## 3 ESTCube-Luna E-Sail Payload and Experiment Operations  
The E-sail employs the solar wind for propulsion by deflecting plasma particles off their original course thanks to the Coulomb drag interaction. For the ESTCube-LuNa concept, we are designing the simplest viable E-sail with a single **tether** and a simple **endmass** pulling it out. Each E-sail tether consists of a multi-thread structure made of thin wires (50 um or thinner), necessary for micrometeoroid tolerance. The tether is stored on a **reel**, which is controlled by a **motor**. The tether is deployed using the centrifugal force, which requires high-rate spin manoeuvring and closed-loop control between tether deployment and angular momentum provision. The tether is charged with a 20 kV or more **high-voltage supply**, and by **electron emitters** continuously pumping out negative charge from the spacecraft.  
E-sail prototypes and demonstration missions have been developed since 2008 by the ESTCube, Aalto and FORESAIL teams in Estonia and Finland. The ESTCube-1, Aalto-1, ESTCube-2 and Foresail-1(p) missions have been developed for the LEO environment, which differs from lunar orbit in two crucial aspects: the E-sail is tested in its ionospheric  
Figure 3: ESTCube-LuNa thrust experiment results from GMAT. LEFT: Orbital view in which the red line indicates the orbital sector of ESTCube-LuNa moving towards the Sun—the thrust period for reducing altitude. The yellow line is from the centre of the Moon to the Sun. RIGHT: Comparison of the orbital period between a “NoSailClone” spacecraft without thrust and ESTCube-LuNa, which emulates the E-sail thrust magnitude and direction with GMAT’s electric thrusters. For the first 0.16 days, both spacecrafts are in the same orbit, and then ESTCube-LuNa starts thrusting. As a result of the applied thrust, the orbital period is reduced along with the altitude. The thrust is not applied while in the eclipse.  
plasma brake mode for deorbiting in LEO and the magnetic field cannot be used for attitude determination and control in lunar orbit. The Foresail-2 team has addressed some of these challenges by designing the plasma brake operations and experiments for highly elliptical orbit around the Earth. In addition, Foresail-2 houses a high-grade magnetometer from the Space Research Institute (IWF) of the Austrian Academy of Sciences, which requires a strict magnetic cleanliness approach. Therefore, a typical combination of reaction wheels and a thruster-based attitude control system cannot be used, as the reaction wheels spin at a frequency too close to the ultra-low frequency (ULF) waves that the mission is designed to observe. On Foresail-2, a purely thruster-based solution is designed to orient the spacecraft towards the Sun and spin it up. The Foresail-2 cubesat is designed to spin around the Y-axis. Thrusters facing in X\(-\) and X+ directions can provide the required control authority for the spin manoeuvres. For further attitude control, at least two thrusters facing in Y\(-\) and Y+ directions, respectively, are needed. To provide redundancy, two thrusters will be used in each direction by the Foresail-2 satellite. For the ESTCube lunar nanospacecraft concept, we propose preliminary E-sail payload and experiment operations, which are based on the previous designs of ESTCube-2 (see Figure 4), Foresail-1(p) and Foresail-2 [14; 24; 27; 28; 29; 30; 31; 46].