# _Sci_
## 4 Discussion
### Advantages--Throughput, Power, Information Protection  
Warfighers like that crosslinks provide from ten to one-hundred times higher data rates than traditional radio frequency [3]; that laser crosslinks can be protocol independent and able to support multiple platforms and interfaces [35]; that laser crosslinks have a low probability of detection, of interception, and of exploitation [36]. The programming and budget personnel like that: laser crosslinks exists in an radio frequency band that is currently license-free; that laser crosslinks components tend to have smaller mass, power, and volume requirements [96]; that laser crosslinks have a low probability of detection, of interception, and of exploitation. Programmers also like that laser crosslinks systems are easier to install (less funding for labor) and have lower cost per bit ratios (i.e., lower signal operating costs) [35]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Condition** & **Scattering Coefficient 1** \\ \hline _Visibility_ \(>\) 50 km & 1.6 \\
6 km \(<\)_Visibility_ \(<\) 50 km & 1.3 \\
1 km \(<\)_Visibility_ \(<\) 6 km & 0.34 + 0.16 (_Visibility_) \\
0.5 km \(<\)_Visibility_ \(<\) 1 km & (_Visibility_) \(-\) 0.5 \\ _Visibility_ \(<\)0.5 km & 0 \\ \hline \hline \end{tabular} 1  
\end{table} 
Table 2: Scattering coefficient. Figure 6: Attenuation for various laser wavelengths ranging from 1047 to 1350 nanometers with visibility range (km) on the abscissa and fog attenuation on the ordinant. The primary advantage of using the small wavelengths of laser crosslinks is that the orders of magnitude-increased throughput-laser crosslinks provide higher bit rates with lower bit error rate. Where a microwave link at geosynchronous orbit ranges can support data rates in the tens of mega-bits per second, at the same ranges, laser crosslinks can support in the tens of giga-bits per second [52]. Laser crosslinks have the potential to support in the terabits per second range--which is akin to streaming two-hundred-thousand high-definition movies simultaneously [96]. Laser crosslinks also support employing the entire bandwidth of the signal [46], providing the opportunity for full duplex operations [61]. Auspiciously, the power requirements for laser crosslinks are much lower (than traditional radio frequency) while the efficiency is higher. As a rule-of-thumb, laser crosslinks can send ten times more data using ten times less power [96]. Additionally, the smaller signal power requirement allows for smaller collecting antennae, an advantage seen in a smaller size, weight, and power [52]. During the early days of human spaceflight, the U.S. national air and space administration's Apollo spacecraft communicated with the Earth using seven-foot antennae. In 2009, the lunar reconnaissance orbiter launched by the U.S. national air and space administration used a two-and-a-half-foot antenna. Meanwhile spacecraft laser terminals can be a mere four inches [42]. Laser crosslinks are advantageous in both ensuring the message gets from sender to receiver, and to assuring that the receiver is confident the message is true and undisturbed. In addressing warfighting information protection, the extremely small beam divergence both minimizes signal loss and increases security by making jamming problematic [7]. The narrow beam makes both in-path interception difficult as well as interference both to and from adjacent satellites [7]. Additionally, using well-selected optical signals makes for immunity from electromagnetic interference, while quantum key distribution adds additional security. _\"Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. However, the distance over which QKD is achievable has been limited to a few hundred kilometers, owing to the channel loss that occurs when using optical fibres or terrestrial free space that exponentially reduces the photon transmission rate.