## 3 Background
### Other Key Components Selection
#### 3.5.3 Guidance, Navigation, and Control System  
This system has two primary functions, to ensure position determination and Altitude determination and control of the CubeSat. Typically, position determination is performed via the use of an on-board Global Positioning System (GPS) receiver, or by utilizing a ground-based tracking system [23]. An altitude determination and control system (ADCS) incorporates sensors used to measure altitude, and the rate of change of this respective altitude. These sensors are usually star trackers or gyroscopes [49]. The CubeSat's altitude is altered using an actuator. These are typically thrusters or a reaction wheel [23]. Figure 32: 3U Monocoque Walled Primary Structure [48]. Reaction Wheels equip the CubeSat with a precision pointing ability [48]. The wheel is also able to apply a generated torque. If a CubeSat requires 3 axis pointing control, three reaction wheels are required to be integrated into the electrical system. Due to the presence of external torques generated by the environment surrounding the CubeSat, periodic desaturation of the wheels is required using an external torque actuator. This is commonly achieved using a magnetorquer or thruster [50]. The magnetorquer is designed to generate a torque, which negates the impact of applied external torques due to magnetic fields which cause deviation of the craft from its intended trajectory [48]. The applied torque is perpendicular to the magnetic field. Recent developments in the technology have introduced Magnetorquer rods (Table 16) onto the CubeSat off-the-shelf product market. The rod generates an amplified effect over an air cored magnetorquer, consuming lower power compared to conventional magnetorquer alternatives. The New Space NSS magnetorquer rod [51; 52]. It is also able to deliver increased maneuverability rates and decrease tumble rate duration. [51; 52]. Figure 34 shows a typical altitude control system. A star sensor is a device with the capability of accurately estimating a CubeSat's altitude by comparing an image captured with a CCD or CMOS sensor, then comparing this to an on-board star catalogue database. These components are typically extremely expensive, an NST-1 Nano star tracker suitable for a CubeSat has a cost of \(\ell\)68,000 [53]. The device has a cross bore-sight accuracy \(<\)7 arcsec and an around bore-sight accuracy \(<\)70 arcsec. The device requires a 5 VDC current with a peak current of 0.2 A with a total weight of 245 g with baffle attached. The device has dimensions of 50 \(\times\) 50 \(\times\) 85 mm, with an operating temperature range of \(-\)30 \({}^{\circ}\)C to 60 \({}^{\circ}\)C. The estimated life span of the product is 3 years [54]. Magnetometer technology measures (Tables 17 and 18) the strength of the local magnetic field, allowing the altitude and orbital position to be estimated. The NSS magnetometer, costing approximately \(\ell\)13,620 per unit [51; 52], has a power consumption of 700 mW maximum and a measurement range of +60,000 nT to \(-\)60,000 nT [50; 51]. It has a mass of 200 g and dimensions of \(96\times 43\times 17\) mm. The operating temperature range of this product is \(-\)35 \({}^{\circ}\)C to 75 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c} \hline
**Performance Criteria** & **Delivered Performance** \\ \hline Magnetic Moment & \(>\)0.2 A m\({}^{2}\) \\ Linearity & \(\pm\)5\% across operating design range \\ Residual Moment & \(<\)0.001 A m\({}^{2}\) \\ Operating Temperature Range & \(-\)35 \({}^{\circ}\)C to +75 \({}^{\circ}\)C \\ Power Draw & 200 mW from 5 V supply \\ Random Vibration & 14 g rms \\ Mass & 30 g \\ Dimensions & 70 mm length \(\times\) 9 mm Diameter \\ Lifetime & 10 years \\ \hline \end{tabular}
\end{table} 
Table 16: NSS Magnetorquer Rod Data [51; 52].