Nanosatellite spin-up using magnetic actuators: ESTCube-1 flight results Hendrik Ehrpais a,b,n , Johan Kütt b , Indrek Sünter a,b , Erik Kulu a,b , Andris Slavinskis a,b,c , Mart Noorma a,b a University of Tartu, Institute of Physics, W. Ostwaldi 1-D601, 50411, Tartu, Estonia b Tartu Observatory, Department of Space Technology, Observatooriumi 1, 61602, Tõravere, Estonia c Finnish Meteorological Institute, Erik Palménin aukio 1, P.O. Box 503, FI-00101, Helsinki, Finland article info Article history: Received 15 November 2015 Accepted 22 July 2016 Available online 25 July 2016 Keywords: CubeSat ESTCube-1 Nanosatellite Magnetic attitude control High spin rate Flight results abstract This paper presents the in-orbit performance of the ESTCube-1 attitude control system that used elec- tromagnetic actuators to achieve a high angular velocity. ESTCube-1 is a one-unit CubeSat that aimed to perform the first electric solar wind sail experiment. The attitude control system was designed to provide enough centrifugal force by spinning up the satellite to deploy a 10 m long tether. The required spin rate was a minimum of one rotation per second. The actuators used were three electromagnetic coils, each able to produce a magnetic moment of up to 0.1 A m 2 . In this paper, we describe the design of the attitude control system, implementation of the spin controller and the in-orbit performance of the system. In addition we describe the effect that a residual magnetic moment had on the attitude control of the satellite and the measures taken to overcome this issue. During testing of the satellite, ESTCube-1 achieved the highest known spin rate of 841°/s for small scale satellites. The satellite ended its operations on the 19th of May, 2015 after 2 years in orbit. & 2016 IAA. Published by Elsevier Ltd. All rights reserved. 1. Introduction Magnetic satellite spin and spin-axis control has been ex- tensively analysed in the literature for specific missions and as theoretical studies [1–6]. On nano- and microsatellites magnetic attitude control has been researched, or used for different appli- cations, such as detumbling [7], Sun-pointing [8], nadir-pointing [9], alignment with the geomagnetic field [10] and spin-stabilisa- tion [11]. Nanosatellites and picosatellites are often influenced by residual magnetic moments that reduce the ability to perform attitude control manoeuvres [12,13]. This problem has been ana- lysed and a method for compensation has been developed pre- viously [14]. Problems with a residual magnetic moment were also encountered on ESTCube-1. However, for ESTCube-1 the residual magnetic moment is similar in magnitude to the magnetic tor- quers and therefore it is not possible to compensate for it fully. Although attitude control using magnetic torquers on nanosa- tellites has a long history, to the best knowledge of the authors, in- orbit performance of magnetic spin control for nanosatellites at high spin rates (in the order of 100°/s and more) has not been presented. In this paper, we present the flight results of the EST- Cube-1 attitude control system (ACS) which was designed to achieve an angular velocity of 360°/s. The large angular velocity was needed for the centrifugal deployment of the tether to be used for the electric solar wind sail (E-sail) mission [15]. During preparations for tether deployment a significant re- sidual magnetic moment was identified on the satellite that had a detrimental effect on attitude control capabilities and aligned the satellite with the Earth's magnetic field vector. This problem was approached by characterising the residual magnetic moment, developing a coil correction function that would alter the coil output to counter the disturbing moment and by modifying the original spin controller to allow spinning up the satellite around an arbitrary axis. Fortunately, the uncontrolled spin axis that is influenced by the inertia tensor and the residual magnetic moment was still perpendicular to the direction of tether deployment so it was not seen as a major issue. The strong residual magnetic moment of the satellite also made it impossible to perfectly realign the spin axis with the Earth's polar axis and maintain the alignment without continuously running the spin controller. Because it was not safe to actively control the satellite's attitude during the experiment, the spin axis alignment was not used while performing the spin-up for the te- ther deployment experiment. The spin controller was originally described in [16] and studied Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/aa Acta Astronautica http://dx.doi.org/10.1016/j.actaastro.2016.07.032 0094-5765/& 2016 IAA. Published by Elsevier Ltd. All rights reserved. n Corresponding author at: University of Tartu, Institute of Physics, W. Ostwaldi 1-D601, 50411, Tartu, Estonia. E-mail address: hendrik.ehrpais@estcube.eu (H. Ehrpais). Acta Astronautica 128 (2016) 210–216