km. During the operations phase several new operations concepts developed in the project, namely the Compass IoT network spanning all ground and satellite systems with more than 50 nodes, or a flexible operations frontend with auto-operations capabilities could be tested and allowed for operating such a multi-satellite network. Additionally, the implemented inter-satellite link among the satellites could be established and tested extensively, marking the first time that four 3U CubeSats were able to successfully demonstrate inter-satellite communication in orbit.