# Novel 3U Stand-Alone CubeSat Architecture for Autonomous Near Earth Asteroid Fly-By
## 4 Subsystems Analysis
### Attitude Determination and Control System
All these three options are perfectly suited to de-saturate reactions wheels; Aurora Technologies product occupies a more compact volume, however, as the Results section will show, an additional subsystem, designed exclusively to de-saturate the wheels, poses several challenges in terms of total mass of the CubeSat. For this reason, it is better to rely on the main engine for wheels de-saturation. Previous studies done for LUMIO showed that the four thrusters of Aerojet Rocktedyne MPS-130 (the best micro-propulsion option highlighted in previous section) are sufficient to perform wheels de-saturation, with only 1-2 m/s of \(\Delta V\). Clearly, the true mission profile has to be re-analyzed to compute more accurately the required \(\Delta V\), taking also into account that LUMIO is a 12U CubeSat; however, few m/s of \(\Delta V\) may be expected, which fully fit with the 385 m/s of total \(\Delta V\) achievable with MPS-130 for this configuration. So, this de-saturation option will be assumed [59]. The minimum FOV for the payloads discussed and selected in the Payload subsection is found for the Argus 2000 IR spectrometer equal to 0.15 degrees. In terms of pointing losses for communication, a previous study [60] determined that for deep space communication in the X-band frequency range, a maximum of 0.5 degrees pointing accuracy is acceptable. These two numbers will drive the selection of the ADCS subsystem, discussed hereafter. Blue Canyon Technologies XACT-15 [61] would represent the best option for a standard CubeSat, due to its fine declared pointing accuracy (\(\pm 0.003-0.007^{\circ},1\sigma\)) and its flight heritage, but its large mass (885 g) combined with the 0.5U volume lower its applicability to this constrained mission. Instead, Hyperion Technologies iADCS-200 [62] represents a more compact solution both in terms of volume and mass (respectively 400 g and 0.3U). Despite its lower mass (328 g), CubeSpace 3-axis ADCS [63] has a larger volume (approximately 0.5U) and a lower resistance to radiation (20 krad compared to 45 krad for iADCS-200). KU Leuven ADCS [64] and Adcole Maryland Aerospace MAI-500 [65] represent two heavier solutions (respectively 715 g and 1049 g), with an approximated volume respectively of 0.5U and 0.6U. NanoAvionics 4 RW0 [66] represents an excellent control system for deep-space applications. It is composed by 4 reaction wheels with large momentum capacity respect to the integrated solutions presented previously. But, its large mass (665 g), volume (92.5 mm \(\times\) 92.5 mm \(\times\) 51.3 mm) and peak power consumption (6 W compared to 0.6 W of its steady state behavior), as it will be shown in the Power subsection, make it hard to integrate in the compact architecture presented here. It has been shown that integrated off-the-shelf ADCS solutions exploit reaction wheels for attitude control, while no solutions exploit reaction thrusters. Integrated solutions offer an immediate advantage over an assembly of attitude sensors, actuators, and processors. This is the reason behind the choice of using reaction wheels for attitude control, rather than reaction thrusters. Star trackers and Sun sensors are needed for attitude determination, but, as it has been shown in the previous section, also for navigation purposes. All of the integrated options presented contain a star tracker and space for allocation of multiple Sun sensors. Mass, volume, and pointing accuracy are taken as driving parameters for the trade-off. The declared pointing accuracy of the integrated ADCS presented in this section are in the order of 0.1-0.2\({}^{\circ}\) (3\(\sigma\)), with the exception of the XACT-15, which has the finest pointing accuracy. As all the options meet the required pointing accuracy for the payload (0.15\({}^{\circ}\)), mass and volume play a significant role in the selection, and due to its lower mass and volume, Hyperion Technologies iADCS200 represents the best solution for this application (declared pointing \(\approx\) 1\({}^{\circ}\)).