# Vulnerability of Satellite Quantum Key Distribution to Disruption from Ground-Based Lasers
## 3 Results
### Orbital Dynamics and Visibility  
Regardless of the optical power level transmitted by the laser terminal, the exact location of the laser terminal relative to the ground station (though, more precisely, the location of the laser terminal relative to the closest point of the satellite's ground track to the ground station) will determine the fraction of the QKD transmission period during which the laser terminal is able to view the satellite.  
Figure 2 shows a contour plot where the contours indicate the fraction of the transmission window for which the laser terminal is able to see the satellite (at 500 km altitude) assuming a minimum elevation limit of \(15^{\circ}\), similar to that of the _Micius_ ground station. The ground track of the satellite is shown by the thin black line and is taken from an actual _Micius_ ground track over Australia. The black dot represents the location of the hypothetical QKD ground station and the thick black bar shows the extent of the satellite's path during which it is visible to the ground station and QKD can take place.  
It can be seen that, depending on the exact location, the satellite is in view of a laser terminal 1000 km away for 50% to 60% of the QKD transmission window, and is in view for over 90% of the transmission duration to a laser terminal around 100 km from the ground station. If the elevation of the mobile laser terminal can be trained as low as \(2^{\circ}\), then the laser terminal will be able to target the satellite through its entire transmission window. However, due to the large distance and atmospheric attenuation at these low angles, the excess photon rate will be significantly reduced.  
It can also be seen that, depending on the exact positioning of the satellite ground track relative to the ground station, it is possible for the laser terminal to cover 100% of the QKD transmission window while still being located several tens of kilometres away from the ground station by positioning itself closer to the mid point of the QKD transmission window than the ground station is.  
Figure 3 shows two example locations for a laser terminal. The left image shows the scenario for a laser terminal deployed 100 km to the east of the ground station, and the right image shows the terminal deployed 1000 km to the south east.  
These orbital dynamics calculations were also used to determine the distance and angles between the ground station, satellite, and laser terminal, which were used to calculate the optical loss from laser terminal to QKD receiver.  
Figure 3: QKD transmission window coverage for laser terminals (**a**) 100 km away and (**b**) 1000 km away from the QKD ground station. The black dot represents the QKD ground station, and the black bar represents the QKD transmission window. The red dot represents an example location for the laser terminal, and the red bar shows the portion of the QKD transmission window that the satellite is visible to the laser terminal from this location.  
Figure 2: Contour plot showing the areas in which different fractions of the QKD transmission window are visible to the laser terminal. The black dot represents the QKD ground station, and the black bar represents the QKD transmission window.