## 3 Background
### General CubeSat Specifications
#### 3.1.4 Mechanical and P-POD Specification  
The CalPoly design specification presents many regulations regarding the CubeSat structure, mainly to ensure compatibility with the P-POD structure. The engineering drawing detailing 3U CubeSat component definition gives the following dimensions [1]: (Table 4).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**CubeSat Size** & **3U** \\ \hline X and Y Dimensions (mm) & 100 \(\pm\) 0.1 \\ Z Dimension (mm) & 340.5 \(\pm\) 0.3 \\ Rail Width (mm) & 8.5 by 8.5 (Minimum) \\ Rail Contact with P-POD (75\% of Z Dimension, mm) & 255.4 (Minimum) \\ Component Protrusion Normal to CubeSat Surface (mm) & 6.5 (Maximum) \\ Mass (g) & 4000 (maximum) \\ \hline \hline \end{tabular}
\end{table}
Table 4: 3U CubeSat Dimensions [1].  
Only the CubeSat rails are permitted to contact the P-POD [1]. This will have a significant impact upon design as components such as communication antenna and deployable solar booms will require a compact release mechanism until deployment is complete. As a 3U CubeSat is placed inside the P-POD alone, separation springs are not required [1]. To prevent cold welding between the CubeSat and P-POD surfaces the satellites primary structure must be constructed from hard anodized Aluminum 7075 or 6061. The center of gravity will be located within 45 mm from its geometric center in respect to the Z direction [1].  
Operators will obtain and provide documentation of proper licenses for use of radio frequencies. CubeSats will comply with their countries radio license agreements and restrictions [1]. CubeSat's mission design and hardware will be in accordance with NPR 8715.6 to limit orbital debris. Any CubeSat component will re-enter with energy less than 15 J. All deployable devices such as booms, antennas and solar panels will wait to deploy a minimum of 30 min after the CubeSat's deployment switches are activated from orbital deployer ejection [1]. No CubeSat will generate or transmit any signal from the time of integration into the orbital deployer through 45 min after on-orbit deployment. However, the CubeSat can be powered on following deployment. Figure 5 illustrates the POD exterior courtesy of [1].  
For a CubeSat to be loaded into a P-POD for flight, it must firstly pass a rigorous testing procedure. Depending on the private launch provider additional testing may be required [1]. If the launch provider is unknown the GSFC-STD-7000 NASA Godard Space Flight Centre standard may be used as a testing baseline [24]. The qualification testing is designed to test both prototype and proto-flight hardware. It is the responsibility of the CubeSat developer to arrange/conduct testing.  
The orbital deployer referred to as the PPOD by CalPoly is a standardized device with the purpose of carrying and ejecting the CubeSat(s) from the launch vehicle safely. It is a rectangular box with spring mechanism powered door. An electronic signal is sent from the launch vehicle to the deployers release mechanism actuator triggering torsion springs to open the release door. The stored CubeSats then slide along rails (specified in the design guide) out of the deployer and into orbit. Rails will have a surface roughness less than 1.6 \(\upmu\)m and the edges of the rails will be rounded to a radius of at least 1 mm [1].