# Interplanetary Student Nanospacecraft: Development of the LEO Demonstrator ESTCube-2
## 2 ESTCube-2 Mission
### Satellite Design
#### 2.3.4 Attitude and Orbit Control System (AOCS)  
On the ESTCube-2 satellite, the AOCS is a virtual system. Its components are housed on the OBC PCB or are integrated within the SPs. The AOCS system can be separated into three different major functional blocks, which work in tandem to fulfill the set mission requirements.  
Mission requirements enforced the inclusion of an ST system (described in Section 2.3.2) and a CGP actuator (described later in this Section). These components enable attitude determination and control functionality outside the Earth's magnetic field, thus, establishing a platform capable of successfully conducting deep-space missions. Still, for the ESTCube-2, they provide the necessary backup options for a successful LEO mission. The sensor group comprises five types of sensors (described in Sections 2.3.2 and 2.3.3):  
1. Magnetometers
2. Gyroscopes
3. Accelerometers
4. Sun sensors
5. Star tracker  
The available actuators for controlling the satellite are:  
1. Three coreless magnetorquers with a magnetic moment of 0.45 A-m\({}^{2}\) made in-house (see Figure 12);
2. Three Hyperion Technologies RW210 Series nanosatellite RWs. Dimensions: 25 \(\times\) 25 \(\times\) 15 mm, Mass: 32 g, Momentum storage: 3.0 mNms;
3. Three Wittenstein Cyber Motors CYBER2 nanosatellite RWs for redundancy. Dimensions: 20 \(\times\) 20 \(\times\) 20 mm, Mass: 30 g, Momentum storage: 2.0 mNms;
4. A GOMSpace NanoProp CGP3 CGP system.  
Figure 11: Side panel configuration table. 1. The bottom Z-axis side panel controls the magnetorquer. However, the coil driver components are physically on the ST PCB. 2. Resistor count for deployable structures. 3. Both internal communication protocol (ICP) buses for redundancy. 4. Additional maximum power point trackers (MPPT) for deployable side panels.  
Sensory data are interpreted in turn by various AOCS algorithms. The main AOCS algorithm is a type of unscented Kalman filter (UKF) capable of accounting for uncertainties arising from sensor measurements and temporal uncertainty of measurements taken.  
The main requirement of the ESTCube-2 mission is to demonstrate the capability of executing each important maneuver, utilizing only the sensors and actuators available for deep-space missions.  
There are four main maneuvers that the satellite must be able to execute for the mission to succeed:  
1. Detumbling of the satellite to increase the reliability of communications between it and the ground station;
2. Satellite pointing for Earth observation camera operations and high-speed data downlink;
3. RW unloading/desaturating for continuous operations;
4. Satellite spin-up for IPB experiment tether deployment.  
Detumbling operations will be achieved by a B-dot algorithm using magnetorquers. However, a specialized slower \"predicting regulator,\" which only uses the cold-gas propulsion module, will be tested for future deep-space operations.  
Satellite pointing maneuvers are conducted using RWs following a PD-regulator control law. As a backup, the satellite can point itself using magnetorquers that employ a special PD-regulator.  
The RW unloading is to be handled by stopping them gradually while using the detumbling controllers, but RW unloading using the CGP system is necessary for technology demonstration only. During the ESTCube-2 mission RWs will be desaturated using the magnetorquers.  
The spin-up of the satellite for the deployment of its main experiment--the ionospheric plasma brake--is handled by a double P-regulator, which uses cold-gas propulsion for technology demonstration, and magnetorquers are kept as a backup.  
To increase the attitude and orbit determination precision externally, a radio satellite ranging experiment will be carried out, which aims to achieve the positioning of the satellite an order of magnitude more accurate than the two-line element set (TLE) using multiple collaborating ground stations and their respective locations.  
Figure 12: Two of three in-house developed coreless magnetorquers.