# Design of Novel Laser Crosslink Systems Using Nanosatellites in Formation Flying: The VISION
## 3 Concept of the Laser Crosslink Systems
### Systems Design Specifications
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Parameter** & \multicolumn{2}{c}{**Requirements**} & **Specifications** & **Remarks** \\ \hline \multirow{3}{*}{**Physical Properties**} & \multirow{3}{*}{Mass} & Payload & \(<\)6 kg & 5.70 kg & wet mass \\  & & Bus & \(<\)6 kg & 5.66 kg & \\  & & Payload & \(<\)0.25 \(\times\) 0.10 \(\times\) 0.10 m\({}^{3}\) & \(<\)0.20 \(\times\) 0.09 \(\times\) 0.09 m\({}^{3}\) & \\  & & Bus & 6U standard & \(<\)0.25 \(\times\) 0.12 \(\times\) 0.34 m\({}^{3}\) & \\ \hline \multirow{3}{*}{**Orbit**} & \multirow{3}{*}{Lifetime} & \(>\)1 years & 3 years & radiation tolerance \\  & & Altitude & 600 \(\pm\) 25 km & 600 km & sun synchronous \\  & & LTAN & 18:00 \(\pm\) 2 h & 18:00 h & - \\ \hline \multirow{3}{*}{**Laser Crosslink**} & \multirow{3}{*}{Range Capacity} & Up to 1000 km & 50–1000 km & - \\  & & Capacity & Up to 1 Gbps & 1 Gbps & uncoded BER 1 \(\times\) 10\({}^{-3}\) \\ \cline{1-1}  & & Residual LOS Jitter (\(\upmu\), \(\upsigma\)) & \(<\)(30, 1) [\(\upmu\)rad] & \(<\)(0.10, 0.96) [\(\upmu\)rad] & fine pointing \\ \cline{1-1}  & & SNR Margin & \(>\)10 dB & \(>\)15.98 dB & communication \\ \hline \multirow{3}{*}{**GNC**} & Body Pointing & \(<\)75 arcsec (3\(\upsigma\)) & \(<\)63.5 arcsec (3\(\upsigma\)) & slewing, LOS error \\ \cline{1-1}  & & Stability & \(<\)5 arcsec (1\(\upsigma\)) & \(<\)2 arcsec (1\(\upsigma\)) & slewing, LOS jitter \\ \cline{1-1}  & & Relative Navigation & \(<\)10 m (3\(\upsigma\)) & \(<\)0.90 m (3\(\upsigma\)) & each axis \\ \cline{1-1}  & & Propellant & \(>\)5.2 m/s & 6.6 m/s & 10\% of residual \\ \hline \multirow{3}{*}{**Electrical Interface**} & \multirow{3}{*}{Data Communication} & \multirow{3}{*}{1 Mbps CAN, SPI} & 1 Mbps CAN, SPI, & Ethernet, JTAG \\  & & & UART, RS422, \({}^{1}\)C & for debugging \\ \cline{1-1}  & & Power Supply & 3.3 V, 5 V, 12 V & 3.3 V, 5 V, 12 V, \\ \cline{1-1}  & & & Battery Voltage & latch-up protection \\ \hline \multirow{3}{*}{**RF Communication**} & S-band (TMTC/ISL) & \(>\)0.5 Mbps/5 kbps & 1 Mbps/10 kbps & margin \(>\) 7.01 dB \\ \cline{1-1}  & X-band (Mission Data) & \(>\)100 Mbps & 90–135 Mbps & margin \(>\) 5.13 dB \\ \cline{1-1}  & UHF (Redundancy) & \(>\)2 kbps & 4.8–9.6 kbps & margin \(>\) 9.56 dB \\ \hline \multirow{3}{*}{**Electrical Power**} & Generation (Average) & \(>\)16 W & \(>\)21.6 W & sun-pointing \\ \cline{1-1}  & & \(<\)4 A (protected) & \(<\)1.68 A & laser crosslink \\ \cline{1-1}  & & \(<\)10 A (unprotected) & \(<\)2.72 A & laser crosslink \\ \cline{1-1}  & Depth of Discharge & \(<\)20\% & \(<\)18.5\% & 77 Wh battery pack \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Systems requirements and design specifications. The GNC system of the bus assisted the laser crosslink by precisely correcting LOS errors. In particular, the relative navigation system using GPS L1/L2 signals compensates for the effects of ionospheric delay from a long baseline and estimates at submeter levels, mitigating the FOU. The propellant budget for orbit maneuvers has approximately 20% of margin, considering a residual at the end of life. Data communications are conducted mainly through CAN-bus interfaces, and the power supply system includes latch-up protection to prevent over-power draws. RF communication systems consist of S-band, X-band, and UHF radio. From the worst-case analyses, it was confirmed that the link margin of each channel exceeded 5 dB. One of the S-band radios is utilized for relative navigation; then, the data rate is faster than 10 kbps, enabling sharing of the GPS measurement data every 5 s. When they orient to the sun, the power generation is maximized up to 21.9 W at the operation orbit. The selected power system ensures battery capability and lifetime from the depth-of-discharge (DOD) analysis. The peak current draw is lower than the limit for either protected or unprojected channels with any system operation. The preliminary design ensured the performance of the laser crosslink systems, supported by the formation of a nanosatellite bus system.