# A Review of Requirements for Gamma Radiation Detection in Space Using CubeSats
## 2 Cubesat Specifications and Constraints
### Attitude Determination and Control Subsystem  
The Attitude Determination and Control Subsystem consists of sensors that determine the attitude, and actuators that control it to point in the required direction. Attitude determination requires the usage of external references, such as the sun, Earth's horizon, stars, and the local magnetic field, and the corresponding sensors are used as per the accuracy requirements. High-speed gyroscopes are also used to provide a short-term spin rate along different axes. Different reference measurements must be used to accurately specify the orientation of a CubeSat; therefore, multiple sensors are used simultaneously [20]. Actuators, such as magnetorquers and reaction wheels, are employed for attitude control.  
The attitude determination and control has in general a critical impact on the satellite operations, for example, to maximize the solar energy collection, to fulfill the requirements of directional data transmission systems, and to comply with the scientific requirements of the mission. The detector layout presented in this paper does not require the finest attitude satellite determination and control; however. its knowledge might be relevant for specific searches (for example for TGF science). As reported in Table 1, the attitude control accuracy is typically within 1 deg.  
Figure 1 shows, as an example, the LIGHT-1 3U CubeSat mainframe. LIGHT-1 (former RAADsat [21]) is the United Arab Emirates mission aiming at detecting Terrestrial Gamma-Ray Flashes and expected to be launched by the end of 2021.  
Vendors now provide highly standardized Commercially Off-The-Shelf (COTS) components and platforms [19]. Being smaller in size and with several design constraints, CubeSats have only a limited capacity to support scientific missions requiring significant resources in terms of mass, volume power, and data rates. Table 1 summarizes some constraints and approximate available resources for payloads. Only 3U, 6U, and 12U are chosen for comparison based on the requirements of the payloads proposed in this work.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter Specification** & **3U CubeSat** & **6U CubeSat** & **12U CubeSat** \\ \hline Satellite Mass Limit [kg] & \(\sim\)5 & \(\sim\)10 & \(\sim\)20 \\ \hline Payload Mass Limit [kg] & \(\sim\)2 & \(\sim\)5 & \(\sim\)14 \\ \hline Downlink S-Band [Mbps] & 2–8 & 2–8 & 2–8 \\ \hline Downlink X-Band [Mbps] & 200–400 & 200–400 & 200–400 \\ \hline Energy Storage [Wh] & 40 & 80 & 160 \\ \hline Payload Available Power (Body & \(\sim\)4 & \(\sim\)10 & \(\sim\)20 \\ \hline Payload Available Power (Deployables) [W] & \(\sim\)10 & \(\sim\)30 & \(\sim\)45 \\ \hline Payload Volume Occupancy [U] & 1.5–2 & 3–4 & 8–9 \\ \hline Pointing Accuracy [deg] & \(<\)1 & \(<\)1 & \(<\)1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Typical constraints on payload requirements in 3U, 6U, and 12U class CubeSats (based on private communication with vendors).  
Figure 1: The 3U mainframe of the LIGHT-1 CubeSat mission. (**Left**) All the subsystems fit in 1.3 U, leaving room for a 1.7 U payload. (**Right**) The satellite is equipped with deployables with embedded solar panels for power harvesting.