# Novel 3U Stand-Alone CubeSat Architecture for Autonomous Near Earth Asteroid Fly-By
## 4 Subsystems Analysis
### Communication  
Deep-space communications usually rely on X or Ka Band. Due to the few available options for the second, this paper focuses on X-Band communication systems. Laser communication technologies are continuously improving and their use for deep-space application cannot be excluded in the near future.  
Due to the fully autonomous navigation strategy highlighted in the previous section, the driver of the communication analysis is the downlink, which can be accomplished by means of X-band transmitter and antennas. A wide range of X-band transmitters and antennas for CubeSat is offered by Syrlinks [67]: EWC27, N-XONOS, SPAN-X-T2 and SPAN-X-T3. However their datasheets are not available. Endurosat [68] and AAC Clyde Space [69] offer both X-Band transmitters and antennas and their performances are evaluated. Telecommunication link budget strongly depends on several factors. Rearranging the classical link budget equation, it is possible to describe the data-rate as [70]:  
\[R=10^{\frac{1}{10}(P_{t}+L_{tr}+G_{ant}+L_{p}+L_{path}+L_{at}+G_{r}+DTP-SN-E_{b} /N0+LM+L_{r})}, \tag{4}\]  
where \(P_{t}\) is the transmitting power, \(L_{tr}\) the transmit loss, \(G_{ant}\) the antenna gain, \(L_{p}\) the pointing loss, \(L_{path}\) the space loss, \(L_{at}\) the atmospheric loss, \(G_{r}\) the receiver antenna gain, DTP the data to total power, SN the system noise, LM the link margin, and \(L_{r}\) the receiver loss. For the evaluation of a deep-space scenario, these assumption have been made: required Eb/N0 can be assumed equal to 1 dB, the required link margin is 3 dB, atmospheric loss is \(-\)0.3 dB, transmit loss is \(-\)2 dB, receiver loss is \(-\)1 dB, atmospheric loss is \(-\)0.3 dB, and DTP is \(-\)0.6 dB, according to Reference [70]. Based on Equation (4), Figure 7 shows the highest data rate for the most appealing off-the-shelf antennas as a function of the distance from the Earth. The ground antenna considered is a Deep-Space Network (DSN) 34-m diameter, with receiving gain equal to 68.2 dBic, and system noise density equal to \(-\)183.6 dBm/Hz. Moreover, to compute the actual time to downlink the entire dataset, ground station availability, together with the actual size of the dataset, shall be investigated. This is left for further analysis, where the actual Earth-target distance has to be considered, to define a proper dataset size and communication time relation, and to evaluate the cost associated to the communication ground station (for this purpose, other ground antenna options, less expensive than DSN antennas, shall be considered).  
MarCO deployable reflectarray has not been included in the evaluation because, despite the small storage volume (\(\sim\)0.1U) and high gain (\(\sim\)29 dBi), its large mass (1 kg) does not match with the strict requirements of this mission. However, even if it is not a proper COTS component (as Iris), it represents a valuable solution for larger CubeSat architectures [71].  
For the X-band transmitter trade-off, many off-the-shelf solutions have been considered: Endurosat X-band transmitter [68], AAC Clyde Space Pulsar-Data [69], Tethers Unlimited SWIFT-XTX[72], Glavkosmos X-band transmitter [73], InnoFlight SCR-106 [74], Sputnik X-band transmitter [75], and Space-SI X-band transmitter [76]. The trade-off was based mainly on four parameters (mass, volume, transmitting power, and power consumption) and highlighted that the best option for this mission is AAC ClydeSpace Pulsar-Data. For the X-band antenna, the best option is represented by Endurosat 4 \(\times\) 4 patch antenna, because it offers a higher data rate, due to its higher gain (16 dBi), while its mass (52 g) is just slightly larger than the other two best options (Endurosat 2 \(\times\) 2 patch antenna with 23 g and AAC ClydeSpace with 29 g).