# Design of Novel Laser Crosslink Systems Using Nanosatellites in Formation Flying: The VISION
## 3 Concept of the Laser Crosslink Systems  
### Systems Architecture  
Figure 6 presents the system architecture of the integrated laser communication payload and nanosatellite bus. The diagram describes the electrical interfaces, including the power supply and data communication. The system should achieve a data rate of 1 Gbps at an inter-satellite distance of 1000 km, securing an SNR margin higher than 10 dB. The size should then be fitted to the 6U nanosatellite standard.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Contents** & \multicolumn{2}{c}{**Coarse PAT Stage (CPS)**} & \multicolumn{2}{c}{**Fine PAT Stage (FPS)**} \\ \hline
**Substage** & **Search** & **Acquisition** & **Detection** & **Hand-Off** &
\begin{tabular}{c} **Tracking and** \\ **Communication** \\ \end{tabular} \\ \hline
**Control** & \(\sim\)60 & \(\sim\)180 & \(\sim\)60 & \(\sim\)60 & \(>\)600 \\ Duration [sec] & Pointing Error & & \(<\)(1200, 400) & & \(<\)(30, 1) \\ (\(\mu\), \(\sigma\)) (\({}^{1}\)) [\(\mu\)rad] & & & & \\ \hline
**Bus Operation** & & & & & \\ Attitude Control & Slewing & AOA Correction & Slewing & Slewing \\ RF Crosslink & &
\begin{tabular}{c} Enabled/ \\ Relative Navigation \\ \end{tabular} & & & & \\ \hline
**LCT Operation** & & Broad/Unsteady & Broad/Steady & Narrow/Steady \\ Beam & & & & \\ Actuator & & & & \\ Detector & CAM On/ & CAM On/ & QC (CAM (\({}^{2}\))) On/ & \\ Unavailable & Available & & Available & \\ \hline
**Optical Link Budget Case** & PAT\#1 & PAT\#2 & PAT\#3 & PAT\#4 & COM\#1 \\ \hline \hline \end{tabular}  
\({}^{(1)}\)\(\mu\): bias errors, \(\sigma\): standard deviations errors. \({}^{(2)}\) Only QC is used for feedback, CAM is available to prevent nanosatellites from missing each other.  
\end{table}
Table 2: PAT sequence descriptions.  
Figure 6: Diagram of the integrated laser communication payload and nanosatellite bus systems architecture.  
The optical train of the payload is a monostatic architecture that shares the aperture for laser communication and PAT. Unlike other laser communication systems with an extra beam-tracking system, the proposed system mitigates steady-state errors for feedback control during the PAT sequence. The aperture has a deployable configuration to enhance the optical power and minimize the stowed size during the launch phase. Moreover, an erbium-doped fiber amplifier (EDFA) pumps a laser generated by the seed laser assembly (SLA) up to 1 W for long-range data transmission. The ratio of laser powers for communication and PAT is 99:1. The instrument control electronics (ICE) of the payload manages the payload electronics, including the regulation and distribution of electrical power provided by the electrical power subsystem (EPS) of the bus.  
The OBC (on-board computer) handles the entire system using FSW (flight software). The guidance, navigation, and control (GNC) subsystem assists the PAT with precise attitude maneuvers. In addition, it provides GPS clock signals for the payloads to synchronize with each other. The RF communication subsystem performs S-band crosslink sharing of the GPS raw data to establish the relative navigation in a long baseline.