# Design of Novel Laser Crosslink Systems Using Nanosatellites in Formation Flying: The VISION
## 5 Formation Flying Nanosatellite Bus
### Subsystems Design
#### 5.2.1 Guidance, Navigation, and Control Subsystem (GNC)  
The GNC subsystem is composed of integrated actuators and sensors for attitude determination and control and a propulsion system for orbit maneuvers. The GNC algorithm for formation flying, similar to relative navigation, is computed using the primary host  
Figure 15: Diagram of the electrical interface for the nanosatellite bus. Except the primary OBC and redundancy systems, all power supplies are switchable with latch-up protections. Data communications are mainly implemented by CAN bus. OBC. The attitude determination and control for the pointing maneuver are executed by the integrated module called the XACT-50, manufactured by Blue Canyon Technologies (BCT), which ensures the most precise pointing performance on the nanosatellite platform. Figure 16 shows a diagram of the formation flying architecture of the VISION system. Three coarse sun sensor (CSS) arrays are attached to acquire the sun vector. Arcsecond-level attitude determination can be achieved using a star tracker and MEMS gyro. While conducting the laser crosslink, the LCT provides the AOA to the host OBC every 10 Hz and the bus corrects the LOS error every 1 Hz. The 3-axis RWs are balanced and provide high momentum and torque capacities, having a low jitter characteristic with viscoelastic dampers [16]. As shown in Figure 17a, the FOU includes the region of the LOS errors yielded by the relative navigation, body pointing, and residual of FSM control. The body pointing, given the relative navigation and hardware performances, is evaluated as presented in Figure 17b,c. The body-pointing errors are smaller than 75 arcsec during the PAT sequence, and the beam spot can remain within the active area of the tracking sensors. Figure 16: Diagram of the GNC architecture for formation flying. The host OBC commands the integrated attitude determination and control module for body pointing. During the PAT sequence, the LOS vector is yielded from the AOA and relative navigation, and the body pointing is executed faster than 1 Hz. Figure 17: _Cont._  
The S-band transceiver and antenna are utilized to transfer the GPS L1 and L2 signals obtained by the GNSS receiver. The differential ionosphere makes usually negligible effects for a short baseline of a few kilometers. However, it is dependent on ionospheric conditions, and an ionospheric uncertainty can be corrected with a dual-frequency GPS receiver for a long baseline, which is greater than a few kilometers [17]. In addition, for precise relative position estimations, the algorithm based on DGPS corrects the delays induced by data acquisition, parsing, and RF crosslinks. Table 7 summarizes the results for each orbit scenario. Relative navigation achieves submeter-level estimation performance. In addition, the propulsion system is utilized for orbit maneuvers. The propulsion system has four MEMS nozzles that provide a maximum thrust of 1 mN along the z-axis for each nozzle. It is a cold-gas type which can vaporize the n-butane by heating the titanium-based tank and nozzles. In addition, continuous thrust is enabled with a pulse width of 10 ms. As presented in Table 8, the total accumulated propellant over the orbit scenario is approximately 5.13 m/s, which is less than the available propellant budget. The remaining propellant is sufficient for reentry maneuvers, following the \"25-year rule\".