# Interplanetary Student Nanospacecraft: Development of the LEO Demonstrator ESTCube-2
## 1 Introduction  
### Nanosatellite Propulsion and Deorbiting  
Nanosatellites have become one of the most important tools for science, education, and commercialization of low-Earth orbit (LEO). Since the inception of the CubeSat standard in 1999 [1], many academic institutes' attention has switched from large-scale missions to developing small-scale nanosatellite missions. Low-cost low-Earth orbit educational and science nanosatellite missions paved the way for the nanosatellite industry. During the last two decades, the nanosatellite industry has successfully created a miniaturized class of nano and microsatellite systems allowing for the development of miniaturized instruments and experiments [2].  
The main benefit of miniaturized systems is the low development cost and the intrinsic ability to increase the mission coverage for specific observations. For instance, it allows the launching of many small satellites rather than a single large-scale satellite. Multiple satellites can increase the temporal resolution of observations, use synthetic scaling to improve measurement precision or perform high-risk mission objectives to which large-scale spacecraft typically would not be subjected.  
One of the main drivers for nanosatellite missions has become rapid proof-of-concept validation thanks to the availability of commercial-off-the-shelf (COTS) satellite buses, reducing the development time of the mission on a lower budget. As a result, the number of LEO satellites, including many nanosatellites, has increased significantly during the last two decades [3], adding to the existing number of orbital debris in LEO. The problem of orbital debris requires new policies, practices, and technologies, including an affordable and lightweight deorbiting device.  
If the satellite has to contain a deorbiting device to comply with the 25-year rule [4] or the recent announcement of FCC's 5-year rule [5], this can significantly increase development and launch costs; therefore, a lightweight deorbiting device is crucial for cost reduction in debris mitigation. Various nanosatellite missions have addressed the space debris problem using passive and active deorbiting techniques [2].  
Using classical chemical and electric propulsion deorbiting devices onboard nanosatellites is challenging due to the incompatible requirements for the propellant and its tank. Propellantless deorbiting devices are atmospheric drag sails, electrodynamic tethers, and electrostatic tethers, like the ionospheric plasma brake. While the drag sail lowers the satellite's altitude by encountering atmospheric particles, it also increases the risk of collision with another satellite or debris item. The electrodynamic tethers use the Lorentz force to increase or decrease the LEO altitude. A typical electrodynamic tether is \(\sim\)1 cm wide tape which makes it dangerous to other space assets, although in one dimension compared to the two-dimensional drag sail.  
The ionospheric plasma brake is the most recent LEO deorbiting invention [6]. By employing the Coulomb drag interaction between the ionosphere and an electrostatically charged hair-thin tether, the satellite can lower its altitude, avoiding the situation where the deorbiting device can be used for a mission extension. To be demonstrated onboard the ESTCube-2 [7], the ionospheric plasma brake has the potential to be the safest propellantless LEO deorbiting solution. The ESTCube-1 and Aalto-1 satellites have attempted to demonstrate the ionospheric plasma brake in LEO, but the first-generation ionospheric plasma brake required several improvements [8; 9] which have been implemented onboard the ESTCube-2 and Foresail-1 [10].