## 4 R-SpaceFibre Use Case Scenario: CubeSats  
R-SpaceFibre combines high data-rate capability with small hardware resources occupation, accepting reduced performances in terms of error recovery. This innovative technology is a suitable solution for applications with relaxed requirements in terms of bit error rate and stringent requirement of size, volume and cost such as CubeSats. Indeed, this class of small spacecraft needs optimised on-board components. In this section, CubeSats features and applications are analysed pointing out why R-SpaceFibre represents a valuable solution for enhancing CubeSats data-rate capability at low cost of volume and price. CubeSat is a class of nanosatellite (with a mass between 1 and 10 Kg) standardised by the California Polytechnic State University in 1999. They are made up of 10 cm \(\times\) 10 cm \(\times\) 10 cm units (1U) with a maximum weight of 1.33 Kg [16] that could be assembled to compose larger satellites (i.e., 2U, 3U, 6U and 12U). In the last few years, CubeSats have become more and more popular and the number of CubeSats launched into space per year is growing, as shown in Figure 5. According to the CubeSat database of the St. Louis University [23], 796 CubeSats had been launched as of 31 December 2018. CubeSats, initially developed for educational purposes, despite their limitation in terms of mass and volume are emerging as important technological platforms, especially for Earth observation application, and represent a cost-effective and fast-to-launch solution [24]. A possible architecture for CubeSat on-board electronics is shown in Figure 6. The Control Unit manages and configures other units through command and control interfaces, characterised by low bandwidth and strict reliability constraints. The payload is connected through a high-speed link to an Instrumentation Control Unit that elaborates received data. Data are stored in a Mass Memory, which is connected as well through a high-speed link, waiting to be sent back to earth. Considering their limitation in terms of mass and volume, CubeSats cannot mount a great number of instruments and the data-handling subsystem is generally as simple as possible privileging point-to-point connections to more complex network topologies. R-SpaceFibre may be a feasible solution for high-speed serial links in CubeSats data-handling subsystem, combining SpaceFibre cable mass reduction and performances with a small footprint on FPGA devices, which allows system designer to potentially fit it in FPGAs which share other tasks (i.e., the Instrument Control Unit, ICU). According to Table 1, it is possible to implement two  
Figure 5: Number of CubeSats launched per year. R-SpaceFibre interfaces (i.e., necessary to the ICU of Figure 6) on a small footprint FPGA like the RTAX2000, employing only 32.36% of the total LUT, 28.46% of DFF and 12.50% of RAM with large part of the FPGA still available for other mission dependent features implementation. The same architecture implementing a regular SpaceFibre needs 54.22% of LUT, 48.46% of DFF and 37.5% of RAM, offering less possibility to integrate extra features on the same device. R-SpaceFibre could help to reduce the number of devices embedding more features on the same FPGA. It also reduces the overall electronic price, which represent a key advantage for low cost missions, such as CubeSats. The state-of-the-art for rad-hardened CubeSat data-handling subsystem is the Sphinx Deep Space Command and Data Handling (CDH) board [25] developed by the Jet Propulsion Laboratory (JPL) that will be mounted on the Lunar Flashlight [26] and NEAScout missions [27].